Nasopharyngeal colonization by Streptococcus pneumoniae is a prerequisite to invasion to the lungs or bloodstream1. This organism is capable of colonizing the mucosal surface of the nasopharynx, where it can reside, multiply and eventually overcome host defences to invade to other tissues of the host. Establishment of an infection in the normally lower respiratory tract results in pneumonia. Alternatively, the bacteria can disseminate into the bloodstream causing bacteraemia, which is associated with high mortality rates2, or else lead directly to the development of pneumococcal meningitis. Understanding the kinetics of, and immune responses to, nasopharyngeal colonization is an important aspect of S. pneumoniae infection models.
Our mouse model of intranasal colonization is adapted from human models3 and has been used by multiple research groups in the study of host-pathogen responses in the nasopharynx4-7. In the first part of the model, we use a clinical isolate of S. pneumoniae to establish a self-limiting bacterial colonization that is similar to carriage events in human adults. The procedure detailed herein involves preparation of a bacterial inoculum, followed by the establishment of a colonization event through delivery of the inoculum via an intranasal route of administration. Resident macrophages are the predominant cell type in the nasopharynx during the steady state. Typically, there are few lymphocytes present in uninfected mice8, however mucosal colonization will lead to low- to high-grade inflammation (depending on the virulence of the bacterial species and strain) that will result in an immune response and the subsequent recruitment of host immune cells. These cells can be isolated by a lavage of the tracheal contents through the nares, and correlated to the density of colonization bacteria to better understand the kinetics of the infection.
21 Related JoVE Articles!
TransFLP — A Method to Genetically Modify Vibrio cholerae Based on Natural Transformation and FLP-recombination
Institutions: Ecole Polytechnique Fédérale de Lausanne (EPFL).
Several methods are available to manipulate bacterial chromosomes1-3
. Most of these protocols rely on the insertion of conditionally replicative plasmids (e.g.
harboring pir-dependent or temperature-sensitive replicons1,2
). These plasmids are integrated into bacterial chromosomes based on homology-mediated recombination. Such insertional mutants are often directly used in experimental settings. Alternatively, selection for plasmid excision followed by its loss can be performed, which for Gram-negative bacteria often relies on the counter-selectable levan sucrase enzyme encoded by the sacB
. The excision can either restore the pre-insertion genotype or result in an exchange between the chromosome and the plasmid-encoded copy of the modified gene. A disadvantage of this technique is that it is time-consuming. The plasmid has to be cloned first; it requires horizontal transfer into V. cholerae
(most notably by mating with an E. coli
donor strain) or artificial transformation of the latter; and the excision of the plasmid is random and can either restore the initial genotype or create the desired modification if no positive selection is exerted. Here, we present a method for rapid manipulation of the V. cholerae
). This TransFLP method is based on the recently discovered chitin-mediated induction of natural competence in this organism6
and other representative of the genus Vibrio
such as V. fischeri7
. Natural competence allows the uptake of free DNA including PCR-generated DNA fragments. Once taken up, the DNA recombines with the chromosome given the presence of a minimum of 250-500 bp of flanking homologous region8
. Including a selection marker in-between these flanking regions allows easy detection of frequently occurring transformants.
This method can be used for different genetic manipulations of V. cholerae
and potentially also other naturally competent bacteria. We provide three novel examples on what can be accomplished by this method in addition to our previously published study on single gene deletions and the addition of affinity-tag sequences5
. Several optimization steps concerning the initial protocol of chitin-induced natural transformation6
are incorporated in this TransFLP protocol. These include among others the replacement of crab shell fragments by commercially available chitin flakes8
, the donation of PCR-derived DNA as transforming material9
, and the addition of FLP-recombination target sites (FRT)5
. FRT sites allow site-directed excision of the selection marker mediated by the Flp recombinase10
Immunology, Issue 68, Microbiology, Genetics, natural transformation, DNA uptake, FLP recombination, chitin, Vibrio cholerae
Measurement of Tactile Allodynia in a Murine Model of Bacterial Prostatitis
Institutions: Northwestern University Feinberg School of Medicine.
Uropathogenic Escherichia coli
(UPEC) are pathogens that play an important role in urinary tract infections and bacterial prostatitis1
. We have recently shown that UPEC have an important role in the initiation of chronic pelvic pain2
, a feature of Chronic prostatitis/Chronic pelvic pain syndrome (CP/CPPS)3,4
. Infection of the prostate by clinically relevant UPEC can initiate and establish chronic pain through mechanisms that may involve tissue damage and the initiation of mechanisms of autoimmunity5
A challenge to understanding the pathogenesis of UPEC in the prostate is the relative inaccessibility of the prostate gland to manipulation. We utilized a previously described intraurethral infection method6
to deliver a clinical strain of UPEC into male mice thereby establishing an ascending infection of the prostate. Here, we describe our protocols for standardizing the bacterial inoculum7
as well as the procedure for catheterizing anesthetized male mice for instillation of bacteria.
CP/CPPS is primarily characterized by the presence of tactile allodynia4
. Behavior testing was based on the concept of cutaneous hyperalgesia resulting from referred visceral pain8-10
. An irritable focus in visceral tissues reduces cutaneous pain thresholds allowing for an exaggerated response to normally non-painful stimuli (allodynia). Application of normal force to the skin result in abnormal responses that tend to increase with the intensity of the underlying visceral pain. We describe methodology in NOD/ShiLtJ mice that utilize von Frey fibers to quantify tactile allodynia over time in response to a single infection with UPEC bacteria.
Infection, Issue 71, Immunology, Infectious Diseases, Microbiology, Medicine, Urology, Pathology, Autoimmune Diseases, Bacterial Infections and Mycoses, Male Urogenital Diseases, Bacterial pathogenesis, pain, autoimmunity, prostatitis, catheterization, mice, animal model
Purification and Visualization of Lipopolysaccharide from Gram-negative Bacteria by Hot Aqueous-phenol Extraction
Institutions: University of Virginia Health System.
Lipopolysaccharide (LPS) is a major component of Gram-negative bacterial outer membranes. It is a tripartite molecule consisting of lipid A, which is embedded in the outer membrane, a core oligosaccharide and repeating O-antigen units that extend outward from the surface of the cell1, 2
. LPS is an immunodominant molecule that is important for the virulence and pathogenesis of many bacterial species, including Pseudomonas aeruginosa, Salmonella
species, and Escherichia coli3-5
, and differences in LPS O-antigen composition form the basis for serotyping of strains. LPS is involved in attachment to host cells at the initiation of infection and provides protection from complement-mediated killing; strains that lack LPS can be attenuated for virulence6-8
. For these reasons, it is important to visualize LPS, particularly from clinical isolates. Visualizing LPS banding patterns and recognition by specific antibodies can be useful tools to identify strain lineages and to characterize various mutants.
In this report, we describe a hot aqueous-phenol method for the isolation and purification of LPS from Gram-negative bacterial cells. This protocol allows for the extraction of LPS away from nucleic acids and proteins that can interfere with visualization of LPS that occurs with shorter, less intensive extraction methods9
. LPS prepared this way can be separated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) and directly stained using carbohydrate/glycoprotein stains or standard silver staining methods. Many anti-sera to LPS contain antibodies that cross-react with outer membrane proteins or other antigenic targets that can hinder reactivity observed following Western immunoblot of SDS-PAGE-separated crude cell lysates. Protease treatment of crude cell lysates alone is not always an effective way of removing this background using this or other visualization methods. Further, extensive protease treatment in an attempt to remove this background can lead to poor quality LPS that is not well resolved by any of the aforementioned methods. For these reasons, we believe that the following protocol, adapted from Westpahl and Jann10
, is ideal for LPS extraction.
Immunology, Issue 63, Microbiology, Gram-negative, LPS, extraction, polysaccharide staining, Western immunoblot
Transurethral Induction of Mouse Urinary Tract Infection
Institutions: Stanford University , Stanford University School of Medicine.
Uropathogenic bacterial strains of interest are grown on agar. Generally, uropathogenic E. coli
(UPEC) and other strains can be grown overnight on Luria-Bertani (LB) agar at 37°C in ambient air. UPEC strains grow as yellowish-white translucent colonies on LB agar. Following confirmation of appropriate colony morphology, single colonies are then picked to be cultured in broth. LB broth can be used for most uropathogenic bacterial strains. Two serial, overnight LB broth cultures can be employed to enhance expression of type I pili, a well-defined virulence factor for uropathogenic bacteria. Broth cultures are diluted to the desired concentration in phosphate buffered saline (PBS). Eight to 12 week old female mice are placed under isoflurane anesthesia and transurethrally inoculated with bacteria using polyethylene tubing-covered 30 gauge syringes. Typical inocula, which must be empirically determined for each bacterial/mouse strain combination, are 106
cfu per mouse in 10 to 50 microliters of PBS. After the desired infection period (one day to several weeks), urine samples and the bladder and both kidneys are harvested. Each organ is minced, placed in PBS, and homogenized in a Blue Bullet homogenizer. Urine and tissue homogenates are serially diluted in PBS and cultured on appropriate agar. The following day, colony forming units are counted.
Microbiology, Issue 42, UTI, urinary tract infection, urethra, mice, bacterial, cystitis, pyelonephritis, mouse, bacteria, urethral
Modified Annexin V/Propidium Iodide Apoptosis Assay For Accurate Assessment of Cell Death
Institutions: University of Alberta, University of Alberta.
Studies of cellular apoptosis have been significantly impacted since the introduction of flow cytometry-based methods. Propidium iodide (PI) is widely used in conjunction with Annexin V to determine if cells are viable, apoptotic, or necrotic through differences in plasma membrane integrity and permeability1,2
. The Annexin V/ PI protocol is a commonly used approach for studying apoptotic cells3
. PI is used more often than other nuclear stains because it is economical, stable and a good indicator of cell viability, based on its capacity to exclude dye in living cells 4,5
. The ability of PI to enter a cell is dependent upon the permeability of the membrane; PI does not stain live or early apoptotic cells due to the presence of an intact plasma membrane 1,2,6
. In late apoptotic and necrotic cells, the integrity of the plasma and nuclear membranes decreases7,8
, allowing PI to pass through the membranes, intercalate into nucleic acids, and display red fluorescence 1,2,9
. Unfortunately, we find that conventional Annexin V/ PI protocols lead to a significant number of false positive events (up to 40%), which are associated with PI staining of RNA within the cytoplasmic compartment10
. Primary cells and cell lines in a broad range of animal models are affected, with large cells (nuclear: cytoplasmic ratios <0.5) showing the highest occurrence10
. Herein, we demonstrate a modified Annexin V/ PI method that provides a significant improvement for assessment of cell death compared to conventional methods. This protocol takes advantage of changes in cellular permeability during cell fixing to promote entry of RNase A into cells following staining. Both the timing and concentration of RNase A have been optimized for removal of cytoplasmic RNA. The result is a significant improvement over conventional Annexin V/ PI protocols (< 5% events with cytoplasmic PI staining).
Cellular Biology, Issue 50, Apoptosis, cell death, propidium iodide, Annexin V, necrosis, immunology
Sublingual Immunotherapy as an Alternative to Induce Protection Against Acute Respiratory Infections
Institutions: Universidad de la República, Trinity College Dublin.
Sublingual route has been widely used to deliver small molecules into the bloodstream and to modulate the immune response at different sites. It has been shown to effectively induce humoral and cellular responses at systemic and mucosal sites, namely the lungs and urogenital tract. Sublingual vaccination can promote protection against infections at the lower and upper respiratory tract; it can also promote tolerance to allergens and ameliorate asthma symptoms. Modulation of lung’s immune response by sublingual immunotherapy (SLIT) is safer than direct administration of formulations by intranasal route because it does not require delivery of potentially harmful molecules directly into the airways. In contrast to intranasal delivery, side effects involving brain toxicity or facial paralysis are not promoted by SLIT. The immune mechanisms underlying SLIT remain elusive and its use for the treatment of acute lung infections has not yet been explored. Thus, development of appropriate animal models of SLIT is needed to further explore its potential advantages.
This work shows how to perform sublingual administration of therapeutic agents in mice to evaluate their ability to protect against acute pneumococcal pneumonia. Technical aspects of mouse handling during sublingual inoculation, precise identification of sublingual mucosa, draining lymph nodes and isolation of tissues, bronchoalveolar lavage and lungs are illustrated. Protocols for single cell suspension preparation for FACS analysis are described in detail. Other downstream applications for the analysis of the immune response are discussed. Technical aspects of the preparation of Streptococcus pneumoniae
inoculum and intranasal challenge of mice are also explained.
SLIT is a simple technique that allows screening of candidate molecules to modulate lungs’ immune response. Parameters affecting the success of SLIT are related to molecular size, susceptibility to degradation and stability of highly concentrated formulations.
Medicine, Issue 90, Sublingual immunotherapy, Pneumonia, Streptococcus pneumoniae, Lungs, Flagellin, TLR5, NLRC4
Following in Real Time the Impact of Pneumococcal Virulence Factors in an Acute Mouse Pneumonia Model Using Bioluminescent Bacteria
Institutions: University of Greifswald.
Pneumonia is one of the major health care problems in developing and industrialized countries and is associated with considerable morbidity and mortality. Despite advances in knowledge of this illness, the availability of intensive care units (ICU), and the use of potent antimicrobial agents and effective vaccines, the mortality rates remain high1
. Streptococcus pneumoniae
is the leading pathogen of community-acquired pneumonia (CAP) and one of the most common causes of bacteremia in humans. This pathogen is equipped with an armamentarium of surface-exposed adhesins and virulence factors contributing to pneumonia and invasive pneumococcal disease (IPD). The assessment of the in vivo
role of bacterial fitness or virulence factors is of utmost importance to unravel S. pneumoniae
pathogenicity mechanisms. Murine models of pneumonia, bacteremia, and meningitis are being used to determine the impact of pneumococcal factors at different stages of the infection. Here we describe a protocol to monitor in real-time pneumococcal dissemination in mice after intranasal or intraperitoneal infections with bioluminescent bacteria. The results show the multiplication and dissemination of pneumococci in the lower respiratory tract and blood, which can be visualized and evaluated using an imaging system and the accompanying analysis software.
Infection, Issue 84, Gram-Positive Bacteria, Streptococcus pneumoniae, Pneumonia, Bacterial, Respiratory Tract Infections, animal models, community-acquired pneumonia, invasive pneumococcal diseases, Pneumococci, bioimaging, virulence factor, dissemination, bioluminescence, IVIS Spectrum
Capsular Serotyping of Streptococcus pneumoniae by Latex Agglutination
Institutions: Murdoch Childrens Research Institute, The University of Melbourne.
Latex agglutination reagents are widely used in microbial diagnosis, identification and serotyping. Streptococcus pneumonia
e (the pneumococcus) is a major cause of morbidity and mortality world-wide. Current vaccines target the pneumococcal capsule, and there are over 90 capsular serotypes. Serotyping pneumococcal isolates is therefore important for assessing the impact of vaccination programs and for epidemiological purposes. The World Health Organization has recommended latex agglutination as an alternative method to the ‘gold standard’ Quellung test for serotyping pneumococci. Latex agglutination is a relatively simple, quick and inexpensive method; and is therefore suitable for resource-poor settings as well as laboratories with high-volume workloads. Latex agglutination reagents can be prepared in-house utilizing commercially-sourced antibodies that are passively attached to latex particles. This manuscript describes a method of production and quality control of latex agglutination reagents, and details a sequential testing approach which is time- and cost-effective.
This method of production and quality control may also be suitable for other testing purposes.
Immunology, Issue 91, Antisera, pneumococci, polysaccharide capsule, slide agglutination
Live Cell Imaging of Bacillus subtilis and Streptococcus pneumoniae using Automated Time-lapse Microscopy
Institutions: University of Groningen.
During the last few years scientists became increasingly aware that average data obtained from microbial population based experiments are not representative of the behavior, status or phenotype of single cells. Due to this new insight the number of single cell studies rises continuously (for recent reviews see 1,2,3
). However, many of the single cell techniques applied do not allow monitoring the development and behavior of one specific single cell in time (e.g. flow cytometry or standard microscopy).
Here, we provide a detailed description of a microscopy method used in several recent studies 4, 5, 6, 7
, which allows following and recording (fluorescence of) individual bacterial cells of Bacillus subtilis
and Streptococcus pneumoniae
through growth and division for many generations. The resulting movies can be used to construct phylogenetic lineage trees by tracing back the history of a single cell within a population that originated from one common ancestor. This time-lapse fluorescence microscopy method cannot only be used to investigate growth, division and differentiation of individual cells, but also to analyze the effect of cell history and ancestry on specific cellular behavior. Furthermore, time-lapse microscopy is ideally suited to examine gene expression dynamics and protein localization during the bacterial cell cycle. The method explains how to prepare the bacterial cells and construct the microscope slide to enable the outgrowth of single cells into a microcolony. In short, single cells are spotted on a semi-solid surface consisting of growth medium supplemented with agarose on which they grow and divide under a fluorescence microscope within a temperature controlled environmental chamber. Images are captured at specific intervals and are later analyzed using the open source software ImageJ.
Immunology, Issue 53, time-lapse fluorescence microscopy, single cell analysis, cell history, cell growth, development, promoter activity, protein localization, GFP, Bacillus subtilis, Streptococcus pneumoniae
Using Coculture to Detect Chemically Mediated Interspecies Interactions
Institutions: University of North Carolina at Chapel Hill .
In nature, bacteria rarely exist in isolation; they are instead surrounded by a diverse array of other microorganisms that alter the local environment by secreting metabolites. These metabolites have the potential to modulate the physiology and differentiation of their microbial neighbors and are likely important factors in the establishment and maintenance of complex microbial communities. We have developed a fluorescence-based coculture screen to identify such chemically mediated microbial interactions. The screen involves combining a fluorescent transcriptional reporter strain with environmental microbes on solid media and allowing the colonies to grow in coculture. The fluorescent transcriptional reporter is designed so that the chosen bacterial strain fluoresces when it is expressing a particular phenotype of interest (i.e.
biofilm formation, sporulation, virulence factor production, etc
.) Screening is performed under growth conditions where this phenotype is not
expressed (and therefore the reporter strain is typically nonfluorescent). When an environmental microbe secretes a metabolite that activates this phenotype, it diffuses through the agar and activates the fluorescent reporter construct. This allows the inducing-metabolite-producing microbe to be detected: they are the nonfluorescent colonies most proximal to the fluorescent colonies. Thus, this screen allows the identification of environmental microbes that produce diffusible metabolites that activate a particular physiological response in a reporter strain. This publication discusses how to: a) select appropriate coculture screening conditions, b) prepare the reporter and environmental microbes for screening, c) perform the coculture screen, d) isolate putative inducing organisms, and e) confirm their activity in a secondary screen. We developed this method to screen for soil organisms that activate biofilm matrix-production in Bacillus subtilis
; however, we also discuss considerations for applying this approach to other genetically tractable bacteria.
Microbiology, Issue 80, High-Throughput Screening Assays, Genes, Reporter, Microbial Interactions, Soil Microbiology, Coculture, microbial interactions, screen, fluorescent transcriptional reporters, Bacillus subtilis
Analysis of Nephron Composition and Function in the Adult Zebrafish Kidney
Institutions: University of Notre Dame.
The zebrafish model has emerged as a relevant system to study kidney development, regeneration and disease. Both the embryonic and adult zebrafish kidneys are composed of functional units known as nephrons, which are highly conserved with other vertebrates, including mammals. Research in zebrafish has recently demonstrated that two distinctive phenomena transpire after adult nephrons incur damage: first, there is robust regeneration within existing nephrons that replaces the destroyed tubule epithelial cells; second, entirely new nephrons are produced from renal progenitors in a process known as neonephrogenesis. In contrast, humans and other mammals seem to have only a limited ability for nephron epithelial regeneration. To date, the mechanisms responsible for these kidney regeneration phenomena remain poorly understood. Since adult zebrafish kidneys undergo both nephron epithelial regeneration and neonephrogenesis, they provide an outstanding experimental paradigm to study these events. Further, there is a wide range of genetic and pharmacological tools available in the zebrafish model that can be used to delineate the cellular and molecular mechanisms that regulate renal regeneration. One essential aspect of such research is the evaluation of nephron structure and function. This protocol describes a set of labeling techniques that can be used to gauge renal composition and test nephron functionality in the adult zebrafish kidney. Thus, these methods are widely applicable to the future phenotypic characterization of adult zebrafish kidney injury paradigms, which include but are not limited to, nephrotoxicant exposure regimes or genetic methods of targeted cell death such as the nitroreductase mediated cell ablation technique. Further, these methods could be used to study genetic perturbations in adult kidney formation and could also be applied to assess renal status during chronic disease modeling.
Cellular Biology, Issue 90,
zebrafish; kidney; nephron; nephrology; renal; regeneration; proximal tubule; distal tubule; segment; mesonephros; physiology; acute kidney injury (AKI)
High Resolution Electron Microscopy of the Helicobacter pylori Cag Type IV Secretion System Pili Produced in Varying Conditions of Iron Availability
Institutions: Vanderbilt University School of Medicine, U. S. Dept. of Veterans Affairs.
is a helical-shaped, gram negative bacterium that colonizes the human gastric niche of half of the human population1,2
. H. pylori
is the primary cause of gastric cancer, the second leading cause of cancer-related deaths worldwide3
. One virulence factor that has been associated with increased risk of gastric disease is the Cag-pathogenicity island, a 40-kb region within the chromosome of H. pylori
that encodes a type IV secretion system and the cognate effector molecule, CagA4,5
. The Cag-T4SS is responsible for translocating CagA and peptidoglycan into host epithelial cells5,6
. The activity of the Cag-T4SS results in numerous changes in host cell biology including upregulation of cytokine expression, activation of proinflammatory pathways, cytoskeletal remodeling, and induction of oncogenic cell-signaling networks5-8
. The Cag-T4SS is a macromolecular machine comprised of sub-assembly components spanning the inner and outer membrane and extending outward from the cell into the extracellular space. The extracellular portion of the Cag-T4SS is referred to as the “pilus”5
. Numerous studies have demonstrated that the Cag-T4SS pili are formed at the host-pathogen interface9,10
. However, the environmental features that regulate the biogenesis of this important organelle remain largely obscure. Recently, we reported that conditions of low iron availability increased the Cag-T4SS activity and pilus biogenesis. Here we present an optimized protocol to grow H. pylori
in varying conditions of iron availability prior to co-culture with human gastric epithelial cells. Further, we present the comprehensive protocol for visualization of the hyper-piliated phenotype exhibited in iron restricted conditions by high resolution scanning electron microscopy analyses.
Infection, Issue 93, Helicobacter pylori, iron acquisition, cag pathogenicity island, type IV secretion, pili
Humanized Mouse Model to Study Bacterial Infections Targeting the Microvasculature
Institutions: Paris Cardiovascular Research Centre, Université Paris Descartes.
causes a severe, frequently fatal sepsis when it enters the human blood stream. Infection leads to extensive damage of the blood vessels resulting in vascular leak, the development of purpuric rashes and eventual tissue necrosis. Studying the pathogenesis of this infection was previously limited by the human specificity of the bacteria, which makes in vivo
models difficult. In this protocol, we describe a humanized model for this infection in which human skin, containing dermal microvessels, is grafted onto immunocompromised mice. These vessels anastomose with the mouse circulation while maintaining their human characteristics. Once introduced into this model, N. meningitidis
adhere exclusively to the human vessels, resulting in extensive vascular damage, inflammation and in some cases the development of purpuric rash. This protocol describes the grafting, infection and evaluation steps of this model in the context of N. meningitidis
infection. The technique may be applied to numerous human specific pathogens that infect the blood stream.
Infection, Issue 86, Disease Models, Bacteria, Bacterial Infections and Mycoses, Neisseria meningitidis, purpura, vascular infection, humanized model
Investigating the Effects of Probiotics on Pneumococcal Colonization Using an In Vitro Adherence Assay
Institutions: Murdoch Childrens Research Institute, Murdoch Childrens Research Institute, The University of Melbourne, The University of Melbourne.
Adherence of Streptococcus pneumoniae
(the pneumococcus) to the epithelial lining of the nasopharynx can result in colonization and is considered a prerequisite for pneumococcal infections such as pneumonia and otitis media. In vitro
adherence assays can be used to study the attachment of pneumococci to epithelial cell monolayers and to investigate potential interventions, such as the use of probiotics, to inhibit pneumococcal colonization. The protocol described here is used to investigate the effects of the probiotic Streptococcus salivarius
on the adherence of pneumococci to the human epithelial cell line CCL-23 (sometimes referred to as HEp-2 cells). The assay involves three main steps: 1) preparation of epithelial and bacterial cells, 2) addition of bacteria to epithelial cell monolayers, and 3) detection of adherent pneumococci by viable counts (serial dilution and plating) or quantitative real-time PCR (qPCR). This technique is relatively straightforward and does not require specialized equipment other than a tissue culture setup. The assay can be used to test other probiotic species and/or potential inhibitors of pneumococcal colonization and can be easily modified to address other scientific questions regarding pneumococcal adherence and invasion.
Immunology, Issue 86, Gram-Positive Bacterial Infections, Pneumonia, Bacterial, Lung Diseases, Respiratory Tract Infections, Streptococcus pneumoniae, adherence, colonization, probiotics, Streptococcus salivarius, In Vitro assays
Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes
Institutions: University at Buffalo, State University of New York, University at Buffalo, State University of New York, University at Buffalo, State University of New York.
Membrane depolarization and ion fluxes are events that have been studied extensively in biological systems due to their ability to profoundly impact cellular functions, including energetics and signal transductions. While both fluorescent and electrophysiological methods, including electrode usage and patch-clamping, have been well developed for measuring these events in eukaryotic cells, methodology for measuring similar events in microorganisms have proven more challenging to develop given their small size in combination with the more complex outer surface of bacteria shielding the membrane. During our studies of death-initiation in Streptococcus pneumoniae
(pneumococcus), we wanted to elucidate the role of membrane events, including changes in polarity, integrity, and intracellular ion concentrations. Searching the literature, we found that very few studies exist. Other investigators had monitored radioisotope uptake or equilibrium to measure ion fluxes and membrane potential and a limited number of studies, mostly in Gram-negative organisms, had seen some success using carbocyanine or oxonol fluorescent dyes to measure membrane potential, or loading bacteria with cell-permeant acetoxymethyl (AM) ester versions of ion-sensitive fluorescent indicator dyes. We therefore established and optimized protocols for measuring membrane potential, rupture, and ion-transport in the Gram-positive organism S. pneumoniae.
We developed protocols using the bis-oxonol dye DiBAC4
(3) and the cell-impermeant dye propidium iodide to measure membrane depolarization and rupture, respectively, as well as methods to optimally load the pneumococci with the AM esters of the ratiometric dyes Fura-2, PBFI, and BCECF to detect changes in intracellular concentrations of Ca2+
, and H+
, respectively, using a fluorescence-detection plate reader. These protocols are the first of their kind for the pneumococcus and the majority of these dyes have not been used in any other bacterial species. Though our protocols have been optimized for S. pneumoniae
, we believe these approaches should form an excellent starting-point for similar studies in other bacterial species.
Immunology, Issue 84, Streptococcus pneumoniae, pneumococcus, potential-sensitive dyes, DiBAC, Propidium Iodide, acetoxymethyl (AM) ester, membrane rupture, Ion transport, bacterial ion concentrations, ion-sensitive fluorescence
Using the Overlay Assay to Qualitatively Measure Bacterial Production of and Sensitivity to Pneumococcal Bacteriocins
Institutions: University of Michigan, University of Michigan.
colonizes the highly diverse polymicrobial community of the nasopharynx where it must compete with resident organisms. We have shown that bacterially produced antimicrobial peptides (bacteriocins) dictate the outcome of these competitive interactions. All fully-sequenced pneumococcal strains harbor a bacteriocin-like peptide
) locus. The blp
locus encodes for a range of diverse bacteriocins and all of the highly conserved components needed for their regulation, processing, and secretion. The diversity of the bacteriocins found in the bacteriocin immunity region (BIR) of the locus is a major contributor of pneumococcal competition. Along with the bacteriocins, immunity genes are found in the BIR and are needed to protect the producer cell from the effects of its own bacteriocin. The overlay assay is a quick method for examining a large number of strains for competitive interactions mediated by bacteriocins. The overlay assay also allows for the characterization of bacteriocin-specific immunity, and detection of secreted quorum sensing peptides. The assay is performed by pre-inoculating an agar plate with a strain to be tested for bacteriocin production followed by application of a soft agar overlay containing a strain to be tested for bacteriocin sensitivity. A zone of clearance surrounding the stab indicates that the overlay strain is sensitive to the bacteriocins produced by the pre-inoculated strain. If no zone of clearance is observed, either the overlay strain is immune to the bacteriocins being produced or the pre-inoculated strain does not produce bacteriocins. To determine if the blp
locus is functional in a given strain, the overlay assay can be adapted to evaluate for peptide pheromone secretion by the pre-inoculated strain. In this case, a series of four lacZ-
reporter strains with different pheromone specificity are used in the overlay.
Infectious Diseases, Issue 91, bacteriocins, antimicrobial peptides, blp locus, bacterial competition, Streptococcus pneumoniae, overlay assay
Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Institutions: Murdoch Childrens Research Institute, The University of Melbourne.
There are over 90 different capsular serotypes of Streptococcus pneumoniae
(the pneumococcus). As well as being a tool for understanding pneumococcal epidemiology, capsular serotyping can provide useful information for vaccine efficacy and impact studies. The Quellung reaction is the gold standard method for pneumococcal capsular serotyping. The method involves testing a pneumococcal cell suspension with pooled and specific antisera directed against the capsular polysaccharide. The antigen-antibody reactions are observed microscopically. The protocol has three main steps: 1) preparation of a bacterial cell suspension, 2) mixing of cells and antisera on a glass slide, and 3) reading the Quellung reaction using a microscope. The Quellung reaction is reasonably simple to perform and can be applied wherever a suitable microscope and antisera are available.
Immunology, Issue 84, Streptococcus pneumoniae, Quellung, serotyping, Neufeld, pneumococcus
Aseptic Laboratory Techniques: Plating Methods
Institutions: University of California, Los Angeles .
Microorganisms are present on all inanimate surfaces creating ubiquitous sources of possible contamination in the laboratory. Experimental success relies on the ability of a scientist to sterilize work surfaces and equipment as well as prevent contact of sterile instruments and solutions with non-sterile surfaces. Here we present the steps for several plating methods routinely used in the laboratory to isolate, propagate, or enumerate microorganisms such as bacteria and phage. All five methods incorporate aseptic technique, or procedures that maintain the sterility of experimental materials. Procedures described include (1) streak-plating bacterial cultures to isolate single colonies, (2) pour-plating and (3) spread-plating to enumerate viable bacterial colonies, (4) soft agar overlays to isolate phage and enumerate plaques, and (5) replica-plating to transfer cells from one plate to another in an identical spatial pattern. These procedures can be performed at the laboratory bench, provided they involve non-pathogenic strains of microorganisms (Biosafety Level 1, BSL-1). If working with BSL-2 organisms, then these manipulations must take place in a biosafety cabinet. Consult the most current edition of the Biosafety in Microbiological and Biomedical Laboratories
(BMBL) as well as Material Safety Data Sheets
(MSDS) for Infectious Substances to determine the biohazard classification as well as the safety precautions and containment facilities required for the microorganism in question. Bacterial strains and phage stocks can be obtained from research investigators, companies, and collections maintained by particular organizations such as the American Type Culture Collection
(ATCC). It is recommended that non-pathogenic strains be used when learning the various plating methods. By following the procedures described in this protocol, students should be able to:
● Perform plating procedures without contaminating media.
● Isolate single bacterial colonies by the streak-plating method.
● Use pour-plating and spread-plating methods to determine the concentration of bacteria.
● Perform soft agar overlays when working with phage.
● Transfer bacterial cells from one plate to another using the replica-plating procedure.
● Given an experimental task, select the appropriate plating method.
Basic Protocols, Issue 63, Streak plates, pour plates, soft agar overlays, spread plates, replica plates, bacteria, colonies, phage, plaques, dilutions
Optimization and Utilization of Agrobacterium-mediated Transient Protein Production in Nicotiana
Institutions: Fraunhofer USA Center for Molecular Biotechnology.
-mediated transient protein production in plants is a promising approach to produce vaccine antigens and therapeutic proteins within a short period of time. However, this technology is only just beginning to be applied to large-scale production as many technological obstacles to scale up are now being overcome. Here, we demonstrate a simple and reproducible method for industrial-scale transient protein production based on vacuum infiltration of Nicotiana
plants with Agrobacteria
carrying launch vectors. Optimization of Agrobacterium
cultivation in AB medium allows direct dilution of the bacterial culture in Milli-Q water, simplifying the infiltration process. Among three tested species of Nicotiana
, N. excelsiana
× N. excelsior
) was selected as the most promising host due to the ease of infiltration, high level of reporter protein production, and about two-fold higher biomass production under controlled environmental conditions. Induction of Agrobacterium
harboring pBID4-GFP (Tobacco mosaic virus
-based) using chemicals such as acetosyringone and monosaccharide had no effect on the protein production level. Infiltrating plant under 50 to 100 mbar for 30 or 60 sec resulted in about 95% infiltration of plant leaf tissues. Infiltration with Agrobacterium
laboratory strain GV3101 showed the highest protein production compared to Agrobacteria
laboratory strains LBA4404 and C58C1 and wild-type Agrobacteria
strains at6, at10, at77 and A4. Co-expression of a viral RNA silencing suppressor, p23 or p19, in N. benthamiana
resulted in earlier accumulation and increased production (15-25%) of target protein (influenza virus hemagglutinin).
Plant Biology, Issue 86, Agroinfiltration, Nicotiana benthamiana, transient protein production, plant-based expression, viral vector, Agrobacteria
A Restriction Enzyme Based Cloning Method to Assess the In vitro Replication Capacity of HIV-1 Subtype C Gag-MJ4 Chimeric Viruses
Institutions: Emory University, Emory University.
The protective effect of many HLA class I alleles on HIV-1 pathogenesis and disease progression is, in part, attributed to their ability to target conserved portions of the HIV-1 genome that escape with difficulty. Sequence changes attributed to cellular immune pressure arise across the genome during infection, and if found within conserved regions of the genome such as Gag, can affect the ability of the virus to replicate in vitro
. Transmission of HLA-linked polymorphisms in Gag to HLA-mismatched recipients has been associated with reduced set point viral loads. We hypothesized this may be due to a reduced replication capacity of the virus. Here we present a novel method for assessing the in vitro
replication of HIV-1 as influenced by the gag
gene isolated from acute time points from subtype C infected Zambians. This method uses restriction enzyme based cloning to insert the gag
gene into a common subtype C HIV-1 proviral backbone, MJ4. This makes it more appropriate to the study of subtype C sequences than previous recombination based methods that have assessed the in vitro
replication of chronically derived gag-pro
sequences. Nevertheless, the protocol could be readily modified for studies of viruses from other subtypes. Moreover, this protocol details a robust and reproducible method for assessing the replication capacity of the Gag-MJ4 chimeric viruses on a CEM-based T cell line. This method was utilized for the study of Gag-MJ4 chimeric viruses derived from 149 subtype C acutely infected Zambians, and has allowed for the identification of residues in Gag that affect replication. More importantly, the implementation of this technique has facilitated a deeper understanding of how viral replication defines parameters of early HIV-1 pathogenesis such as set point viral load and longitudinal CD4+ T cell decline.
Infectious Diseases, Issue 90, HIV-1, Gag, viral replication, replication capacity, viral fitness, MJ4, CEM, GXR25
Experimental Human Pneumococcal Carriage
Institutions: Liverpool School of Tropical Medicine, University Hospital Trust, Comprehensive Local Research Network, Royal Liverpool and Broadgreen University Hospitals NHS Trust, University Hospitals of Leicester NHS Trust & University of Leicester, University of Liverpool .
Experimental human pneumococcal carriage (EHPC) is scientifically important because nasopharyngeal carriage of Streptococcus pneumoniae
is both the major source of transmission and the prerequisite of invasive disease. A model of carriage will allow accurate determination of the immunological correlates of protection, the immunizing effect of carriage and the effect of host pressure on the pathogen in the nasopharyngeal niche. Further, methods of carriage detection useful in epidemiologic studies, including vaccine studies, can be compared.
We aim to develop an EHPC platform that is a safe and useful reproducible method that could be used to down-select candidate novel pneumococcal vaccines with prevention of carriage as a surrogate of vaccine induced immunity. It will work towards testing of candidate vaccines and descriptions of the mechanisms underlying EHPC and vaccine protection from carriage1
. Current conjugate vaccines against pneumococcus protect children from invasive disease although new vaccines are urgently needed as the current vaccine does not confer optimal protection against non-bacteraemic pneumonia and there has been evidence of serotype replacement with non-vaccine serotypes2-4
We inoculate with S. pneumoniae
suspended in 100 μl of saline. Safety is a major factor in the development of the EHPC model and is achieved through intensive volunteer screening and monitoring. A safety committee consisting of clinicians and scientists that are independent from the study provides objective feedback on a weekly basis.
The bacterial inoculum is standardized and requires that no animal products are inoculated into volunteers (vegetable-based media and saline). The doses required for colonization (104
) are much lower than those used in animal models (107
. Detecting pneumococcal carriage is enhanced by a high volume (ideally >10 ml) nasal wash that is relatively mucus free. This protocol will deal with the most important parts of the protocol in turn. These are (a) volunteer selection, (b) pneumococcal inoculum preparation, (c) inoculation, (d) follow-up and (e) carriage detection.
Our current protocol has been safe in over 100 volunteers at a range of doses using two different bacterial serotypes6
. A dose ranging study using S. pneumoniae
6B and 23F is currently being conducted to determine the optimal inoculation dose for 50% carriage. A predicted 50% rate of carriage will allow the EHPC model to have high sensitivity for vaccine efficacy with small study numbers.
Infection, Issue 72, Medicine, Immmunology, Microbiology, Infectious Diseases, Anatomy, Physiology, Biomedical Engineering, Streptococcus pneumoniae, carriage, nasal wash, inoculation, human, vaccine studies, pneumonia, volunteer selection, clinical