L. monocytogenes are facultative intracellular bacterial pathogens that cause food borne infections in humans. Very little is known about the gastrointestinal phase of listeriosis due to the lack of a small animal model that closely mimics human disease. This paper describes a novel mouse model for oral transmission of L. monocytogenes. Using this model, mice fed L. monocytogenes-contaminated bread have a discrete phase of gastrointestinal infection, followed by varying degrees of systemic spread in susceptible (BALB/c/By/J) or resistant (C57BL/6) mouse strains. During the later stages of the infection, dissemination to the gall bladder and brain is observed. The food borne model of listeriosis is highly reproducible, does not require specialized skills, and can be used with a wide variety of bacterial isolates and laboratory mouse strains. As such, it is the ideal model to study both virulence strategies used by L. monocytogenes to promote intestinal colonization, as well as the host response to invasive food borne bacterial infection.
17 Related JoVE Articles!
Assessing Bacterial Invasion of Cardiac Cells in Culture and Heart Colonization in Infected Mice Using Listeria monocytogenes
Institutions: College of Medicine, University of Illinois at Chicago.
is a Gram-positive facultative intracellular pathogen that is capable of causing serious invasive infections in immunocompromised patients, the elderly, and pregnant women. The most common manifestations of listeriosis in humans include meningitis, encephalitis, and fetal abortion. A significant but much less documented sequelae of invasive L. monocytogenes
infection involves the heart. The death rate from cardiac illness can be up to 35% despite treatment, however very little is known regarding L. monocytogenes
colonization of cardiac tissue and its resultant pathologies. In addition, it has recently become apparent that subpopulations of L. monocytogenes
have an enhanced capacity to invade and grow within cardiac tissue. This protocol describes in detail in vitro
and in vivo
methods that can be used for assessing cardiotropism of L. monocytogenes
isolates. Methods are presented for the infection of H9c2 rat cardiac myoblasts in tissue culture as well as for the determination of bacterial colonization of the hearts of infected mice. These methods are useful not only for identifying strains with the potential to colonize cardiac tissue in infected animals, but may also facilitate the identification of bacterial gene products that serve to enhance cardiac cell invasion and/or drive changes in heart pathology. These methods also provide for the direct comparison of cardiotropism between multiple L. monocytogenes
Infection, Issue 99, Bacterial pathogenesis, intracellular pathogen, tissue tropism, bacterial invasion, cardiac infection, listeriosis
Tracking Microbial Contamination in Retail Environments Using Fluorescent Powder - A Retail Delicatessen Environment Example
Institutions: University of Houston, University of Arkansas.
Cross contamination of foodborne pathogens in the retail environment is a significant public health issue contributing to an increased risk for foodborne illness. Ready-to-eat (RTE) processed foods such as deli meats, cheese, and in some cases fresh produce, have been involved in foodborne disease outbreaks due to contamination with pathogens such as Listeria monocytogenes
. With respect to L. monocytogenes
, deli slicers are often the main source of cross contamination. The goal of this study was to use a fluorescent compound to simulate bacterial contamination and track this contamination in a retail setting. A mock deli kitchen was designed to simulate the retail environment. Deli meat was inoculated with the fluorescent compound and volunteers were recruited to complete a set of tasks similar to those expected of a food retail employee. The volunteers were instructed to slice, package, and store the meat in a deli refrigerator. The potential cross contamination was tracked in the mock retail environment by swabbing specific areas and measuring the optical density of the swabbed area with a spectrophotometer. The results indicated that the refrigerator (i.e.
deli case) grip and various areas on the slicer had the highest risk for cross contamination. The results of this study may be used to develop more focused training material for retail employees. In addition, similar methodologies could also be used to track microbial contamination in food production environments (e.g.
small farms), hospitals, nursing homes, cruise ships, and hotels.
Environmental Sciences, Issue 85, cross contamination, retail deli, fluorescent powder, Listeria monocytogenes, foodborne pathogens
Measuring Bacterial Load and Immune Responses in Mice Infected with Listeria monocytogenes
Institutions: The University of Melbourne, The University of Melbourne.
Listeria monocytogenes (Listeria)
is a Gram-positive facultative intracellular pathogen1
. Mouse studies typically employ intravenous injection of Listeria
, which results in systemic infection2
. After injection, Listeria quickly disseminates to the spleen and liver due to uptake by CD8α+
dendritic cells and Kupffer cells3,4
. Once phagocytosed, various bacterial proteins enable Listeria
to escape the phagosome, survive within the cytosol, and infect neighboring cells5
. During the first three days of infection, different innate immune cells (e.g. monocytes, neutrophils, NK cells, dendritic cells) mediate bactericidal mechanisms that minimize Listeria
T cells are subsequently recruited and responsible for the eventual clearance of Listeria
from the host, typically within 10 days of infection6
Successful clearance of Listeria
from infected mice depends on the appropriate onset of host immune responses6
. There is a broad range of sensitivities amongst inbred mouse strains7,8
. Generally, mice with increased susceptibility to Listeria
infection are less able to control bacterial proliferation, demonstrating increased bacterial load and/or delayed clearance compared to resistant mice. Genetic studies, including linkage analyses and knockout mouse strains, have identified various genes for which sequence variation affects host responses to Listeria
. Determination and comparison of infection kinetics between different mouse strains is therefore an important method for identifying host genetic factors that contribute to immune responses against Listeria
. Comparison of host responses to different Listeria
strains is also an effective way to identify bacterial virulence factors that may serve as potential targets for antibiotic therapy or vaccine design.
We describe here a straightforward method for measuring bacterial load (colony forming units [CFU] per tissue) and preparing single-cell suspensions of the liver and spleen for FACS analysis of immune responses in Listeria
-infected mice. This method is particularly useful for initial characterization of Listeria
infection in novel mouse strains, as well as comparison of immune responses between different mouse strains infected with Listeria
. We use the Listeria monocytogenes
that, when cultured on blood agar, exhibits a characteristic halo zone around each colony due to β-hemolysis1
(Figure 1). Bacterial load and immune responses can be determined at any time-point after infection by culturing tissue homogenate on blood agar plates and preparing tissue cell suspensions for FACS analysis using the protocols described below. We would note that individuals who are immunocompromised or pregnant should not handle Listeria
, and the relevant institutional biosafety committee and animal facility management should be consulted before work commences.
Immunology, Issue 54, Listeria, intracellular bacteria, genetic susceptibility, liver, spleen, blood, FACS analysis, T cells
Detection of Live Escherichia coli O157:H7 Cells by PMA-qPCR
Institutions: Food and Drug Administration.
A unique open reading frame (ORF) Z3276 was identified as a specific genetic marker for E. coli
O157:H7. A qPCR assay was developed for detection of E. coli
O157:H7 by targeting ORF Z3276. With this assay, we can detect as low as a few copies of the genome of DNA of E. coli
O157:H7. The sensitivity and specificity of the assay were confirmed by intensive validation tests with a large number of E. coli
O157:H7 strains (n = 369) and non-O157 strains (n = 112). Furthermore, we have combined propidium monoazide (PMA) procedure with the newly developed qPCR protocol for selective detection of live cells from dead cells. Amplification of DNA from PMA-treated dead cells was almost completely inhibited in contrast to virtually unaffected amplification of DNA from PMA-treated live cells. Additionally, the protocol has been modified and adapted to a 96-well plate format for an easy and consistent handling of a large number of samples. This method is expected to have an impact on accurate microbiological and epidemiological monitoring of food safety and environmental source.
Microbiology, Issue 84, Propidium monoazide (PMA), real-time PCR, E. coli O157:H7, pathogen, selective detection, live cells
'Bioluminescent' Reporter Phage for the Detection of Category A Bacterial Pathogens
Institutions: Guild Associates, Inc., University of Texas at Austin, Medical University of South Carolina.
and Bacillus anthracis
are Category A bacterial pathogens that are the causative agents of the plague and anthrax, respectively 1
. Although the natural occurrence of both diseases' is now relatively rare, the possibility of terrorist groups using these pathogens as a bioweapon is real. Because of the disease's inherent communicability, rapid clinical course, and high mortality rate, it is critical that an outbreak be detected quickly. Therefore methodologies that provide rapid detection and diagnosis are essential to ensure immediate implementation of public health measures and activation of crisis management.
Recombinant reporter phage may provide a rapid and specific approach for the detection of Y. pestis
and B. anthracis.
The Centers for Disease Control and Prevention currently use the classical phage lysis assays for the confirmed identification of these bacterial pathogens 2-4
. These assays take advantage of naturally occurring phage which are specific and lytic for their bacterial hosts. After overnight growth of the cultivated bacterium in the presence of the specific phage, the formation of plaques (bacterial lysis) provides a positive identification of the bacterial target. Although these assays are robust, they suffer from three shortcomings: 1) they are laboratory based; 2) they require bacterial isolation and cultivation from the suspected sample, and 3) they take 24-36 h to complete. To address these issues, recombinant "light-tagged" reporter phage were genetically engineered by integrating the Vibrio harveyi luxAB
genes into the genome of Y. pestis
and B. anthracis
specific phage 5-8
. The resulting luxAB
reporter phage were able to detect their specific target by rapidly (within minutes) and sensitively conferring a bioluminescent phenotype to recipient cells. Importantly, detection was obtained either with cultivated recipient cells or with mock-infected clinical specimens 7
For demonstration purposes, here we describe the method for the phage-mediated detection of a known Y. pestis
isolate using a luxAB
reporter phage constructed from the CDC plague diagnostic phage ΦA1122 6,7
(Figure 1). A similar method, with minor modifications (e.g. change in growth temperature and media), may be used for the detection of B. anthracis
isolates using the B. anthracis
reporter phage Wβ::luxAB 8
. The method describes the phage-mediated transduction of a biolumescent phenotype to cultivated Y. pestis
cells which are subsequently measured using a microplate luminometer. The major advantages of this method over the traditional phage lysis assays is the ease of use, the rapid results, and the ability to test multiple samples simultaneously in a 96-well microtiter plate format.
Figure 1. Detection schematic.
The phage are mixed with the sample, the phage infects the cell, luxAB
are expressed, and the cell bioluminesces. Sample processing is not necessary; the phage and cells are mixed and subsequently measured for light.
Immunology, Issue 53, Reporter phage, bioluminescence, detection, plague, anthrax
Imaging InlC Secretion to Investigate Cellular Infection by the Bacterial Pathogen Listeria monocytogenes
Institutions: Pasteur Institute, INSERM U604, Institut National de la Recherche Agronomique (INRA), USC2020, ETH Zürich, University of Basel.
Bacterial intracellular pathogens can be conceived as molecular tools to dissect cellular signaling cascades due to their capacity to exquisitely manipulate and subvert cell functions which are required for the infection of host target tissues. Among these bacterial pathogens, Listeria monocytogenes
is a Gram positive microorganism that has been used as a paradigm for intracellular parasitism in the characterization of cellular immune responses, and which has played instrumental roles in the discovery of molecular pathways controlling cytoskeletal and membrane trafficking dynamics. In this article, we describe a robust microscopical assay for the detection of late cellular infection stages of L. monocytogenes
based on the fluorescent labeling of InlC, a secreted bacterial protein which accumulates in the cytoplasm of infected cells; this assay can be coupled to automated high-throughput small interfering RNA screens in order to characterize cellular signaling pathways involved in the up- or down-regulation of infection.
Immunology, Issue 79, HeLa Cells, Listeria monocytogenes, Gram-positive Bacterial Infections, Fluorescence, High-Throughput Screening Assays, RNA Interference, Listeria monocytogenes, Infection, microscopy, small interfering RNA
Colorimetric Paper-based Detection of Escherichia coli, Salmonella spp., and Listeria monocytogenes from Large Volumes of Agricultural Water
Institutions: University of Wyoming, Colorado State University, Colorado State University, Colorado State University, University of California, Davis, University of Florida, McGill University.
This protocol describes rapid colorimetric detection of Escherichia coli
spp., and Listeria monocytogenes
from large volumes (10 L) of agricultural waters. Here, water is filtered through sterile Modified Moore Swabs (MMS), which consist of a simple gauze filter enclosed in a plastic cartridge, to concentrate bacteria. Following filtration, non-selective or selective enrichments for the target bacteria are performed in the MMS. For colorimetric detection of the target bacteria, the enrichments are then assayed using paper-based analytical devices (µPADs) embedded with bacteria-indicative substrates. Each substrate reacts with target-indicative bacterial enzymes, generating colored products that can be detected visually (qualitative detection) on the µPAD. Alternatively, digital images of the reacted µPADs can be generated with common scanning or photographic devices and analyzed using ImageJ software, allowing for more objective and standardized interpretation of results. Although the biochemical screening procedures are designed to identify the aforementioned bacterial pathogens, in some cases enzymes produced by background microbiota or the degradation of the colorimetric substrates may produce a false positive. Therefore, confirmation using a more discriminatory diagnostic is needed. Nonetheless, this bacterial concentration and detection platform is inexpensive, sensitive (0.1 CFU/ml detection limit), easy to perform, and rapid (concentration, enrichment, and detection are performed within approximately 24 hr), justifying its use as an initial screening method for the microbiological quality of agricultural water.
Environmental Sciences, Issue 88, Paper-based analytical device (µPAD), Colorimetric enzymatic detection, Salmonella spp., Listeria monocytogenes, Escherichia coli, Modified Moore Swab (MMS), agricultural water, food safety, environmental microbiology
The Portable Chemical Sterilizer (PCS), D-FENS, and D-FEND ALL: Novel Chlorine Dioxide Decontamination Technologies for the Military
Institutions: United States Army-Natick Soldier RD&E Center, Warfighter Directorate, University of Connecticut Health Center, Lawrence Livermore National Laboratory, Children's Hospital Oakland Research Institute.
There is a stated Army need for a field-portable, non-steam sterilizer technology that can be used by Forward Surgical Teams, Dental Companies, Veterinary Service Support Detachments, Combat Support Hospitals, and Area Medical Laboratories to sterilize surgical instruments and to sterilize pathological specimens prior to disposal in operating rooms, emergency treatment areas, and intensive care units. The following ensemble of novel, ‘clean and green’ chlorine dioxide technologies are versatile and flexible to adapt to meet a number of critical military needs for decontamination6,15
. Specifically, the Portable Chemical Sterilizer (PCS) was invented to meet urgent battlefield needs and close critical capability gaps for energy-independence, lightweight portability, rapid mobility, and rugged durability in high intensity forward deployments3
. As a revolutionary technological breakthrough in surgical sterilization technology, the PCS is a Modern Field Autoclave that relies on on-site, point-of-use, at-will generation of chlorine dioxide instead of steam. Two (2) PCS units sterilize 4 surgical trays in 1 hr, which is the equivalent throughput of one large steam autoclave (nicknamed “Bertha” in deployments because of its cumbersome size, bulky dimensions, and weight). However, the PCS operates using 100% less electricity (0 vs. 9 kW) and 98% less water (10 vs. 640 oz.), significantly reduces weight by 95% (20 vs. 450 lbs, a 4-man lift) and cube by 96% (2.1 vs. 60.2 ft3
), and virtually eliminates the difficult challenges in forward deployments of repairs and maintaining reliable operation, lifting and transporting, and electrical power required for steam autoclaves.
Bioengineering, Issue 88, chlorine dioxide, novel technologies, D-FENS, PCS, and D-FEND ALL, sterilization, decontamination, fresh produce safety
Particle Agglutination Method for Poliovirus Identification
Institutions: National Institute of Infectious Diseases, Fujirebio Inc..
In the Global Polio Eradication Initiative, laboratory diagnosis plays a critical role by isolating and identifying PV from the stool samples of acute flaccid paralysis (AFP) cases. In the World Health Organization (WHO) Global Polio Laboratory Network, PV isolation and identification are currently being performed by using cell culture system and real-time RT-PCR, respectively. In the post-eradication era of PV, simple and rapid identification procedures would be helpful for rapid confirmation of polio cases at the national laboratories. In the present study, we will show the procedure of novel PA assay developed for PV identification. This PA assay utilizes interaction of PV receptor (PVR) molecule and virion that is specific and uniform affinity to all the serotypes of PV. The procedure is simple (one step procedure in reaction plates) and rapid (results can be obtained within 2 h of reaction), and the result is visually observed (observation of agglutination of gelatin particles).
Immunology, Issue 50, Poliovirus, identification, particle agglutination, virus receptor
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
Isolation of Native Soil Microorganisms with Potential for Breaking Down Biodegradable Plastic Mulch Films Used in Agriculture
Institutions: Western Washington University, Washington State University Northwestern Research and Extension Center, Texas Tech University.
Fungi native to agricultural soils that colonized commercially available biodegradable mulch (BDM) films were isolated and assessed for potential to degrade plastics. Typically, when formulations of plastics are known and a source of the feedstock is available, powdered plastic can be suspended in agar-based media and degradation determined by visualization of clearing zones. However, this approach poorly mimics in situ
degradation of BDMs. First, BDMs are not dispersed as small particles throughout the soil matrix. Secondly, BDMs are not sold commercially as pure polymers, but rather as films containing additives (e.g.
fillers, plasticizers and dyes) that may affect microbial growth. The procedures described herein were used for isolates acquired from soil-buried mulch films. Fungal isolates acquired from excavated BDMs were tested individually for growth on pieces of new, disinfested BDMs laid atop defined medium containing no carbon source except agar. Isolates that grew on BDMs were further tested in liquid medium where BDMs were the sole added carbon source. After approximately ten weeks, fungal colonization and BDM degradation were assessed by scanning electron microscopy. Isolates were identified via analysis of ribosomal RNA gene sequences. This report describes methods for fungal isolation, but bacteria also were isolated using these methods by substituting media appropriate for bacteria. Our methodology should prove useful for studies investigating breakdown of intact plastic films or products for which plastic feedstocks are either unknown or not available. However our approach does not provide a quantitative method for comparing rates of BDM degradation.
Microbiology, Issue 75, Plant Biology, Environmental Sciences, Agricultural Sciences, Soil Science, Molecular Biology, Cellular Biology, Genetics, Mycology, Fungi, Bacteria, Microorganisms, Biodegradable plastic, biodegradable mulch, compostable plastic, compostable mulch, plastic degradation, composting, breakdown, soil, 18S ribosomal DNA, isolation, culture
An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium
Institutions: University of Georgia.
Current commercial PCRs tests for identifying Salmonella
target genes unique to this genus. However, there are two species, six subspecies, and over 2,500 different Salmonella
serovars, and not all are equal in their significance to public health. For example, finding S. enterica subspecies
IIIa Arizona on a table egg layer farm is insignificant compared to the isolation of S. enterica
subspecies I serovar Enteritidis, the leading cause of salmonellosis linked to the consumption of table eggs. Serovars are identified based on antigenic differences in lipopolysaccharide (LPS)(O antigen) and flagellin (H1 and H2 antigens). These antigenic differences are the outward appearance of the diversity of genes and gene alleles associated with this phenotype.
We have developed an allelotyping, multiplex PCR that keys on genetic differences between four major S. enterica
subspecies I serovars found in poultry and associated with significant human disease in the US. The PCR primer pairs were targeted to key genes or sequences unique to a specific Salmonella
serovar and designed to produce an amplicon with size specific for that gene or allele. Salmonella
serovar is assigned to an isolate based on the combination of PCR test results for specific LPS and flagellin gene alleles. The multiplex PCRs described in this article are specific for the detection of S. enterica
subspecies I serovars Enteritidis, Hadar, Heidelberg, and Typhimurium.
Here we demonstrate how to use the multiplex PCRs to identify serovar for a Salmonella
Immunology, Issue 53, PCR, Salmonella, multiplex, Serovar
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
Detection of Foodborne Bacterial Pathogens from Individual Filth Flies
Institutions: U.S. Food and Drug Administration.
There is unanimous consensus that insects are important vectors of foodborne pathogens. However, linking insects as vectors of the pathogen causing a particular foodborne illness outbreak has been challenging. This is because insects are not being aseptically collected as part of an environmental sampling program during foodborne outbreak investigations and because there is not a standardized method to detect foodborne bacteria from individual insects. To take a step towards solving this problem, we adapted a protocol from a commercially available PCR-based system that detects foodborne pathogens from food and environmental samples, to detect foodborne pathogens from individual flies.Using this standardized protocol, we surveyed 100 wild-caught flies for the presence of Cronobacter
spp., Salmonella enterica,
and Listeria monocytogenes
and demonstrated that it was possible to detect and further isolate these pathogens from the body surface and the alimentary canal of a single fly. Twenty-two percent of the alimentary canals and 8% of the body surfaces from collected wild flies were positive for at least one of the three foodborne pathogens. The prevalence of Cronobacter
spp. on either body part of the flies was statistically higher (19%) than the prevalence of S. enterica
(7%) and L.monocytogenes
(4%). No false positives were observed when detecting S. enterica
and L. monocytogenes
using this PCR-based system because pure bacterial cultures were obtained from all PCR-positive results. However, pure Cronobacter
colonies were not obtained from about 50% of PCR-positive samples, suggesting that the PCR-based detection system for this pathogen cross-reacts with other Enterobacteriaceae
present among the highly complex microbiota carried by wild flies. The standardized protocol presented here will allow laboratories to detect bacterial foodborne pathogens from aseptically collected insects, thereby giving public health officials another line of evidence to find out how the food was contaminated when performing foodborne outbreak investigations.
Environmental Sciences, Issue 96, Synanthropy, filth flies, Cronobacter, Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, shiga-toxigenic E. coli, STEC, PCR-based methods, foodborne illness, foodborne outbreak investigations.
Screening Foodstuffs for Class 1 Integrons and Gene Cassettes
Institutions: Macquarie University.
Antibiotic resistance is one of the greatest threats to health in the 21st
century. Acquisition of resistance genes via lateral gene transfer is a major factor in the spread of diverse resistance mechanisms. Amongst the DNA elements facilitating lateral transfer, the class 1 integrons have largely been responsible for spreading antibiotic resistance determinants amongst Gram negative pathogens. In total, these integrons have acquired and disseminated over 130 different antibiotic resistance genes. With continued antibiotic use, class 1 integrons have become ubiquitous in commensals and pathogens of humans and their domesticated animals. As a consequence, they can now be found in all human waste streams, where they continue to acquire new genes, and have the potential to cycle back into humans via the food chain. This protocol details a streamlined approach for detecting class 1 integrons and their associated resistance gene cassettes in foodstuffs, using culturing and PCR. Using this protocol, researchers should be able to: collect and prepare samples to make enriched cultures and screen for class 1 integrons; isolate single bacterial colonies to identify integron-positive isolates; identify bacterial species that contain class 1 integrons; and characterize these integrons and their associated gene cassettes.
Environmental Sciences, Issue 100, integron, lateral gene transfer, epidemiology, resistome, antibiotic resistance, pollution, xenogenetic
Use of Artificial Sputum Medium to Test Antibiotic Efficacy Against Pseudomonas aeruginosa in Conditions More Relevant to the Cystic Fibrosis Lung
Institutions: University of Liverpool , University of Liverpool .
There is growing concern about the relevance of in vitro
antimicrobial susceptibility tests when applied to isolates of P. aeruginosa
from cystic fibrosis (CF) patients. Existing methods rely on single or a few isolates grown aerobically and planktonically. Predetermined cut-offs are used to define whether the bacteria are sensitive or resistant to any given antibiotic1
. However, during chronic lung infections in CF, P. aeruginosa
populations exist in biofilms and there is evidence that the environment is largely microaerophilic2
. The stark difference in conditions between bacteria in the lung and those during diagnostic testing has called into question the reliability and even relevance of these tests3
Artificial sputum medium (ASM) is a culture medium containing the components of CF patient sputum, including amino acids, mucin and free DNA. P. aeruginosa
growth in ASM mimics growth during CF infections, with the formation of self-aggregating biofilm structures and population divergence4,5,6
. The aim of this study was to develop a microtitre-plate assay to study antimicrobial susceptibility of P. aeruginosa
based on growth in ASM, which is applicable to both microaerophilic and aerobic conditions.
An ASM assay was developed in a microtitre plate format. P. aeruginosa
biofilms were allowed to develop for 3 days prior to incubation with antimicrobial agents at different concentrations for 24 hours. After biofilm disruption, cell viability was measured by staining with resazurin. This assay was used to ascertain the sessile cell minimum inhibitory concentration (SMIC) of tobramycin for 15 different P. aeruginosa
isolates under aerobic and microaerophilic conditions and SMIC values were compared to those obtained with standard broth growth. Whilst there was some evidence for increased MIC values for isolates grown in ASM when compared to their planktonic counterparts, the biggest differences were found with bacteria tested in microaerophilic conditions, which showed a much increased resistance up to a >128 fold, towards tobramycin in the ASM system when compared to assays carried out in aerobic conditions.
The lack of association between current susceptibility testing methods and clinical outcome has questioned the validity of current methods3
. Several in vitro
models have been used previously to study P. aeruginosa
. However, these methods rely on surface attached biofilms, whereas the ASM biofilms resemble those observed in the CF lung9
. In addition, reduced oxygen concentration in the mucus has been shown to alter the behavior of P. aeruginosa2
and affect antibiotic susceptibility10
. Therefore using ASM under microaerophilic conditions may provide a more realistic environment in which to study antimicrobial susceptibility.
Immunology, Issue 64, Microbiology, Pseudomonas aeruginosa, antimicrobial susceptibility, artificial sputum media, lung infection, cystic fibrosis, diagnostics, plankton
Systemic Bacterial Infection and Immune Defense Phenotypes in Drosophila Melanogaster
Institutions: Cornell University.
The fruit fly Drosophila melanogaster
is one of the premier model organisms for studying the function and evolution of immune defense. Many aspects of innate immunity are conserved between insects and mammals, and since Drosophila
can readily be genetically and experimentally manipulated, they are powerful for studying immune system function and the physiological consequences of disease. The procedure demonstrated here allows infection of flies by introduction of bacteria directly into the body cavity, bypassing epithelial barriers and more passive forms of defense and allowing focus on systemic infection. The procedure includes protocols for the measuring rates of host mortality, systemic pathogen load, and degree of induction of the host immune system. This infection procedure is inexpensive, robust and quantitatively repeatable, and can be used in studies of functional genetics, evolutionary life history, and physiology.
Immunology, Issue 99, Drosophila, immunity, infection, resistance, tolerance, bacteria, Providencia, antimicrobial peptides, immune defense