Mouse Models Of Helicobacter Infection And Gastric Pathologies

Summary

Mice represent an invaluable in vivo model to study infection and diseases caused by gastrointestinal microorganisms. Here, we describe the methods used to study bacterial colonization and histopathological changes in mouse models of Helicobacter pylori-related disease.

Abstract

Helicobacter pylori is a gastric pathogen that is present in half of the global population and is a significant cause of morbidity and mortality in humans. Several mouse models of gastric Helicobacter infection have been developed to study the molecular and cellular mechanisms whereby H. pylori bacteria colonize the stomach of human hosts and cause disease. Herein, we describe protocols to: 1) prepare bacterial suspensions for the in vivo infection of mice via intragastric gavage; 2) determine bacterial colonization levels in mouse gastric tissues, by polymerase chain reaction (PCR) and viable counting; and 3) assess pathological changes, by histology. To establish Helicobacter infection in mice, specific pathogen-free (SPF) animals are first inoculated with suspensions (containing ≥10⁵ colony-forming units, CFUs) of mouse-colonizing strains of either Helicobacter pylori or other gastric Helicobacter spp. from animals, such as Helicobacter felis. At the appropriate time-points post-infection, stomachs are excised and dissected sagittally into two equal tissue fragments, each comprising the antrum and body regions. One of these fragments is then used for either viable counting or DNA extraction, while the other is subjected to histological processing. Bacterial colonization and histopathological changes in the stomach may be assessed routinely in gastric tissue sections stained with Warthin-Starry, Giemsa or Haematoxylin and Eosin (H&E) stains, as appropriate. Additional immunological analyses may also be undertaken by immunohistochemistry or immunofluorescence on mouse gastric tissue sections. The protocols described below are specifically designed to enable the assessment in mice of gastric pathologies resembling those in human-related H. pylori diseases, including inflammation, gland atrophy and lymphoid follicle formation. The inoculum preparation and intragastric gavage protocols may also be adapted to study the pathogenesis of other enteric human pathogens that colonize mice, such as Salmonella Typhimurium or Citrobacter rodentium.

Introduction

Helicobacter pylori is a spiral-shaped, Gram-negative, human gastric pathogen present in all populations across the world, with infection rates in developing countries estimated to be in the order of 80%¹. Although most H. pylori-infected individuals are asymptomatic, some develop more severe diseases, ranging from peptic ulceration to gastric cancer². H. pylori-associated cancers are broadly characterized either by malignant changes in epithelial cells (GECs) or by the formation of extra-nodal lymphoid tissues in the stomach, resulting in gastric adenocarcinoma or mucosa-associated lymphoid ti....

Protocol

1. Growth and Preparation of Bacterial Inocula

1. Thaw glycerol stocks of H. pylori or H. felis¹⁵ from -80 °C and subculture on horse blood agar (HBA) plates comprising: Blood Agar Base No.2 (see Table of Materials); a modified “Skirrow’s antibiotic selective supplement” (consisting of vancomycin, 10 μg/mL; polymyxin B, 25 ng/mL; trimethoprim, 5 µg/mL; amphotericin B, 2.5 μg/mL); and 5–10% (v/v) horse blood^15,16. The bacteria grow well under microaerobic conditions in 2.5 or 3.5 L anaerobic jars cont....

Results

This protocol describes an oral gavage technique to achieve intragastric infection with H. pylori or H. felis in murine mouse models (Figure 1). Following euthanasia, stomachs are removed, weighed and divided into 2 equal halves comprising the antrum, body and non-glandular regions of gastric tissues (Figure 2). The non-glandular region is removed prior to performing any analyses.

Successful colonization of animals i.......

Discussion

This protocol describes the use of an in vivo mouse model for Helicobacter infection. The critical steps of the procedure are the: 1) preparation of Helicobacter inocula containing viable and motile bacteria; 2) delivery of the appropriate numbers of bacteria to the mouse via intragastric gavage; 3) detection of bacterial infection by colony counting and/or PCR; and 4) processing of gastric tissues to enable the assessment of histopathology in infected stomachs. Further suggestions for modifica.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bacteriological reagents
Oxoid Blood Agar Base No.2	Thermo Fischer Scientific	CM0271B	Dissolve in deinonized water prior to sterilization
Premium Defibrinated Horse blood	Australian Ethical Biologicals	PDHB100
Bacto Brain Heart Infusion Broth	BD Bioscience	237500	Dissolve in deinonized water prior to sterilization
CampyGen gas packs	Thermo Fischer Scientific	CN0035A/CN0025A
Histological reagents
Formalin, neutral buffered, 10%	Sigma Aldrich	HT501128
Absolute alcohol, 100% Denatured	ChemSupply	AL048-20L-P
Isopropanol (2-propanol)	Merck	100995
Xylene (sulphur free)	ChemSupply	XT003-20L
Mayer's Haematoxylin	Amber Scientific	MH-1L	Filter before use
Eosin, Aqueous Stain	Amber Scientific	EOCA-1L	Filter before use
Wright-Giemsa Stain, modified	Sigma Aldrich	WG80-2.5L	Dilute before use (20% Giemsa, 80% deionized water)
Histolene	Grale Scientific	11031/5
DPX mounting medium	VWR	1.00579.0500
Molecular biology reagents
Qubit dsDNA BR Assay Kit	Thermo Fischer Scientific	Q32850
Oligonucleotides	Sigma Aldrich		The annealing temperature of ureB primers used in this study is 61 °C
GoTaq Flexi DNA Polymerase	Promega	M8291	Kit includes 10x PCR buffer and Magnesium Chloride
dNTPs	Bioline	BIO-39028	Dilute to 10 mM in sterile nuclease free water before use
Molecular Grade Agarose	Bioline	BIO-41025
Sodium Hydrogen Carbonate	Univar (Ajax Fine Chemicals)	A475-500G
Magnesium Sulphate Heptahydrate	Chem-Supply	MA048-500G
Antibiotics
Vancomycin	Sigma Aldrich	V2002-1G	Dissolve in deionized water
Polymyxin B	Sigma Aldrich	P4932-5MU	Dissolve in deionized water
Trimethoprim (≥98% HPLC)	Sigma Aldrich	T7883	Dissolve in 100% (absolute) Ethanol
Amphotericin	Amresco (Astral Scientific)	E437-100MG	Dissolve in deionized water
Bacitracin from Bacillus licheniformis	Sigma Aldrich	B0125	Dissolve in deionized water
Naladixic acid	Sigma Aldrich	N8878	Dissolve in deionized water
Other reagents
Methoxyflurane (Pentrhox)	Medical Developments International	Not applicable
Paraffin Wax	Paraplast Plus, Leica Biosystems	39601006
Equipment and plasticware
Oxoid Anaerobic Jars	Thermo Fischer Scientific	HP0011/HP0031
COPAN Pasteur Pipettes	Interpath Services	200CS01
Eppendorf 5810R centrifuge			Collect bacterial pellets by centrifugation at 2,200 rpm for 10 mins at 4 °C
23 g precision glide needle	BD Bioscience	301805
Parafilm M	Bemis, VWR	PM996
Portex fine bore polythene tubing	Smiths Medical	800/100/200
Plastic feeding catheters	Instech  Laboratories	FTP20-30
1 mL tuberculin luer slip disposable syringes	BD Bioscience	302100
Eppendorf micropestle for 1.2 - 2 mL tubes	Sigma Aldrich	Z317314	Autoclavable polypropylene pestles used for stomach homogenization
GentleMACs Dissociator	Miltenyi Biotec	130-093-235	Use a pre-set gentleMACS Programs for mouse stomach tissue
M Tubes (orange cap)	Miltenyi Biotec	30-093-236
Qubit Fluorometer	Thermo Fischer Scientific	Q33216
Sterile plastic loop	LabServ	LBSLP7202
Cold Plate, Leica EG1160 Embedding System	Leica Biosystems	Not applicable
Tissue-Tek Base Mould System, Base Mold 38 x 25 x 6	Sakura, Alphen aan den Rijn	4124
Tissue-Tek III Uni-Casette System	Sakura, Alphen aan den Rijn	4170
Microtome, Leica RM2235	Leica Biosystems
Charged SuperFrost Plus glass slides	Menzel Glaser, Thermo Fischer Scientific	4951PLUS4