Exposure to Metronidazole In Vivo Readily Induces Resistance in Helicobacter pylori and Reduces the Efficacy of Eradication Therapy in Mice

ABSTRACT The Helicobacter pylori SS1 mouse model was used to characterize the development of resistance in H. pyloriafter treatment with metronidazole monotherapy and to examine the effect of prior exposure to metronidazole on the efficacy of a metronidazole-containing eradication regimen. Mice colonized with the metronidazole-sensitive H. pyloriSS1 strain were treated for 7 days with either peptone trypsin broth or the mouse equivalent of 400 mg of metronidazole once a day or three times per day (TID). In a separate experiment,H. pylori-infected mice were administered either peptone trypsin broth or the mouse equivalent of 400 mg of metronidazole TID for 7 days, followed 1 month later by either peptone trypsin broth or the mouse equivalent of 20 mg of omeprazole, 250 mg of clarithromycin, and 400 mg of metronidazole twice a day for 7 days. At least 1 month after the completion of treatment, the mice were sacrificed and their stomachs were cultured for H. pylori. The susceptibilities of isolates to metronidazole were assessed by agar dilution determination of the MICs. Mixed populations of metronidazole-resistant and -sensitive strains were isolated from 70% of mice treated with 400 mg of metronidazole TID. The ratio of resistant to sensitive strains was 1:100, and the MICs for the resistant strains varied from 8 to 64 μg/ml. In the second experiment, H. pylori was eradicated from 70% of mice treated with eradication therapy alone, compared to 25% of mice pretreated with metronidazole (P < 0.01). Mice still infected after treatment with metronidazole and eradication therapy contained mixed populations of metronidazole-resistant and -sensitive isolates in a ratio of 1:25. These results demonstrate thatH. pylori readily acquires resistance to metronidazole in vivo and that prior exposure of the organism to metronidazole is associated with failure of eradication therapy. H. pylori-infected mice provide a suitable model for the study of resistance mechanisms inH. pylori and will be useful in determining optimal regimens for the eradication of resistant strains.

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Analysis of rdxA and Involvement of Additional Genes Encoding NAD(P)H Flavin Oxidoreductase (FrxA) and Ferredoxin-Like Protein (FdxB) in Metronidazole Resistance of Helicobacter pylori

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.44.8.2133-2142.2000 ◽

2000 ◽

Vol 44 (8) ◽

pp. 2133-2142 ◽

Cited By ~ 78

Author(s):

Dong-Hyeon Kwon ◽

Fouad A. K. El-Zaatari ◽

Mototsugu Kato ◽

Michael S. Osato ◽

Rita Reddy ◽

...

Keyword(s):

Helicobacter Pylori ◽

Resistant Strain ◽

Resistance Mechanisms ◽

Sensitive Strain ◽

Metronidazole Resistance ◽

Genes Encoding ◽

Resistant Strains ◽

Flavin Oxidoreductase ◽

H Pylori

ABSTRACT Metronidazole (Mtz) is a critical ingredient of modern multidrug therapies for Helicobacter pylori infection. Mtz resistance reduces the effectiveness of these combinations. Although null mutations in a rdxA gene that encodes oxygen-insensitive NAD(P)H nitroreductase was reported in Mtz-resistant H. pylori, an intact rdxA gene has also been reported in Mtz-resistant H. pylori, suggesting that additional Mtz resistance mechanisms exist in H. pylori. We explored the nature of Mtz resistance among 544 clinical H. pyloriisolates to clarify the role of rdxA inactivation in Mtz resistance and to identify another gene(s) responsible for Mtz resistance in H. pylori. Mtz resistance was present in 33% (181 of 544) of the clinical isolates. There was marked heterogeneity of resistance, with Mtz MICs ranging from 8 to ≥256 μg/ml.rdxA inactivation resulted in Mtz MICs of up to 32 μg/ml for 6 Mtz-sensitive H. pylori strains and 128 μg/ml for one Mtz-sensitive strain. Single or dual (with rdxA) inactivation of genes that encode ferredoxin-like protein (designatedfdxB) and NAD(P)H flavin oxidoreductase (frxA) also increased the MICs of Mtz for sensitive and resistant strains with low to moderate levels of Mtz resistance. fdxB inactivation resulted in a lower level of resistance than that from rdxAinactivation, whereas frxA inactivation resulted in MICs similar to those seen with rdxA inactivation. Further evidence for involvement of the frxA gene in Mtz resistance included the finding of a naturally inactivated frxA but an intact rdxA in an Mtz-resistant strain, complementation of Mtz sensitivity from an Mtz-sensitive strain to an Mtz-resistant strain or vice versa by use of naturally inactivated or functionalfrxA genes, respectively, and transformation of an Mtz-resistant Escherichia coli strain to an Mtz sensitive strain by a naturally functional frxA gene but not an inactivated frxA gene. These results are consistent with the hypothesis that null mutations in fdxB,frxA, or rdxA may be involved in Mtz resistance.

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ANTIBIOTIC RESISTANCE SURVEILLANCE OF HELICOBACTER PYLORI AT THE BIOBÍO REGION (CHILE) IN A DECADE

Arquivos de Gastroenterologia ◽

10.1590/s0004-2803.201900000-72 ◽

2019 ◽

Vol 56 (4) ◽

pp. 361-366

Author(s):

Cristian PARRA-SEPÚLVEDA ◽

José S MERINO ◽

Katia SÁEZ-CARRILLO ◽

Carlos GONZÁLEZ ◽

Apolinaria GARCÍA-CANCINO

Keyword(s):

Health Care ◽

Helicobacter Pylori ◽

Antibiotic Resistance ◽

Blood Cells ◽

Eradication Therapy ◽

Clarithromycin Resistance ◽

Resistant Strains ◽

H Pylori ◽

Horse Red Blood Cells ◽

Co2 Atmosphere

ABSTRACT BACKGROUND: Helicobacter pylori infection in Chile remains as a public and private health-care system’s challenge, with a prevalence of the infection over 70%. Nowadays, antibiotic treatment of the infection is mandatory to prevent the arising of severe associated diseases but failures in the eradication therapy mainly due to clarithromycin resistance has been observed worldwide and first line eradication therapy seems to be not effective anymore in several geographical areas. Thus, health-care systems are committed to maintain an epidemiological surveillance upon the evolution of the antibiotic resistance of this priority 2 pathogen. OBJECTIVE: This work reports a 10 years surveillance of the primary antibiotic resistance of H. pylori clinical isolates at the Biobío region-Chile, and the evolution of resistance toward amoxicillin, clarithromycin, levofloxacin, metronidazole, and tetracycline among the species. METHODS: H. pylori strains were investigated during the periods 2005-2007 (1435 patients analysed) and 2015-2017 (220 patients analysed) by inoculating a saline homogenate biopsy onto the surface of Columbia agar (Oxoid, Basingstoke, UK) - supplemented with 7% horse red blood cells plus DENT inhibitor (Oxoid, Basingstoke, UK) - following by incubation at 37ºC under 10% CO2 atmosphere for five days. Antibiotic resistance pattern of the isolates was assessed using the disk diffusion test in Müeller-Hinton agar supplemented with 7% horse red blood cells followed by incubation for further three days under 10% CO2 atmosphere. Statistical analysis was done using the SPSS v22 software and P values <0.05 were considered statistically significant. RESULTS: A total of 41% of 1435 patients were detected to be infected with H. pylori by bacteriological culture in 2005-2007 period, meanwhile 32.7% from 220 patients were also infected in 2015-2017 period. The clinical isolates of H. pylori are mostly susceptible to amoxicillin and tetracycline (both over 98% of strains), but less susceptible to levofloxacin in both periods analysed (over 79% of the strains). On the other hand, metronidazole continuous showing the highest score of resistant isolates (over 40% of resistant strains), although an 18% fewer resistant strains were observed in 2015-2017 period. Clarithromycin, the key antibiotic in eradication therapies, has an increased frequency of resistant strain isolated in the decade (22.5% in 2005-2007 and 29.2% in 2015-2017). Multidrug resistant strains (two, three and four antibiotics) were also detected in both periods with the highest scores for simultaneous resistance to clarithromycin-metronidazole (18%) and clarithromycin-metronidazole-levofloxacin (12.5%) resistant strains. According to gender, the isolates resistant to amoxicillin, clarithromycin and metronidazole were more frequent in female, with a specific increment in amoxicillin and clarithromycin resistance. CONCLUSION: The frequency of clarithromycin resistance (29.2%) detected in 2015-2017 suggests that conventional triple therapy is no longer effective in this region.

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Treatment of Helicobacter pylori infections in the light of the increase of antibiotic resistance

Postępy Higieny i Medycyny Doświadczalnej ◽

10.5604/01.3001.0011.6469 ◽

2018 ◽

Vol 72 ◽

pp. 143-158

Author(s):

Eliza Mnich ◽

Jakub Ibran ◽

Magdalena Chmiela

Keyword(s):

Fatty Acids ◽

Ascorbic Acid ◽

Helicobacter Pylori ◽

Antibiotic Resistance ◽

Eradication Therapy ◽

The World ◽

Potential Alternative ◽

Resistant Strains ◽

Treatment Mechanisms ◽

H Pylori

The aim of this study was to present the risks associated with the occurrence of Helicobacter pylori (H. pylori) infection in humans and the problems related to eradication procedures with the use of antibiotic treatment. The content provides an overview of the available methods of infection diagnosis and recommended therapeutic schemes as well as potential alternative schedules of treatment. Mechanisms of H. pylori resistance to commonly used antibiotics including the mutations in the genome leading to resistance and the incidence of resistant strains in the world has been described. Finally, we introduced substances with some potential in eradication therapy, including probiotics, plant formulations as well as polyunsaturated fatty acids and ascorbic acid.

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Resistotype of Helicobacter pylori isolates: the impact on eradication outcome

Journal of Medical Microbiology ◽

10.1099/jmm.0.069781-0 ◽

2014 ◽

Vol 63 (5) ◽

pp. 703-709 ◽

Cited By ~ 16

Author(s):

Hanafiah Alfizah ◽

Ahmad Norazah ◽

Razlan Hamizah ◽

Mohamed Ramelah

Keyword(s):

Helicobacter Pylori ◽

Antibiotic Resistance ◽

Eradication Therapy ◽

Fluoroquinolone Resistance ◽

23S Rrna ◽

Nonsense Mutations ◽

Metronidazole Resistance ◽

Resistant Strains ◽

H Pylori ◽

The Impact

Antibiotic resistance is increasing worldwide, and it has been regarded as the main factor reducing the efficacy of Helicobacter pylori therapy. The aim of this study was to determine the phenotype and genotype of antibiotic-resistant strains of H. pylori in the Malaysian population and to evaluate the impact of antibiotic resistance to eradication outcome. One hundred and sixty-one H. pylori isolates were analysed in this study. Metronidazole, clarithromycin, fluoroquinolone, amoxicillin and tetracycline susceptibilities were determined by Etest. PCR followed by DNA sequencing was carried out to determine mutations. The medical records of the patients infected with resistant strains were reviewed to determine the eradication outcome. Metronidazole resistance was encountered in 36.6 % of H. pylori isolates, whereas clarithromycin and fluoroquinolone resistance was observed in 1.2 and 1.9 % of isolates, respectively. All strains tested were susceptible to amoxicillin and tetracycline. Frameshift and nonsense mutations in rdxA and frxA genes resulting in stop codons contributed to metronidazole resistance, which leads to reduced eradication efficacy. A2142G and A2143G mutations of 23S rRNA were identified as causing failure of the eradication therapy. Mutation at either codon 87 or 91 of the gyrA gene was identified in fluoroquinolone-resistant strains. However, the effect of resistance could not be assessed. This study showed that frameshift and nonsense mutations in rdxA or frxA genes and point mutations in the 23S rRNA affected the efficacy of H. pylori eradication therapy.

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Anti-Helicobacter pylori Potential of Artemisinin and Its Derivatives

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00407-12 ◽

2012 ◽

Vol 56 (9) ◽

pp. 4594-4607 ◽

Cited By ~ 24

Author(s):

Suchandra Goswami ◽

Rajendra S. Bhakuni ◽

Annalakshmi Chinniah ◽

Anirban Pal ◽

Sudip K. Kar ◽

...

Keyword(s):

Helicobacter Pylori ◽

Artemisia Annua ◽

Infection Model ◽

Strong Activity ◽

Content Type ◽

Content Development ◽

Candidate Drug ◽

Resistant Strains ◽

H Pylori

ABSTRACTThe antimalarial drug artemisinin fromArtemisia annuademonstrated remarkably strong activity againstHelicobacter pylori, the pathogen responsible for peptic ulcer diseases. In an effort to develop a novel antimicrobial chemotherapeutic agent containing such a sesquiterpene lactone endoperoxide, a series of analogues (2 natural and 15 semisynthetic molecules), including eight newly synthesized compounds, were investigated against clinical and standard strains ofH. pylori. The antimicrobial spectrum against 10H. pyloristrains and a few other bacterial and fungal strains indicated specificity against the ulcer causing organism. Of five promising molecules, a newly synthesized ether derivative β-artecyclopropylmether was found to be the most potent compound, which exhibited MIC range, MIC90, and minimum bactericidal concentration range values of 0.25 to 1.0 μg/ml, 1.0 μg/ml, and 1 to 16 μg/ml, respectively, against both resistant and sensitive strains ofH. pylori. The molecule demonstrated strong bactericidal kinetics with extensive morphological degeneration, retained functional efficacy at stomach acidic pH unlike clarithromycin, did not elicit drug resistance unlike metronidazole, and imparted sensitivity to resistant strains. It is not cytotoxic and exhibitsin vivopotentiality to reduce theH. pyloriburden in a chronic infection model. Thus, β-artecyclopropylmether could be a lead candidate for anti-H. pyloritherapeutics. Since the recurrence of gastroduodenal ulcers is believed to be mainly due to antibiotic resistance of the commensal organismH. pylori, development of a candidate drug from this finding is warranted.

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Searching for New Tools to Counteract the Helicobacter pylori Resistance: The Positive Action of Resveratrol Derivatives

Antibiotics ◽

10.3390/antibiotics9120891 ◽

2020 ◽

Vol 9 (12) ◽

pp. 891

Author(s):

Paola Di Fermo ◽

Silvia Di Lodovico ◽

Rosa Amoroso ◽

Barbara De Filippis ◽

Simonetta D’Ercole ◽

...

Keyword(s):

Helicobacter Pylori ◽

Galleria Mellonella ◽

Soft Agar ◽

Swarming Motility ◽

Phenol Derivatives ◽

Antibiotic Compounds ◽

Resistant Strains ◽

H Pylori ◽

Motility Inhibition

The drug-resistance phenomenon in Helicobacter pylori underlines the need of novel strategies to improve the eradication rate including alternative treatments combining antibiotic and non-antibiotic compounds with synergistic action. In this study, the antibacterial (MIC/MBC) and anti-virulence effects (biofilm reduction and swarming motility inhibition) of resveratrol-RSV and new synthetized RSV-phenol derivatives, with a higher bioavailability, alone and combined with levofloxacin-LVX were evaluated against resistant H. pylori clinical strains. The experiments were confirmed in vivo using the Galleria mellonella model. Among the studied RSV derivatives, RSV-3 and RSV-4 possessed higher antibacterial activity with respect to RSV (MICs from 6.25 to 200 µg/mL and from 3.12 to 200 µg/mL, respectively). RSV, RSV-3, and RSV-4 were able to synergize with LVX restoring its effect in two out of seven clinical resistant strains tested for the study. RSV, RSV-3, and RSV-4, alone and with LVX at sub-MIC and sub-synergistic concentrations, significantly reduced the biofilm formation. Moreover, RSV-3 and RSV-4 reduced the H. pylori swarming motility on soft agar. RSV, RSV-3, and RSV-4 were non-toxic for G. mellonella larvae and displayed a protective effect against H. pylori infection. Overall, RSV–phenol derivatives should be considered interesting candidates for innovative therapeutic schemes to tackle the H. pylori antibiotic resistance.

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Appearance of a metronidazole-resistant Helicobacter pylori strain in an infected-ICR-mouse model and difference in eradication of metronidazole-resistant and -sensitive strains.

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.41.12.2602 ◽

1997 ◽

Vol 41 (12) ◽

pp. 2602-2605 ◽

Cited By ~ 15

Author(s):

S Matsumoto ◽

Y Washizuka ◽

Y Matsumoto ◽

S Tawara ◽

F Ikeda ◽

...

Keyword(s):

Helicobacter Pylori ◽

Mouse Model ◽

Resistant Strain ◽

Sensitive Strain ◽

Original Strain ◽

Antibiotic Resistant ◽

Icr Mouse ◽

Resistant Strains ◽

H Pylori

We tested whether antibiotic-resistant strains appeared in vivo after the failure of treatment using the Helicobacter pylori-infected euthymic mouse model. The numbers of colonies isolated from 56 ICR mice 2 weeks after 4 days of treatment with metronidazole (3.2, 10, or 32 mg/kg of body weight) or amoxicillin (1, 3.2 or 10 mg/kg), with treatment started 4 days after H. pylori CPY2052 inoculation, were counted, and the isolated strains were tested for their sensitivities to two antibiotics to rule out the presence of antibiotic-resistant strains. One metronidazole-resistant strain was detected in a mouse treated with 10 mg of metronidazole per kg, and the MIC of metronidazole for this strain was 25 microg/ml, compared to a MIC of 1.56 microg/ml for the original strain. However, no resistant strain was detected in the amoxicillin treatment group. After the examination described above, mice challenged with a metronidazole-resistant or -sensitive strain isolated from the stomach of a mouse were treated with metronidazole or amoxicillin. The metronidazole-resistant strain was more difficult to eradicate in vivo than the sensitive strain after treatment with metronidazole but not after treatment with amoxicillin. Thus, a metronidazole-resistant H. pylori strain was selected by insufficient treatment, but no resistant strain was selected with amoxicillin. Eradication of a metronidazole-resistant H. pylori strain in vivo required a higher dosage than eradication of a metronidazole-sensitive H. pylori strain. These results may explain one of the reasons for H. pylori treatment failure.

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Cholestenone functions as an antibiotic against Helicobacter pylori by inhibiting biosynthesis of the cell wall component CGL

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2016469118 ◽

2021 ◽

Vol 118 (16) ◽

pp. e2016469118

Author(s):

Junichi Kobayashi ◽

Masatomo Kawakubo ◽

Chifumi Fujii ◽

Nobuhiko Arisaka ◽

Masaki Miyashita ◽

...

Keyword(s):

Cell Wall ◽

Helicobacter Pylori ◽

Gastric Mucosa ◽

Control Diet ◽

Inhibitory Effects ◽

Oral Medicine ◽

Resistant Strains ◽

H Pylori

Helicobacter pylori, a pathogen responsible for gastric cancer, contains a unique glycolipid, cholesteryl-α-D-glucopyranoside (CGL), in its cell wall. Moreover, O-glycans having α1,4-linked N-acetylglucosamine residues (αGlcNAc) are secreted from gland mucous cells of gastric mucosa. Previously, we demonstrated that CGL is critical for H. pylori survival and that αGlcNAc serves as antibiotic against H. pylori by inhibiting CGL biosynthesis. In this study, we tested whether a cholesterol analog, cholest-4-en 3-one (cholestenone), exhibits antibacterial activity against H. pylori in vitro and in vivo. When the H. pylori standard strain ATCC 43504 was cultured in the presence of cholestenone, microbial growth was significantly suppressed dose-dependently relative to microbes cultured with cholesterol, and cholestenone inhibitory effects were not altered by the presence of cholesterol. Morphologically, cholestenone-treated H. pylori exhibited coccoid forms. We obtained comparable results when we examined the clarithromycin-resistant H. pylori strain “2460.” We also show that biosynthesis of CGL and its derivatives cholesteryl-6-O-tetradecanoyl-α-D-glucopyranoside and cholesteryl-6-O-phosphatidyl-α-D-glucopyranoside in H. pylori is remarkably inhibited in cultures containing cholestenone. Lastly, we asked whether orally administered cholestenone eradicated H. pylori strain SS1 in C57BL/6 mice. Strikingly, mice fed a cholestenone-containing diet showed significant eradication of H. pylori from the gastric mucosa compared with mice fed a control diet. These results overall strongly suggest that cholestenone could serve as an oral medicine to treat patients infected with H. pylori, including antimicrobial-resistant strains.

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Systems Modeling of the Role of Interleukin-21 in the Maintenance of Effector CD4+ T Cell Responses during Chronic Helicobacter pylori Infection

mBio ◽

10.1128/mbio.01243-14 ◽

2014 ◽

Vol 5 (4) ◽

Cited By ~ 36

Author(s):

Adria Carbo ◽

Danyvid Olivares-Villagómez ◽

Raquel Hontecillas ◽

Josep Bassaganya-Riera ◽

Rupesh Chaturvedi ◽

...

Keyword(s):

Gastric Cancer ◽

Helicobacter Pylori ◽

T Cell ◽

Wild Type ◽

Content Type ◽

Interleukin 21 ◽

H Pylori ◽

Deficient Mice

ABSTRACTThe development of gastritis duringHelicobacter pyloriinfection is dependent on an activated adaptive immune response orchestrated by T helper (Th) cells. However, the relative contributions of the Th1 and Th17 subsets to gastritis and control of infection are still under investigation. To investigate the role of interleukin-21 (IL-21) in the gastric mucosa duringH. pyloriinfection, we combined mathematical modeling of CD4+T cell differentiation within vivomechanistic studies. We infected IL-21-deficient and wild-type mice withH. pyloristrain SS1 and assessed colonization, gastric inflammation, cellular infiltration, and cytokine profiles. ChronicallyH. pylori-infected IL-21-deficient mice had higherH. pyloricolonization, significantly less gastritis, and reduced expression of proinflammatory cytokines and chemokines compared to these parameters in infected wild-type littermates. Thesein vivodata were used to calibrate anH. pyloriinfection-dependent, CD4+T cell-specific computational model, which then described the mechanism by which IL-21 activates the production of interferon gamma (IFN-γ) and IL-17 during chronicH. pyloriinfection. The model predicted activated expression of T-bet and RORγt and the phosphorylation of STAT3 and STAT1 and suggested a potential role of IL-21 in the modulation of IL-10. Driven by our modeling-derived predictions, we found reduced levels of CD4+splenocyte-specifictbx21androrcexpression, reduced phosphorylation of STAT1 and STAT3, and an increase in CD4+T cell-specific IL-10 expression inH. pylori-infected IL-21-deficient mice. Our results indicate that IL-21 regulates Th1 and Th17 effector responses during chronicH. pyloriinfection in a STAT1- and STAT3-dependent manner, therefore playing a major role controllingH. pyloriinfection and gastritis.IMPORTANCEHelicobacter pyloriis the dominant member of the gastric microbiota in more than 50% of the world’s population.H. pyloricolonization has been implicated in gastritis and gastric cancer, as infection withH. pyloriis the single most common risk factor for gastric cancer. Current data suggest that, in addition to bacterial virulence factors, the magnitude and types of immune responses influence the outcome of colonization and chronic infection. This study uses a combined computational and experimental approach to investigate how IL-21, a proinflammatory T cell-derived cytokine, maintains the chronic proinflammatory T cell immune response driving chronic gastritis duringH. pyloriinfection. This research will also provide insight into a myriad of other infectious and immune disorders in which IL-21 is increasingly recognized to play a central role. The use of IL-21-related therapies may provide treatment options for individuals chronically colonized withH. pylorias an alternative to aggressive antibiotics.

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Enhanced fitness of a Helicobacter pylori babA mutant in a murine model

Infection and Immunity ◽

10.1128/iai.00725-20 ◽

2021 ◽

Author(s):

M. Lorena Harvey ◽

Aung Soe Lin ◽

Lili Sun ◽

Tatsuki Koyama ◽

Jennifer H. B. Shuman ◽

...

Keyword(s):

Helicobacter Pylori ◽

Outer Membrane Proteins ◽

Population Diversity ◽

Fitness Advantage ◽

Neutral Locus ◽

Mutant Strains ◽

Bacterial Fitness ◽

H Pylori

Helicobacter pylori genomes encode >60 predicted outer membrane proteins (OMPs). Several OMPs in the Hop family act as adhesins, but the functions of most Hop proteins are unknown. To identify hop mutant strains that exhibit altered fitness in vivo compared to fitness in vitro , we used a genetic barcoding method that allowed us to track changes in the proportional abundance of H. pylori strains within a mixed population. We generated a library of hop mutant strains, each containing a unique nucleotide barcode, as well as a library of control strains, each containing a nucleotide barcode in an intergenic region predicted to be a neutral locus unrelated to bacterial fitness. We orogastrically inoculated each of the libraries into mice and analyzed compositional changes in the populations over time in vivo compared to changes detected in the populations during library passage in vitro . The control library proliferated as a relatively stable community in vitro, but there was a reduction in the population diversity of this library in vivo and marked variation in the dominant strains recovered from individual animals, consistent with the existence of a non-selective bottleneck in vivo . We did not identify any OMP mutants exhibiting fitness defects exclusively in vivo without corresponding fitness defects in vitro . Conversely, a babA mutant exhibited a strong fitness advantage in vivo but not in vitro . These findings, when taken together with results of other studies, suggest that production of BabA may have differential effects on H. pylori fitness depending on the environmental conditions.

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