Abstract
Genomic analysis of a metronidazole resistant H. bizzozeronii strain revealed a frame length extension of the oxygen-insensitive NAD(P)H-nitroreductase HBZC1_00960 (RdxA), associated with the disruption of the C-terminal cysteine-containing conserved region (IACLXALGK). This was the result of the extension (from C8 to C9) of a simple sequence cytosine repeat (SSCR) located in the 3’ of the gene. A 3' SSCR is also present in the rdxA homolog of H. heilmannii sensu stricto, but not in H. pylori. We showed that in the majority of in vitro spontaneous H. bizzozeronii metronidazole resistant mutants, the extension of the 3′ SSCR of rdxA was the only mutation observed. In addition, we observed that H. bizzozeronii ΔrdxA mutant strain showed the same MIC value of metronidazole observed in the spontaneous mutants. These data indicate that loss of function mutations in rdxA and in particular the disruption of the conserved region IACLXALGK is associated with reduced susceptibility to metronidazole in H. bizzozeronii. Slipped-strand mispairing of the SSCR located in the 3′ of the H. bizzozeronii rdxA appears to be the main mechanism. We also observed that H. bizzozeronii acquires resistance to metronidazole at high mutation rate, and that serial passages in vitro without selection induced an increased level of susceptibility. In conclusion, contrary to what was previously described in H. pylori, the H. bizzozeronii rdxA appears to be a contingency gene which undergoes phase variation. The contingency nature of rdxA should be carefully considered when metronidazole is used in the treatment of H. heilmannii-associated gastritis.
Highlights
The human-adapted pathogen Helicobacter pylori is one of the most common causes of bacterial infections worldwide, and it is recognized as an etiologic agent of chronic gastritis, peptic ulcers, gastric adenocarcinoma and MALT lymphoma [1]
To better understand the molecular mechanisms of antibiotic resistance in H. heilmannii s.l., we investigated the potential reasons behind the failed treatment of a H. bizzozeronii infection in a 47 year-old woman suffering with chronic gastritis [7]
To verify whether the instability of the 3’ simple sequence cytosine repeat (SSCR) of H. bizzozeronii rdxA was associated with metronidazole resistance, the rdxA genes of 11 metronidazole-resistant H. bizzozeronii CIII-1GEN isogenic spontaneous mutants were sequenced
Summary
The human-adapted pathogen Helicobacter pylori is one of the most common causes of bacterial infections worldwide, and it is recognized as an etiologic agent of chronic gastritis, peptic ulcers, gastric adenocarcinoma and MALT lymphoma [1]. The patient’s symptoms became less severe and the patient started to gain weight She continued to suffer from mild nausea associated with eating warm foods, and, after a few months, H. bizzozeronii was re-isolated from antrum samples obtained in a follow-up endoscopy [7]. H. bizzozeronii CIII-1ORG (an isolate obtained from the corpus of the patient‘s stomach before the treatment) showed an MIC of metronidazole equal to 32 μg/mL, but the MIC value for its derived clone CIII-1GEN, obtained by amplification of a single colony, was 4 μg/ mL. These data indicated the simultaneous presence of metronidazole susceptible and resistant H. bizzozeronii variants before the treatment [15]. Conflicting evidence correlating the oxygen-insensitive nitroreductase RdxA and/or the NAD(P)H flavin oxidoreductase FrxA with the resistant phenotype, indicate that the molecular basis of resistance in this species remains unclear [16,17]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
