The discovery of Helicobacter pylori in 1982 was the starting point of a revolution concerning the concepts and management of gastroduodenal diseases. It is now well accepted that the most common stomach disease, peptic ulcer disease, is an infectious disease, and all consensus conferences agree that the causative agent, H. pylori, must be treated with antibiotics. Furthermore, the concept emerged that this bacterium could be the trigger of various malignant diseases of the stomach, and it is now a model for chronic bacterial infections causing cancer. Most of the many different techniques involved in diagnosis of H. pylori infection are performed in clinical microbiology laboratories. The aim of this article is to review the current status of these methods and their application, highlighting the important progress which has been made in the past decade. Both invasive and noninvasive techniques will be reviewed.

Helicobacter pylori Detection and Antimicrobial Susceptibility Testing

https://www.gastrojournal.org/article/S0016-5085(16)30108-1/pdf

The Toronto Consensus for the Treatment of Helicobacter pylori Infection in Adults

Summary


Background Information regarding the effects of drug resistance on therapies for Helicobacter pylori is limited.



Aims  To determine the effect of drug resistance on the efficacy of first-line treatment regimens for H. pylori and identify the most efficacious treatments in the presence of drug resistance.



Methods  We searched for studies using the keywords: ‘Helicobacter pylori’,‘resistance’ and ‘treatment’ or ‘therapy’. Multilevel meta-regression models were used to determine the effect of drug resistance on treatment efficacy.



Results  We analysed data from 93 studies with 10 178 participants. For triple therapies, clarithromycin resistance had a greater effect on treatment efficacy than nitroimidazole resistance. Metronidazole resistance reduced efficacy by 26% in triple therapies containing a nitroimidazole, tetracycline and bismuth, while efficacy was reduced by only 14% when a gastric acid inhibitor was added to the regimen. Quadruple therapies containing both clarithromycin and metronidazole were the most efficacious; >80% of H. pylori infections were consistently eradicated with these regimens.



Conclusions  Drug resistance was a strong predictor of efficacy across triple therapies for the eradication of H. pylori in adults. Resistance to either clarithromycin or metronidazole, but not both simultaneously, may be overcome by using quadruple therapies, especially those containing both clarithromycin and metronidazole.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2036.2007.03386.x

Meta-analysis: the effect of antibiotic resistance status on the efficacy of triple and quadruple first-line therapies for Helicobacter pylori.

During the period reviewed, prevalence studies were essentially performed in less economically advanced countries and a high prevalence was found. The traditional risk factors for Helicobacter pylori positivity were mostly found. Transmission studied by molecular typing showed a familial transmission. The eventual role of water transmission was explored in several studies with controversial results. Concerning diagnosis, most of the invasive and noninvasive methods used for the diagnosis of H. pylori infection are long standing with efficient performance. The most interesting recent improvements in H. pylori diagnosis include advances in endoscopy, developments in molecular methods, and the introduction of omics-based techniques. Interpretation of old or newer method should take into account the pretest probability and the prevalence of H. pylori in the population under investigation.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/hel.12250

Epidemiology and diagnosis of Helicobacter pylori infection

Isolates of the gastric pathogen Helicobacter pylori harvested from different individuals are highly polymorphic. Strain variation also has been observed within a single host. To more fully ascertain the extent of H. pylori genetic diversity within the ecological niche of its natural host, we harvested additional isolates of the sequenced H. pylori strain J99 from its human source patient after a 6-year interval. Randomly amplified polymorphic DNA PCR and DNA sequencing of four unlinked loci indicated that these isolates were closely related to the original strain. In contrast, microarray analysis revealed differences in genetic content among all of the isolates that were not detected by randomly amplified polymorphic DNA PCR or sequence analysis. Several ORFs from loci scattered throughout the chromosome in the archival strain did not hybridize with DNA from the recent strains, including multiple ORFs within the J99 plasticity zone. In addition, DNA from the recent isolates hybridized with probes for ORFs specific for the other fully sequenced H. pylori strain 26695, including a putative traG homolog. Among the additional J99 isolates, patterns of genetic diversity were distinct both when compared with each other and to the original prototype isolate. These results indicate that within an apparently homogeneous population, as determined by macroscale comparison and nucleotide sequence analysis, remarkable genetic differences exist among single-colony isolates of H. pylori. Direct evidence that H. pylori has the capacity to lose and possibly acquire exogenous DNA is consistent with a model of continuous microevolution within its cognate host.

https://www.pnas.org/content/pnas/98/25/14625.full.pdf

Helicobacter pylori genetic diversity within the gastric niche of a single human host

The influence of in vitro nitroimidazole resistance on the efficacy of nitroimidazole-containing anti-Helicobacter pylori regimens: a meta-analysis.

The efficacy of a nitroimidazole-containing regimen for the treatment of Helicobacter pylori infection is decreased by nitroimidazole resistance. Nitroimidazoles are meta- bolized by H. pylori by several nitro-reductases of which an oxygen-insensitive NADPH nitroreductase encoded by the rdxA gene is the most important. Null mutations in this gene are associated with resistance. Susceptibility testing to nitroimidazoles may give variable results. This is not only related to the slow growth under specific conditions, but also to variability in the activity of the other nitroreductases and the ability to deactivate toxic metabolites of an NI and to repair DNA damage. Moreover, co-infections with resistant and susceptible bacteria are frequently found. The presence of nitroimidazole resistance is related to the previous use of this drug. The prevalence of resistance is rising and nowadays 10-50% of the isolates are resistant. Resistance reduces the efficacy of a treatment regimen to a variable degree. This is related to efficacy of the other components of the regimen and the treatment duration. Whether a nitroimidazole is still effective in resistant strains remains unresolved. When nitroimidazole resistance is present, a nitro-imidazole-containing regimen should be avoided or a regimen with other highly effective components should be used.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2036.2000.00675.x

Review article: nitroimidazole resistance in Helicobacter pylori

Aim

: To assess the influence of metronidazole resistance on the efficacy of ranitidine bismuth citrate-based triple therapy regimens in two consecutive studies.



Methods

: In the first study, patients with a culture-proven Helicobacter pylori infection were treated with ranitidine bismuth citrate 400 mg, metronidazole 500 mg, and clarithromycin 500 mg, all twice daily for 1 week (RMC). In the second study, amoxycillin 1000 mg was substituted for clarithromycin (RMA). Susceptibility testing for metronidazole was performed with the E-test. Follow-up endoscopy was performed after ≥ 4 weeks. Antral biopsy samples were taken for histology and urease test, and culture and corpus samples for histology and culture.



Results

: 112 patients, 53 males, age 55 ± 14 years (39 duodenal ulcer, 7 gastric ulcer and 66 gastritis) were treated with RMC, and 89 patients, 52 males, age 58 ± 15 years (23 duodenal ulcer, 7 gastric ulcer and 59 gastritis) were treated with RMA. For RMC, intention-to-treat eradication results were 98% (59/60, 95% CI: 91–100%) and 95% (20/21, 95% CI: 76–100%) for metronidazole susceptible and resistant strains, respectively (P = 0.45). For RMA these figures were 87% (53/61, 95% CI: 76–94%) for metronidazole susceptible strains and 22% (2/9, 95% CI: 3–60%) for resistant strains (P = 0.0001).



Conclusion

: Both regimens are effective in metronidazole susceptible strains. However, in contrast to the amoxycillin-containing regimen, that containing clarithromycin is also effective in resistant strains.

The influence of metronidazole resistance on the efficacy of ranitidine bismuth citrate triple therapy regimens for Helicobacter pylori infection

Metronidazole susceptibility testing by E test was compared to that by disk diffusion for 263 Helicobacter pylori isolates and to that by breakpoint agar dilution for 90 H. pylori isolates. In 5% and 6% of the cases, respectively, results were discrepant. For each of 52 clinical isolates an E test was performed on 10 separate colonies. Subpopulations of resistant and susceptible bacteria were found in five cases. From three isolates, each colony was subcultured and tested up to 10 times. All but 1 of 292 tests showed the same result. We conclude that the E test is reliable and that subpopulations are responsible for discordant results.

Subpopulations of Helicobacter pylori are responsible for discrepancies in the outcome of nitroimidazole susceptibility testing

Metronidazole was introduced in 1959 for the treatment of Trichomonas vaginalis, but was subsequently shown to be active against anaerobic and some micro-aerophilic bacteria as well. In anaerobic microorganisms with their low redox potential, metronidazole is reduced to its active metabolite by a one-electron transfer step. Metronidazole is often used in treatment regimens for Helicobacter pylori, a microaerophilic bacterium, but resistance to this drug is frequently encountered. The metabolism of metronidazole in H. pylori must differ from that in anaerobic bacteria as metabolites formed by a one-electron transfer are readily re-oxidized in the micro-aerophilic environment of H. pylori. This process is called 'futile cycling' and is accompanied by the formation of toxic oxygen radicals that are neutralized by an active scavenger system. Recently, it has been shown that in H. pylori, in contrast to the situation in anaerobes, an oxygen-insensitive nitroreductase. encoded by the rdxA gene, is responsible for the activation of metronidazole. Activation by this enzyme is by a two-electron transfer step, preventing futile cycling' and thereby enabling the activation of metronidazole in a micro-aerophilic environment. Metronidazole resistance has been shown to be associated with null mutations in the rdxA gene in most clinical isolates. However, there may be some 'background metronidazole susceptibility' in metronidazole-resistant strains caused by other (oxygen-sensitive) nitroreductases. Recently, three meta-analyses of the impact of metronidazole resistance on treatment efficacy have all shown a significant reduction in efficacy of metronidazole containing regimens in patients infected with a resistant strain. The impact of resistance proved to be dependent on the other components of the regimen and on treatment duration.

EJ van der Wouden

Papers

The influence of in vitro nitroimidazole resistance on the efficacy of nitroimidazole-containing anti-Helicobacter pylori regimens: a meta-analysis.

Review article: nitroimidazole resistance in Helicobacter pylori

The influence of metronidazole resistance on the efficacy of ranitidine bismuth citrate triple therapy regimens for Helicobacter pylori infection

Subpopulations of Helicobacter pylori are responsible for discrepancies in the outcome of nitroimidazole susceptibility testing

Mechanism and clinical significance of metronidazole resistance in Helicobacter pylori.