Sergio Mendonça

Prevalence of Helicobacter pylori Resistance to Metronidazole, Clarithromycin, Amoxicillin, Tetracycline, and Furazolidone in Brazil

Background. Helicobacter pylori infection is associated with a wide range of digestive diseases and is very prevalent in developing countries, although few data exist on the susceptibility of H. pylori to antimicrobials commonly used in eradication schedules in these countries. The aim of this study was to evaluate the resistance of H. pylori to metronidazole, clarithromycin, amoxicillin, tetracycline, and furazolidone in dyspeptic Brazilian patients.

Analysis of antimicrobial susceptibility and virulence factors in Helicobacter pylori clinical isolates

BackgroundIn this study, we evaluated the prevalence of primary resistance of Brazilian H. pylori isolates to metronidazole, clarithromycin, amoxicillin, tetracycline, and furazolidone. In addition, the vacA, iceA, cagA and cagE genotypes of strains isolated from Brazilian patients were determined and associated with clinical data in an effort to correlate these four virulence markers and antibiotic resistance.MethodsH. pylori was cultured in 155 H. pylori-positive patients and MICs for metronidazole, clarithromycin, amoxicillin, tetracycline, and furazolidone were determined by the agar dilution method. Genomic DNA was extracted, and allelic variants of vacA, iceA, cagA and cagE were identified by the polymerase chain reaction.ResultsThere was a strong association between the vacA s1/cagA -positive genotype and peptic ulcer disease (OR = 5.42, 95% CI 2.6–11.3, p = 0.0006). Additionally, infection by more virulent strains may protect against GERD, since logistic regression showed a negative association between the more virulent strain, vacA s1/cagA-positive genotype and GERD (OR = 0.26, 95% CI 0.08–0.8, p = 0.03). Resistance to metronidazole was detected in 75 patients (55%), to amoxicillin in 54 individuals (38%), to clarithromycin in 23 patients (16%), to tetracycline in 13 patients (9%), and to furazolidone in 19 individuals (13%). No significant correlation between pathogenicity and resistance or susceptibility was detected when MIC values for each antibiotic were compared with different vacA, iceA, cagA and cagE genotypes.ConclusionThe analysis of virulence genes revealed a specific association between H. pylori strains and clinical outcome, furthermore, no significant association was detected among pathogenicity and resistance or susceptibility.

New once-daily, highly effective rescue triple therapy after multiple Helicobacter pylori treatment failures: a pilot study.

Background:  Helicobacter pylori treatment failure is a growing problem in daily practice.

Detection of high‐level tetracycline resistance in clinical isolates of Helicobacter pylori using PCR‐RFLP

Tetracycline is one of four antibiotics commonly used for the treatment of Helicobacter pylori infection, but its effectiveness is decreasing as the incidence of tetracycline resistance is increasing. In five Brazilian tetracycline-resistant (Tet(R)) H. pylori isolates, high-level tetracycline resistance is mediated by the triple-base-pair substitution AGA(926-928)-->TTC in both 16S rRNA genes, as was previously observed in two independent high-level Tet(R) H. pylori strains. A polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP) assay was developed for the detection of the AGA(926-928)-->TTC substitution, and confirmed the presence of the aforementioned triple-base-pair substitution in all five Brazilian Tet(R) isolates. This PCR-RFLP-based approach distinguishes the high-level Tet(R) isolates from low-level Tet(R) and Tet(S) H. pylori strains and thus allows the direct detection of Tet(R) H. pylori isolates.

Multiple mutations in or adjacent to the conserved penicillin-binding protein motifs of the penicillin-binding protein 1A confer amoxicillin resistance to Helicobacter pylori

Background:  Amoxicillin‐based therapies are highly effective for the treatment of Helicobacter pylori infections, but the efficacy may decrease as the incidence of amoxicillin resistance is increasing. So far, the molecular mechanism underlying stable amoxicillin resistance has only been identified for a few naturally occurring amoxicillin‐resistant (AmxR) H. pylori isolates, and is mediated by mutations in penicillin‐binding protein 1A (PBP1A). In this study the molecular mechanism underlying amoxicillin resistance of seven additional AmxR H. pylori isolates has been established.

Increased Primary Resistance to Recommended Antibiotics Negatively Affects Helicobacter pylori Eradication

Objective. To evaluate the efficacy of two commonly employed treatments for Helicobacter pylori infection and the impact of bacterial resistance to antibiotics on eradication rate.

Clinical relevance of the cagA, vacA and iceA genotypes of Helicobacter pylori in Brazilian clinical isolates

Infection with Helicobacter pylori strains harboring determinants of pathogenicity may lead to a strong inflammatory response in gastric mucosa. In this work, we examined the frequency of the cagA, vacA and iceA genotypes in H. pylori strains isolated from Brazilian patients and correlated these with the clinical manifestations. H. pylori was isolated from 165 patients [30 with non-ulcer dyspepsia cases (NUD); 93 peptic ulcer disease (PUD): 31 gastric ulcers (GU) and 62 duodenal ulcer disease (DU); 18 with erosive gastritis (EG); and 24 gastroesophageal reflux disease (GERD)]. Allelic variants of cagA, vacA and iceA were identified using the polymerase chain reaction. More than one H. pylori strain was detected in 28 cases (17%), and these were excluded from the statistical analysis. We were unable to confirm an association between iceA status and clinical outcome. There was a strong association between the genotype cagA-positive vacA s1 and PUD. However, logistic regression analysis showed that vacA s1 was the only predictive factor for PUD (OR=4.19; 95% CI 1.95-8.98). The presence of the less virulent strain vacA s2 was related to GERD (OR=8.59; 95% CI 2.85-25.91). Our results support the hypothesis that virulent strains may protect against the development of GERD.

Mutations in the 23S rRNA gene are associated with clarithromycin resistance in Helicobacter pylori isolates in Brazil

BackgroundResistance of Helicobacter pylori to clarithromycin has been associated with A2142G and A2143G point mutations in the 23S rRNA gene. Thus, the purpose of the present study was to determine the prevalence of each mutation in 52 clarithromycin-resistant H. pylori strains and to characterize the influence each type of mutation on the MIC.MethodsThe MIC for clarithromycin was determined by the agar dilution method, and the point mutations of H. pylori were detected by PCR followed by restriction fragment length polymorphism.ResultsClarithromycin MICs ranged from 2 to >256 microgram ml-1 among the 52 strains included in this study. Both the A2142G and the A2143G mutations were present in 94.2% of clarithromycin-resistant H. pylori strains examined. A relationship was observed between the presence of the A2142G mutation and the highest MIC values (p = 0.01).ConclusionIn an H. pylori- infected population, the A2142G mutation may incur to a greater probability of treatment failure if clarithromycin is used.

Quantitative real-time PCR for the clinical detection of Helicobacter pylori

Abstract Accurate diagnosis of Helicobacter pyloriinfection is very important in both clinical practice and research. We evalu-ated the sensitivity of real-time PCR (RT-PCR) for the detection and quantification of Helicobacter pyloriusing DNAfrom 91 human gastric biopsy samples divided into three groups: 46 biopsies from untreated patients who accordingtothereferencesmethodswereconsideredH.pylori-negative(groupA);35biopsiesfrompatientspreviouslytreatedagainst H. pyloriand considered to be cured by “gold standard” tests (group B); and 10 biopsies from patients H.pylori-positive by all available methods (group C). The sensitivity of the RT-PCR assay was higher than that of stan-dard methods. Of the 81 patients considered to be uninfected according to the references methods, 16 were H.pylori-positive by PCR, 10 of which were patients who had received H. pylorieradication therapy and 6 were un-treated patients. Based on these findings we recommend that RT-PCR should be use in addition to standard meth-ods in clinical studies to monitor the results of H. pylorieradication therapy.

Acute inflammatory response induced by Helicobacter pylori in the rat air pouch

Infection by Helicobacter pylori elicits persistent neutrophil infiltration in the gastric mucosa and stimulates the release of substances that may contribute to the establishment of gastritis. In this study, we used the rat air pouch model to evaluate the acute inflammatory response to H. pylori, in vivo. A pronounced neutrophil infiltration was observed 6 h and 12 h after the injection of H. pylori into the air pouch. Strains with different genotypes were able to induce cellular influx. This response was dependent upon the amount of bacteria injected and still occurred when heat-killed bacteria were employed. An increase in prostaglandin E(2) levels was observed, indicating that H. pylori induced cyclooxygenase 2 in this model. The production of interleukin-1 beta and tumor necrosis factor-alpha by leukocytes was also enhanced, suggesting that this model may be useful for studying the direct activation of neutrophils by H. pylori in vivo.