High-level beta-lactam resistance associated with acquired multidrug resistance in Helicobacter pylori

Prevalence and evolution of Helicobacter pylori resistance to 6 antibacterial agents over 12 years and correlation between susceptibility testing methods

The aim of this study was to evaluate Helicobacter pylori antibacterial resistance in 2005 to 2007, resistance evolution since 1996 to 1999, and performance of breakpoint susceptibility testing (BST) compared with E test for clarithromycin or agar dilution method (ADM) for metronidazole, amoxicillin, tetracycline, and ciprofloxacin. Resistance in 613 untreated adults, 91 treated adults, and 75 untreated children was 25%, 48.4%, and 16% for metronidazole; 17.8%, 45.1%, and 18.7% for clarithromycin; 4.4%, 13.3%, and 2.7% for tetracycline; and 7.7%, 18.2%, and 6.8% for ciprofloxacin, respectively. Resistance to amoxicillin (0.9%) and nitrofurantoin (1.3%) was uncommon. Three strains (0.4%) exhibited triple resistance to amoxicillin, metronidazole, and clarithromycin. Primary resistance rates in adults and children were comparable. Metronidazole resistance was less common in ulcer adults than in the rest. Primary clarithromycin resistance increased significantly from 10% in 1996 to 1999 to 17.9% in 2005 to 2007. Many strains (26.4%) from treated adults showed resistance to metronidazole and clarithromycin. Category agreement between the BST and E test or ADM results was good (93.3-100%). In conclusion, the increasing clarithromycin resistance and presence of multidrug resistance are worrying. Fluoroquinolones should be used with caution for H. pylori eradication in treated patients.

Correlation between substitutions in penicillin-binding protein 1 and amoxicillin resistance in Helicobacter pylori

The correlation between the substitutions of penicillin-binding protein 1 (PBP1) and amoxicillin resistance was studied for the determination of the substitutions in PBP1 which confer amoxicillin resistance in Helicobacter pylori. By the comparison of the amino acid sequences of PBP1 in the amoxicillinresistant (n=3), low-susceptible (n=3), and susceptible (n=13) H. pylori isolates, the substitution Asn562-->Tyr, which is adjacent to KTG motif (555-557), was common and specific to amoxicillin-resistant H. pylori. Additionally, all amoxicillin-resistant isolates had multiple substitutions such as Ser414-->Arg in the transpeptidase region of PBP1 of H. pylori. Furthermore all transformants obtained by the natural transformation using the pbp1 genes of amoxicillin-resistant H. pylori isolates had multiple substitutions including Asn562-->Tyr. These results suggest that multiple amino acid substitutions in the transpeptidase region of PBP1 are closely related to amoxicillin resistance in H. pylori.

Progress in research into the molecular mechanism of drug resistance of Helicobacter pylori

Helicobacter pylori is a pathogen of chronic and active gastritis. It is the main cause of chronic gastritis and peptic ulcer disease, and is directly related to diseases of the stomach and duodenum. This pathogen can also induce gastric carcinoma. With the extensive use of antibiotics, the number of drug resistant strains of H. pylori has rapidly increased. As a result, there are some difficulties in applying clinical therapy for diseases related to H. pylori. This paper aimed to first analyze the status and prevalence of antibiotic resistance, and then to review various drugs such as macrolides, imidazoles, tetracyclines, β-lactams and quinolones for systematically treating H. pylori infection. The mechanisms of various drug resistances, as well as detection and identification assays for typing drug resistance, are discussed. This paper presents accumulated clinical data and evidence for the clinical diagnosis and treatment of diseases related to H. pylori.

Differentially expressed genes in response to amoxicillin inHelicobacter pylorianalyzed by RNA arbitrarily primed PCR

Because the molecular mechanism of amoxicillin resistance in Helicobacter pylori seems to be partially explained by several mutational changes in the pbp1A gene, the aim of the present study was to evaluate the gene expression pattern in response to amoxicillin in the Amx(R) Hardenberg strain using RNA arbitrarily primed PCR (RAP-PCR). In the experiments, c. 100 differentially expressed RAP-PCR products were identified using five arbitrary primers. The cDNAs that presented the highest levels of induction or repression were cloned and sequenced, and the sequences were compared with those present in databases using the blast search algorithm. The differential expression of the isolated cDNAs was confirmed by real-time PCR. The preliminary results showed that amoxicillin alters the expression of five cDNAs involved in biosynthesis, two involved with pathogenesis, four related to cell envelope formation, two involved in cellular processes, three related with transport and binding proteins, one involved with protein degradation, one involved with energy metabolism and seven hypothetical proteins. Further analysis of these cDNAs will allow a better comprehension of both the molecular mechanism(s) of amoxicillin resistance and the adaptative mechanism(s) used by H. pylori in the presence of this antibiotic.

Helicobacter pylori and antimicrobial resistance: molecular mechanisms and clinical implications

Helicobacter pylori is an important human pathogen that colonises the stomach of about half of the world's population. The bacterium has now been accepted as the causative agent of several gastroduodenal disorders, ranging from chronic active gastritis and peptic ulcer disease to gastric cancer. The recognition of H pylori as a gastric pathogen has had a substantial effect on gastroenterological practice, since many untreatable gastroduodenal disorders with uncertain cause became curable infectious diseases. Treatment of H pylori infection results in ulcer healing and can reduce the risk of gastric cancer development. Although H pylori is susceptible to many antibiotics in vitro, only a few antibiotics can be used in vivo to cure the infection. The frequent indication for anti-H pylori therapy, together with the limited choice of antibiotics, has resulted in the development of antibiotic resistance in H pylori, which substantially impairs the treatment of H pylori-associated disorders. Antimicrobial resistance in H pylori is widespread, and although the prevalence of antimicrobial resistance shows regional variation per antibiotic, it can be as high as 95%. We focus on the treatment of H pylori infection and on the clinical relevance, mechanisms, and diagnosis of antimicrobial resistance.

Effect of aspirin and celecoxib on Helicobacter pylori in vitro

AIM: To investigate the possible effects of aspirin and celecoxib on the growth, virulence factors and outer membrane protein of Helicobacter pylori (H. pylori).

METHODS: Two standard strains of H. pylori were treated with a series concentration of aspirin or celecoxib (a specific inhibitor of cyclooxygenase 2) and were incubated in brucella broth under microaerobic condition for 24 and 48 h. The growth and urease activity were assessed by viable colony counting and spectrophotometry. After 48-hour treatment, the supernatants were incubated with Hela cells to estimate vacuolating cytotoxin activity. The outer membrane protein of H. pylori was analyzed by SDS-PAGE.

RESULTS: Aspirin or celecoxib inhibited the growth of H. pylori in a dose-dependent manner with the lowest inhibitory concentrations of 0.5 or 0.01 mmol/L, and the lethal concentrations of 2.0 and 0.04 mmol/L, respectively. Aspirin and celecoxib inhibited the urease activity and vacuolating cytotoxin activity of H. pylori. The inhibitory effect of celecoxib on H. pylori was superior to that of aspirin. Both aspirin and celecoxib had some effects on the expression of the outer membrane protein.

CONCLUSION: Aspirin or celecoxib can inhibit the growth, urease activity and vacuolating cytotoxin activity of H. pylori in vitro significantly. Both aspirin and celecoxib may have some effects on the outer membrane protein expression of H. pylori.

Resistance mechanisms in an in vitro-selected amoxicillin-resistant strain of Helicobacter pylori

We investigated the beta-lactam resistance mechanism(s) of an in vitro-selected amoxicillin-resistant Helicobacter pylori strain (AmoxR). Our results demonstrated that resistance is due to a combination of amino acid substitutions in penicillin binding protein 1 (PBP1), HopB, and HopC identified in AmoxR, resulting in decreased affinity of PBP1 for amoxicillin and decreased accumulation of penicillin.

Sel1-like repeat proteins in signal transduction

Solenoid proteins, which are distinguished from general globular proteins by their modular architectures, are frequently involved in signal transduction pathways. Proteins from the tetratricopeptide repeat (TPR) and Sel1-like repeat (SLR) families share similar alpha-helical conformations but different consensus sequence lengths and superhelical topologies. Both families are characterized by low sequence similarity levels, rendering the identification of functional homologous difficult. Therefore current knowledge of the molecular and cellular functions of the SLR proteins Sel1, Hrd3, Chs4, Nif1, PodJ, ExoR, AlgK, HcpA, Hsp12, EnhC, LpnE, MotX, and MerG has been reviewed. Although SLR proteins possess different cellular functions they all seem to serve as adaptor proteins for the assembly of macromolecular complexes. Sel1, Hrd3, Hsp12 and LpnE are activated under cellular stress. The eukaryotic Sel1 and Hrd3 proteins are involved in the ER-associated protein degradation, whereas the bacterial LpnE, EnhC, HcpA, ExoR, and AlgK proteins mediate the interactions between bacterial and eukaryotic host cells. LpnE and EnhC are responsible for the entry of L. pneumophila into epithelial cells and macrophages. ExoR from the symbiotic microorganism S. melioti and AlgK from the pathogen P. aeruginosa regulate exopolysaccaride synthesis. Nif1 and Chs4 from yeast are responsible for the regulation of mitosis and septum formation during cell division, respectively, and PodJ guides the cellular differentiation during the cell cycle of the bacterium C. crescentus. Taken together the SLR motif establishes a link between signal transduction pathways from eukaryotes and bacteria. The SLR motif is so far absent from archaea. Therefore the SLR could have developed in the last common ancestor between eukaryotes and bacteria.

Comparison of primary and secondary antimicrobial minimum inhibitory concentrations for Helicobacter pylori isolated from Korean patients

In this study we assessed minimum inhibitory concentration (MIC) values and resistance rates of several antibiotics in 65 primary and 324 secondary Helicobacter pylori isolates from Korean patients. Primary resistance to amoxicillin, clarithromycin, metronidazole, tetracycline, azithromycin, ciprofloxacin, levofloxacin and moxifloxacin was 18.5%, 13.8%, 66.2%, 12.3%, 32.3%, 33.8%, 21.5% and 21.5%, respectively. Secondary resistance was 31.3%, 85.1%, 70.1%, 0%, 89.6%, 35.8%, 32.8% and 32.8%, respectively. Sequence analysis of pbp1A in H. pylori strains with an amoxicillin MIC >or=2 microg/mL revealed C206T (Asp69-->Val), C1667G (Thr556-->Ser), A1684T (Asn562-->Tyr), A1777G (Thr593-->Ala) and C1798A (Pro600-->Thr) substitutions. Eleven (16.4%) of 67 treatment failures showed mixed infections with antibiotic-susceptible and -resistant H. pylori. The most common multidrug resistance profile was to clarithromycin, metronidazole and azithromycin. These results indicate that MIC values of secondary isolates were higher than those of primary isolates and that resistance to amoxicillin is probably mediated through mutations in pbp1A.

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 (Amx) 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 Amx H. pylori isolates has been established.

METHODS

H. pylori strain 26695 (minimal inhibitory concentration (MIC) 0.125 mg/l) was naturally transformed with total DNA and pbp1A polymerase chain reaction (PCR) products from the seven Amx H. pylori isolates, and the MIC of amoxicillin and pbp1A gene sequence of the obtained Amx transformants were determined.

RESULTS

Replacement of the wild-type pbp1A gene of H. pylori reference strain 26695 by the pbp1A gene of the Amx H. pylori isolates resulted in an increased MIC (0.5-1.0 mg/l). Sequence analysis of the smallest PBP1A fragments able to transfer the resistance indicated that several amino acid substitutions in or adjacent to the second (SKN402-404) and third (KTG555-557) conserved penicillin-binding protein motifs (PBP-motifs) mediate amoxicillin resistance in H. pylori. This was confirmed by site-directed mutagenesis using oligonucleotides that contained defined mutations in or adjacent to these PBP-motifs.

CONCLUSION

In naturally occurring Amx H. pylori isolates, amoxicillin resistance is mediated by various mutational changes located in or adjacent to the second and third PBP-motifs of the PBP1A. Although we cannot exclude the role of the other genes in amoxicillin resistance, it is likely that multiple mutational changes in the PBP1A gene are the predominant cause of amoxicillin resistance in H. pylori. The findings of this study currently preclude the rapid detection of amoxicillin resistance in H. pylori by molecular tests.

Antibacterial resistance in Helicobacter pylori strains isolated from Bulgarian children and adult patients over 9 years

The aim of this study was to evaluate the primary, combined and post-treatment antibacterial resistance rates in 1205 Helicobacter pylori strains from non-treated (786 adults, 282 children) and treated (109 adults, 28 children) patients in Bulgaria. Susceptibility was tested by the limited agar dilution method. Overall primary resistance rates to metronidazole, clarithromycin, amoxicillin, tetracycline and both metronidazole and clarithromycin were respectively 15·0, 12·5, 1·5, 3·4 and 4·7 % in children and 25·6, 12·6, 0·8, 5·2 and 4·9 % in adults. Primary metronidazole resistance in adults was more common than in children, but the differences for other agents tested were not significant. Primary resistance rates were in the range of those reported worldwide. There was no significant increase in primary resistance rates from 1996/1999 to 2003/2004; however, clarithromycin resistance rates exhibited a slight tendency to increase. Post-treatment resistance to amoxicillin was detected in 1·6 % of 63 strains. Post-treatment resistance to metronidazole was common (81·6 %) and that to clarithromycin was considerable (36 %). Alarming emergence of strains with triple resistance to amoxicillin, metronidazole and clarithromycin was found in two non-treated and three treated patients. The results motivate a larger and continuing surveillance of H. pylori resistance in Bulgaria and worldwide.

Development of a highly sensitive method for detection of clarithromycin-resistant Helicobacter pylori from human feces

Gastric infection of clarithromycin (CAM)-resistant Helicobacter pylori is one of the major causes of failure to eradicate this organism. A noninvasive and useful method for the detection of CAM-resistant H. pylori from human feces by restriction fragment length polymorphism (RFLP)-nested polymerase chain reaction (PCR) targeting the mutation of the 23S rRNA gene that confers CAM-resistance in H. pylori was developed in this study. Our nested PCR method detected DNA of H. pylori in feces with high sensitivity and specificity compared with both an enzyme-linked immunoadsorbent assay (ELISA) of H. pylori in feces and the isolation of H. pylori from gastric biopsy. Furthermore, the results of mutation analysis of the H. pylori 23S rRNA gene amplified from feces completely correlated with both that of the H. pylori 23S rRNA gene amplified from the isolates of gastric biopsy and the susceptibility of H. pylori isolates to CAM. Therefore, our results show that this RFLP/nested PCR method is useful for the accurate diagnosis of CAM-resistant H. pylori infection from feces.

Tetracycline-resistant clinical Helicobacter pylori isolates with and without mutations in 16S rRNA-encoding genes

Tetracycline-resistant Helicobacter pylori strains have been increasingly reported worldwide. However, only a small number of tetracycline-resistant strains have been studied with regard to possible mechanisms of resistance and those studies have focused on mutations in the tetracycline binding sites of 16S rRNA-encoding genes. We here report studies of 41 tetracycline-resistant H. pylori strains (tetracycline MICs, 4 to 32 microg/ml) from North America (n = 12) and from East Asia (n = 29). DNA sequence analyses of 16S rRNA-encoding genes revealed that 22 (54%) of the resistant isolates carried one of five different single-nucleotide substitutions (CGA, GGA, TGA, AGC, or AGT) at the putative tetracycline binding site (AGA(965-967)). Single-nucleotide substitutions were associated with reduced ribosomal binding and with slightly increased tetracycline MICs (1 to 2 microg/ml). The 19 tetracycline-resistant isolates with no detectable mutations in the tetracycline binding site had normal tetracycline-ribosome binding. All tetracycline-resistant isolates, including those with and those without mutations in the tetracycline binding site, showed decreased accumulation of tetracycline. These results suggest that tetracycline resistance is multifactorial, involving alterations both in ribosomal binding and in membrane permeability.

Molecular biology methods for the characterization of Helicobacter pylori infections and their diagnosis

Helicobacter pylori infects approximately half of the human population; however, the outcome of infection is affected by many factors, including strain and host genotype characteristics and bacterial density within the stomach. Many molecular methods have been developed to provide information with respect to these characteristics. Methods that provide results within 24 h of endoscopy may be used to develop individualized treatment that is more effective, results in fewer side effects, cuts costs,decreases the number of treatment failures and results in the development of fewer antibiotic-resistant H. pylori strains.

High levels of dual resistance to clarithromycin and metronidazole and in vitro activity of levofloxacin against Helicobacter pylori isolates from patients after failure of therapy

Current treatment for Helicobacter pylori infections generally includes two or more antimicrobials (amoxicillin, clarithromycin, nitroimidazoles, tetracycline, etc.), but treatment fails in 10-20% of all cases, often because of drug resistance. Levofloxacin has been proposed as an alternative for these refractory infections. We examined 67 H. pylori isolates from patients unsuccessfully treated with amoxicillin, clarithromycin, metronidazole and levofloxacin. Minimum inhibitory concentrations determined with the epsilometer test revealed clarithromycin and metronidazole resistance in 91 and 82.1% of the isolates, respectively; 52 (77.6%) were resistant to both drugs. All 67 isolates were susceptible to amoxicillin and tetracycline. Fifty-two isolates had levofloxacin MICs of 0.01-2 mg/l; the remaining 15 (22.4%), all clarithromycin- and metronidazole-resistant, had MICs >/= 8 mg/l. Levofloxacin may be an option for refractory H. pylori infections, but the choice should be based on in vitro susceptibility data, and physicians should consider local resistance patterns when treating these infections empirically.

Review article: impact of Helicobacter pylori on society-role for a strategy of 'search and eradicate'

Helicobacter pylori infection is causally related to gastric cancer, a malignancy associated with high morbidity and poor prognosis, and to peptic ulcer disease, a disease with high morbidity and modest mortality. Theoretically, H. pylori eradication is the most practical means of preventing gastric cancer and peptic ulcer disease. From a public policy perspective, the current evidence is insufficient to assess accurately the magnitude of the benefits of a universal 'search and treat' approach. Nonetheless, it is possible to identify high-risk patients for whom testing for the presence of H. pylori infection, with the intention-to-treat infected individuals is currently indicated. This list includes patients with ulcers or dyspepsia, first-degree relatives of patients with peptic ulcer or gastric cancer, gastric cancer patients after potentially curative resection of their gastric cancer, patients in whom long-term acid antisecretory therapy or long-term nonsteroidal anti-inflammatory drug therapy (including low-dose aspirin) is planned, and finally those who desire testing. Population screening among asymptomatic individuals with a high risk of gastric cancer, such as Korean- and Japanese-Americans, appears logical, but from a public health perspective should be done as a component of controlled intervention studies. There are no known H. pylori infections without risk of a symptomatic outcome, therefore screening represents a rational strategy for cancer prevention. Adoption of such a policy will require carefully balancing the costs of the programme with its benefits.

Susceptibilities to different antibiotics of Helicobacter pylori strains isolated from patients at the pediatric medical center of Tehran, Iran

Antibiotic susceptibility testing of 70 pediatric Helicobacter pylori isolates was performed by using screening agar and disk diffusion methods. Resistance to metronidazole and tinidazole was 72 to 79% and 71 to 81% by modified disk diffusion and 77% and 78% by screening agar, respectively. Susceptibilities to amoxicillin, ampicillin, clarithromycin, tetracycline, erythromycin, and ciprofloxacin were 58, 69, 75, 68, 68, and 65%, respectively.