Efflux pump gene hefA of Helicobacter pylori plays an important role in multidrug resistance

Change of point mutations in Helicobacter pylori rRNA associated with clarithromycin resistance in Italy

Primary clarithromycin resistance is the main factor affecting the efficacy of Helicobacter pylori therapy. This study aimed: (i) to assess the concordance between phenotypic (culture) and genotypic (real-time PCR) tests in resistant strains; (ii) to search, in the case of disagreement between the methods, for point mutations other than those reported as the most frequent in Europe; and (iii) to compare the MICs associated with the single point mutations. In order to perform real-time PCR, we retrieved biopsies from patients in whom H. pylori infection was successful diagnosed by bacterial culture and clarithromycin resistance was assessed using the Etest. Only patients who had never been previously treated, and with H. pylori strains that were either resistant exclusively to clarithromycin or without any resistance, were included. Biopsies from 82 infected patients were analysed, including 42 strains that were clarithromycin resistant and 40 that were clarithromycin susceptible on culture. On genotypic analysis, at least one of the three most frequently reported point mutations (A2142C, A2142G and A2143G) was detected in only 23 cases (54.8%), with a concordance between the two methods of 0.67. Novel point mutations (A2115G, G2141A and A2144T) were detected in a further 14 out of 19 discordant cases, increasing the resistance detection rate of PCR to 88% (P<0.001; odds ratio 6.1, 95% confidence interval 2-18.6) and the concordance to 0.81. No significant differences in MIC values among different point mutations were observed. This study suggests that: (i) the prevalence of the usually reported point mutations may be decreasing, with a concomitant emergence of new mutations; (ii) PCR-based methods should search for at least six point mutations to achieve good accuracy in detecting clarithromycin resistance; and (iii) none of the tested point mutations is associated with significantly higher MIC values than the others.

Impact of Helicobacter pylori biofilm formation on clarithromycin susceptibility and generation of resistance mutations

The human gastric pathogen Helicobacter pylori forms biofilms in vitro and in vivo. The purpose of this study was to evaluate the effects of H. pylori biofilm formation in vitro on clarithromycin (CLR) susceptibility. CLR susceptibility of H. pylori intermediate (2-day) and mature (3-day) biofilms on glass coverslips was determined at concentrations from 0.03 to 0.5 µg/ml. H. pylori biofilm biomass was increased after treatment with CLR at minimum inhibitory concentration levels by up to 4-fold (2-day biofilm) and 16-fold (3-day biofilm). Minimum bactericidal concentrations of CLR against cells in a biofilm were higher (1.0 µg/ml) than that for planktonic cells (0.25 µg/ml). It was shown that the expression of efflux pump genes was significantly increased in biofilm cells. In addition, exposure of biofilms to CLR resulted in high level resistance generation compared to planktonic cells with increased resistance associated with the presence of a point mutation at either position 2142 or 2143 in the domain V loop of the 23S rRNA gene. These results demonstrate that H. pylori biofilm formation decreases the susceptibility to CLR and that H. pylori CLR resistance mutations are more frequently generated in biofilms than in planktonic cells.

Progress in research of Helicobacter pylori efflux pumps

The wide use and abuse of antibiotics have led to serious drug resistance of Helicobacter pylori (H. pylori), and strains simultaneously resistant to metronidazole, clarithromycin and amoxicillin have appeared. As a result, the rate of H. pylori eradication declines clinically. The presence of bacterial efflux pumps is an important mechanism responsible for bacterial resistance to most antibiotics, especially multiple drug resistance (MDR). In recent years, much attention has been paid to the research of efflux pumps and their inhibitors to solve the problem of drug resistance of H. pylori. In this paper we will introduce main efflux pumps and efflux pump inhibitors in H. pylori.

Prevalence of primary and secondary antimicrobial resistance of Helicobacter pylori in Korea from 2003 through 2012

BACKGROUND

Antimicrobial resistance of Helicobacter pylori (H. pylori) affects the efficacy of eradication therapy. The aim of this study was to estimate the prevalence of primary and secondary resistance of H. pylori isolates to antibiotics and to characterize the risk factors associated with antimicrobial resistance in Korea.

MATERIALS AND METHODS

This study was performed during the period of 2003-2012. Primary resistance was evaluated from 347 patients without any history of eradication, and secondary resistance was evaluated in 86 patients from whom H. pylori was cultured after failure of eradication. Minimal inhibitory concentration test was performed for amoxicillin, clarithromycin, metronidazole, tetracycline, azithromycin, levofloxacin, and moxifloxacin using agar dilution method. Primary and secondary resistance rates of H. pylori to 7 antibiotics were evaluated and risk factors for the antibiotic resistance were analyzed.

RESULTS

Increase in the primary resistance rate was found in amoxicillin (6.3-14.9%, p = .051), clarithromycin (17.2-23.7%, p = .323), and both of levofloxacin and moxifloxacin (4.7-28.1%, p = .002) during the study period. Secondary resistance rate significantly increased in metronidazole, levofloxacin, and moxifloxacin. Increase of resistance occurred after initial failure of eradication therapy in case of clarithromycin (p < .001), azithromycin (p < .001), levofloxacin (p = .011), and moxifloxacin (p = .020). Multivariable analyses showed that clarithromycin, azithromycin, levofloxacin, and moxifloxacin resistance was associated with previous eradication treatment history.

CONCLUSIONS

The increased primary and secondary antibiotic resistance of H. pylori in Korea is ongoing, and it will become a significant limitation for effective eradication of H. pylori in the future.

RND multidrug efflux pumps: what are they good for?

Multidrug efflux pumps are chromosomally encoded genetic elements capable of mediating resistance to toxic compounds in several life forms. In bacteria, these elements are involved in intrinsic and acquired resistance to antibiotics. Unlike other well-known horizontally acquired antibiotic resistance determinants, genes encoding for multidrug efflux pumps belong to the core of bacterial genomes and thus have evolved over millions of years. The selective pressure stemming from the use of antibiotics to treat bacterial infections is relatively recent in evolutionary terms. Therefore, it is unlikely that these elements have evolved in response to antibiotics. In the last years, several studies have identified numerous functions for efflux pumps that go beyond antibiotic extrusion. In this review we present some examples of these functions that range from bacterial interactions with plant or animal hosts, to the detoxification of metabolic intermediates or the maintenance of cellular homeostasis.

Polysorbate 80 and Helicobacter pylori: a microbiological and ultrastructural study

BACKGROUND

The frequent occurrence of chemoresistant strains reduces the chances of eradication of H. pylori infection and prompted the investigation of non-antibiotic substances active against this organism. Some surfactants enhance the effectiveness of antibiotics for their permeabilizing properties towards bacteria. We examined the antimicrobial activity to H. pylori of the surfactant polysorbate 80, used alone and in association with amoxicillin, clarithromycin, metronidazole, levofloxacin and tetracycline. We also aimed to study the ultrastructural alterations caused upon H. pylori by polysorbate 80, alone and in combination with antibiotics. Twenty-two H. pylori strains were tested using the broth dilution method. After incubation, broth from each dilution was subcultured onto agar enriched with foetal bovine serum to determine the minimum bactericidal concentration (MBC). Synergistic effect of polysorbate 80 with antibiotics was investigated by the broth dilution and disc diffusion techniques. Ultrastructural alterations of organisms treated with polysorbate 80, alone and in association with antibiotics were analyzed by transmission electron microscopy.

RESULTS

MBCs of polysorbate 80 ranged from 2.6 (1.1) μg/ml to 32 (0) μg/ml. Polysorbate 80 exerted a synergistic effect when associated with metronidazole and clarithromycin: polysorbate 80 and metronidazole MBCs decreased by ≥ 4 fold; clarithromycin MBCs for two resistant strains decreased by 20 and 1000 times. The principal alteration caused by polysorbate 80 consisted in the detachment of the outer membrane of bacteria.

CONCLUSIONS

The bactericidal activity of polysorbate 80 and the synergistic effect of the association with metronidazole and clarithromycin could be useful in the treatment of H. pylori infection.

Mutations of Helicobacter pylori associated with fluoroquinolone resistance in Korea

BACKGROUND AND AIM

Fluoroquinolone resistance of Helicobacter pylori is known to be dependent on mutations in the QRDR of gyrA. This study was performed to investigate the distribution of gyrA point mutations and to evaluate the impact of the mutations on second-line H. pylori eradication therapy.

METHODS

After H. pylori isolation from gastric mucosal specimens, fluoroquinolone resistance was examined using the agar dilution method. DNA sequencing of the QRDR of gyrA was performed in 89 fluoroquinolone-resistant and 27 fluoroquinolone-susceptible isolates. Transformation experiments were performed to confirm mutations in the resistant strains. The eradication rates of moxifloxacin-containing triple therapy were evaluated depending on the resistance of fluoroquinolone.

RESULTS

The gyrA mutations were detected in 75.3% (55 of 73 strains) of the primary resistant strains and 100% (16 strains) of the secondary resistant strains. The most common mutations were Asp-91 (36.0%) and Asn-87 (33.7%). The MIC values in the transformed strains differed depending on the gyrA mutations, N87, and D91. Six patients with fluoroquinolone-resistant strains received moxifloxacin-containing triple therapy as the second-line therapy, and two of three patients with Asn-87 mutations (66.7%) failed in the eradication. By contrast, three patients with Asp-91 mutations had successful eradication treatment.

CONCLUSIONS

Fluoroquinolone resistance of H. pylori was caused by gyrA Asn-87 and Asp-91 point mutations. The Asn-87 mutation seems to be an important determinant of failure of fluoroquinolone-containing triple eradication therapy based on eradication results.

Role of ABC transporter genes msbA and spab in multidrug resistance of Helicobacter pylori

AIM: To evaluate the potential role of ATP-binding cassette (ABC) transporter genes msbA and spab in multidrug resistance (MDR) of Helicobacter pylori (H.pylori).

METHODS: H.pylori strains were isolated from patients with peptic ulcer or gastritis. The minimal inhibitory concentrations (MICs) of ampicillin, ceftriaxone, tetracycline, clarithromycin, ofloxacin and furazolidone for H.pylori strains were determined by agar dilution test. Five sensitive H.pylori strains (four is H.pylori olates and one standard strain NCTC11637) were used to induce multidrug resistance with chloramphenicol. The mRNA expression of msbA and spab in these multidrug-resistant strains was determined by RT-PCR. Two H.pylori gene knockout mutants (MZ1006ΔmsbA and MZ1006Δspab) were constructed by inserting the kanamycin resistance cassette from the pEGFP-N2 vector into the msbA and spab genes, and their susceptibility profiles to nine antibiotics were estimated.

RESULTS: The expression levels of ABC transporter genes msbA and spab in multidrug-resistant H.pylori strains were higher than those in sensitive strains (1.8200 ± 0.5310 vs 0.8420 ± 0.0789, P = 0.018, for msbA; 1.8340 ± 0.2726 vs 1.2180 ± 0.0743, P = 0.015, for spab). MZ1006ΔmsbA and H.pylori MZ1006spab mutants were constructed successfully, and their sensitivity to four of nine antibiotics was significantly enhanced compared to their parental wild-type strains. Both the msbA and spab genes were detected in all isolated strains.

CONCLUSION: ABC transporter genes msbA and spab play an important role in multidrug resistance of H.pylori.

Rapid detection of clarithromycin resistant Helicobacter pylori strains in Spanish patients by polymerase chain reaction-restriction fragment length polymorphism

INTRODUCTION

The aim of this study was to characterize the mutations types present in the 23S rRNA gene related to H. pylori clarithromycin-resistance strains in Spain and evaluate a novel PCR-RFLP method for detection of the most frequent point mutation in our population.

METHODS

Gastric biopsies were obtained by endoscopy from patients with gastric symptoms. H. pylori was cultured according to standard microbiological procedures and clarithromycin resistance was determined by E-test. DNA extraction was performed by NucliSens platform with the NucliSens magnetic extraction reagents (bioMérieux) according to the manufacturer instructions. Analyses for point mutations in 23S rRNA gene strains were performed by sequence analysis of amplified polymerase chain reaction products. Restriction fragment length polymorphism was performed using BsaI enzyme to detect restriction sites that correspond to the mutation (A2143G).

RESULTS

We found 42 out of 118 (35.6%) strains resistant to clarithromycin by E-test. E-test results were confirmed for the presence of point mutation in 34 (88.1%) of these strains. Mutation A2143G was found in 85.3% of the strains. Analyses with the restriction enzyme BsaI was able to confirm the presence of A2143G mutation. There were 8 H. pylori strains resistant to clarithromycin by E-test but without any point mutation in the 23 rRNA gene.

CONCLUSIONS

We conclude that PCR-RFLP is a reliable method to detect clarithromycin-resistance H. pylori strains in countries with a high prevalence of clarithromycin-resistance as Spain. It may be useful before choosing regimens of H. pylori eradication.

Enhanced bacterial efflux system is the first step to the development of metronidazole resistance in Helicobacter pylori

Although metronidazole (Mtz) is an important component of Helicobacter pylori eradication regimens, it has been pointed out that the increasing use of Mtz may result in increase in the incidence of Mtz-resistant strains. The present study was designed to examine the initial mechanism of resistance acquisition of H. pylori to Mtz. After 10 Mtz-susceptible strains were cultured on plates containing sub-inhibitory concentrations of Mtz, the MIC of Mtz for 9 of the 10 strains increased to levels of the Mtz-resistant strains. In the Mtz-resistance-induced strains, the expression of the TolC efflux pump (hefA) was significantly increased under Mtz exposure, without the reduction of the Mtz-reductive activity. Our finding suggests that overexpression of hefA may be the initial step in the acquisition of Mtz resistance in H. pylori.

Complexomics study of two Helicobacter pylori strains of two pathological origins: potential targets for vaccine development and new insight in bacteria metabolism

Helicobacter pylori infection plays a causal role in the development of gastric mucosa-associated lymphoid tissue (MALT) lymphoma (LG-MALT) and duodenal ulcer (DU). Although many virulence factors have been associated with DU, many questions remain unanswered regarding the evolution of the infection toward this exceptional event, LG-MALT. The present study describes and compares the complexome of two H. pylori strains, strain J99 associated with DU and strain B38 associated with LG-MALT, using the two-dimensional blue native/SDS-PAGE method. It was possible to identify 90 different complexes (49 and 41 in the B38 and J99 strains, respectively); 12 of these complexes were common to both strains (seven and five in the membrane and cytoplasm, respectively), reflecting the variability of H. pylori strains. The 44 membrane complexes included numerous outer membrane proteins, such as the major adhesins BabA and SabA retrieved from a complex in the B38 strain, and also proteins from the hor family rarely studied. BabA and BabB adhesins were found to interact independently with HopM/N in the B38 and J99 strains, respectively. The 46 cytosolic complexes essentially comprised proteins involved in H. pylori physiology. Some orphan proteins were retrieved from heterooligomeric complexes, and a function could be proposed for a number of them via the identification of their partners, such as JHP0119, which may be involved in the flagellar function. Overall, this study gave new insights into the membrane and cytoplasm structure, and those which could help in the design of molecules for vaccine and/or antimicrobial agent development are highlighted.

Role of the HefC efflux pump in Helicobacter pylori cholesterol-dependent resistance to ceragenins and bile salts

The human gastric pathogen Helicobacter pylori modifies host cholesterol via glycosylation and incorporates the glycosylated cholesterol into its membrane; however, the benefits of cholesterol to H. pylori are largely unknown. We speculated that cholesterol in the H. pylori membrane might alter the susceptibility of these organisms to membrane-disrupting antibacterial compounds. To test this hypothesis, H. pylori strains were cultured in Ham's F-12 chemically defined medium in the presence or absence of cholesterol. The two cultures were subjected to overnight incubations with serial 2-fold dilutions of 10 bile salts and four ceragenins, which are novel bile salt derivatives that mimic membrane-disrupting activity of antimicrobial peptides. H. pylori cultured with cholesterol was substantially more resistant to seven of the bile salts and three ceragenins than H. pylori cultured without cholesterol. In most cases, these cholesterol-dependent differences ranged from 2 to 7 orders of magnitude; this magnitude depended on concentration of the agent. Cholesterol is modified by glycosylation using Cgt, a cholesteryl glycosyltransferase. Surprisingly, a cgt knockout strain still maintained cholesterol-dependent resistance to bile salts and ceragenins, indicating that cholesterol modification was not involved in resistance. We then tested whether three putative, paralogous inner membrane efflux pumps, HefC, HefF, or HefI, played a role. While HefF and HefI appeared unimportant, HefC was shown to play a critical role in the resistance to bile salts and ceragenins by multiple methods in multiple strain backgrounds. Thus, both cholesterol and the putative bile salt efflux pump HefC play important roles in H. pylori resistance to bile salts and ceragenins.

High prevalence of clarithromycin-resistant Helicobacter pylori strains and risk factors associated with resistance in Madrid, Spain

Clarithromycin is one of the antibiotics used for the treatment of Helicobacter pylori infections, and clarithromycin resistance is the most important factor when it comes to predicting eradication failure. The present study analyzed H. pylori isolates for the presence of 23S rRNA gene mutations and determined the risk factors associated with resistance among H. pylori isolates collected in Madrid, Spain, in 2008. We studied 118 H. pylori strains isolated from the same number of patients. A total of 76.3% of the patients were born in Spain, 52.7% were children, 20.3% had previously been treated, and 66.1% were female. Clarithromycin resistance was determined by Etest. H. pylori strains were considered resistant if the MIC was ≥1 mg/liter. DNA extraction was carried out by use of the NucliSens easyMAG platform with NucliSens magnetic extraction reagents (bioMérieux). The DNA sequences of the 23S rRNA genes of clarithromycin-resistant and -sensitive strains were determined to identify specific point mutations. The vacA genotype and cagA status were determined by PCR. We found that 42 (35.6%) strains were resistant to clarithromycin by Etest. Etest results were confirmed by detection of the presence of point mutations in 34 (88.1%) of these strains. Eight H. pylori strains were resistant to clarithromycin by Etest but did not have a point mutation in the 23S rRNA gene. Mutation at A2143G was found in 85.3% of the strains, mutation at A2142G in 8.8%, and mutation at T2182C in 5.9%. Dual mutations were found in 8.8% of the strains. H. pylori clarithromycin-resistant strains were strongly associated with pediatric patients, with patients born in Spain, and with patients who had previously been treated (P ≤ 0.02). In addition, H. pylori strains resistant to clarithromycin more frequently presented the vacA s2/m2 genotype and were more likely to be cagA negative than susceptible strains (39.1% and 11.2%, respectively; P value < 0.001). We concluded that, in the present study, H. pylori clarithromycin-resistant strains are more frequently found in children, in patients mostly born in Spain, and in individuals who were previously treated for H. pylori infection and that these individuals are more likely colonized with a less virulent H. pylori strain.

Influence of efflux pump inhibitors on the multidrug resistance of Helicobacter pylori

AIM: To evaluate the effect of efflux pump inhibitors (EPIs) on multidrug resistance of Helicobacter pylori (H. pylori).

METHODS: H. pylori strains were isolated and cultured on Brucella agar plates with 10% sheep’s blood. The multidrug resistant (MDR) H. pylori were obtained with the inducer chloramphenicol by repeated doubling of the concentration until no colony was seen, then the susceptibilities of the MDR strains and their parents to 9 antibiotics were assessed with agar dilution tests. The present study included periods before and after the advent of the EPIs, carbonyl cyanide m-chlorophenyl hydrazone (CCCP), reserpine and pantoprazole), and the minimum inhibitory concentrations (MICs) were determined accordingly. In the same way, the effects of 5 proton pump inhibitors (PPIs), used in treatment of H. pylori infection, on MICs of antibiotics were evaluated.

RESULTS: Four strains of MDR H. pylori were induced successfully, and the antibiotic susceptibilities of MDR strains were partly restored by CCCP and pantoprazole, but there was little effect of reserpine. Rabeprazole was the most effective of the 5 PPIs which could decrease the MICs of antibiotics for MDR H. pylori significantly.

CONCLUSION: In vitro, some EPIs can strengthen the activities of different antibiotics which are the putative substrates of the efflux pump system in H. pylori.

Effects of efflux pump inhibitors on the multidrug resistance of Helicobacter pylori

AIM: To evaluate the effects of efflux pump inhibitors (EPIs) on the multidrug resistance (MDR) of Helicobacter pylori

(H.pylori).

METHODS: H.pylori strains were isolated and cultured on Brucella agar plates containing 10% sheep blood. The MDR of H.pylori strains was induced with chloramphenicol. The susceptibility of multidrug-resistant H.pylori strains and their parental strains to nine antibiotics was assessed by agar dilution test in the presence and absence of EPIs such as CCCP, reserpine and pantoprazole. The minimal inhibitory concentrations (MICs) of different antibiotics against multidrug-resistant H.pylori strains were determined. Similarly, the impact of five proton pump inhibitors (PPIs) on the MICs of these antibiotics was also tested and compared.

RESULTS: Four multidrug-resistant H.pylori strains were induced successfully. The susceptibility of these multidrug-resistant strains to some antibiotics such as cefotaxime were partly restored by CCCP and pantoprazole, but not by reserpine. Of the five PPIs tested, rabeprazole reduced the MICs of metronidazole and amoxicillin against multidrug-resistant H.pylori strains to one forth and one third, respectively, pantoprazole reduced both of them to one half, and the remaining two PPIs showed no obvious effects.

CONCLUSION: Some EPIs can potentiate the activity of antibiotics that are putative substrates of the efflux pump system of H.pylori. Of all PPIs tested, rabeprazole is the most effective one to reduce the MDR of H.pylori.

Efflux-mediated drug resistance in bacteria: an update

Drug efflux pumps play a key role in drug resistance and also serve other functions in bacteria. There has been a growing list of multidrug and drug-specific efflux pumps characterized from bacteria of human, animal, plant and environmental origins. These pumps are mostly encoded on the chromosome, although they can also be plasmid-encoded. A previous article in this journal provided a comprehensive review regarding efflux-mediated drug resistance in bacteria. In the past 5 years, significant progress has been achieved in further understanding of drug resistance-related efflux transporters and this review focuses on the latest studies in this field since 2003. This has been demonstrated in multiple aspects that include but are not limited to: further molecular and biochemical characterization of the known drug efflux pumps and identification of novel drug efflux pumps; structural elucidation of the transport mechanisms of drug transporters; regulatory mechanisms of drug efflux pumps; determining the role of the drug efflux pumps in other functions such as stress responses, virulence and cell communication; and development of efflux pump inhibitors. Overall, the multifaceted implications of drug efflux transporters warrant novel strategies to combat multidrug resistance in bacteria.

The Helicobacter hepaticus hefA gene is involved in resistance to amoxicillin

BACKGROUND

Gastrointestinal infections with pathogenic Helicobacter species are commonly treated with combination therapies, which often include amoxicillin. Although this treatment is effective for eradication of Helicobacter pylori, the few existing reports are less clear about antibiotic susceptibility of other Helicobacter species. In this study we have determined the susceptibility of gastric and enterohepatic Helicobacter species to amoxicillin, and have investigated the mechanism of amoxicillin resistance in Helicobacter hepaticus.

MATERIALS AND METHODS

The minimal inhibitory concentration (MIC) of antimicrobial compounds was determined by E-test and agar/broth dilution assays. The hefA gene of H. hepaticus was inactivated by insertion of a chloramphenicol resistance gene. Transcription was measured by quantitative real-time polymerase chain reaction.

RESULTS

Three gastric Helicobacter species (H. pylori, H. mustelae, and H. acinonychis) were susceptible to amoxicillin (MIC < 0.25 mg/L). In contrast, three enterohepatic Helicobacter species (H. rappini, H. bilis, and H. hepaticus) were resistant to amoxicillin (MIC of 8, 16, and 6-64 mg/L, respectively). There was no detectable beta-lactamase activity in H. hepaticus, and inhibition of beta-lactamases did not change the MIC of amoxicillin of H. hepaticus. A H. hepaticus hefA (hh0224) mutant, encoding a TolC-component of a putative efflux system, resulted in loss of amoxicillin resistance (MIC 0.25 mg/L), and also resulted in increased sensitivity to bile acids. Finally, transcription of the hefA gene was not responsive to amoxicillin, but induced by bile acids.

CONCLUSIONS

Rodents are frequently colonized by a variety of enterohepatic Helicobacter species, and this may affect their global health status and intestinal inflammatory responses. Animal facilities should have treatment strategies for Helicobacter infections, and hence resistance of enterohepatic Helicobacter species to amoxicillin should be considered when designing eradication programs.