Helicobacter pylori resistance to tetracycline

Some current applications, limitations and future perspectives of lactic acid bacteria as probiotics

Several mechanism and non-mechanism-based studies supporting the claim that lactic acid bacteria (LAB) strains confer health benefits and play immune-modulatory roles were examined in this review. Probiotic applications of LAB on global burdens such as obesity and type-2 diabetes were discussed as well as the use of yoghurt and ice cream as important vehicles to convey several beneficial LAB strains. Probiotic and symbiotic dairy products may be used in the nearest future to treat a variety of health disorders. Current studies suggest that lactic acid bacteria possess anti-obesity and anti-diabetic propensities on their hosts and thus can play a crucial role in human health care. Research in the rheological and physicochemical properties of ice cream as well as its applications are also on the increase. These applications face certain hurdles including technological (for less developed countries), consumer acceptability of new functional foods may be influenced by culture, ethics or religion. There is need for more studies on the genetic basis for probiotic properties which will give further understanding regarding novel manipulation skills and applicability in nutrition and health sectors. More studies confirming the direct effects of probiotic LABs in lowering the spread of food-borne and other pathogens are also anticipated.

Sequential metronidazole-furazolidone or clarithromycin-furazolidone compared to clarithromycin-based quadruple regimens for the eradication of Helicobacter pylori in peptic ulcer disease: a double-blind randomized controlled trial

BACKGROUND

Furazolidone is a much cheaper drug with a very low resistance against Helicobacter pylori compared to clarithromycin. We aim to evaluate safety and efficacy of a sequential furazolidone-based regimen versus clarithromycin-based therapy in H. pylori eradication for ulcer disease.

MATERIALS

Patients with proven peptic ulcer or duodenitis were randomized into three groups: OAB-M-F; metronidazole (M) (500 mg bid) for the first 5 days, followed by furazolidone (F) (200 mg bid) for the second 5 days; OAC-P; clarithromycin (C) (500 mg bid) for 10 days; and OAB-C-F; clarithromycin (500 mg bid) for the first 5 days and furazolidone (200 mg bid) for the second 5 days. All groups received omeprazole (O) (20 mg bid) and amoxicillin (A) (1 g bid). Groups OAB-M-F and OAB-C-F were also given bismuth subcitrate (B) (240 mg bid), whereas a placebo (P) was given to group OAC-P. Adverse events were scored and recorded. Two months after treatment, a C(13) -urea breath test was performed.

RESULTS

Three hundred and ten patients were enrolled and 92 (OAB-M-F), 95 (OAC-P), and 98 (OAB-C-F) completed the study. The intention-to-treat eradication rates were 78.5% (95% CI = 69-85), 81.1% (95% CI = 73-88), and 82% (95% CI = 74-89), and per-protocol eradication rates were 91.3% (95% CI = 83-96), 90.4% (95% CI = 82-95), and 88.7% (95% CI = 81-94), for group OAB-M-F, OAC-P, and OAB-C-F, respectively. Eradication rate differences did not reach statistical significance. The most common adverse event, bad taste, occurred in all groups, but more frequently in groups OAC-P (34%) and OAB-C-F (32%), than OAB-M-F (14%) (p < .05). Adverse symptoms score were 0.88 ± 2.05 in group OAB-M-F, 1.15 ± 1.40 in group OAC-P, and 1.87 ± 1.62 in group OAB-C-F.

CONCLUSION

Furazolidone can replace clarithromycin in H. pylori eradication regimens because of lack of development of resistance and very low cost.

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.

Antibiotic Susceptibility of Helicobacter pylori Clinical Isolates: Comparative Evaluation of Disk-Diffusion and E-Test Methods

Antimicrobial susceptibility of 25 Helicobacter pylori strains isolated from patients with acid peptic diseases were tested for in vitro sensitivity to commonly used antibiotics using disk-diffusion and E-test, methods. All strains tested were susceptible to tetracycline by E-test, with the minimum inhibitory concentration (MIC) values being <0.125 microg/ml for all strains except for 6 (<0.023 microg/ml). However 1 strain was resistant by disk-diffusion method. One strain was resistant to clarithromycin both by disk diffusion and E-test (MIC <48 microg/ml), and 1 strain was resistant only by disk diffusion. Only one strain was resistant to amoxicillin by disk diffusion and E-test (MIC >256 microg/ml). For ciprofloxacin, three strains were resistant by disk diffusion and two by E-test (MIC <32 microg/ml). Sixteen strains were resistant to metronidazole by disk diffusion and E-test (MIC >or= 8 microg/ml), and 1 was resistant only by E-test (MIC <48 microg/ml). Overall, 64% of the strains were resistant to metronidazole. The MIC for metronidazole was also tested by agar-dilution method, and metronidazole resistant strains had an, MIC >8 microg/ml. The disk-diffusion method showed excellent correlation with E-test results; there was 100% agreement for amoxicillin a other antibiotics showed 90% to 95% accuracy. Disk diffusion is cheaper than E-test (approximately 2.6 cents vs. 2.60 US dollars), is easy to perform, and is a reliable method for testing H. pylori susceptibility to antimicrobial agents in the clinical microbiology laboratory.

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.

Antagonism of Helicobacter pylori by bacteriocins of lactic acid bacteria

Antimicrobial activity of seven bacteriocins produced by lactic acid bacteria against Helicobacter pylori strains (ATCC 43504, Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [DSM] 4867, DSM 9691, and DSM 10242) was investigated in vitro using a broth microdilution assay. The bacteriocins chosen for the study were nisin A; lacticins A164, BH5, JW3, and NK24; pediocin PO2; and leucocin K. Antimicrobial activity of the bacteriocins varied among the H. pylori strains tested, of which strain ATCC 43504 was the most tolerant. Among the bacteriocins tested, lacticins A164 and BH5 produced by Lactococcus lactis subsp. lactis A164 and L. lactis BH5, respectively, showed the strongest antibacterial activity against H. pylori strains. MICs of the lacticins against H. pylori strains, when assessed by the critical dilution micromethod, ranged from 0.097 to 0.390 mg/liter (DSM strains) or from 12.5 to 25 mg/liter (ATCC 43504), supporting the strain-dependent sensitivity of the pathogen. Pediocin PO2 was less active than the lacticins against four strains of H. pylori, and leucocin K was the least active peptide, with no inhibition toward H. pylori ATCC 43504. Anti-Helicobacter activity of lacticin A164 was dependent on initial inoculum size as well as concentration of the bacteriocin added.

Furazolidone-based triple 'rescue therapy' vs. quadruple 'rescue therapy' for the eradication of Helicobacter pylori resistant to metronidazole

BACKGROUND

The optimal treatment of patients with Helicobacter pylori resistant to metronidazole has not been established.

AIM

To compare the efficacy of quadruple and furazolidone-based triple therapy in the eradication of H. pylori resistant to metronidazole.

METHODS

Duodenal ulcer patients (n = 70) in whom initial eradication therapy failed and who harboured H. pylori strains resistant to metronidazole were randomized to receive one of the following 7-day regimens: colloidal bismuth subcitrate, 240 mg, tetracycline, 750 mg, and furazolidone, 200 mg, each given twice daily (BTF), or omeprazole, 20 mg b.d., colloidal bismuth subcitrate, 240 mg b.d., tetracycline, 500 mg q.d.s., and metronidazole, 500 mg b.d. (OBTM). H.pylori status was assessed by culture, histology and rapid urease test before treatment and 4-6 weeks after therapy. Susceptibility to metronidazole was assessed by the agar dilution method.

RESULTS

H. pylori eradication rates with intention-to-treat/per protocol analyses were: BTF, 85.7%/90.9%; OBTM, 74.2%/89.6%. Duodenal ulcers were healed in nine of 10 (90%) patients in the BTF group and in all patients (12/12) (100%) in the OBTM group (P = N.S.). A significantly lower rate of adverse events was observed in the BTF group than in the OBTM group (31.4% vs. 60%, P = 0.03), but there was no difference in terms of discontinuation of treatment (2/35 vs. 6/35, P = N.S.).

CONCLUSIONS

The 1-week BTF regimen was as effective as the OBTM regimen, and produced less adverse events. Thus, it may be used in patients in whom resistance of H. pylori to metronidazole is suspected.

Mutations in the 16S rRNA genes of Helicobacter pylori mediate resistance to tetracycline

Low-cost and rescue treatments for Helicobacter pylori infections involve combinations of several drugs including tetracycline. Resistance to tetracycline has recently emerged in H. pylori. The 16S rRNA gene sequences of two tetracycline-resistant clinical isolates (MIC = 64 microg/ml) were determined and compared to the consensus H. pylori 16S rRNA sequence. One isolate had four nucleotide substitutions, and the other had four substitutions and two deletions. Natural transformation with the 16S rRNA genes from the resistant organisms conferred tetracycline resistance on susceptible strains. 16S rRNA genes containing the individual mutations were constructed and tested for the ability to confer resistance. Only the 16S rRNA gene containing the triple mutation, AGA965-967TTC, was able to confer tetracycline resistance on H. pylori 26695. The MICs of tetracycline for the transformed strains were equivalent to those for the original clinical isolates. The two original isolates were also metronidazole resistant, but this trait was not linked to the tetracycline resistance phenotype. Serial passage of several H. pylori strains on increasing concentrations of tetracycline yielded mutants with only a very modest increase in tetracycline resistance to a MIC of 4 to 8 microg/ml. These mutants all had a deletion of G942 in the 16S rRNA genes. The mutations in the 16S rRNA are clearly responsible for tetracycline resistance in H. pylori.

[Evolution of the sensitivity of 235 strains of Helicobacter pylori from 1995 to 1998 and impact of antibiotic treatment]

BACKGROUND

The aim of this study was to investigate the sensitivity of Helicobacter pylori to the antibiotics used in its eradication over a period of four years and to determine the influence of previous treatment on sensitivity.

MATERIAL AND METHODS

During the period from 1995 to 1998 we determined the sensitivity of 235 consecutive Helicobacter pylori isolates to amoxicillin, metronidazole, clarythromycin and tetracycline by means of E-test methodology. The MIC values found were related with the prior use of eradicating treatment.

RESULTS

The percentage of resistant strains were as follows: 23.5% to metronidazole, 12.9% to clarythromycin and 0.7% to tetracycline; none of the strains was resistant to amoxicillin. There were no significant changes in percentage of resistance to the drugs studied over the 4-year period. Resistance to metronidazole and clarythromycin was significantly higher (p 5 0.03 and p < 0.001 respectively) in strains isolated from patients who had received previous treatment.

CONCLUSIONS

Monitorization of H. pylori sensitivity to the drugs used in its eradication is particularly important in patients who have undergone prior treatment.

Amoxicillin/tetracycline combinations are inadequate as alternative therapies for Helicobacter pylori infection

BACKGROUND

Triple therapy with proton pump inhibitors or ranitidine bismuth citrate, clarithromycin and either amoxicillin or nitroimidazole derivatives are the present gold standards for cure of Helicobacter pylori infection. However, primary resistance to either clarithromycin or nitroimidazole derivatives is increasing and alternative therapies are needed.

AIM

To determine the efficacy and safety of three regimens consisting of amoxicillin and tetracycline or doxycycline combined with either lansoprazole or ranitidine bismuth citrate.

METHODS

Two hundred and seventy H. pylori infected patients were randomly given one of the following treatments: amoxicillin 1 g twice a day (b.i.d.) plus tetracycline 500 mg four times a day (q.i.d.) with either lansoprazole 30 mg b.i.d. (group LAT) or ranitidine bismuth citrate 400 mg b.i.d. (group RBCAT) for 7 days and amoxicillin 1 g b.i.d. plus doxycycline 100 mg b.i.d. and lansoprazole 30 mg b.i.d. for 14 days (group LAD). Eradication rate was assessed by UBT at 4-6 weeks after therapy.

RESULTS

The three groups (LAT, RBCAT, and LAD) of patients achieved eradication rates of 35% (25-45), 20% (12-29) and 36% (25-46), respectively, on intention-to-treat analysis. Patient compliance was optimal and side-effects minimal in all three groups.

CONCLUSIONS

Although the amoxicillin/tetracycline combination is attractive (inexpensive, safe, and with low primary resistance rate), it can not be recommended for H. pylori eradication.

Tetracycline antibiotics: mode of action, applications, molecular biology, and epidemiology of bacterial resistance

Tetracyclines were discovered in the 1940s and exhibited activity against a wide range of microorganisms including gram-positive and gram-negative bacteria, chlamydiae, mycoplasmas, rickettsiae, and protozoan parasites. They are inexpensive antibiotics, which have been used extensively in the prophlylaxis and therapy of human and animal infections and also at subtherapeutic levels in animal feed as growth promoters. The first tetracycline-resistant bacterium, Shigella dysenteriae, was isolated in 1953. Tetracycline resistance now occurs in an increasing number of pathogenic, opportunistic, and commensal bacteria. The presence of tetracycline-resistant pathogens limits the use of these agents in treatment of disease. Tetracycline resistance is often due to the acquisition of new genes, which code for energy-dependent efflux of tetracyclines or for a protein that protects bacterial ribosomes from the action of tetracyclines. Many of these genes are associated with mobile plasmids or transposons and can be distinguished from each other using molecular methods including DNA-DNA hybridization with oligonucleotide probes and DNA sequencing. A limited number of bacteria acquire resistance by mutations, which alter the permeability of the outer membrane porins and/or lipopolysaccharides in the outer membrane, change the regulation of innate efflux systems, or alter the 16S rRNA. New tetracycline derivatives are being examined, although their role in treatment is not clear. Changing the use of tetracyclines in human and animal health as well as in food production is needed if we are to continue to use this class of broad-spectrum antimicrobials through the present century.

Evolution of metronidazole and tetracycline susceptibility pattern in Helicobacter pylori at a hospital in Saudi Arabia

The association of Helicobacter pylori with chronic gastritis and peptic ulcer disease led to new therapeutic approaches including the use of antibiotics. Recently, resistance of H. pylori to antibiotics has emerged as the major cause of treatment failure. This retrospective analysis was aimed at investigating the development of antimicrobial susceptibility patterns amongst H. pylori strains isolated at King Fahd Hospital of the University, Al-Khobar. Susceptibility patterns obtained using isolates from a pilot study (1987-1988) were compared with those subsequently isolated (1990-1996). Metronidazole resistance was estimated to be 35.2% in the first period but more than doubled (78.5%) during the second period. Isolates from females showed a higher resistance rate to metronidazole than those from males. Only one strain was tetracycline resistant. The extremely high resistance rate to metronidazole indicates that it may not be very effective for eradication of H. pylori. Tetracycline should prove a useful component of treatment regimens in this geographical region.

Negative effect of ranitidine on the results of urea breath test for the diagnosis of Helicobacter pylori

OBJECTIVES

In analogy with proton pump inhibitors, H2-antagonists may also be responsible for false-negative results on urea breath test for the detection of Helicobacter pylori. In this study we assessed the frequency and duration of false-negative urea breath tests in patients given different doses of ranitidine.

METHODS

A total of 120 consecutive dyspeptic patients infected with H. pylori on the basis of concomitant positive results of CLO-test, histology and urea breath test were recruited for this prospective, open, parallel-group study performed in an urban university gastroenterological clinic. They were randomized to receive an acute treatment with either ranitidine 300 mg once a day in the evening, ranitidine 300 mg once a day in the morning, ranitidine 150 mg b.i.d., or ranitidine 300 mg b.i.d. for 14 days. The urea breath test was performed on day 14 while patients were still taking ranitidine, and on day 21, 1 wk after completion of therapy. The test was repeated on day 28 in those patients who were still negative on day 21. Duplicate breath samples were collected after ingestion of 75 mg 13C-urea plus citric acid. A delta value >5/1000 was considered positive.

RESULTS

Of 118 patients infected with H. pylori, 15 (13%) had a negative urea breath test on day 14. The false-negative results were equally distributed among the four groups of ranitidine dosage. Nine of these patients reverted to positive at 7 days and the remaining six at 14 days after completion of therapy.

CONCLUSIONS

Our study shows that ranitidine negatively affects the results of urea breath testing, independent of the given dosage. Patients undergoing this examination for H. pylori diagnosis should discontinue use of H2-antagonists 2 wk before testing.

How to treat Helicobacter pylori. First-line, second-line, and future therapies

Numerous trials were performed in the 1990s to define the optimal therapy for Helicobacter pylori infections. The proposed proton-pump inhibitor (PPI)-based and ranitidine bismuth citrate (RBC)-based triple therapies led to satisfactory results. Their first drawback is cost, and, for this reason, many people worldwide cannot benefit from these regimens. Failures of first-line therapies essentially are because of antimicrobial resistance, which increases with the selection pressure resulting from the use of these drugs. Second-line treatments using antimicrobial agents for which H. pylori resistance is low or nonexistent are being tested to find alternatives to the quadruple therapy. There is a need for new drugs, which should be highly effective, nonselective of resistant strains, and without side effects, to improve current regimens. These drugs may be the results of postgenomic studies.

Isolation and characterization of tetracycline-resistant clinical isolates of Helicobacter pylori

Tetracycline is an important component of combination therapies for Helicobacter pylori eradication. Twenty-nine tetracycline-resistant isolates requiring MICs ranging from 4 to 16 microgram/ml were isolated from Korean (22 of 460) and Japanese (7 of 105) patients. Interestingly, all of the 29 tetracycline-resistant isolates exhibited cross-resistance to metronidazole, and the cross-resistance was transferred to tetracycline-sensitive H. pylori strains.

Metronidazole containing quadruple therapy for infection with metronidazole resistant Helicobacter pylori: a prospective study

BACKGROUND

Metronidazole remains a key component of H. pylori infection therapy. It has been suggested that despite resistance, metronidazole may be effective when given at high dose with bismuth, tetracycline, and a proton pump inhibitor (quadruple therapy).

AIM

To prospectively evaluate metronidazole quadruple therapy for treatment of metronidazole resistant H. pylori infection in the United States.

METHODS

Patients infected with metronidazole resistant H. pylori were prospectively prescribed 14 days of quadruple therapy consisting of metronidazole 500 mg t.d.s., tetracycline 500 mg q.d.s., two bismuth subsalicylate tablets q.d.s., and omeprazole 20 mg o.d.

RESULTS

A total of 26 patients were entered into the study; 22 for their first treatment and four as re-treatment for failed therapy. Of the 26 patients, 24 were cured (cure rate 92%; 95% CI: 78-99%). Both treatment failures reported full compliance to 14 days of therapy. Side-effects were common and resulted in premature discontinuation of therapy in 31%. Premature discontinuation did not reduce the cure rate.

CONCLUSION

Quadruple metronidazole combination therapy is effective despite the presence of metronidazole resistance and should be considered as either first line therapy or for failures of twice-a-day combination therapies.

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. Material and Methods. Ninety consecutive H. pylori-positive patients were enrolled. Resistance was evaluated by an agar dilution test.

RESULTS

Resistance to metronidazole was detected in 38 patients (42%); to amoxicillin in 26 individuals (29%); to clarithromycin in 6 patients (7%); to tetracycline in 6 patients (7%); and to furazolidone in 4 individuals (4%). Thirteen strains were resistant to two agents, and eight strains were resistant to three antimicrobials.

CONCLUSIONS

These results confirm the need for culture and susceptibility testing to define H. pylori resistance patterns in particular geographical areas before the general use of an eradication schedule. They also suggest the possibility of resistance to such antimicrobials as amoxicillin or tetracycline in geographical areas with a high prevalence of H. pylori infection and still not fully evaluated for antimicrobial susceptibility.

Review article: nitroimidazole resistance in Helicobacter pylori

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.

beta-Lactamase inhibitors have antibacterial activities against Helicobacter pylori

Recently, it was reported that amoxicillin-clavulanate has slightly higher activity than amoxicillin against Helicobacter pylori. In this study, we evaluated the in-vitro antibacterial activity of beta-lactamase inhibitors against H. pylori. We investigated the susceptibility of 30 H. pylori strains to beta-lactamase inhibitors, including clavulanate, sulbactam, and tazobactam. In short-term bactericidal studies, a clinical isolate of H. pylori NU27 was exposed to 1 x minimum inhibitory concentration (MIC) of the beta-lactamase inhibitors, amoxicillin, clarithromycin, and amoxicillin-clavulanate for 3 and 6 h. The MICs90 for these beta-lactamase inhibitors were 2, 4, and 2 mg/l, respectively. The short-term bactericidal studies showed that these beta-lactamase inhibitors decreased viable counts of H. pylori during 6-h exposure at 1 x MIC. Our results suggest that beta-lactamase inhibitors have in-vitro antibacterial activity against H. pylori. Amoxicillin and clavulanate used in combination resulted in increased antibacterial activity.

Antibiotic resistance problems with Helicobacter pylori

Helicobacter pylori is very susceptible in vitro to most antibiotics, but when they are used in the clinical setting, eradication of the bacteria from the gastric mucosa is not obtained. Dual or triple therapy including two of the following antibiotics: amoxicillin, tetracycline, metronidazole or clarithromycin, plus a proton pump inhibitor, bismuth salt or ranitidine bismuth citrate is the most frequently used. Various in vitro susceptibility methods have been used: disk diffusion, agar dilution and Epsilometer test (E-test). Metronidazole resistance among H. pylori strains is now found worldwide, and resistance rates vary according to the population studied. It is higher in developing than in developed countries and it could reach 80-90% in Africa. The prevalence on clarithromycin resistance is much lower, usually below 10%, although very high values are reported in Peru. Infection with metronidazole- or clarithromycin-resistant H. pylori strains is correlated with treatment failure when using regimens including these antibiotics.

Prevalence of Helicobacter pylori resistance to metronidazole, clarithromycin, amoxycillin, tetracycline and trovafloxacin in The Netherlands

Successful treatment of Helicobacter pylori infection is becoming compromised by emerging resistance. We report the prevalence rates of H. pylori resistance to metronidazole, clarithromycin, amoxycillin, tetracycline and trovafloxacin in The Netherlands. A total of 231 H. pylori clinical isolates were collected throughout the country over a period of 6 months during 1997-1998. The MICs of the above-mentioned antibiotics were determined in a single laboratory. The overall percentage of resistance for clarithromycin and metronidazole was 1.7% and 21.2%, respectively. None of the strains was resistant to amoxycillin or tetracycline. The primary resistance rate of trovafloxacin was as high as 4.7%. Since trovafloxacin has not yet been introduced on to the Dutch market, the resistance is probably induced by the use of other quinolones. Our data indicate that treatment outcome would benefit from susceptibility testing before starting therapy, especially when prescribing metronidazole.

Prevalence of Helicobacter pylori resistance to several antimicrobial agents in a region of Germany

To evaluate the prevalence of resistance among Helicobacter pylori in Germany, the minimum inhibitory concentrations of amoxicillin, tetracycline, clarithromycin, and metronidazole were determined by means of the E test, for 271 Helicobacter pylori isolates cultured from biopsies taken during routine endoscopies in 1996 and 1997. The prevalence of metronidazole resistance was 32.1%, with resistance found more frequently in women (38.5%) than in men (24.4%). Clarithromycin resistance was rare (3.3%). Eight of nine strains resistant to clarithromycin were also resistant to metronidazole. Resistance to either metronidazole or clarithromycin was significantly (P=0.022) higher in patients with duodenal ulcer. No strain was found to be resistant to amoxicillin or tetracycline.

Antimicrobial resistance in Helicobacter pylori: a global overview

Helicobacter pylori resistance to antimicrobial agents is of particular concern because it is a major determinant in the failure of eradication regimens. Antimicrobial drug resistance has been reported to occur for nitroimidazoles, macrolides, fluoroquinolones, rifampin and tetracyclines. Resistance to nitroimidazoles is the most common, in the range of 30-40% on the average in Europe while the overall prevalence rate of resistance to macrolides is lower, probably ranging between 2-10% in most countries. Development of secondary (acquired) resistance to nitroimidazoles and to the macrolides usually occurs as a rule (> 70-100%) in case of failed eradication therapy. Data available from several centres seems however to indicate that a significant shift towards increasing resistance to metronidazole and to the macrolides might have possibly occurred in many countries over the last years. Resistances to both metronidazole and to clarithromycin are the most significant ones because they influence the success of the treatments although this seems to be less marked and more dependent on the treatment regimens considered in the case of metronidazole resistance than in the setting of clarithromycin resistance. These differences may in part relate to methodological variations and to the inherent difficulties in assessing the susceptibility of H. pylori to metronidazole. It is possible that different resistance cut-off might also have to be considered for metronidazole depending on the treatment regimens administered. The mechanisms of resistance have been well defined for the macrolides and are beginning to be unraveled for the nitroimidazoles. In all cases, resistance of H. pylori to antimicrobial agent seems to be due to the development of single mutational events in chromosomal genes rather than to the acquisition of exogenous resistance genes. Owing to the restricted ability of microbiology laboratories with expertise in H. pylori culture and the lack of standardised methodology for susceptibility testing, H. pylori culture is not often performed routinely. It should however be considered after documented treatment failure or in patients from a geographic area or of an ethnic origin with higher likelihood of antimicrobial drug resistance. Likewise it is deemed very important to institute national and regional surveillance programs to follow the evolution of H. pylori resistance and to better adapt treatment regimens to changes in resistance patterns.

Novel bismuth compounds have in vitro activity against Helicobacter pylori

The increasing antimicrobial resistance in Helicobacter pylori has led to the search for new therapeutic agents. In this in vitro study, novel compounds combining bismuth with sialic acid inhibitors were investigated for bactericidal activity using time-kill methodology. The activity of these compounds was compared to bismuth subcitrate against a type strain and a clinical isolate of H. pylori. The compounds tested showed cidal activity which was related to the bismuth component of each drug. These compounds may offer a potential advantage over current bismuth preparations with the sialic acid inhibitor moiety interfering with adhesion of H. pylori to gastric epithelium.

Antimicrobial resistance testing of Helicobacter pylori: a comparison of Etest and disk diffusion methods

Routine antimicrobial resistance testing of Helicobacter pylori is more commonly performed since the correlation between metronidazole resistance and failure to eradicate using this drug, has been made. While resistance testing of H. pylori by Etest is simple to perform, it is expensive compared to disk diffusion methods. In this study the Etest was compared with a modified Kirby-Bauer disk diffusion (NCCLS) method for routine resistance screening of H. pylori. Fifty one pre-treatment isolates were tested against amoxycillin, metronidazole, tetracycline and erythromycin by both Etest and disk diffusion using NCCLS guideline strength disks. Clarithromycin was tested by Etest only. Nitroimidazole and macrolide resistance were detected using the modified Kirby-Bauer disk diffusion method which correlated with Etest minimum inhibitory concentration (MIC). Resistance rates were 49% for metronidazole and 8% for clarithromycin. Cross resistance occurs with macrolides against H. pylori and allows testing of erythromycin to predict resistance to clarithromycin. The very low MICs obtained with H. pylori against amoxycillin and tetracycline require the use of Etest or lower strength disk methods to be used.