Susceptibility of Helicobacter pylori isolates against agents commonly administered for eradication therapy and the efficacy of chemotherapy

Review article: the global emergence of Helicobacter pylori antibiotic resistance

BACKGROUND

Helicobacter pylori is one of the most prevalent global pathogens and can lead to gastrointestinal disease including peptic ulcers, gastric marginal zone lymphoma and gastric carcinoma.

AIM

To review recent trends in H. pylori antibiotic resistance rates, and to discuss diagnostics and treatment paradigms.

METHODS

A PubMed literature search using the following keywords: Helicobacter pylori, antibiotic resistance, clarithromycin, levofloxacin, metronidazole, prevalence, susceptibility testing.

RESULTS

The prevalence of bacterial antibiotic resistance is regionally variable and appears to be markedly increasing with time in many countries. Concordantly, the antimicrobial eradication rate of H. pylori has been declining globally. In particular, clarithromycin resistance has been rapidly increasing in many countries over the past decade, with rates as high as approximately 30% in Japan and Italy, 50% in China and 40% in Turkey; whereas resistance rates are much lower in Sweden and Taiwan, at approximately 15%; there are limited data in the USA. Other antibiotics show similar trends, although less pronounced.

CONCLUSIONS

Since the choice of empiric therapies should be predicated on accurate information regarding antibiotic resistance rates, there is a critical need for determination of current rates at a local scale, and perhaps in individual patients. Such information would not only guide selection of appropriate empiric antibiotic therapy but also inform the development of better methods to identify H. pylori antibiotic resistance at diagnosis. Patient-specific tailoring of effective antibiotic treatment strategies may lead to reduced treatment failures and less antibiotic resistance.

Efficacy of PPI, levofloxacin and amoxicillin in the eradication of Helicobacter pylori compared to conventional triple therapy at a Venezuelan hospital

BACKGROUND AND STUDY AIMS

Helicobacter pylori is the main cause of gastritis, gastroduodenal ulcers and gastric cancer. In the past two decades, the recommended treatment for its eradication as a first-line regimen is the standard triple therapy consisting of a proton pump inhibitor (PPI), amoxicillin and clarithromycin or metronidazole. However, the effectiveness of this traditional regime, which initially was 90%, progressively declined in many parts of the world and is currently 57-73%. The aim of this study was to evaluate whether the eradication rate with triple therapy with levofloxacin is superior as first-line therapy to that with treatment using clarithromycin in the population that attended as outpatients at the Hospital of Lídice.

PATIENTS AND METHODS

We designed a prospective study, with two groups of patients presenting dyspeptic symptoms, from October 2010 to October 2011, who underwent upper gastrointestinal endoscopy and whose biopsies were positive for infection with H. pylori. At the end, 81 patients were included in the order of biopsy result arrival to fill the quota of each group. The first group with 42 patients underwent triple therapy with clarithromycin and the second group with 39 patients underwent therapy with levofloxacin, amoxicillin and a PPI. The patients' age ranged between 23 and 76years, the average being 49.5. The predominant sex was female, at 72.84%. Both treatments lasted for 10days and the patients were clinically re-evaluated 15days after their conclusion and programmed for a second endoscopy to verify H. pylori eradication.

RESULTS

Among the 42 patients in the control group, there were 14 eradication failures with 33.33% resistance to clarithromycin. Among the 39 patients in the experimental group, two eradication failures with 5.13% resistance to levofloxacin were observed. The χ(2) value was 6.96.

CONCLUSIONS

Treatment with levofloxacin was more effective than conventional triple therapy. Triple therapy with levofloxacin can be implemented in populations where resistance to clarithromycin has been observed.

Introduction of an examination and treatment for Helicobacter pylori infection in high school health screening

BACKGROUND

Recently, a significant relationship between gastric cancer and Helicobacter pylori infection has been proven. The purpose of this study was to elucidate the actual conditions of H. pylori infection in Japanese teenagers.

METHODS

The study subjects were students at a certain high school between 2007 and 2009. They were first examined with a urinary rapid test kit based on immunochromatographic technology [corrected] for detection of the antibody to H. pylori (RAPIRAN®). [corrected]. Students who tested positive on this screening examination visited Shinshu University Hospital and received esophagogastroduodenoscopy, and biopsy samples were taken to examine their H. pylori status. The resolution of H. pylori infection was assessed by urea breath test.

RESULTS

For 3 years, 1,224 of 1,232 students (99.4%) received a screening examination for H. pylori infection. Sixty-four of these 1,224 students (5.2%) were found to be positive for H. pylori. Thirty of these 64 H. pylori-positive students visited our hospital, and 24 of them (80%) were confirmed to be infected by H. pylori. The most common endoscopic findings for students with H. pylori infection were nodular gastritis (58.3%) and closed-type atrophic gastritis (45.8%). Histological findings showed no evidence of intestinal metaplasia, except in one of the students. All 24 students were successfully cured of H. pylori infection. If this procedure were to be introduced into the nationwide health screening at Japanese high schools, we calculated that the cost of the prevention of a gastric cancer would be 454,073 yen for each person.

CONCLUSIONS

The low rate of prevalence of H. pylori infection in Japanese teenagers would make it possible to perform examinations and carry out treatment for this infection in high school health screenings from the standpoint of medical economy.

Helicobacter pylori isolates recovered from gastric biopsies of patients with gastro-duodenal pathologies in Cameroon: current status of antibiogram

OBJECTIVE

To determine the prevalence of Helicobacter pylori in patients with gastro-duodenal pathologies and the susceptibility patterns of isolates to the currently recommended antibiotic treatment regimen used in Cameroon.

METHODS

Consecutive dyspeptic patients referred to Douala General Hospital, Cameroon for endoscopy were recruited in the study. Gastric biopsies were collected from the patients and H. pylori isolated and identified following standard microbiology and biochemical techniques. Antibiotic susceptibility was determined by disk diffusion and agar dilution methods against clarithromycin, tetracycline, amoxicillin and metronidazole. Data were analysed using chi-square test and significance considered at P < 0.05.

RESULTS

Seventy-one (92.2%) of the 77 patients (mean age 44.5 +/- 15.7, range 15-77 years) were positive for H. pylori. The antibiotic susceptibility rates were 56% for tetracycline, 55.3% for clarithromycin, 14.4% for amoxicillin and 6.8% for metronidazole. The prevalence of clarithromycin resistance in males vs. females was 42.1%vs. 46.7%, while for metronidazole it was 89.5%vs. 94.7% (P > 0.05). Antimicrobial susceptibility results also revealed 12 antibiotypes based on resistance to the antimicrobial agents investigated. The resistance pattern, amoxicillin and metronidazole (AMR(R) MET(R)) was the most common (23.7%) amongst the isolates. More than 60% of the isolates exhibited multi-drug resistance to three or four antibiotics.

CONCLUSION

Multi-drug resistance is common against the current treatment regimen in Cameroon and, therefore, calls for urgent studies involving newer and broad spectrum antibiotics to address the problem.

In vitro bactericidal activities of Japanese rice-fluid against Helicobacter pylori strains

BACKGROUND

Helicobacter pylori has now been widely recognized as a causative agent of gastroduodenal diseases. The development of safer anti- H. pylori compounds is desirable due to the antibiotic-resistant strains emerged to date.

METHODS

We successfully developed the compounds of Rice-fluid derived from unpolished, polished, and usually cooked Japanese rice, and investigated their in vitro antibacterial activities by means of the Time-Kill-Curve methods against various species of bacteria including H. pylori strains.

RESULTS

All of the compounds revealed keen bactericidal activities against H. pylori, followed by Streptococcus pneumoniae and Campylobacter jejuni strains, but failed to affect the viability of other bacterial species investigated including staphylococci, enterococci, Pseudomonas aeruginosa, and other gram-negative rods belonging to the family Enterobacteraceae. The bactericidal activities were demonstrated to be time- and concentration-dependent.

CONCLUSIONS

The compounds of Rice-fluid are considered to be potentially new and safe therapeutic regimens against H. pylori infections. The mechanism of their bactericidal activities against H. pylori strains remains to be elucidated.

DNA typing for Helicobacter pylori isolates from eradication-failed patients: comparison of the isolates before and after therapy

BACKGROUND

Failure of Helicobacter pylori eradication occurs frequently despite use of multiple microbial agents.

AIM

We aimed to study differences between H. pylori strains isolated before and after eradication failure.

METHODS

We treated 87 patients with peptic ulcer using triple therapy consisting of omeprazole plus combinations of clarithromycin, amoxicillin, or metronidazole. We studied the status of cagA, vacA, and iceA by PCR, and examined the differences in H. pylori isolates by pulsed-field gel electrophoresis and arbitrary primer polymerase chain reaction. The minimum inhibitory concentration of clarithromycin, amoxicillin, or metronidazole was determined by an agar dilution method.

RESULTS

Eradication therapy failed in 12 patients (14%); H. pylori isolates were obtained from all of these both before and after therapy. After eradication therapy, 10 patients were colonized with the same strain as before therapy, while the other two patients were colonized with different strains from those before therapy. In the former group, one isolate changed from metronidazole-sensitive to -resistant, one changed from clarithromycin- and metronidazole-sensitive to -resistant, and four were resistant to clarithromycin or metronidazole both before and after therapy. The other four isolates remained sensitive to clarithromycin and metronidazole after therapy. In the two patients who yielded apparently different isolates after therapy, they changed from clarithromycin- and metronidazole-sensitive to -resistant.

CONCLUSION

Eradication of H. pylori by first-line therapy is an important goal in the treatment of H. pylori-positive peptic ulcer, and that appropriate antimicrobial sensitivity testing should be conducted in patients with eradication failure.

Additive effect of pronase on the efficacy of eradication therapy against Helicobacter pylori

BACKGROUND

Helicobacter pylori (H. pylori) colonizes not only the surface of the surface mucous cells but also the surface mucous gel layer (SMGL). Thus, we examined the possible value of pronase, a mucolytic agent, as a potential eradication therapy.

MATERIALS AND METHODS

One hundred and thirty-five patients were randomly assigned to two treatment groups. Sixty-eight patients received 30 mg of lansoprazole once daily, 500 mg of amoxicillin and 250 mg of metronidazole thrice daily for 2 weeks (LAM group), while the other 67 patients received the same dosage of those agents plus 18,000 tyrosine units of pronase thrice daily for 2 weeks (LAMP group). Eradication was assessed 4-6 weeks after treatment by immunohistochemical tests and cultures. We also determined the in vitro activity of pronase against H. pylori, and evaluated the synergistic effects between pronase and the other three drugs. To investigate the effect of pronase on the structure of the SMGL, surgically removed stomachs obtained from patients who had taken pronase were examined histopathologically.

RESULTS

The cure rates for H. pylori infection in the LAMP group were significantly higher than those in the LAM group (intention to treat analysis: 94.0 vs. 76.5%, p =.0041). Pronase exhibited no antibacterial activity against H. pylori., and no in vitro synergistic effects were observed. In the patients who took pronase before surgery, the SMGL was thinner than in the patients who did not take pronase, and the structure of the SMGL was markedly disrupted.

CONCLUSIONS

Pronase has an additive effect in curing H. pylori infection. Pronase has no apparent in vitro activity against H. pylori, but may improve the local delivery of antibiotics by virtue of its removal and disruption of the SMGL.

[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.

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.

METHODS

Ninety-two consecutive H. pylori-positive patients with active peptic ulcer disease were randomly enrolled to receive a 7-day treatment with either lansoprazole 30 mg plus amoxicillin 1 g and clarithromycin 500 mg [all twice a day (b.i.d.), Group A, n = 46]; or bismuth subcitrate 125 mg four times a day (q.i.d.) plus tetracycline 500 mg q.i.d and furazolidone 200 mg b.i.d. (Group B, n = 46) H. pylori status was reassessed 30 days after completion of the therapy and bacterial resistance to the antibiotics was investigated using an in vitro assay.

RESULTS

Five patients from each study group were lost to follow up. Both treatments resulted in similar H. pylori eradication rate: 66-60% (per protocol), 59-52% (intention-to-treat) in Groups A and B, respectively (non significant). However, eradication improved to 79% in the absence of H. pylori resistance to clarithromycin or amoxicillin.

CONCLUSION

Primary resistance to clarithromycin or amoxicillin may underscore a potentially serious problem for the eradication of H. pylori infection. Testing for bacterial resistance may become necessary to improve therapeutic efficacy.

Antibiotic resistance of Helicobacter pylori strains in Japanese children

The resistance of Helicobacter pylori to the recently available antibiotic treatment regimens has been a growing problem. We investigated the prevalence of H. pylori resistance to clarithromycin, metronidazole, and amoxicillin among 51 H. pylori isolates from Japanese children. In addition, the mutations of the corresponding gene were studied by PCR and restriction fragment length polymorphism analysis. Primary resistance to clarithromycin, metronidazole, and amoxicillin was detected in 29, 24, and 0% of strains, respectively. The eradication rates in clarithromycin-susceptible and -resistant strains were 89 and 56%, respectively (P < 0.05). The prevalence of strains with acquired resistance to clarithromycin (78%) was higher than that of strains with primary resistance (P < 0.01). Among the clarithromycin-resistant strains studied, 92% showed cross-resistance to azithromycin. No acquired resistance to amoxicillin was demonstrated. The A2144G mutation in the 23S rRNA gene was detected in 11 of 12 (92%) clarithromycin-resistant strains tested, whereas the mutation was not detected in any of the 15 susceptible strains. The deletion of the rdxA gene was not demonstrated in any of the strains. The results indicate that a high prevalence of clarithromycin-resistant strains is associated with eradication failure. Testing of susceptibility to clarithromycin is recommended.

Antibiotic resistance in Helicobacter pylori

OBJECTIVE

To describe antibiotic resistance patterns in Helicobacter pylori.

DESIGN

Culture and antibiotic sensitivity testing of antral and gastric body biopsy samples from patients having gastroscopy.

PARTICIPANTS

Consecutive consenting patients aged 18 years or more presenting for gastroscopy from 1 July 1998 to 30 June 1999.

SETTING

An open-access gastroscopy service at an urban university tertiary hospital.

MAIN OUTCOME MEASURES

Number of H. pylori isolates showing resistance to antibiotics; correlates of such resistance with demographic and clinical information.

RESULTS

Of 1580 patients undergoing endoscopy, 434 agreed to participate in the study. 108 (24.9%) had positive cultures for H. pylori, and 88 of these isolates (81%) were available for further testing. Resistance to metronidazole and clarithromycin was detected in 36% and 11%, respectively. No resistance was found to tetracycline or amoxycillin. Metronidazole resistance was commoner in younger patients (P = 0.0004) and macrolide resistance was commoner in those born outside Australia or New Zealand (P = 0.03).

CONCLUSIONS

We found substantial resistance to metronidazole, and emerging clarithromycin resistance, but complete susceptibility to amoxycillin, tetracycline, gentamicin and cefaclor. These factors may influence the effectiveness of presently recommended eradication regimens.

Mutagenicity of Helicobacter pylori in the Ames test using Salmonella typhimurium TA100

Infection with Helicobacter pylori has been recognized as a risk factor for gastric cancer, although it is still unclear whether strains of this organism behave as carcinogens. We have studied 30 H. pylori clinical isolates from 15 patients with gastric cancer and 15 patients with other gastroduodenal diseases. Bacterial pellet and supernatant fluid of broth cultures were tested for mutagenicity by means of the Ames test using the pre-incubation technique. The average Ames ratio was 1.111 in the bacterial pellet and 1.312 in the supernatant of strains from the gastric-cancer group, and 0.858 and 0.950 in those from the non-gastric-cancer group, respectively. The strains from the gastric-cancer group had a significantly higher ratio than those from the non-gastric-cancer group, although all results were below the cut-off ratio of the Ames test, and were thus regarded as having no mutagenicity. The Ames ratio of the supernatant was higher than that of the bacterial pellet in both groups. The results indicate that all of the H. pylori strains tested revealed no mutagenicity, but the difference in Ames ratio between strains might reflect differences in genotoxicity between the strains.

Clarithromycin-resistance and point mutations in the 23S rRNA gene in Helicobacter pylori isolates from Japan

BACKGROUND

Resistance of Helicobacter pylori to clarithromycin is mostly due to the point mutations in the 23S rRNA. In Japan, however, the frequency of these mutations has not been fully investigated. Furthermore, no study has used gastric biopsy specimens to detect these point mutations.

METHODS

The frequency of primary clarithromycin-resistant H. pylori was examined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Eighty-two strains (42 isolated from patients with gastric cancer and 40 isolated from patients with chronic gastritis) were examined. Two biopsy specimens obtained from patients in whom eradication therapy including clarithromycin had failed were also studied.

RESULTS

Either A2143G or A2144G point mutation was detected in 90% of clarithromycin-resistant H. pylori strains. Eight out of 82 strains (9.8%) had either A2143G or A2144G point mutation. Only one out of 42 strains in patients with gastric cancer had A2143G mutation, whereas five strains had A2144G and two had A2143G mutations in 40 strains isolated from control subjects. The proportion was significantly lower in patients with early gastric cancer (P < 0.05). This PCR-RFLP was also applicable for DNA samples extracted from biopsy specimens and infection of clarithromycin-resistant H. pylori was observed.

CONCLUSION

The results suggest that the point mutation in the 23S rRNA gene is commonly seen in clarithromycin-resistant H. pylori and it contributes to the treatment failure in Japan. The PCR-RFLP system is a sensitive method by which to diagnose H. pylori infection as well as a simple method for detecting clarithromycin resistance without bacterial culture.

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.

In vitro activities of rabeprazole, a novel proton pump inhibitor, and its thioether derivative alone and in combination with other antimicrobials against recent clinical isolates of Helicobacter pylori

The MICs of rabeprazole sodium (RPZ), a newly developed benzimidazole proton pump inhibitor (PPI), against 133 clinical Helicobacter pylori strains revealed a higher degree of activity than the another two PPIs, lansoprazole and omeprazole. Time-kill curve assays of RPZ, when combined with amoxicillin, clarithromycin, or metronidazole, disclosed that synergistic effects were demonstrated in combination with each antibiotic examined. Moreover, no apparent antagonistic effect appeared among all of the strains tested.

Detection of clarithromycin-resistant helicobacter pylori strains by a preferential homoduplex formation assay

It has been shown that resistance to clarithromycin, a major cause of failure in Helicobacter pylori eradication therapy, is associated with point mutations in the 23S rRNA gene. We sought to apply the preferential homoduplex formation assay (PHFA), a novel technique for the efficient detection of point mutations, to detection of the mutations. PHFA was performed on streptavidin-coated microtiter plates with biotin- and dinitrophenyl-labeled amplicons to detect the wild-type gene or each mutant gene. DNA samples were extracted from gastric juice specimens of 412 patients with H. pylori infection and were applied to the assay. The detection threshold of PHFA was as few as 10 gene copies. The sensitivity of PHFA for the detection of H. pylori infection was higher than those of culture and the rapid urease test. A total of 337 (81.8%) samples had the wild-type gene, 38 (9.2%) had the A2144G mutation, and 37 (9.0%) contained both the wild type and a mutation (A2144G in 30 samples, A2143G in 5 samples, and A2143G plus A2144G in 2 samples). About half the strains isolated from patients with mixed infection were susceptible by the agar dilution method (MIC, <0.1 mg/liter). Therefore, PHFA can detect clarithromycin-resistant H. pylori strains, even in patients with mixed infections with the wild type, that are not detectable by the agar dilution method.

Pretreatment antimicrobial susceptibilities of paired gastric Helicobacter pylori isolates: antrum versus corpus

BACKGROUND

Antimicrobial susceptibility testing of Helicobacter pylori isolates is the most useful tool for guiding specific therapy, especially when primary resistance is suspected. However, the most informative gastric biopsy site for detection of resistant H. pylori isolates is uncertain. We sought to determine whether susceptibilities to commonly used antimicrobials (amoxicillin, clarithromycin, minocycline, and metronidazole) were related to biopsy site.

METHODS

H. pylori isolates were obtained from patients who had duodenal ulcer and had not received any therapy directed against H. pylori. Agar-dilution minimum inhibitory concentrations of each antimicrobial were compared between paired H. pylori isolates from the antrum and the proximal corpus.

RESULTS

Differences in minimum inhibitory concentrations exceeding twofold were observed within the pairs of H. pylori isolates in 5 of the 40 patients tested. In three patients with clarithromycin-resistant isolates and two with metronidazole-resistant isolates, both antral and corporeal specimens revealed resistance. However, no patient had pairs of isolates categorized as resistant at one site and sensitive at the other.

CONCLUSIONS

While we found that an individual may have a mixed H. pylori infection with respect to differing antimicrobial susceptibility in different parts of the stomach, a single biopsy specimen from either the antrum or the corpus should provide reliable detection of H. pylori isolates with primary resistance.

Gastric penetration of amoxicillin in a human Helicobacter pylori-infected xenograft model

The delivery of antibiotics into Helicobacter pylori-infected human stomachs is still poorly understood. Human embryonic gastric xenografts in nude mice have recently been proposed as a new model for the study of H. pylori infection. Using this model, we compared the penetration of amoxicillin, after intraperitoneal administration of a dose of 20 mg/kg of body weight, into the gastric mucosae of infected and uninfected xenografts. The concentrations of this drug in serum and superficial gastric mucosae were determined at 20 min and 1 and 3 h after injection. Ten mice with H. pylori-infected grafts (n = 5) or uninfected grafts (n = 5) were studied. Mucosal samples were obtained by cryomicrotomy. The concentrations in serum were similar to those obtained in the serum of humans after oral administration of 1 g of amoxicillin. The mean area under the tissue concentration-versus-time curve from 0 to 3 h obtained for mice with infected grafts was significantly higher than that obtained for the animals with uninfected grafts (P = 0.01). These results suggest that the penetration of amoxicillin into the superficial gastric mucosa may be substantially increased in the case of H. pylori infection. Thus, human xenografts in nude mice represent a new, well-standardized model for investigation of systemic delivery of drugs into H. pylori-infected gastric mucosa.

Combined activity of azithromycin and lansoprazole against Helicobacter pylori

BACKGROUND

Due to its unique pharmacokinetic properties, azithromycin may be an attractive combination partner for H. pylori eradication regimens. However, up to 15% of clinical isolates are primarily resistant to azithromycin as well as to other macrolide antibiotics. Combination therapy with lansoprazole, a proton pump inhibitor known to have intrinsic antibacterial activity against H. pylori, may be useful to counteract such resistance. We therefore evaluated the combined effects of azithromycin and lansoprazole in vitro.

MATERIALS AND METHODS

Minimal inhibitory concentrations (MICs) of azithromycin and lansoprazole alone and in combination were determined for 106 clinical H. pylori isolates by means of an agar dilution technique. Killing kinetics of seven isolates were also studied in fluid medium.

RESULTS

MIC values for 50 and 90% of the isolates (MIC50, MIC90) were 0.19 and 0.5 mg/l for azithromycin, and 44.5 and 104 mg/l for lansoprazole. Nine strains (8.5%) had an MIC of azithromycin > or = 16 mg/l and were regarded as resistant. An additive interaction between the two drugs was found in 72 (68%), and indifferent effects in 24 strains (23%). Three of 9 azithromycin-resistant strains regained sensitivity in the presence of lansoprazole. In fluid culture, synergism between the two drugs occurred in 6 out of 7 strains tested.

CONCLUSION

In the majority of strains, lansoprazole and azithromycin interacted in an additive or synergistic manner depending on the test method employed. Addition of lansoprazole restored in vitro sensitivity to azithromycin in 3 out of 9 azithromycin-resistant strains. Such effects may enhance the elimination of H. pylori during clinical eradication therapy.

Helicobacter pylori infection, chronic gastritis, and proton pump inhibitors

The proton pump inhibitors (PPIs) omeprazole, lansoprazole, and pantoprazole are widely used as antisecretory drugs and, in association with antibiotics, for the treatment of Helicobacter pylori infections. PPIs possess antibacterial activity against H. pylori in vitro, and may also exert an anti-inflammatory effect by interfering with the cellular immune response to infection. Their antimicrobial activity is selective for H. pylori. Lansoprazole is the most effective, although its bactericidal activity is similar to that of omeprazole. Pantoprazole is the least effective. The mechanisms that account for the antibacterial effects of PPIs may depend on a structural similarity of PPIs to antibiotics which are active against H. pylori, on the inhibition of bacterial urease exerted by PPIs, or on the possible interaction of PPIs with bacterial ATPases that regulate the transmembrane ion flux. Recent studies have shown that PPIs have anti-inflammatory actions and can interfere with the host-bacteria interactions. Lansoprazole can bind to polymorphonuclear leukocytes that infiltrate the gastric mucosa colonized by H. pylori and can thus inhibit the oxidative burst of activated inflammatory cells. In an in vivo study, lansoprazole reduced the degree of activity of histologic gastritis independently of the presence of H. pylori. In another study, omeprazole was capable of inhibiting the cytotoxic activity of NK T cells. Investigation of PPI interactions with H. pylori activities and the cellular immune response to the infection may help us to understand the pathogenic mechanisms of H. pylori-associated diseases and enable clinicians to better treat them.

Interaction of drugs for eradication therapy against antibiotic-resistant strains of Helicobacter pylori

To clarify the interactions of drugs for combination therapy of Helicobacter pylori infection, especially due to antibiotic-resistant strains, we have evaluated the in vitro effect of combining different drugs. Using a modified time-kill assay, we tested the effect of combining 2 drugs from 4 agents; amoxicillin (AMPC), clarithromycin (CAM), metronidazole (MTZ) and lansoprazole (a proton pump inhibitor). The H. pylori in the study consisted of 4 strains sensitive to the all drugs, 2 strains resistant only to CAM, 2 strains resistant only to MTZ, and 2 strains resistant to both CAM and MTZ. From the 6 different drug combinations, synergism was observed for 5 of the combinations, among which the combination of AMPC and CAM revealed such effects most frequently. However, all of the strains which showed synergism were sensitive to both of the drugs. In the case of the strains resistant to CAM and/or MTZ, no synergism was demonstrated in any of the combinations including CAM and/or MTZ. When a strain was resistant to one drug from a combination, no synergism was detected. Thus, the administration of a drug to which the strains are resistant may have no advantage in the eradication therapy of H. pylori. For a more effective and safer therapy, susceptibility testing should be performed before treatment.

Successful development of air-dried microplates (HP-Plates) for susceptibility testing against Helicobacter pylori isolates

We have successfully developed and evaluated a new susceptibility testing procedure against Helicobacter pylori strains using air-dried microplates "HP-Plates" containing eight serially-diluted anti-H. pylori agents. HP-Plate wells were reconstituted by the inoculation of 100 microliters of H. pylori cell suspensions. After incubation at 37 C for 48 hr under humidified microaerophilic conditions, HP-Plates were read visually with a circular mirror. We investigated the within-day reproducibility tests of HP-Plates using the six quality control (QC) strains we proposed. Of the 20 testings, determining the minimum inhibitory concentrations (MICs) of all the QC strains fell within +/- 1 log2 dilution ranges. When 200 clinical isolates were tested with HP-Plates and compared with the results obtained with the modified broth macrodilution method of NCCLS, more than 90% of the MICs also fell within +/- 1 log2 dilution ranges. We concluded that the HP-Plate susceptibility test method is a practical and easily applicable alternative of susceptibility testing for clinical microbiology laboratories in determining the MICs of H. pylori isolates.