Antimicrobial susceptibility testing of Helicobacter pylori to selected agents by agar dilution method in Shiraz-Iran

PURPOSE: To assess the pattern of antimicrobial susceptibility profile of Helicobacter pylori isolates from patients with gastritis, duodenal ulcer (DU) and gastroesophageal reflux disease (GERD) residing in Shiraz, Iran. METHODS: One hundred and six H. pylori isolates from patients with gastritis, DU and GERD undergoing endoscopy at our university hospitals and clinics were analysed for their antimicrobial susceptibility to metronidazole, clarithromycin, amoxicillin, co-amoxiclav, tetracycline, ciprofloxacin and furazolidone. The minimum inhibitory concentrations were determined by agar dilution method. RESULTS: Overall H. pylori resistance rate was 72.6% to metronidazole, 9.4% to clarithromycin and furazolidone, 20.8% to amoxicillin and 4.7% to tetracycline and ciprofloxacin. No resistance to co-amoxiclav was detected among H. pylori isolates. No significant differences between antimicrobial resistance and clinical outcome were detected. CONCLUSIONS: With regard to the increasing resistance of H. pylori isolates to various antibiotics, susceptibility testing of H. pylori isolates prior to the treatment of infection must be performed to achieve better eradication and to reduce the risk of selection of H. pylori resistant strains.     

Alaska sentinel surveillance study of Helicobacter pylori isolates from Alaska Native persons from 2000 to 2008

Helicobacter pylori infection is more common in Alaska Native persons than in the general U.S. population, with seroprevalence to H. pylori approaching 75%. Previous studies in Alaska have demonstrated elevated proportions of antimicrobial resistance among H. pylori isolates. We analyzed H. pylori data from the Centers for Disease Control and Prevention's sentinel surveillance in Alaska from January 2000 to December 2008 to determine the proportion of culture-positive biopsy specimens with antimicrobial resistance from Alaska Native persons undergoing endoscopy. The aim of the present study was to monitor antimicrobial resistance of H. pylori isolates over time and by region in Alaska Native persons. Susceptibility testing of H. pylori isolates to metronidazole, clarithromycin, amoxicillin, and tetracycline was performed using agar dilution. Susceptibility testing for levofloxacin was performed by Etest. Overall, 45% (532/1,181) of persons undergoing upper endoscopy were culture positive for H. pylori. Metronidazole resistance was demonstrated in isolates from 222/531 (42%) persons, clarithromycin resistance in 159/531 (30%) persons, amoxicillin resistance in 10/531 (2%) persons, and levofloxacin resistance in 30/155 (19%) persons; no tetracycline resistance was documented. The prevalence of metronidazole, clarithromycin, and levofloxacin resistance varied by region. Female patients were more likely than male patients to demonstrate metronidazole (P < 0.05) and clarithromycin (P < 0.05) resistance. No substantial change in the proportion of persons with resistant isolates was observed over time. Resistance to metronidazole, clarithromycin, and levofloxacin is more common among H. pylori isolates from Alaska Native persons than those from elsewhere in the United States.     

Prevalence of resistant Helicobacter pylori isolates in Bulgarian children

The aim of this study was to assess the primary and combined resistances of Helicobacter pylori isolates obtained from paediatric patients in 2000-2001 to seven antimicrobial agents. Resistance rates of pre-treatment isolates from 115 children were investigated by the limited agar dilution method alone and by the E-test. The cut-off concentrations for resistance were: metronidazole >8 mg/L, clarithromycin and azithromycin >1 mg/L, clindamycin >4 mg/L, amoxicillin >0.5 mg/L, tetracycline >4 mg/L and ciprofloxacin >1 mg/L. Primary resistance rates were: metronidazole 15.8%, clarithromycin 12.4%, azithromycin 14.6%, clindamycin 20.0%, amoxicillin 0%, metronidazole + clarithromycin 4.5%, ciprofloxacin 6.0%, metronidazole + clarithromycin + ciprofloxacin 1.2%, tetracycline 3.1% and metronidazole + ciprofloxacin 1.2%. There were no significant age (1-9 years versus 10-18 years) or gender differences. Prevalence of both macrolide-resistant and intermediately susceptible strains was 21.9% for azithromycin and 15.9% for clarithromycin. Of 18 metronidazole-resistant isolates, 77.8% exhibited a metronidazole MIC > or = 32 mg/L. H. pylori resistance rates to metronidazole, clarithromycin and both agents were relatively low in Bulgarian children. However, resistance was found to all drugs tested except for amoxicillin. The consumption of newer macrolides and tetracyclines could be related to the prevalence of resistance to the corresponding agents. There were no significant differences in primary resistance rates of H. pylori to antimicrobial agents between children and adults except for metronidazole. Multi-drug resistance to newer macrolides, metronidazole and ciprofloxacin in association with a slightly elevated amoxicillin MIC (0.38 mg/L) was detected in one strain.     

The status of antimicrobial resistance of Helicobacter pylori in eastern Europe

Objective   To evaluate the primary, secondary and combined resistance to five antimicrobial agents of 2340 Helicobacter pylori isolates from 19 centers in 10 countries in eastern Europe.
Methods   Data were available for centers in Bulgaria, Croatia, the Czech Republic, Estonia, Greece, Lithuania, Poland, Russia, Slovenia and Turkey. Susceptibility was tested by agar dilution (seven countries), E test (five countries) and disk diffusion (three countries) methods. Resistance breakpoints (mg/L) were: metronidazole 8, clarithromycin 1, amoxicillin 0.5, tetracycline 4, and ciprofloxacin 1 or 4 in most centers. Primary and post-treatment resistance was assessed in 2003 and 337 isolates respectively. Results for 282 children and 201 adults were compared.
Results   Primary resistance rates since 1998 were: metronidazole 37.9%, clarithromycin 9.5%, amoxicillin 0.9%, tetracycline 1.9%, ciprofloxacin 3.9%, and both metronidazole and clarithromycin 6.1%. Isolates from centers in Slovenia and Lithuania exhibited low resistance rates. Since 1998, amoxicillin resistance has been detected in the southeastern region. From 1996, metronidazole resistance increased significantly from 30.5% to 36.4%, while clarithromycin resistance increased slightly from 8.9% to 10.6%. In centers in Greece, Poland, and Bulgaria, the mean metronidazole resistance was slightly higher in adults than in children (39% versus 31.2%, P  > 0.05); this trend was not found for clarithromycin or amoxicillin ( P  > 0.20). Post-treatment resistance rates exhibited wide variations.
Conclusions   In eastern Europe, primary H. pylori resistance to metronidazole is considerable, and that to clarithromycin is similar to or slightly higher than that in western Europe. Resistance to amoxicillin, ciprofloxacin and tetracycline was detected in several centers. Primary and post-treatment resistance rates vary greatly between centers.     

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.     

Primary and combined resistance to four antimicrobial agents in Helicobacter pylori in Sofia, Bulgaria

The aim of this study was to evaluate the primary and combined resistance of Helicobacter pylori against four antimicrobial agents by a screening agar method (SAM) and a modified disk diffusion method (MDDM) alone and in combination. Pre-treatment H. pylori isolates from 192 consecutive H. pylori-positive patients at three hospitals in Sofia were investigated. MDDM was performed with disks containing metronidazole (5 microg), clarithromycin (15 microg) or erythromycin (15 microg), ciprofloxacin (5 microg) and tetracycline (30 microg). Resistance was determined by an inhibitory zone of <16 mm for metronidazole and < or =30 mm for other agents tested. The cut-off concentrations used to define resistance by SAM were: metronidazole >8 mg/L, clarithromycin >2 mg/L, tetracycline >4 mg/L and ciprofloxacin >1 mg/L. Primary resistance rates in H. pylori were: metronidazole 28.6%, clarithromycin 9.7%, metronidazole + clarithromycin 2.8%, ciprofloxacin 3.9%, metronidazole + ciprofloxacin 2.3%, tetracycline 1.9% and metronidazole + tetracycline 1.2%. Among metronidazole-resistant isolates, combined resistance to clarithromycin, ciprofloxacin and tetracycline was present in 11.4% (5 of 44 strains), 8.3% (3 of 36) and 4.9% (2 of 41), respectively. Two strains exhibited triple resistance to macrolides, metronidazole and either ciprofloxacin or tetracycline. Three tetracycline-resistant strains were detected in 1999; however, resistance rates to other agents were relatively stable during the 6 years. Primary H. pylori resistance to metronidazole is moderate and resistance to clarithromycin and to ciprofloxacin is considerable in comparison with results in most other countries. The alarming appearance of strains harbouring combined resistance or multiresistance provides the motivation for continued surveillance of H. pylori at global, national and regional levels.     

Helicobacter pylori: prevalence of antimicrobial resistance in clinical isolates

This study aims to determine the in vitro susceptibility of Helicobacter pylori to clarithromycin, metronidazole, amoxycillin and tetracycline, the four antibiotics commonly used in eradication therapies. These data are used to evaluate the efficacy of current empiric treatment of H. pylori infection in the Southern Region of Ireland. Culture is performed on gastric biopsy samples obtained from 147 consecutive patients undergoing gastroscopy for investigation of dyspepsia. Susceptibility testing to metronidazole, clarithromycin, amoxycillin and tetracycline is performed on the isolates by Etest. Isolates demonstrating clarithromycin resistance are subjected to polymerase chain reaction (PCR) amplification and nucleotide sequence analysis to identify the presence of point mutations in the peptidyltransferase region of the 23S rRNA gene previously associated with resistance to clarithromycin. Prevalence of H. pylori in the population studied was 31% (45 isolates). Antimicrobial resistance to metronidazole and clarithromycin was detected in nine (20%) and four (8.9%) of the isolates, respectively. A single isolate demonstrated co-resistance to metronidazole and clarithromycin (2.2%). No resistance was detected to either amoxycillin or tetracycline. The low level of resistance demonstrated among this group of isolates indicates that the empiric treatment currently in place in the Southern Region of Ireland is likely to be successful.     

Multicenter survey of routine determinations of resistance of Helicobacter pylori to antimicrobials over the last 20 years (1990 to 2009) in Belgium

We analyzed the rates of antimicrobial resistance of Helicobacter pylori strains isolated from patients from 1990 to 2009 and identified risk factors associated with resistance. Gastric biopsy specimens were collected from several digestive disease centers in Brussels, Belgium. We routinely performed antimicrobial susceptibility testing for clarithromycin (CLR), metronidazole, amoxicillin, tetracycline, and ciprofloxacin. Evaluable susceptibility testing was obtained for 9,430 strains isolated from patients who were not previously treated for Helicobacter pylori infection (1,527 isolates from children and 7,903 from adults) and 1,371 strains from patients who were previously treated (162 isolates from children and 1,209 from adults). No resistance to amoxicillin was observed, and tetracycline resistance was very rare (<0.01%). Primary metronidazole resistance remained stable over the years, with significantly lower rates for isolates from children (23.4%) than for isolates from adults (30.6%). Ciprofloxacin resistance remained rare in children, while it increased significantly over the last years in adults. Primary clarithromycin resistance increased significantly, reaching peaks in 2000 for children (16.9%) and in 2003 for adults (23.7%). A subsequent decrease of resistance rates down to 10% in both groups corresponded to a parallel decrease in macrolide consumption during the same period. Multivariate logistic regression revealed that female gender, age of the patient of 40 to 64 years, ethnic background, the number of previously unsuccessful eradication attempts, and the different time periods studied were independent risk factors of resistance to clarithromycin, metronidazole, and ciprofloxacin. Our study highlights the need to update local epidemiological data. Thus, the empirical CLR-based triple therapy proposed by the Maastricht III consensus report remains currently applicable to our population.     

Antimicrobial susceptibility of Helicobacter pylori strains isolated in Bangladesh

Antimicrobial susceptibility of 120 Helicobacter pylori isolates to metronidazole, tetracycline, clarithromycin, and amoxicillin was determined, and 77.5, 15, 10, and 6.6% of the isolates, respectively, were resistant. Only rdxA inactivation and both rdxA and frxA inactivation were responsible for metronidazole resistance in 66% (8 of 12) and 33% (4 of 12) of the isolates, respectively.     

Resistance rates of metronidazole and other antibacterials in Helicobacter pylori from previously untreated patients in Norway

The aim of the study was to describe the antimicrobial resistance rate of Helicobacter pylori isolated from previously untreated patients in Norway, including the application of two different methods for the determination of metronidazole susceptibility. Altogether 102 isolates obtained in 2008 and 2009 from previously untreated patients suspected of H. pylori related disease, were examined applying a standardized European study protocol. The activity of amoxicillin, tetracycline, clarithromycin, metronidazole, rifabutin and levofloxacin was recorded after an incubation period of 72–96 h in a microaerobic atmosphere. Strains resistant to metronidazole were re‐examined for metronidazole resistance applying anaerobic conditions for the first 24 h. None of the isolates were resistant to amoxicillin or tetracycline, whereas 5, 9% were resistant to clarithromycin and 22, 5% resistant to metronidazole tested conventionally. Applying local standards the metronidazole resistance rate fell to 7, 8%, highlighting the importance of the methodology applied for metronidazole susceptibility testing.     

Emerging antimicrobial resistance pattern of Helicobacter pylori in central Gujarat

Background: Antimicrobial resistance is a growing problem in H. pylori treatment. The study was intended to evaluate the prevalence of resistance amongst 80 H.pylori isolates cultured from biopsy taken during routine endoscopies in 2008-2011. Materials and Methods: 855 gastro duodenal biopsies were collected and cultured on H.pylori selective medium (containing Brucella agar and Columbia agar (Hi media), with Skirrow’s supplement (antibiotic supplement) and 7% human blood cells). H.pylori was isolated from 80 specimens. The antimicrobial susceptibility of H.pylori isolates was carried out by the Kirby Bauer technique against metronidazole (5 µg), clarithromycin (15 µg), ciprofloxacin (5 µg), amoxicillin (10 µg), tetracycline (30 µg), erythromycin (15 µg), levofloxacin (5 µg), and furazolidone (50 µg) (Sigma- Aldrich, MO). Results: 83.8% isolates were resistant to metronidazole, 58.8% were resistant to Clarithromycin 72.5% were resistant to Amoxicillin, 50% to Ciprofloxacin and 53.8% to tetracycline. furazolidone, erythromycin and Levofloxacin showed only 13.8% resistance to H.pylori. Multi drug resistance with metronidazole+ clarithromycin+ tetracycline was 85%. For all the drugs Antimicrobial resistance rate was found higher in males compare to females. Metronidazole and amoxicillin resistance was found noteworthy in patients with duodenal ulcer (p = 0.018), gastritis (P = 0.00), and in reflux esophagitis (P = 0.00). clarithromycin and tetracycline resistance was suggestively linked with duodenitis (P = 0.018), while furazolidone, erythromycin and levofloxacin showed excellent sensitivity in patients with duodenitis (P value- 0.018), gastritis (P= 0.00) and reflux esophagitis (P = 0.00). Resistance with metronidazole (P = 0.481), clarithromycin (P= 0.261), amoxicillin (P = 0.276), tetracycline (P = 0.356), ciprofloxacin (P = 0.164) was not correlated well with Age-group and Gender of the patients. Conclusion: A very high percentage of patients were infected with metronidazole and clarithromycin resistant strains. The use of antibiotics for other indications seems to be the major risk factor for the development of primary resistance. High incidence should alarm the gastroenterologist while prescribing the eradication regimen.     

High levels of resistance to metronidazole and clarithromycin in Helicobacter pylori strains in children

The aim of the study was to evaluate the prevalence of resistance to amoxicillin, metronidazole, and clarithromycin before treatment of Helicobacter pylori infection in children and to assess the evolution of resistance with time. The study was carried out between 1994 and 1999 with 150 H. pylori-positive children through gastric culture (antimicrobial susceptibility) and histology. All cultured H. pylori strains were sensitive to amoxicillin, 64 (43%) were resistant to metronidazole, 32 (21%) were resistant to clarithromycin, and 14 (9%) were resistant to both metronidazole and clarithromycin. The overall prevalence of resistance to metronidazole and clarithromycin did not change significantly with time. The study highlights the generalized high-level and stable metronidazole and clarithromycin resistance of H. pylori strains from children.     

Role of screening agar plates for in vitro susceptibility testing of Helicobacter pylori in a routine laboratory setting

BACKGROUND: Resistance of Helicobacter pylori to the more frequently used antibiotics (metronidazole and clarithromycin) reduces eradication rates even with triple treatment. Determining the antibiogram profile of H pylori can take up to 14 days and delays appropriate treatment. AIMS: To determine the role of screening agar plates for more rapid in vitro susceptibility of H pylori to metronidazole, amoxicillin, and clarithromycin. METHODS: Routine gastric biopsy specimens from 507 dyspeptic patients were inoculated on to 10% lysed blood agar plates containing metronidazole (8 microg/ml), clarithromycin (2 microg/ml), or amoxicillin (0.5 microg/ml). The minimum inhibitory concentration (MIC) of the 90 isolates was determined using the E test. RESULTS: Metronidazole resistance was detected in 28 of 90 isolates by E test and nine of 98 by screening agar. The screening agar detected none of the four clarithromycin resistant isolates detected by the E test. CONCLUSIONS: The screening agar method is not sufficiently sensitive to be used alone.     

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

To evaluate the prevalence of resistance amongHelicobacter pylori in Germany, the minimum inhibitory concentrations of amoxicillin, tetracycline, clarithromycin, and metronidazole were determined by means of the E test, for 271Helicobacter 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 tetracyline.     

Changing antimicrobial susceptibility epidemiology of Helicobacter pylori strains in Japan between 2002 and 2005

Surveillance of Helicobacter pylori antimicrobial susceptibility reflecting the general population in Japan is limited. The antimicrobial susceptibilities of 3,707 H. pylori strains isolated from gastric mucosa samples of previously untreated patients diagnosed with gastroduodenal diseases at 36 medical facilities located throughout Japan between October 2002 and September 2005 were evaluated. Using an agar dilution method for antimicrobial susceptibility testing of H. pylori, the MIC distributions and trends during the study period for clarithromycin, amoxicillin, and metronidazole were studied. While the MIC(50) and MIC(90) for clarithromycin did not change during the 3-year period, the MIC(80) showed a 128-fold increase. Furthermore, the rate of resistance increased yearly from 18.9% (2002 to 2003) to 21.1% (2003 to 2004) and 27.7% (2004 to 2005). With a resistance rate of 19.2% among males compared to 27.0% among females, a significant gender difference was observed (P < 0.0001). Our study shows that in Japan, there is an evolving trend towards increased resistance to clarithromycin with geographical and gender differences as well as between clinical disease conditions. No significant changes in resistance were observed for amoxicillin and metronidazole during the period. While the benefit of H. pylori antimicrobial susceptibility testing has been debated in Japan, current empirical regimens are not based on susceptibility data representative of the general population. The development of an effective H. pylori eradication regimen in Japan will require continued resistance surveillance as well as a better understanding of the epidemiology of resistance.     

Antibiotic resistance of Helicobacter pylori in Reunion Island: therapeutic consequences

The aims of this paper were to assess resistance of Helicobacter pylori to antibiotics included in the so-called French triple regimens and to identify the possible causes of therapeutic failure in Reunion island. Antibiotic resistance was determined for 109 strains. All the strains were sensitive to amoxicillin and tetracycline, 93.6% were sensitive to ciprofloxacin, 92.7% to erythromycin and 60.6% to metronidazole. Fifty three patients who had previously tested positive for H. pylori received for one week regimen of amoxicillin (1 g bd), clarithromycin (0.5 g bd) and omeprazole (20 mg bd). Eradication rate after therapy was of 73.6%. Therapeutic failure was analysed for 9 patients using random amplified polymorphic DNA and the presence or not of antibiotic resistance. One cause of failure is clarithromycin resistance. These data show that triple therapy can be used in Reunion Island. In case of failure, sensitivity must be detected because the rate of resistance to metronidazole is over 30%.     

Susceptibilities to clarithromycin, amoxycillin and metronidazole of Helicobacter pylori isolates from the antrum and corpus in Tokyo, Japan, 1995–2001

The aim of this study was to determine the susceptibilities to clarithromycin, amoxycillin and metronidazole of Helicobacter pylori isolates from the antrum and corpus of Japanese patients examined during the period 1995-2001. There was an increase, from 6.2% in 1995 to 22.1% in 2000-2001, in the proportion of patients infected with clarithromycin-resistant H. pylori. Of patients infected with clarithromycin-resistant H. pylori, 39.1% were infected with both clarithromycin-susceptible and -resistant H. pylori. Furthermore, the MIC90 of clarithromycin for H. pylori rose from < 1 mg/L in 1995-1998 to 8 mg/L in 1999. In contrast, the MIC90s of amoxycillin and metronidazole were < or = 0.125 and 4 mg/L, respectively, throughout the study period. The results showed that, while most H. pylori isolates were susceptible to amoxycillin and metronidazole, resistance to clarithromycin among H. pylori isolates increased markedly in Japan during 1995-2001. The results also indicated a need to test the susceptibility of H. pylori isolates from more than two samples obtained from two different sites in the stomach of a single patient in order to diagnose the presence of clarithromycin-resistant H. pylori correctly.     

Evolution of Helicobacter pylori susceptibility to antibiotics during a 10‐year period in Lithuania

The study evaluated the changes in the prevalence of Helicobacter pylori strains with primary resistance to antibiotics during the last 10 years in Lithuania. H. pylori susceptibilities to antibiotics were tested in 89 patients in 1998, in 81 patients in 2001 and in 90 patients in 2007/2008. Susceptibility to metronidazole, clarithromycin, amoxicillin and tetracycline was tested using E‐test or agar dilution method. Susceptibility to ciprofloxacin was only tested in 2007/2008. Data about utilization of all authorized and available on market macrolides and clindamycin in Lithuania during 2003–2007 were evaluated using WHO ATC/DDD methodology. A total of 260 H. pylori strains cultured from untreated adult patients were investigated. Primary resistance rates (1998, 2001 and 2007/2008) for metronidazole were 24.7%, 33.3%, and 35.6%, for clarithromycin 1.1%, 3.7%, and 3.3% and for tetracycline 0%, 2.5% and 0% respectively. No cases of amoxicillin resistance have been detected. The resistance rate for ciprofloxacin was 5.6% in 2007/2008. Data of total macrolides and clarithromycin utilization in Lithuania revealed that despite an increase of consumption of these drugs in Lithuania during 2003–2007 in 1.5 times, the total macrolide consumption remains one of the lowest in Europe. We have not observed any significant changes in the susceptibility of H. pylori to the most widely used antibiotics during the recent 10‐year period. The low resistance rate to clarithromycin might be related to the policy to avoid use of macrolides as first‐line treatment for pulmonary and other infections.     

Clarithromycin resistance among Helicobacter pylori strains isolated from children: prevalence and study of mechanism of resistance by PCR-restriction fragment length polymorphism analysis

Clarithromycin and metronidazole resistance was 29.1 and 23.9%, respectively, in 96 Helicobacter pylori strains obtained from pediatric patients. No resistance to amoxicillin was observed. Resistance according to patients' ages to clarithromycin and metronidazole was 45.4 and 18.2% in 22 patients from 4 to 8 years old, 30.2 and 20.7% in 53 patients from 9 to 13 years old, and 9.5 and 38.1% in 21 patients from 14 to 18 years old, respectively. The A2143G mutation was the most prevalent (82.1%) among clarithromycin-resistant strains.