a Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; c Internal Medicine, Korea University College of Medicine, Seoul, Korea; b Department of Medicine Baylor College of Medicine, Veterans Affairs Medical Center, 2002 Holcombe Boulevard, Houston, TX 77030, USA
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Abstract |
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Introduction |
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Materials and methods |
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H. pylori were isolated from gastric mucosal biopsy specimens obtained from Seoul, Korea, from 1994 to 1999 as described previously.5 One biopsy specimen from antrum or corpus per patient (total 652 strains from 456 patients) was used to isolate H. pylori. Some patients provided two separate isolates for study. Briefly, biopsy specimens were ground between the frosted ends of two sterile microscope slides and plated on to 7% horse blood brainheart infusion (BHI; Difco Laboratories, Detroit, MI, USA) agar plates supplemented with 1% nalidixic acid, 0.5% trimethoprim, 0.3% vancomycin, 0.2% amphotericin (selective media), and the plates incubated under microaerobic conditions at 37°C for up to 14 days. The bacterial growth (multiple colonies) resulting from the primary culture plates was identified as H. pylori by colony morphology and Gram's stain reaction, and by catalase, urease and oxidase reactions. All stock cultures were maintained at 80°C in Brucella broth supplemented with 20% glycerol (Sigma Chemical Company, St Louis, MO, USA).
Determination of MIC
Measurement of MICs for the recovered H. pylori strains was performed by the serial two-fold agar dilution method as described previously.5 All antibiotics used in this investigation were purchased from Sigma, except for clarithromycin, which was obtained from Abbott Laboratories (Abbott Park, IL, USA).
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Results and discussion |
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The 456 patients studied consisted of 314 men and 142 women, median age 45 years (range 1682 years). Of the 456 patients, 217 failed previous anti-H. pylori therapies containing metronidazole, amoxycillin, clarithromycin or tetracycline, and the others had never received any anti- H. pylori therapy. Endoscopic diagnosis of the 456 patients showed that 109 had chronic gastritis, 224 had peptic ulcer diseases (88 gastric ulcer and 136 duodenal ulcer) and 126 had gastric cancer. Statistical analyses revealed that antibiotic resistance was not significantly associated with disease or age. Metronidazole-resistant strains were found more frequently in women compared with men (48.6 versus 36.9%, P < 0.05).
According to the literature, metronidazole resistance varies from <10 to >80% between geographical regions.8 In the present study, the overall rate of primary metronidazole resistance among H. pylori isolates in Korea was well within the rates described between geographical regions (i.e. 40%). The prevalence of metronidazole resistance gradually increased from 33.3% in 1994 to 47.7% in 19981999. This phenomenon has also been reported in other countries.8 Metronidazole resistance occurs by functional alterations of nitroreductase encoding genes (rdxA and frxA) in H. pylori,5 and these alterations can be caused by the mutagenic effect of metronidazole.9 Therefore, the occurrence of metronidazole-resistant strains may be the consequence of increased consumption of metronidazole in the community. Metronidazole has been widely prescribed for other infections such as parasitic or genital infections in Korea, and increased use or abuse of this inexpensive drug may contribute to the increase in metronidazole resistance. Interestingly, all furazolidone-resistant strains were also resistant to nitrofurantoin with an identical MIC value (4 mg/L of furazolidone or nitrofurantoin). These results indicate that, compared with metronidazole, most H. pylori isolates were susceptible to furazolidone and nitrofurantoin. In addition, all furazolidone- or nitrofurantoin-resistant strains were also metronidazole resistant. While all the furazolidone- and nitrofurantoin-resistant strains also showed metronidazole resistance, the converse was not true. This suggests that although the bactericidal mechanism is similar among these related agents, the resistance mechanism of metronidazole is dissimilar to that of furazolidone and nitrofurantoin. Furazolidone and nitrofurantoin are nitrofurans, and metronidazole is a nitroimidazole. The mechanism of action of these antibiotics is via active nitroreduction of the drugs, which leads to killing of bacteria.5 However, furazolidone and nitrofurantoin resistance involves additional mechanisms not found in metronidazole-resistant H. pylori, which may relate to this differential resistance pattern.
The reported prevalence of primary resistance to clarithromycin varies from 2 to 50%.4 Primary resistance to tetracycline is rare.6 The prevalence of clarithromycin-resistant strains was relatively low (5.9%), whereas tetracycline resistance was high (5.3%) compared with other reports.10 Because primary clarithromycin and tetracycline resistance rates were not very high, the routine pre-treatment testing for clarithromycin and tetracycline susceptibility may not yet be cost effective in Korea. Continuous surveillance of clarithromycin and tetracycline susceptibilities is needed because the prevalence of primary resistance to clarithromycin and tetracycline appears to be increasing in this population. Further increases in antibiotic resistance and the development of dual and/or triple antibiotic resistance among H. pylori isolates from Korea would require susceptibility testing before treatment to maximize efficacy of H. pylori therapies.
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Acknowledgments |
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Notes |
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References |
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Received 12 July 2000; returned 4 October 2000; revised 2 November 2000; accepted 28 December 2000