Increase in resistance rates of H. pylori isolates to metronidazole and tetracycline--comparison of three 3-year studies.

BACKGROUND Antimicrobials have been useful in the treatment of H. pylori-related dyspeptic diseases. However, emergence of resistant strains often decreases the eradication rates of H. pylori infections. Large-scale use of antimicrobials will lead to the diminishment of susceptible strains while allowing resistant survivors to outgrow and spread resistance genes. The aim of this study was to assess the change in antimicrobial resistance rate of H. pylori isolates from 2005 to 2008 and indicate the consequences of indiscriminate and widespread use of antimicrobials against H. pylori- and non-H. pylori-related infections. METHODS A total of 110 H. pylori strains were isolated from dyspeptic patients during 2005 to 2008 and tested for their susceptibility to antimicrobials using the disk diffusion method. MICs were determined for metronidazole (8 microg/mL), tetracycline (0.5 microg/mL), clarithromycin (2 microg/mL), amoxicillin (1 microg/mL) and furazolidone (0.5 microg/mL). Since the rates of resistance to metronidazole and tetracycline were remarkably high, another 50 isolates were tested for their susceptibility to metronidazole at the same MIC (8 microg/mL) and tetracycline at MICs of 0.5,1 and 2 microg/mL. Resistance rates were compared to those obtained in our two previous studies between 1997-2000 and 2001-2004. RESULTS The resistance rates of 110 H. pylori isolates to clarithromycin, amoxicillin and furazolidone were 7.3%, 7.3%, and 4.5%, respectively. Among 160 H. pylori isolates, 55.6% exhibited resistance to metronidazole and 38.1% to tetracycline. DISCUSSION Compared to our two previous studies, the resistance rates of H. pylori isolates to current antimicrobials has changed over time. The change in resistance rates of clarithromycin, amoxicillin and furazolidone was not statistically significant. However, resistance to metronidazole and tetracycline showed a considerable increase from 33-36.3% to 55.6% and 0-0.7% to 38.1%, respectively. Emergence of resistance due to the intensive use of antibiotics has become a global public health problem. It appears that plasmid-carried genes are involved in the spread of resistance traits among bacteria. Results obtained in this study indicate that the increase in resistance rates of H. pylori isolates to metronidazole and tetracycline could be the indication of indiscriminate and frequent use of antibiotics in Iran.