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

LUDMILA BOYANOVA, IRINA STANCHEVA^*, ZOYA SPASSOVA, NIKOLAI KATZAROV, IVAN MITOV and RADKA KOUMANOVA

Department of Microbiology, Medical University, Sofia, *Department of Gastroenterology, Hospital of the Ministry of Internal Affairs, Sofia, Department of Gastroenterology, University Hospital ‘St Ivan Rilski', Sofia and Department of Gastroenterology, University Paediatric Hospital, Sofia, Bulgaria

Corresponding author Dr L. Boyanova.

Received 5 April 1999; revised version accepted 10 Oct. 1999.

Abstract

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 µg), clarithromycin (15 µg) or erythromycin (15 µg), ciprofloxacin (5 µg) and tetracycline (30 µg). Resistance was determined by an inhibitory zone of <16 mm for metronidazole and 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.

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