Metronidazole resistance and microaerophily in Campylobacter species

Metronidazole is active against most anaerobic organisms and is also used in the treatment of the microaerophilic bacterium Helicobacter pylori. Resistance to metronidazole is uncommon in most anaerobic organisms, but it is increasingly prevalent in H. pylori. Previously we have suggested that metronidazole resistance in H. pylori is inherent in the microaerophilic nature of the organism and therefore would be present in other microaerophiles such as Campylobacter. Short periods of anaerobiosis caused metronidazole-resistant (Mtr^R) strains of Campylobacter spp. to become sensitive to metronidazole. Under microaerophilic conditions, cultures of the Mtr^R mutant Campylobacter coli R1 at bacterial cell densities of greater than 10⁸ cfu/ml lost viability, whereas no loss in viability was observed in cultures at cell densities of less than 10⁸. The Mtr^S C. coli strain lost viability at all cell densities. Comparisons of NAD(P)H oxidase activity between MtrS and Mtr^R strains indicated that the Mtr^S C. coli strain contained fourfold higher NADH oxidase activity and twofold higher NADPH oxidase activity than did the Mtr^R Campylobacter strains. These results show that Mtr^R Campylobacter spp. display resistance characteristics similar to those of H. pylori, suggesting that the resistance mechanism is a phenomenon of the microaerophilic nature of these bacteria. Received: 9 March 1998 / Accepted: 17 June 1998