a Service de Bactériologie-Virologie-Hygiène, Centre Hospitalier Universitaire Henri-Mondor, Créteil; b Aventis Pharma, Hoechst Marion Roussel, Romainville; c Service de Bactériologie-Virologie, Centre Hospitalier Universitaire Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75571 Paris cedex 12, France
Sir,
Clarithromycin is the most active macrolide against Helicobacter pylori, but pH reduction markedly decreases its activity.1 This is a cause of concern because H. pylori is found on the gastric mucosa, where the pH is low, c. 5.5. In addition, clarithromycin resistance is increasing in H. pylori, with prevalences attaining at least 10% in several countries. Telithromycin is a new ketolide antibiotic that has been found to be highly active against a variety of microorganisms.2 We determined its activity, at pH 7.4, 6.5 and 5.9, against 30 macrolide-susceptible and 15 -resistant clinical strains of H. pylori isolated from gastric biopsies in Henri-Mondor hospital between 1997 and 1999. H. pylori ATCC 43504 was used as a control strain. MICs of clarithromycin and telithromycin were determined by the agar dilution technique using MuellerHinton agar (Oxoid, Lyon, France) supplemented with 10% fresh horse blood. A Steers inoculating device was used to place 105106 cfu per spot (2 µL per spot) on to the plates (52 spots per plate), which were examined for growth after 72 h of incubation at 37°C under microaerophilic conditions. Strains were considered resistant to clarithromycin if the MIC was 1 mg/L.3
At pH 7.4, telithromycin was four-fold less active than clarithromycin against clarithromycin-susceptible strains, the MIC50 of telithromycin being 0.125 mg/L (Table). In agreement with previous findings,1 pH reduction caused a marked increase in the MICs of clarithromycin for clarithromycin-susceptible strains: at pH 6.5, the MIC50 and MIC90 increased two- and eight-fold, respectively; at pH 5.9, eight- and 16-fold increases were observed (Table). The activity of telithromycin against clarithromycinsusceptible strains was similarly affected by pH reduction (Table). None the less, the MICs of telithromycin at pH 5.9 for most strains remained below the maximum achievable serum concentration of telithromycin: 2.27 mg/L after 800 mg od for 7 days.4
The A2142G and A2143G mutations in the 23S rRNA gene that are implicated in clarithromycin resistance of H. pylori were detected by restriction fragment length polymorphism analysis of PCR-amplified DNA, using MboII and BsaI restriction enzymes (New England Biolabs, Beverly, MA, USA), as described previously.5 All clarithromycin-resistant strains carried either a A2142G (five strains) or A2143G mutation (10 strains). H. pylori possesses two 23S rRNA genes and both were mutated in all strains. In agreement with previous findings,5 MICs of clarithromycin at pH 7.4 were significantly higher for A2142G mutants (64128 mg/L) than for A2143G mutants (832 mg/L) (Table). Telithromycin was not spared by resistance but the two mutations, and especially the A2142G mutation, were associated with a lower increase in the MICs of telithromycin, MICs for A2142G and A2143G mutants being 832 and 432 mg/L, respectively (Table).
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Notes
* Corresponding author. Tel: +33-1-49-28-29-10; Fax: +33-1-49-28-24-72; E-mail: jacques.tankovic{at}sat.ap-hop-paris.fr
References
1 . Debets-Ossenkopp, Y. J., Namavar, F. & MacLaren, D. M. (1995). Effect of an acidic environment on the susceptibility of Helicobacter pylori to trospectomycin and other antimicrobial agents. European Journal of Clinical Microbiology and Infectious Diseases 14, 3535.[ISI][Medline]
2 . Bryskier, A. (2000). Ketolidestelithromycin, an example of a new class of antibacterial agents. Clinical Microbiology and Infection 6, 6619.[ISI][Medline]
3 . Groupe d'Etudes Français des Helicobacter. (1999). Validation of a disk diffusion method for macrolide susceptibility testing of Helicobacter pylori. Gut 45, Suppl. 3, A9.
4
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Namour, F., Wessels, D. H., Pascual, M. H., Reynolds, D., Sultan, E. & Lenfant, B. (2001). Pharmacokinetics of the new ketolide telithromycin (HMR 3647) administered in ascending single and multiple doses. Antimicrobial Agents and Chemotherapy 45, 1705.
5 . Versalovic, J., Osato, M. S., Spakovsky, K., Dore, M. P., Reddy, R., Stone, G. G. et al. (1997). Point mutations in the 23S rRNA gene of Helicobacter pylori associated with different levels of clarithromycin resistance. Journal of Antimicrobial Chemotherapy 40, 2836.[Abstract]
6 . Xiong, L., Shah, S., Mauvais, P. & Mankin, A. S. (1999). A ketolide resistance mutation in domain II of 23S rRNA reveals the proximity of hairpin 35 to the peptidyl transferase centre. Molecular Microbiology 31, 6339.