Antimicrobial susceptibilities and serogroups of clinical strains of Clostridium difficile isolated in France in 1991 and 1997

Glycopeptides (vancomycin and teicoplanin) and metronidazole are the drugs of choice for the treatment of Clostridium difficile infections, but trends in susceptibility patterns have not been assessed in the past few years. T he objective was to study the MICs of glycopeptides and metronidazole for u nrelated C. difficile strains isolated in 1991 (n = 100) and in 1997 (n = 9 8) by the agar macrodilution, the E-test, and the disk diffusion methods, S train susceptibilities to erythromycin, clindamycin, tetracycline, rifampin , and chloramphenicol were also determined by the ATE ANA gallery (bioMerie ux, La Balme-les-Grottes, France). The MICs at which 50% of isolates are in hibited (MIC(50)s) and MIC(90)s of glycopeptides and metronidazole remained stable between 1991 and 1997. All the strains were inhibited by concentrat ions that did not exceed 2 mu g/ml for vancomycin and 1 mu g/ml for teicopl anin. Comparison of MICs determined by the agar dilution method recommended by the National Committee for Clinical Laboratory Standards and the E test showed correlations (+/- 2 dilutions) of 86.6, 95.9, and 99% for metronida zole, vancomycin, and teicoplanin, respectively. The E test always underest imated the MICs. Strains with decreased susceptibility to metronidazole (MI Cs, greater than or equal to 8 mu g/ml) were isolated from six patients (n = 4 in 1991 and n = 2 in 1997). These strains were also detected by the dis k diffusion method (zone inhibition diameter, less than or equal to 21 mm); they belonged to nontoxigenic serogroup D (n = 5) and toxigenic serogroup H (n = 1). Decreased susceptibility to erythromycin (MICs, greater than or equal to 1 mu g/ml), clindamycin (MICs, greater than or equal to 2 mu g/ml) , tetracycline (MICs, greater than or equal to 8 mu g/ml), rifampin (MICs, greater than or equal to 4 mu g/ml), and chloramphenicol (MICs, greater tha n or equal to 16 mu g/ml) was observed in 64.2, 80.3, 23.7, 22.7, and 14.6% of strains, respectively. Strains isolated in 1997 were more susceptible t han those isolated in 1991, and this trend was correlated to a major change in serogroup distribution. Periodic studies are needed in order to detect changes in serogroups and the emergence of strains with decreased susceptib ility to therapeutic drugs.