Bacteroides fragilis Group: Trends in Resistance

Representing the major part of the human colon microflora, members of the Bacteroides fragilis group are frequently involved in mixed aerobic and anaerobic infections. Recent studies show an increased resistance of the B. fragilis group against several antimicrobial agents. The aim of the present study was to determine the susceptibility of 87 B. fragilis group strains isolated in 2003/2004 in Western Austria against eight antimicrobial agents by Etest. Furthermore, the resistance patterns were compared with those of 45 B. fragilis group strains isolated in 1992 and referred to the world wide trend towards increased resistance. In 1992 as well as in 2003/2004, all strains were susceptible against metronidazole and imipenem. However, comparing the MIC-values of the B. fragilis group strains collected 1992 with data from 2003/2004, a significant increase in resistance was found for clindamycin (p<0.01). Regarding cefoxitin, a similar trend could be observed. However, this difference was not yet significant (p=0.144). Our findings underline the emerging resistance of the B. fragilis group against antimicrobial agents and underscore the importance of susceptibility testing of anaerobes even in routine laboratories.