Recent evolution of antibiotic resistance in the anaerobes as compared to previous decades

• Data covering 2000–2013, as compared to previous years, were included.
• Bacteroides and Clostridium difficile resistance to moxifloxacin increased globally.
• Bacteroides, Prevotella, C. difficile and anaerobic cocci showed resistance changes.
• Decrease in antibiotic resistance in anaerobes was also found.
• Five main factors were associated with evolution of the resistance.

Evolution of antibiotic resistance in the anaerobes was reviewed using recent data covering 2000–2013 as compared to previous years. All studies reported growing moxifloxacin resistance in Bacteroides/Parabacteroides spp. in Europe and USA and in Clostridium difficile in Europe. In half or more studies, the resistance rates in Bacteroides/Parabacteroides spp. to amoxicillin–clavulanate or ampicillin–sulbactam and clindamycin rose. In some studies, an increase in resistance was found in Bacteroides/Parabacteroides spp. to cefoxitin/cefotetan and carbapenems, in Prevotella spp. to penicillins, in anaerobic cocci to clindamycin and in Bacteroides/Parabacteroides spp. and C. difficile to metronidazole. Decreasing resistance was also observed, e.g. in Bacteroides/Parabacteroides spp. to cephalosporins, in Prevotella spp. and C. difficile to tetracyclines and in C. difficile to rifampin. No resistance changes were found to tigecycline, in Bacteroides/Parabacteroides spp. to chloramphenicol and in C. difficile to vancomycin. Factors influencing the resistance were the species, ribotype, country, hospital centre, antibiotic consumption and specimen type. In conclusion, the antibiotic resistance changes in the anaerobes are diverse and dynamic. Regular national surveys of resistance and both anaerobic microbiology and susceptibility testing of the isolates become more and more valuable.