title: Resistance patterns in clinical isolates of pathogenic Actinomyces species.
abstract: OBJECTIVE
  Actinomyces spp. are commensals that may occasionally invade deep tissue structures, causing difficult-to-treat and disfiguring lesions. Information on antimicrobial resistance patterns is limited to observations from two previous studies. Therefore, we examined antimicrobial resistance patterns in clinical isolates of Actinomyces spp.
  
  
  METHODS
  In this retrospective assessment of antimicrobial resistance patterns, we identified 392 Actinomyces spp. at a tertiary care centre from January 2008 to December 2014. MICs of various antimicrobial agents, including ampicillin/sulbactam, meropenem, clindamycin, metronidazole and vancomycin for anaerobic actinomycetes, were obtained by Etest. For aerobic actinomycetes, imipenem, cefotaxime, amikacin, linezolid, moxifloxacin, trimethoprim/sulfamethoxazole and clarithromycin were tested. MIC results were interpreted based on guidelines published by the CLSI (formerly NCCLS).
  
  
  RESULTS
  Actinomyces meyeri was predominantly isolated and accounted for 34% of all Actinomyces spp. identified, followed by Actinomyces turicensis with 23%. Actinomyces neuii is considered to be a rare Actinomyces sp., but accounted for 8% of isolates. Antimicrobial susceptibility testing of isolates showed that the Actinomyces spp. were almost uniformly susceptible to β-lactam antimicrobials (with and without β-lactamase inhibitors), carbapenems, tetracyclines and vancomycin. In contrast, Actinomyces spp. isolates were almost uniformly resistant to metronidazole.
  
  
  CONCLUSIONS
  β-Lactam antimicrobial agents remain the first choice, whereas metronidazole should be avoided, in the treatment of actinomycosis. Reasonable alternatives for treatment are tetracyclines and carbapenems.
authors.affiliation: Department of Medicine I, Division of Infectious Diseases and Tropical Medicine, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: C
authors.initials: C
authors.lastname: Steininger
authors.affiliation: Department of Laboratory Medicine, Division of Clinical Microbiology, Medical University of Vienna, Währinger Gürtel 18-20/5P, 1090, Vienna, Austria birgit.willinger@meduniwien.ac.at.
authors.forename: Birgit
authors.initials: B
authors.lastname: Willinger
mesh_terms: D000190:Actinomyces / Q000187:drug effects* / Q000302:isolation & purification; D000196:Actinomycosis / Q000382:microbiology*; D000332:Aerobiosis; D000693:Anaerobiosis; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D052978:Disk Diffusion Antimicrobial Tests; D024881:Drug Resistance, Bacterial; D006801:Humans; D012189:Retrospective Studies; D062606:Tertiary Care Centers
chemical_list: D000900:Anti-Bacterial Agents