Antimicrobial susceptibility of clinical isolates of Actinomyces and related genera reveals an unusual clindamycin resistance among Actinomyces urogenitalis strains

Abstract

Objectives: Patterns of antimicrobial susceptibility in Actinomyces and related genera are very limited inthe literature. Data of predominant susceptibility profiles could contribute to the establishment of anaccurate empirical treatment.Methods: A total of 113 isolates from clinical samples were included in this study. Each isolate wasidentified using phenotypic methods and MALDI-TOF/MS. When discrepancies were observed, 16S rRNAgene sequencing was performed. The minimum inhibitory concentrations (MICs) of nine antimicrobialagents (penicillin, ceftriaxone, linezolid, tetracycline, clindamycin, erythromycin, ciprofloxacin,levofloxacin and vancomycin) were tested against the species Actinotignum schaalii (n = 23), Actinomycesturicensis (n = 18), Actinomyces europaeus (n = 13), Actinomyces naeslundii/Actinomyces viscosus group(n = 12), Actinomyces urogenitalis (n = 11), Actinomyces radingae (n = 11), Actinomyces neuii (n = 9),Actinomyces odontolyticus (n = 8), Bifidobacterium scardovii (n = 3), Actinomyces graevenitzii (n = 2),Alloscardovia omnicolens (n = 2) and Varibaculum cambriense (n = 1).Results: All of the isolates were susceptible to penicillin, ceftriaxone, vancomycin and linezolid. Almost allof the A. urogenitalis isolates (8/11) were resistant to clindamycin and showed susceptibility toerythromycin, suggesting an L-phenotype, however no determinants of clindamycin resistance (lnu andlsa genes) were detected by PCR. High MIC values to quinolones were observed in 54/113 isolates (47.8%).All of the A. urogenitalis isolates were highly resistant to ciprofloxacin and levofloxacin.Conclusions: These data highlight the importance of ongoing surveillance to provide relevant informationfor empirical management of infections caused by these organisms.© 2017 International Society for Chemotherapy of Infection and Can