Evaluation of methods for studying susceptibility to oxacillin and penicillin in 60 Staphylococcus lugdunensis isolates

• Published in: Enfermedades infecciosas y microbiología clínica Vol. 27; no. 3; pp. 148 - 152
• Main Authors: Batista, Nínive, Fernández, M Paula, Lara, Magdalena, Laich, Federico, Méndez, Sebastián
• Format: Journal Article
• Language: Spanish
• Published: Spain 01.03.2009
• Subjects: Bacterial Proteins - analysis; Bacterial Proteins - genetics; beta-Lactamases - analysis; beta-Lactamases - genetics; Drug Resistance, Multiple, Bacterial; Humans; Microbial Sensitivity Tests - methods; Oxacillin - pharmacology; Penicillin Resistance; Penicillins - pharmacology; Staphylococcal Infections - microbiology; Staphylococcus - drug effects; Staphylococcus - genetics; Staphylococcus - isolation & purification
• ISSN: 0213-005X
• DOI: 10.1016/j.eimc.2008.04.005

Staphylococcus lugdunensis is a coagulase-negative staphylococcus associated with a variety of clinical infections. In this paper we present the results of a comparative study using 4 methods to determine antimicrobial susceptibility to oxacillin and penicillin in 60 S. lugdunensis isolates. We studied 60 S. lugdunensis isolates obtained from clinical specimens sent to our laboratory over an 8-year period. All isolates were free coagulase-negative and DNase-negative, and biochemically identified by API ID 32 STAPH (bioMérieux). Presence of mecA and ss-lactamase production were studied in all cases. Antimicrobial susceptibility was determined by the Vitek 2 System (bioMérieux) and broth microdilution (Wider) (Soria Melguizo) for penicillin and oxacillin, and the E-test (AB Biodisk) and cefoxitin disk diffusion test (BD BBLTM) for oxacillin. All isolates lacked the mecA gene and were susceptible to oxacillin by broth microdilution, E-test, and cefoxitin disk diffusion test. Only two isolates were oxacillin-resistant by the Vitek 2 System. Twenty-four isolates (40%) were ss-lactamase-positive, 4 after induction. Susceptibility testing to penicillin determined that 48 isolates showed concordance between the results obtained by broth microdilution and Vitek 2, but 12 isolates (20%), showed divergent results. We detected no resistance to oxacillin in S. lugdunensis. All the methods evaluated were adequate for determining oxacillin resistance. The Vitek 2 System is useful for detecting penicillin resistance, but the ss-lactamase test should be applied to isolates with a MIC=0.25microg/ml to avoid the interpretation of false resistance to this antibiotic.