To Be or Not to Be Resistant: CLSI Versus EUCAST Guidelines for Staphylococcus lugdunensis

Abstract

Abstract Introduction/Objective Staphylococcus lugdunensis is a coagulase-negative Staphyloccocus, but infections can be as severe as S. aureus. Performing antimicrobial susceptibility testing (AST) is paramount to appropriate treatment. Recently, the College of American Pathologists is requiring clinical labs to implement updated guidelines. We evaluated how the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines would impact our hospital’s resistance rates for S. lugdunensis. Methods/Case Report Cultures with S. lugdunensis isolated between 04/2018 to 02/2022 were included. Minimal inhibitory concentrations (MICs) (Vitek2 and Microscan Walkaway) reported (clindamycin, doxycycline, daptomycin, linezolid, and vancomycin) were interpreted using CLSI (M100Ed32) and EUCAST (v12.0) guidelines. The range of MICs (95% Confidence Interval) was calculated. Results (if a Case Study enter NA) A total of 125 isolates from 120 patients from specimen types including wound (49%), tissue (42%), blood (6%), and body fluid (3%) were identified. Five patients had multiple cultures of S. lugdunensis, four from two wound/tissue sites and one with blood and biopsy positive. For clindamycin (0.7-1.3 ug/mL), EUCAST guidelines determined two more isolates (from blood and wound, MIC=0.5 ug/mL) as resistant. Most drastically, the rate of resistance for doxycycline (0.6-1.0 ug/mL) was 11% higher per EUCAST guidelines (susceptible: 89% EUCAST vs 100% CLSI). The difference was seen in isolates > 2 ug/mL, all isolated from wound and tissue. Regardless of the guidelines used, 100% of the isolates were susceptible to daptomycin (0.4-0.5 ug/mL), linezolid (1.2-1.4 ug/mL), and vancomycin (0.6-0.7 ug/mL); 23% were resistant to oxacillin (1.7-2.0 ug/mL). Conclusion EUCAST guidelines would have reported more resistant doxycycline and clindamycin isolates at our institution. To ensure that clinical teams are utilizing AST results to provide appropriate care, a team effort consisting of the microbiology lab, infectious diseases physicians, and antibiotic stewardship committee is needed to determine which guidelines should be followed.