Evaluation of penicillin G susceptibility testing methods for Staphylococcus lugdunensis

• Published in: Journal of antimicrobial chemotherapy Vol. 75; no. 5; pp. 1206 - 1211
• Main Authors: Hagstrand Aldman, Malin, Påhlman, Lisa I
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.05.2020
• Subjects: Clinical Medicine; Infectious Medicine; Infektionsmedicin; Klinisk medicin; Medical and Health Sciences; Medicin och hälsovetenskap; Original Research
• ISSN: 0305-7453; 1460-2091; 1460-2091
• DOI: 10.1093/jac/dkaa004

Abstract Background Staphylococcus lugdunensis belongs to the CoNS group, but is regarded to be more virulent than most other CoNS. It is also remarkably susceptible to antibiotics, including penicillin G. Objectives To evaluate different methods for penicillin susceptibility testing, to assess penicillin susceptibility rates among S. lugdunensis and to describe the clinical presentation including antibiotic treatment. Methods Clinical isolates of S. lugdunensis were tested for penicillin susceptibility using disc diffusion according to CLSI (10 U disc) and EUCAST (1 U disc), assessment of zone-edge appearance, nitrocefin test and Etest for MIC determination. PCR of the blaZ gene was used as a reference method. Results Of the 112 isolates included in the study, 67% were susceptible to penicillin G according to blaZ PCR. The EUCAST disc diffusion test had 100% sensitivity, whereas the CLSI method had one very major error with a false-susceptible isolate. When zone-edge appearance was included in the assessment, the false-susceptible isolate was correctly classified as resistant. Foreign-body infection was the most common focus of infection, affecting 49% of the participants. Only 4% of the patients were treated with penicillin G. Conclusions Penicillin susceptibility is common in S. lugdunensis and the disc diffusion method according to EUCAST had a higher sensitivity than that of CLSI. Assessment of zone-edge appearance could increase the sensitivity of the disc diffusion test. Penicillin susceptibility testing and treatment should be considered in S. lugdunensis infections.