Evaluation of methods for detection of β-lactamase production in MSSA

Abstract

Objectives Correct determination of penicillin susceptibility is pivotal for using penicillin in the treatment of Staphylococcus aureus infections. This study examines the performance of MIC determination, disc diffusion and a range of confirmatory tests for detection of penicillin susceptibility in S. aureus. Methods A total of 286 consecutive penicillin-susceptible S. aureus blood culture isolates as well as a challenge set of 62 MSSA isolates were investigated for the presence of the blaZ gene by PCR and subjected to penicillin-susceptibility testing using broth microdilution MIC determination, disc diffusion including reading of the zone edge, two nitrocefin tests and the cloverleaf test. Results Using PCR-based detection of blaZ as the gold standard, both broth microdilution MIC testing and disc diffusion testing resulted in a relatively low accuracy (82%–93%) with a sensitivity ranging from 49%–93%. Among the confirmatory tests, the cloverleaf test performed with 100% accuracy, while zone edge interpretation and nitrocefin-based tests increased the sensitivity of β-lactamase detection to 96%–98% and 82%–96% when using MIC determination or disc diffusion as primary test, respectively. Conclusions This investigation showed that reliable and accurate detection of β-lactamase production in S. aureus can be obtained by MIC determination or penicillin disc diffusion followed by interpretation of the zone edge as a confirmatory test for apparently penicillin-susceptible isolates. The more cumbersome cloverleaf test can also be used. Nitrocefin-based tests should not be used as the only test for confirmation of a presumptive β-lactamase-negative isolate.

Case report: Methicillin-resistant Staphylococcus aureus with penicillin susceptible (PS-MRSA): first clinical report from a psychiatric hospital in China

“…In addition to standard testing with automated susceptibility testing instruments, we specifically included disc diffusion tests for penicillin and cefoxitin. This comprehensive approach to antibiotic susceptibility testing enabled the timely identification of this rare PS-MRSA strain, highlighting the importance of employing diverse susceptibility testing methods in resistance research and the critical role of precise diagnosis in antibiotic treatment ( 11 ). Although the empirical use of β-lactam antibiotics in this case was effective, it also serves as a reminder of the broader implications of antibiotic use and the development of resistance.…”

Molecular Epidemiology of Penicillin-Susceptible Staphylococcus aureus Bacteremia in Australia and Reliability of Diagnostic Phenotypic Susceptibility Methods to Detect Penicillin Susceptibility

“…Different studies have questioned the reliability of phenotypic susceptibility testing to detect PRSA. In a recent study, Skov et al demonstrated that although phenotypic testing could reliably detect blaZ-negative PSSA, detection of blaZ-positive PSSA proved troublesome [38]. BMD, CLSI disc diffusion, and cefinase testing could only identify 49%, 51%, and 78% of blaZ-positive PSSA, respectively.…”