Improved Detection of mecA-Mediated β-Lactam Resistance in Staphylococcus lugdunensis Using a New Oxacillin Salt Agar Screen

Abstract

Oxacillin resistance mediated by mecA in Staphylococcus lugdunensis is emerging in some geographic areas. We evaluated cefoxitin disk diffusion (DD) and a new oxacillin agar (supplemented with 2 μg/ml oxacillin and 2% sodium chloride) screen for the detection of mecA-mediated resistance in S. lugdunensis. A total of 300 consecutive, non-duplicated clinical S. lugdunensis isolates from diverse sources in Hong Kong in 2019 were tested. The categorical agreement and errors obtained between cefoxitin DD test, oxacillin agar screen and mecA PCR were analyzed. Isolates with discordant results were further tested by MIC, penicillin binding protein 2a (PBP2a) assays, population analysis and molecular typing. PCR showed that 62 isolates were mecA-positive and 238 isolates were mecA-negative. For cefoxitin DD results interpreted using S. aureus/S. lugdunensis breakpoints, the categorical agreement (CA) for two brands of Muller-Hinton agars, MH-II (Becton Dickinson) and MH-E (bioMérieux) were both 96.0%; MEs were both 0%; and VMEs were 19.4 and 12.9%, respectively. The new oxacillin agar reliably differentiated mecA-positive and mecA-negative isolates (100% CA) without any ME or VME results. The 8 isolates with false susceptibility in the cefoxitin DD testing had cefoxitin and oxacillin MICs in the susceptible range. The isolates showed heterogeneous oxacillin resistance with resistant subpopulations at low frequencies. All had positive PBP2a results and were typed as sequence type 27/SCCmec V. The findings highlight the inability of cefoxitin DD and MIC tests for reliable detection of some mecA-positive S. lugdunensis isolates.

Clinical and microbiological characteristics of Staphylococcus lugdunensis

“…Ho et al [49] reported 52 out of 179 S. lugdunensis isolates in their study were mecA positive. Cefoxitin DD using CLSI S. aureus / S. lugdunensis breakpoints demonstrated 88% categorical agreement with mecA status and a 12% VME rate (false susceptibility), which was reproducible in a subsequent study by Ho et al [53 ▪ ] where the reported VME rate was 12.9 to 19.4% utilising two different brands of commercial Mueller-Hinton agar. Cefoxitin disk diffusion correctly identified just 60% (31/52) of mecA positive isolates [49].…”

CRISPR/Cas12a-Based APE1 Enzyme Cleavage Assay for Drug Resistance Analysis of Staphylococcus aureus-Related Pneumonia

“…Nevertheless, these techniques typically necessitate a lengthy period for identification, significant manipulation of samples, and the use of costly apparatus. The mecA gene encodes a novel penicillin-binding protein that is responsible for the antibiotic resistance observed in MRSA. , There is an urgent need to develop fast, inexpensive, and highly sensitive methods for detecting the mecA gene in order to discover drug resistance in MRSA.…”

“…The mecA gene encodes a novel penicillin-binding protein that is responsible for the antibiotic resistance observed in MRSA. 12 , 13 There is an urgent need to develop fast, inexpensive, and highly sensitive methods for detecting the mecA gene in order to discover drug resistance in MRSA.…”