Distribution and characteristics of methicillin-resistant staphylococci from non-clinical environments in southern Vietnam

Methicillin-resistance in pathogenic staphylococci such as Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE) represents a major global health concern. Acquisition of methicillin-resistance (mec) genes enables these organisms to evade β-lactam antibiotics and has facilitated their spread beyond hospitals to the wider community and environment. Non-pathogenic Methicillin-resistant staphylococci (MRS), which inhabit various environments, are considered potential reservoirs of mec genes. However, information on MRS in non-clinical settings remains limited. This study conducted a survey on MRS in Vietnam between 2022 and 2024, targeting five categories: meats, livestock, animal-feces, environments, and pets. MRS isolates were obtained using Mannitol-Salt agar containing cefoxitin (CFX) and the presence of resistance genes (mecA, mecB, mecC, mecD) and SCCmec types were confirmed by polymerase chain reaction (PCR). Species identification was performed by Time-of-Flight Mass Spectrometry (TOF–MS) for all isolates. Methicillin resistance phenotypes were determined by disk diffusion tests using oxacillin (MPI) and cefoxitin (CFX). A total of 167 MRS were isolated from 183 swabs. The isolates comprised 19 species and 7 SCCmec types. The detection rate of MRS was highest in meats (89.3%), followed by livestock (65.3%), animal-feces (58.8%), environments (53.6%), and pets (31.6%). Species commonly colonized in humans were detected at higher rates in meats and pets. In disk diffusion tests, inhibition zone diameters for MPI and CFX were correlated among the MRS carrying hospital-acquired SCCmec types (I, II and III), but not among those carrying other types. Isolates showing a faint mecA-PCR signal intensity tended to exhibit lower resistance. Heterogeneous resistance, characterized by colonies within inhibitory CFX zones, was observed in 11 species with the highest frequency in Staphylococcus sciuri (43.8%). This study identified the species, SCCmec types, and the MPI and CFX susceptibilities of MRS isolates from non-clinical settings in Vietnam. The high detection rate indicates the widespread dissemination of diverse MRS in the environment. A correlation between MPI and CFX inhibitory zone diameters was observed only among isolates carrying certain SCCmec types.