The Thai Journal of Veterinary Medicine


Staphylococcus aureus (S. aureus) has been shown to adhere, invade, and induce the death of various host cells. The prominent lineage of livestock-associated methicillin-resistant S. aureus (LA-MRSA) in Asia is the sequence type (ST) 9 that has emerged as a potential zoonotic pathogen. However, the virulence of LA-MRSA ST9 remains not clear. In this study, sixteen representative Taiwan LA-MRSA isolates were selected for adherence, invasion, and cytotoxicity studies against the human lung carcinoma epithelial cell line A549. The isolates showed 100% of cytotoxicity, 35.2% - 61% of adhesion, and 18% - 52.5% of invasion against A549 cells. Different adherent abilities to A549 cells were found for the isolates from swine nasal group (43.3±8.4%) and the isolates from environmental group (31.4±6.2%) (p < 0.05), but no differences were found against A549 cells on invasion of both groups. Differences of cell cycle distribution in the apoptotic (sub-G1) phase of the A549 cells were also noted, with significantly more cells in the swine nasal group than that in environmental group, implying differential gene expression patterns resulting in physiological changes. This study characterized the adhesion and invasion capabilities as well as the cytotoxicity of LA-MRSA ST9 isolates against A549 cells for the first time. These findings reveal the risk for humans and animals to have potential invasion by this novel emerging MRSA lineage. More attention is needed concerning the spread of this bacterium between hospitaland community-associated environments.

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