Determination of mecA expression and other resistance mechanisms in methicillin-resistant Staphylococcus aureus isolated from Oreochromis niloticus (Nile tilapia)

Methicillin-resistant Staphylococcus aureus is a major cause of infection worldwide. Production of β-lactamases and penicillin-binding protein 2a are the two main mechanisms of resistance in S. aureus. The aim of this work was to study the mechanisms of resistance produced by the S. aureus strain isolated from Oreochromis niloticus (Nile tilapia) during an outbreak. β-Lactamases production was detected by iodometric and clover leaf techniques. The induction of mecA gene was done using oxacillin and the gene expression was detected by real time reverse transcription-polymerase chain reaction in the induced isolate and compared with the non-induced one. Also, the studied mecA gene was sequenced to check the similarity between the gene of the tested isolate and the published mecA genes. Results showed that this isolate produces β-lactamase and mecA expression was seven times increased in the case of oxacillin induction. Sequencing results showed 99% identity between the studied gene and the published reference genes. Extensive use of antibiotics in fish farms resulted in the emergence of multidrug resistant staphylococci and this resistance may be induced by the continuous use of some antibiotics.