Extracellular Proteases Production in Methicillin Resistant Staphylococcus aureus Clinical Isolates

Methicillin resistant Staphylococcus aureus (MRSA) bacteria are responsible for wide range of infections, while the treatment of such infections has become a challenge for public health. Moreover, the production of extracellular proteases by these pathogens has recently been considered as a major virulence factor as the staphylococcal proteases can inactivate and cleave several important host proteins, including elastin, proteinase inhibitors and heavy chains of all human immunoglobulins. The present study was carried out to isolate and identify MRSA strains from various clinical samples (pus, blood, urine and skin) followed by screening for the production of extracellular proteolytic enzymes. The identification of the clinical isolates was achieved by microscopic and specific biochemical methods. MRSA strains were identified by Kirby-Bauer disc diffusion method using cefoxitin antibiotic discs. The extracellular protease activity was detected using casein medium by agar plate and well-diffusion bioassay methods. A total of 114 MRSA clinical isolates were isolated and pure cultured from different (n=191) clinical specimens (pus, blood, urine and skin). It was observed that 51.7% (n=59) MRSA isolates were recovered from pus samples, while 23.7% (n=27), 16.7% (n=19) and 7.9% (n=09), were obtained from blood, urine and skin samples, respectively. The enzymatic analysis of the MRSA isolates showed that 68.4% of them were highly positive for the production of the extracellular protease enzymes. Extracellular protease production was frequent in the clinical isolates of MRSA suggesting a critical role of the production of extracellular proteases in pathogenesis of MRSA in humans.