Long regarded as a contaminant in clinical cultures, Staphylococcus haemolyticus has emerged as a major bacterial species responsible for a variety of serious human infections. This species is increasingly prevalent as an opportunistic agent, and the evolution of S. haemolyticus as a multiple drug-resistant strain is emerging as a major threat in worldwide healthcare facilities. In this study, 50 commensal and 98 clinical strains of S. haemolyticus were isolated and confirmed via superoxide dismutase gene sequence analysis. All isolates were tested against a series of antibiotics from ten different classes and screened for Staphylococcus Chromosomal Cassette (SCC) Types I, II, III, IV, and V. Staphylococcus haemolyticus resistance to antibiotics was observed in both the clinical and commensal strains isolated from healthy adults. In clinical isolates, the highest resistance was observed against erythromycin at 79.6% followed by cefoxitin (71.4%), while a high percentage of the commensals were resistant against cefoxitin (56.0%) and tigecycline (40.0%). More than half of the S. haemolyticus clinical isolates are multidrug resistance (MDR) strains at 54.1%, while 20.0% of the S. haemolyticus commensals are MDR strains. The majority of these MDR strains are methicillin-resistant S. haemolyticus (MRSH) suggesting a close relationship between the methicillin-resistant strains and resistance to multiple classes of antibiotics. SCCmec Type II is the most abundant type observed in both commensal (92.0%) and clinical (99.0%) isolates of S. haemolyticus followed by Type V at 38.0% and 46.9%, respectively. The similar pattern of typing observed indicates the possibility that the clinical isolates of S. haemolyticus could have originated from the commensal strains that had successfully entered the host and caused infections. The antibiotic profile indicates the natural resistance of S. haemolyticus to antibiotics, even among the commensal strains. It also appears that transmission of genetic determinants for antibiotic resistance is common and widespread among all the S. haemolyticus isolates. Commensal strains of S. haemolyticus may thus serve as reservoirs for the transmission of antibiotic resistance and the development of opportunistic strains.
Key words: Keywords: Commensals, Clinical, MDR, MRSH, SCCmec
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