Bacteriological and Molecular Aspects of Staphylococcous aureus Clinical Isolates Carrying Genes for Exfoliative Toxins and Panton-Valentine Leukocidin
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Within the genus Staphylococci, Staphylococcus aureus (S. aureus) is the causal agent of most staphylococcal infections and is associated with serious community-acquired and nosocomial diseases. S. aureus toxins are considered the main effector molecules in a wide variety of human skin infections. This work aims to investigate the presence of exfoliative toxins (ETs) and Panton-Valentine leukocidin (PVL) encoding genes (eta, etb and lukS-lukF-PV) in S. aureus clinically isolated from patients with furuncles, impetigo (bullous and non-bullous) and staphylococcal scalded skin syndrome (SSSS) by using PCR and to determine the antimicrobial susceptibility patterns of these clinical isolates. The study included 80 patients with skin infections. In this work, a total of 56 S. aureus isolates were revealed from all patients. Among the 21 isolates from patients with furuncles, 20 (95.2%) carried lukS-lukF-PV and only one (4.8%) carried eta. Of the 18 isolates from patients with bullous impetigo, 6 (333%) carried eta, 10 (55.6%) carried etb and 2 (11.1%) carried both eta and etb. Of the 12 isolates from patients with non-bullous impetigo, 3 (25%) were eta positive, 7 (58.3%) were etb positive and one (83%) was positive for both eta and etb. Among the 5 isolates from patients with SSSS, eta was detected in one (20%) isolate, while each of etb and both eta and etb were detected in 2 (40%) isolates. Among the 56 S. aureus isolates, 10 (17.9%) isolates were methicillin-resistant S. aureus (MRSA), of which 7 (70%) carried lukS-lukF-PV and 3 (30%) carried etb. Most isolates were resistant to penicillin (98.2%), cephalosporins (76.8% for cephalothin and 73.2% for cefotaxime), erythromycin (51.8%), sulphamethoxazole-trimethoprim (48.2%). Whereas, the resistance to rifampicin, chloramphenicol, gentamycin, ciprofloxacin, fuisidic acid and mupirocin were 25%, 21.4%, 14.3%, 10.7%, 7.1% and 53% respectively. No resistance was detected to vancomycin. In conclusion, PVL-encoding gene is not only a possible virulence factor associated with staphylococcal necrotic lesions of the skin and subcutaneous tissues but also a stable genetic marker of MRSA isolates responsible for primary skin infections. The staphylococcal ETs are important factors in the development and progression of SSSS and impetigo. Monitoring of the drug resistance of S. aureus clinical isolates and establishment of an appropriate antibiotic therapy guideline for the treatment of staphylococcal skin infections are definitely required to control the dissemination of the emerging PVL- or ET-positive MRSA isolates. Further studies are recommended for identifying additional virulence factors of PVLpositive S. aureus isolates, as this may lead to specific therapeutic approaches targeting PVL in severe PVL-related staphylococcal infections.