Incomplete Hemolytic MRSA Strains Associated with Hemolysin and Panton-Valentine Leucocidin Virulence Genes as a Cause of Blood Stream Infections

Background: Staphylococcus aureus (S. aureus) with the incomplete hemolytic phenotype (SIHP) is known for its dark hemolytic ring, which differs from the transparent S. aureus with complete hemolytic phenotype (SCHP). SIHP is recently linked to severe infections and antimicrobial resistance. Panton-Valentine leucocidin (PVL) and hemolysin are documented virulence factors for S. aureus infection. Objectives : We conducted this study to recognize methicillin-resistant S. aureus (MRSA) strains with SIHP phenotype and evaluate its association with the PVL and hemolysin in patients with bloodstream infections (BSIs). Methodology: Ninety-Three S. aureus isolates were recognized during the study period, and they were evaluated for resistance to thirteen antibiotics. Blood agar plates were used to culture these isolates, and they underwent ten passages for identification of their hemolytic phenotype. PVL and hemolysin genes were tested via polymerase chain reaction (PCR). Results: SIHP constituted 34.4% of the collected isolates. PVL positivity was significantly increased in SIHP (34.4% vs. 16.4% in SCHP). Also, SIHP was strongly associated with MRSA (62.5% vs. 39.3% of SCHP). In SIHP isolates, PVL positivity was associated with MRSA (55% vs. 0 % in MSSA) and increased resistance to Augmentin, cefoxitin, and gentamycin. Conclusion: The prevalence of SIHP is increasing among S. aureus. The prevalence of the PVL gene is higher in SIHP, and it is associated with the presence of MRSA.