Phenotypic and genotypic detection of antimicrobial resistance and virulence factors among Staphylococcus aureus clinical isolates

Abstract

Background: Staphylococcus aureus (S. aureus) is a world-wide nosocomial and community-acquired infectious agent. This study aimed to determine the prevalence rate of S. aureus infections with assessment of their antibiotic susceptibility patterns and virulence profiles using available phenotypic and genotypic methods. Methodology: Staphylococcus aureus isolates were collected and identified by conventional methods. Antimicrobial susceptibility testing was done and interpreted according to Clinical and Laboratory Standards Institute guidelines (2022) followed by macrolide lincosamide streptogramin B (MLSB) phenotyping by D test. Detection of staphylococcal virulence (hla and etb) and antibiotic resistance (ermB and msrA) genes were also done. Results: Out of 152 S. aureus isolates, 84 (55.3%) and 68 (44.7%) were methicillin resistant (MRSA) and methicillin susceptible S. aureus (MSSA) respectively. Almost all MRSA isolates were beta hemolytic and susceptible to linezolid, streptogramins (100% for each) vancomycin (95.2%) and ceftaroline (90.5%). About 84.5% and 45.2% of MRSA compared to 36.8% and 27.9% of MSSA were resistant to erythromycin and clindamycin respectively. Regarding MLSB phenotyping 44%, 9.5% and 31% of MRSA and 28.1%, 1.5% and 10.3% of MSSA were constitutive cMLSB, inducible iMLSB and MSB phenotypes respectively. hla, erm B and msrA genes were detected in 91.7%, 10.7% and 1.2% of MRSA isolates respectively. While etb gene was not detected at all among them. Conclusion: Methicillin and MLSB resistance among S. aureus are concerning. Therefore, great efforts should be made for their accurate detection in hospital settings. Proper antibiotic stewardship program is strongly recommended to keep the benefit of antibiotics with acceptable susceptibility pattern.