Antibiotic resistance patterns and molecular characterization of Staphylococcus aureus in diverse human infections

H. K. Judi; H. H. Naser

doi:10.15421/0225103

H. K. Judi University of Al-Qadisiyah
H. H. Naser University of Al-Qadisiyah

Keywords: Staphylococcus aureus, antibiotic resistance, multidrug resistance (MDR), PCR detection.

Abstract

This study examined the prevalence, antibiotic resistance profiles, and molecular mechanisms of Staphylococcus aureus in human clinical infections, including wound, burn, mastitis, and otitis media samples. A total of 137 clinical samples were co l lected from patients. Samples were cultured on Mannitol Salt Agar and Blood Agar and incubated at 37 °C for 24–48 hours. Antibiotic resistance profiles were determined using VITEK 2 AST-P639 card s , then molecular detection of resistance genes by using the PCR technique. Among 137 clinical specimens, S. aureus was isolated at an overall prevalence of 87. 6 % (120/137), with significant variation across infection types (χ² = 10.04, P = 0.018). The highest prevalence was observed in otitis media (94. 3 %, 33/35) and mastitis (90. 4 %, 47/52), followed by burn (81. 6 %, 31/38) and wound infections (75.0%, 9/12). Antibiotic susceptibility testing revealed near-universal resistance to benzylpenicillin (100 .0 %) and high resistance to oxacillin (57–78%) and erythromycin (57–78%). In contrast, isolates remained fully susceptible to gentamicin, azithromycin, fluoroquinolones (c i profloxacin, ofloxacin), and doxycycline (100% susceptibility). Multidrug resistance (MDR) was widespread (65 .0 %, 78/120 isolates), with the highest proportion in wound infections (77.8%, 7/9) and the lowest in mastitis (57.4%, 27/47), though diffe r ences were not statistically significant (χ² = 4.851, P = 0.183). No extensively drug-resistant (XDR) or pan-drug-resistant (PDR) strains were detected. Molecular analysis identified key resistance genes: mecA (82.1% prevalence in MDR isolates), blaZ (56.4%), NorA (38.5%), and VanA (5.1%). The mecA gene was most prevalent in burn (85.7%, 18/21) and mastitis (81.5%, 22/27) isolates, while VanA was rare across all sources. Statistical analysis showed no significant differences in gene distribution (χ² range: 0.89–1.45, P > 0.05). These findings highlight the persistent challenge of antibiotic resistance in S. aureus infections and underscore the need for targeted therapeutic strategies.

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