Abstract
BACKGROUND: Bloodstream infections caused by Staphylococcus aureus (S. aureus) and its methicillin-resistant S. aureus (MRSA) represent a major clinical challenge, contributing to prolonged illness, increased healthcare costs, and high mortality worldwide. In low-resource settings, these infections are further aggravated by overcrowding, poor sanitation, and limited access to healthcare. Mukuru, the second-largest informal settlement in Nairobi, Kenya, is characterized by such socioenvironmental conditions, which plausibly facilitate the transmission and persistence of antimicrobial-resistant pathogens, including MRSA. Therefore, the aim of the study was to characterize the phenotypic and genotypic antibiotic resistance patterns of S. aureus isolated from outpatient blood samples collected in Mukuru Slum settlement. METHODS: This cross-sectional study analyzed blood samples collected from outpatients in Mukuru informal settlement. S. aureus isolates were identified using standard microbiological cultures and biochemical tests. Antimicrobial susceptibility testing (AST) was performed using the Kirby-Bauer disk diffusion method against a panel of 10 antibiotics. The molecular detection of antimicrobial resistance genes (mecA, mecC, gyrA, gyrB, and tetM) was conducted using polymerase chain reaction (PCR), agarose gel electrophoresis, and sequencing (mecA). RESULTS: A total of 53 S. aureus isolates were recovered. Phenotypic resistance rates were sulfamethoxazole-trimethoprim (54.7%), ampicillin (50.9%), cefoxitin (37.7%), tetracycline (35.9%), ciprofloxacin (28.3%), gentamicin (28.3%), amoxicillin-clavulanic acid (28.3%), and erythromycin (18.9%). Multidrug resistance (MDR) was observed in 35.8% of the isolates. Genotypic analysis revealed that 82.4% of the cefoxitin-resistant MRSA isolates harbored the mecA gene, while mecC was not detected. Among ciprofloxacin-resistant isolates, 91.7% possessed the gyrA gene and 75.0% carried gyrB. The tetM gene was detected in 60.0% of tetracycline-resistant isolates. CONCLUSION: The study reveals a high prevalence of MDR S. aureus and MRSA in the study population, driven by significant resistance to commonly prescribed antibiotics such as penicillin and trimethoprim-sulfamethoxazole. The strong concordance between phenotypic resistance and the presence of mecA, gyrA, and tetM genes underscores the genetic basis of resistance in this setting. These findings highlight the urgent need for enhanced antimicrobial stewardship and infection control measures in informal settlements.