Epidemiology and Antimicrobial Susceptibility Patterns of staphylococcus aureus Isolates from Clinical Specimens at Meru Teaching and Referral Hospital, Kenya

Objective: To determine the prevalence of S. aureus among clinical specimens processed at MeTRH and assess the antimicrobial susceptibility patterns and proportion of MRSA among confirmed isolates. Methods: A retrospective descriptive cross-sectional study was conducted using microbiology laboratory records for clinical specimens submitted for bacteriological culture at MeTRH during the study period. A census approach was used, whereby all eligible laboratory records were included. Clinical specimens were processed using routine microbiological procedures, and suspected S. aureus isolates were identified using conventional methods and the VITEK(R) 2 Compact automated identification system. Antimicrobial susceptibility testing was performed using VITEK(R) 2 Compact, with interpretation based on Clinical and Laboratory Standards Institute criteria. Methicillin resistance was determined phenotypically using cefoxitin susceptibility as the surrogate marker. Data were analysed using frequencies and percentages. Results: A total of 1,082 clinical specimens were analysed, of which 37 yielded S. aureus, giving an overall prevalence of 3.42%. Among the confirmed isolates, 21 (56.8%) were recovered from male patients and 16 (43.2%) from female patients. Pus was the predominant specimen type, accounting for 25 (67.6%) isolates, followed by other specimens at 8 (21.6%) and urine at 4 (10.8%). Antimicrobial susceptibility varied considerably. Resistance was highest to benzylpenicillin and amoxicillin, with 100% resistance among tested isolates. Resistance to amoxicillin-clavulanic acid was 75.0%, while 63.3% of isolates tested were resistant to oxacillin. Susceptibility was relatively high to gentamicin (82.8%), ciprofloxacin (77.3%) and clindamycin (75.0%). All isolates tested against linezolid and vancomycin were susceptible. Among 30 isolates with methicillin susceptibility results, 19 (63.3%) were classified as MRSA and 11 (36.7%) as methicillin-susceptible S. aureus (MSSA). Conclusion: The prevalence of S. aureus among clinical specimens processed at MeTRH was relatively low; however, a substantial proportion of isolates demonstrated antimicrobial resistance, particularly to commonly used {beta}-lactam antibiotics. The high proportion of MRSA is of clinical and public health importance. Routine antimicrobial susceptibility testing, hospital-specific antibiograms, antimicrobial stewardship and strengthened infection prevention and control measures are recommended to support appropriate treatment and limit the spread of resistant S. aureus.