Beta-Lactamase Production in Staphylococcus Aureus from Urine of Symptomatic and Asymptomatic Subjects in Keffi, Nigeria

Staphylococcus aureus is a common pathogen associated with urinary tract infection. The production of beta-lactamase by S. aureus from urine of symptomatic and asymptomatic subjects in Keffi, Nigeria was investigated. Urine samples were collected from patients with suspected cases of urinary tract infection (UTI) attending two health facilities in Keffi; and asymptomatic volunteering students, staff and others within and around the Nasarawa State University Keffi main campus. Staphylococcus aureus were isolated from the urine samples using standard cultural, microscopical and biochemical methods. Antibiotic susceptibility testing and minimum inhibitory concentration (MIC) were evaluated as described by the Clinical and Laboratory Standards Institute (CLSI). Beta-lactamase production was evaluated by iodometric methods. A total of hundred (100) isolates (50 symptomatic, 50 asymptomatic) were isolated from the urine samples. Symptomatic isolates had susceptibility which decreased as follows: streptomycin (86%) > gentamicin (84%) and erythromycin (84%) > rifampicin (80%) > norfloxacin (78%) > amoxicillin (70%) and chloramphenicol (70%) > levofloxacin (68%) > ciprofloxacin (60%) > ampicillin (58%). Asymptomatic isolates had susceptibility which decreased as follows: gentamicin (92%), streptomycin (92%) and rifampicin (92%) > erythromycin (88%) > ciprofloxacin (84%) > levofloxacin (80%) > norfloxacin (78%) > chloramphenicol (76%) > amoxicillin (72%) and ampicillin (72%). The differences in the susceptibility of symptomatic and asymptomatic isolates to the antibiotics tested were insignificant (p > 0.05).The MICs of amoxicillin against amoxicillin resistant S. aureus isolates for 50% and 90% of for symptomatic isolates were ≤ 8 μg/ml and ≤ 16 μg/ml respectively; for asymptomatic isolates, the MICs for 50% and 90% isolates were ≤ 34 µg/ml and ≤ 64 µg/ml respectively. Beta-lactamase was detected in 4 (23.5%) and 5 (35.7%) of amoxicillin resistant symptomatic and asymptomatic isolates respectively. Molecular characterization of beta-lactamase genes in these amoxicillin resistant S. aureus isolates from Keffi is on-going.