Species Identification and Antibiotic Susceptibilities of Coagulase- Negative Staphylococci Isolated from Urinary Tract Infection Specimens

Abstract

Objective: To determine the incidence of Coagulase- negative S. aureusin urinary tract infections and sensitivities of these isolates to antimicrobial agents.

Study design: Cohort study.

Place and duration of study: Dr. Essa Laboratory and Immunology and Infectious Disease Research Laboratory (IIDRL), Microbiology Department, University of Karachi, from January 2009 to January 2010.

Methodology: Urine specimens, suggestive of urinary tract infection (UTI), were identified. Speciation of isolates was done using API-20 Staph.system. Screening of extracellular products was done using SDS-PAGE electrophoresis and Hemolysin on blood-agar plates. Minimum inhibitory concentration (MICs) of antibiotics was estimated by microtiter well plate method. Frequency and percentages were determined and chi-square test was used for comparing proportions with significance at p < 0.05.

Results: Coagulase - negative S. aureus(CONS) were the cause of urinary tract infection in 56 out of 1866 outpatient (3%) and 164 of 1261 inpatient (13%), urinary tract infections (p < 0.001). Two hundred and twenty CONS isolates were identified. The most common CONS identified was S. saprophyticus (31%, 68 strains). The relative frequency of Coagulase - negative S. aureuswas 6% (13 strains). All isolates were sensitive to Vancomycin and Linezolid. Resistance was 69% to Ampicillin, 53% to Methicillin, and 37.5% to Ciprofloxacin.

Conclusion: CONS are a potential uropathogens, with capability of slime production and resistance to common empirical prescriptions. This also warrants formulation of an appropriate antibiotic policy that covers CONS.