Betalactamase production of Staphylococcus aureus: a comparison study of different iodometric methods

ABSTRACT

This study was undertaken to detect Beta-lactamase producing Staphylococcus aureus among healthy individuals by using different iodometric methods [filter paper, agar plate and tube]. The study was carried out among 127 normal healthy volunteers of Gulf Medical University and Gulf Medical College Hospital and Research Center, Ajman. Nasal and throat swabs were collected with strict aseptic precautions. All the swabs were examined by direct microscopy and inoculated into appropriate culture media. Staphylococcus aureus was identified by tube coagulase test and growth on MSA. Beta-lactamase enzyme activity of Staph. aureus was determined by the filter paper, agar plate and tube lodometric methods. Antimicrobial susceptibility testing by Kirby-Bauer's method was performed for all Beta-lactamase producing Staph. aureus. Out of 127 healthy volunteers screened, Staph. aureus were isolated from the nasal and throat swabs from 62 subjects. Of the 62 Staph. aureus isolates, 40 [64.5%] were positive by all the three iodometric methods. Six isolates [9.6%] were positive by two methods [4 isolates by filter paper and tube methods, one isolate by filter paper and agar plate methods and one isolate by agar plate and tube methods]. Four isolates [6.4%] were positive by one of these methods. Twelve isolates [19.4%] were totally negative by all the three methods. Overall susceptibility of filter paper and tube methods were found to have similar results 45 [72.5%]. Whereas the overall susceptibility of agar plate method was 42 [67.7%]. Antimicrobial susceptibility was 100% to Vancomycin and Rifampicin, and 100% resistance to Penicillin and Ampicillin. The study indicates that the filter paper and tube iodometric methods were accurate and superior to the agar plate method in the detection of Staphylococcal Beta-lactamase. We conclude that the alarming prevalence rate of Beta-lactamase among normal healthy individuals indicates the need for treatment by Beta-lactamase-susceptible antibiotics