Correlation between beta-lactamase production and MIC values against penicillin with coagulase negative staphylococci

Two hundred strains of coagulase negative staphylococci (CNS) isolated from various clinical specimens (116) and healthy hospital personnel (84) were investigated for the production of beta-lactamases by means of three iodometric techniques and correlated with the minimum inhibitory concentration (MIC) values of penicillin-G by agar dilution technique and disc diffusion technique. One hundred and fifty (75.0%) of the 200 strains tested produced beta-lactamases. Seventy two per cent of the CNS were found to be beta-lactamase positive by the starch paper technique which was the most sensitive one in our study. The MIC values of penicillin against CNS ranged from less than or equal to 1.25 to greater than or equal to 2000 units. The present study indicated the higher prevalence of beta-lactamase producers with increased penicillin resistance among CNS strains isolated from healthy carriers and hospitalised patients.