Iodine test for express estimation of beta-lactamase activity in isolates of Staphylococcus aureus

Background. Beta-lactamases are widely spreadin methicillin-susceptible Staphylococcus aureus (MSSA) isolates and confer this pathogen spenicillin-resistance. At the same time 50% of isolates that are penicillin-susceptible in disk diffusion test are beta-lactamase producers. Antibiotic resistance evaluation is time-consumin gand prolongs the process of adequate treatment prescribing. So the introduction of express-tests for antibiotic resistance evaluation is an actual problem. The aim of this study. The estimation of iodine test sensitivity for penicillin susceptibility and potential beta-lactamase activity in staphylococci (i.e. isolates with beta-lactamase operon in their genomes). Materials and methods. Beta-lactamase activity of 81 MSSA clinical isolates was evaluated by iodine test with preliminary stimulation of beta-lactamase production and without it. To estimate the sensitivity and specificity of this method for identification of penicillin-resistant isolates and potential beta-lactamase producers the results of the iodine test were compared with the data about beta-lactamase operon presence in isolates genomes recived in real-time PCR and statements of penicillin-resistance in disk diffusion test. Results. Iodine test was highly sensitive for identification penicillin-susceptible MSSA isolates. The sensitivity of iodine test for penicillin-resistant is olates was 61% if the test was formed without preliminary stimulation or 86% if the test was performed after stimulation. In the same time iodine test was low-sensitive for isolates that contain beta-lactamase operon in their genomes identification, the iodine test sensitivity in this case was less than 63%. So iodine test without preliminary stimulation maybe regarded as possible screening method for penicillin-susceptible MSSA identification immediately after pathogen isolation, that will be helpful to decrease the time-loss for decision making in antibiotic treatment choose. Conclusion. Despite the low sensitivity of iodine test for identification of beta-lactamase operon containing MSSA, this method is attractive for fast identification of penicillin-resistance in S. aureus.

Staphylococcus aureus, Staphylococcus aureus, beta-lactamase, antibiotic resistance, diagnosis