Comparison between optochin and rifampicin tests to assess mutation rate in Streptococcus pneumoniae

CORTES, P., PIÑAS GE., ALBARRACÍN ORIO A., Y ECHENIQUE, J.

MAR DEL PLATA

Encuentro; XLIII REUNION ANUAL SOCIEDAD ARGENTINA DE INVESTIGACION EN BIOQUIMICA Y BIOLOGIA MOLECULAR; 2007

SAIB

Rifampicin test is the most common assay to assess mutation rate in bacteria. Here, we evaluated the subinhibitory concentration (SIC) effects on the mutation rate of using an additional assay, the optochin test. Three capsulated strains were exposed to SIC of penicillin, chloramphenicol and erythromycin (corresponding to 75% of each minimum inhibitory concentration) for 2 hours, and the mutation rate to optochin and rifampicin was determinated. While optochin test showed that the exposure only to penicillin increased the mutation rate between 2.0-3.2 fold for all three strains, we could not detect this phenomenon using the classical rifampicin test. With the purpose to investigate the cause of this difference, we analysed the and point mutations (that conferred optochin and rifampicin resistance, respectively) in the optochin- and rifampicin-resistant strains generated by penicillin exposure. We found differences in the GC content corresponding to the 20 pair bases surrounding the point mutation that conferred rifampicin or optochin resistance, suggesting that it could influence the repair efficiency, and in consequence, the mutation rate. We proposed that optochin test was more appropriated than the rifampicin test to detect transient hypermutator state in and it should be considerate for further mutability analysis