[Is penicillin still the drug of choice in the treatment of diseases caused by beta-hemolytic streptococci?].

During the last ten years a new pathomorphosis of streptococci was noticed and described in the USA, Europe and New Zealand. It was expressed by the rise of virulence of beta haemolytic streptococci (BHS) and development of new clinical and epidemiological features. In such circumstances it appears to be very relevant to examine the susceptibility of BHS to penicillin, which is still considered as a drug of choice for the most of streptococcal diseases. Therefore it was decided: 1. to make an analysis of continuous susceptibility testing of BHS to penicillin and 2. to test the possibility of induction and selection of penicillin resistant mutants in vitro. Penicillin susceptibility was examined by broth dilution method Penicillin tolerant strains were separated on the basis of MBC/MIC ratio MBC/MIC > 16 and construction of "killing curves". The possibility of induction and selection of penicillin resistant mutants was tested by subcultivation technique. MIC values for BHS groups: A, B, C and G were: 0.015, 0.060, 0.015 and 0.030 micrograms/ml respectively. The percentage of penicillin tolerant strains was in the range of 3% for group A BHS to 33% for group G BHS. After 60 subcultures in liquid medium containing increasing concentrations of penicillin. MIC values were raised by 2-32 times in comparison with parental strains. As the maximal induced MIC values were 1 and 2 micrograms/ml (one group G and three groups B BHS strains) it can be concluded that BHS at least in vitro expressed penicillin resistance. Although the obtained results are encouraging (there is so far no penicillin resistant clinical isolates), the increasing percent of penicillin tolerant strains and the possibility to induce penicillin resistance in vitro should be considered as a very serious warning. That makes further investigation of the development of penicillin tolerance and resistance mechanisms very current.