Effects of penicillin and erythromycin on adherence of invasive and noninvasive isolates of Streptococcus pyogenes to laminin

This study investigated the possible relationship between the invasiveness of group A Streptococcus (GAS) strains and their abilities to adhere to laminin and assessed the effects of subinhibitory concentrations of penicillin and erythromycin on the ability of GAS to adhere to laminin. The adherence of noninvasive and highly invasive isolates of GAS to laminin was significantly higher than the adherence displayed by isolates of low invasiveness. Antibiotic treatment caused significant reductions in adherence to laminin in all three groups of strains. Penicillin was more successful in reducing the adherence abilities of the tested GAS strains than erythromycin.

Epidemiology of diseases caused by Streptococcus pyogenes in Serbia during a nine-year period (1991-1999).

BACKGROUND & OBJECTIVES: Streptococcus pyogenes (group A Streptococcus - GAS) is an important human pathogen which causes a variety of diseases, including tonsillopharyngitis, scarlet fever and rheumatic fever. It is important to understand the changes in epidemiology of the diseases caused by the pathogen for improved control of such infections. Hence, the aim of the present study was to carry out an epidemiological analysis of GAS infections in Serbia in a 9-yr period (1991-1999) and evaluation of susceptibility of GAS isolates obtained during the same period to penicillin and erythromycin. METHODS: Occurrence of tonsillopharyngitis, scarlatina and rheumatic fever was analyzed and GAS carrier status in healthy children was examined over a 9-yr period from 1991 to 1999. Susceptibility to penicillin and erythromycin was determined for 1657 GAS isolates obtained from patients diagnosed with pharyngitis or scarlet fever and 512 isolates from healthy carriers. M-type antigen was also determined in these isolates. RESULTS: The average incidences of tonsillopharyngitis and scarlet fever were 76.2 and 30.8 per cent respectively. A total of 166 cases of rheumatic fever were registered. Per cent of carriers varied from 5.5 to 11.4 per cent over the study period. Predominating M serotypes among GAS isolates tested were M1, M3, M4, M6, M11, M12 and M18, depending on the source of clinical material and period of isolation. Antimicrobial susceptibility testing showed susceptibility to penicillin in all isolates tested and resistance to erythromycin in 2.41 per cent of the isolates. INTERPRETATION & CONCLUSION: Although the fluctuations in incidence were noted during the nine-year period, the incidence of streptococcal tonsillopharyngitis is low but with a steady raise in Serbia. No significant changes in the incidence of scarlet fever and rheumatic fever were noted. Susceptibility to penicillin remained unchanged, but the number or erythromycin resistant strains have increased.

Influence of decreased penicillin susceptibility on growth rate of beta haemolytic streptococci.

BACKGROUND & OBJECTIVES: Beta haemolytic streptococci (BHS), especially group A are still highly susceptible to penicillin. One possible explanation for this could be reduced growth capability in penicillin resistant BHS mutants. The present study was therefore undertaken to analyze the growth rates of BHS with decreased susceptibility to penicillin. METHODS: Serial passages in the medium with subinhibitory concentration of penicillin were done to induce resistance to this antibiotic in 12 clinical isolates of BHS serogroups A, B, C, and G. Both penicillin susceptible (parental) and variants with decreased susceptibility to penicillin (laboratory strains) were grown in three different media and their growth rates were determined by counting the number of bacterial colonies and by measuring optical density of bacterial culture. RESULTS: The lowest increase in minimal inhibitory concentration (MIC) value for penicillin (8-16 times) was obtained in BHS group A isolates, while the increase in MIC values of BHS groups B, C and G strains was higher (64-128 times) and they reached the level of complete resistance. Laboratory variants differed significantly from parental in their morphological and cultural characteristics. There were no statistically significant differences between the growth rates of penicillin susceptible and variants with decreased susceptibility to penicillin, though a delay in multiplication of the laboratory strains during exponential phase of growth was noted. INTERPRETATION & CONCLUSION: Though significant differences in phenotypic characteristics of penicillin susceptible and laboratory variants were noted, the results of this study provides no support to the assumption that variants of BHS with decreased susceptibility to penicillin of BHS were incapable for normal growth. Further studies needs to be done to find out the association between the decreased susceptibility to penicillin in the BHS and decreased growth capability in these bacteria.