A concentração mínima inibitória e os efeitos pós-antibióticos (EPA) de um agente antimicrobiano são parâmetros que devem ser levados em consideração quando da determinação do esquema de dosagem. Os efeitos pós-antibióticos in vitro na hidrofobicidade de superfície celular e na aderência foram pesquisados em uma amostra de estreptococos do grupo B. A exposição do microrganismo por 2 h a 37 °C a 1 x CMI de penicilina induziu um EPA de 1,1 h. A carga da superfície celular da bactéria foi alterada significativamente durante a fase pós-antibiótica revelada através da capacidade de ligação ao xileno, indicada pela diminuição da hidrofobicidade. A aderência bacteriana às células epiteliais bucais humanas também foi reduzida. Os resultados da investigação demonstram que estudos clínicos destinados a determinar regimes terapêuticos deveriam incluir o conhecimento da fisiologia bacteriana durante o período pós-antibiótico.

The minimum inhibitory concentration and post-antibiotic effects of an antimicrobial agent are parameters to be taken into consideration when determining its dosage schedules. The in vitro post-antibiotic effects on cell surface hydrophobicity and bacterial adherence were examined in one strain of group B streptococci. Exposure of the microorganism for 2 h at 37 °C to 1 x MIC of penicillin induced a PAE of 1.1 h. The cell surface charge of the Streptococcus was altered significantly during the post-antibiotic phase as shown by its ability to bind to xylene: hydrophobicity was decreased. Bacterial adherence to human buccal epithelial cells was also reduced. The results of the present investigation indicate that studies designed to determine therapeutic regimens should evaluate the clinical significance of aspects of bacterial physiology during the post-antibiotic period.

Penicillin tolerance among 67 strains of beta-hemolytic streptococci was examined by determining the ratio of the minimal bactericidal concentration to the minimal inhibitory concentration as 32 or greater. Tolerance was demonstrated in 15 group A strains and in 11,7, and 4 of groups B, C and G, respectively. Thereafter the effects of a subminimal inhibitory concentration (1/2MIC) of penicillin on the bacterial products of four tolerant and four nontolerant strains (two of each Lancefield group) were analyzed and compared. The antibiotic caused a marked increase in the expression of the group carbo-hydrates for strains of group B. Penicillin was found to reduce the cell-bound hemolysin activities of the four tolerant strains and to increase the activity of the other (free) form of nontolerant groups A, C and G hemolysins. Penicillin caused an increase in the extracellular hyaluronidase activities of one group A and groups B, C and G streptococci. With added antibiotic the production of deoxyribonuclease by tolerant groups A, C and G was greatly enhanced and that of the group B streptococcus was arrested.

O efeito de concentrações subinibitórias de penicilina sobre a produção do antígeno grupo-específico e da hialuronidase extracelular foi avaliado em uma amostra de estreptococo pertencente ao grupo G de Lancefield. Em todas as concentrações uma maior quantidade de antígeno grupo-específico foi extraída das células e a atividade específica de hialuronidase se mostrou aumentada em até 1400% nos sobrenadantes das culturas. O maior aumento na expressão de ambos os antígenos foi observado em 1/2 da CMI.

The effect of subinhibitory concetrations of penicillin on a strain of streptococcus belonging to Lancefield group G was studied. Production of the group-specific antigen and extra- cellular hyaluronidase by drug-exposed cells were examined. At all concentrations levels a higher amount of group-specific antigen was extracted from cells and increases of up to 1400% in the specific activity of hyaluronidase were determined in culture supernates. The higher increase in the expression of both antigens was observed at 1/2 MIC.