A longitudinal, three-year study of the epidemiology of group B Streptococcus was conducted with repeated (four to 11) observations of 382 patients followed through pregnancy, delivery, and the postpartum period. Group B streptococci (2.3% of which were nonhemolytic) were isolated from the birth canal at first visit from 15% of the patients and from 28% with repeated cultures. Overall, group B streptococci were isolated at 12% of culture visits. Streptococcal carriage was significantly less common among patients who were Mexican-American, 20 years old or older, or in a fourth or later pregnancy. Multivariate analysis indicated that each of these three factors had a significant, independent bearing upon carriage of group B streptococci. Of 108 patients harboring these organisms in the birth canal, 36% could be classified as chronic, 20% as transient, and 15% as intermittent carriers. The relationship of infant colonization to the presence of streptococci in the birth canal at delivery and not to previous or subsequent carriage by the mother was consistent with the observation that maternal colonization was often inconstant.

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The minimal inhibitory concentrations of penicillin against 96 strains of group B streptococci and of methicillin against 10 strains of Staphylococcus aureus were unrelated to the growth phase of test bacteria. However, the minimal bactericidal concentrations were significantly higher in the stationary phase than the logarithmic phase for both organisms (P < 0.001 and < 0.05, respectively).The in vitro determination of bacterial susceptibility to antimicrobial agents is commonly done by disk diffusion. More quantitative determination of growth-inhibiting activity (minimal inhibitory concentration; MIC) is accomplished by agar or broth dilution, and determination of bacterial-killing activity (miniimal bactericidal concentration; MBC) is accomplished by a modification of the latter. Although there have been attempts at standardization of these procedures, various methods have been recommended for the preparation of the bacterial inoculum. These include logarithmic, early-stationary, and overnight cultures to be appropriately diluted as the inoculum for the dilution tests (2, 5, 7). In studies of antibiotic tolerance of group B streptococci, we observed that normal, nontolerant organisms were killed more rapidly when exposed to penicillin in the logarithmic phase of growth than when tested after overnight incubation (K. S. Kim and B. F. Anthony, Pediatr. Res. 14:560, abstr. no. 808, 1980). The present study extends these observations to examine the effect of the bacterial growth phase on the MICs and MBCs of penicillin against group B streptococci and of methicillin against Staphylococcus aureus.Ninety-six strains of group B streptococci were shown to be nontolerant for penicillin. Briefly, the criteria for tolerance were (i) delayed killing by penicillin concentrations of 16 times the MIC during the logarithmic phase of growth, (ii) additive rather than synergistic response to penicillin-gentamicin combinations, and (iii) relatively deficient autolytic enzyme activity (Kim and Anthony, Pediatr. Res. 14:560, abstr. no. 808, 1980). The organisms were isolated from either blood or cerebrospinal fluid of septic infants at the Harbor-UCLA Medical Center, the University of Minnesota Hospitals, the University of Alabama Medical Center, and the Charity Hospital of Louisiana. They were grouped and typed by the methods of Lancefield (4) and Wilkinson et al. (8) with sera provided by the Centers for Disease Control, Atlanta, Ga. Ten strains of penicillin-resistant S. aureus were isolated from blood cultures at Harbor-UCLA Medical Center and identified on the basis of colonial morphology, Gram strain, and coagulase reaction. The presence or absence of tolerance was not determined.Potassium penicillin G in a potency of 1,595 U/mg and sodium methicillin in a potency of 890 ug/ml (Bristol Laboratories, Syracuse, N.Y.) were dissolved at a concentration of 1 and 10 mg/ml, respectively, in sterile distilled water, passed through a 0.45-ytm pore filter (Gelman Instrument Co., Ann Arbor, Mich.), and stored in aliquots at -70°C fo...

Serial observations including cultures of the upper respiratory tract and of infected skin lesions and streptococcal antibody determinations were made over a two-year period in a semi-closed population of children between 10 months and 15 years of age. There was a high prevalence of group A streptococci in nose and throat cultures and of skin lesions containing these organisms. Almost 90% of the study population developed streptococcal impetigo during the study period. A slightly higher proportion of males than females developed skin infection but there was no relationship to age. Impetigo was observed throughout the calendar year, exceeding 12% of child-visits in one winter month, but was generally more common in the summer and fall. Conversely, group A streptococci were more often isolated from nose and throat cultures in the winter months. The increase in recovery of streptococci from nose and throat cultures lagged behind the increase in streptococcal impetigo and continued into the winter months, when the prevalence of impetigo had declined. Calculation of ratios for individual streptococcal serotypes isolated from different body sites revealed a clear cut distinction between "respiratory" and "impetigo" serotypes, with respect to both prevalence and acquisition rates. Respiratory serotypes were more commonly isolated in the winter and impetigo serotypes in the summer and fall. Significant antibody responses to extracellular antigens of the streptococcus were documented for pharyngeal acquisitions of both impetigo and respiratory serotypes and for skin lesions associated with impetigo serotypes. Group A streptococcal serotypes may be divided into three categories on the basis of their human pathogenicity for body sites: some with the potential for respiratory infection, others with the potential for skin infection and a few unusual serotypes with the potential for infecting both sites.

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