Résumé
A total of 156 recent distinct isolates of Group B streptococcus [GBS] were recovered from clinical specimens of female patients at Madinah Maternity and Children Hospital and King Khalid University Hospital, Saudi Arabia. Serotyping results revealed that 96 percent of the strains were serotypable and the most frequent serotypes were III, II, and Ia which accounted for 35.26, and 15 percent strains respectively. Whereas serotypes Ib, IV, and V constituted 9, 7, and 4 percent respectively. The minimum inhibitory concentrations [MIC] of antibiotics against GBS isolates were determined by an agar dilution method. All GBS strains were susceptible to 0.125 mg/L of either penicillin, ampicillin, erythromycin, or clindamycin. Whereas at 0.06 mg/L the inhibitory effect of these antibiotics were 80, 69, 45, and 86 percent respectively. Cefoxtin, gentamicin, and tetracycline, however, showed remarkable variation in their activities. The majority of GBS strains showed intermediate susceptibility towards cefoxitin, whereas 35 and 77 percent of the isolates were resistant to gentamicin [GM] and tetracycline [Tc] respectively. The genetic basis of Tc-resistance was investigated was investigated. No plasmids were detected among the randomly selected different GBS sterotypes resistant to Tc. However, in all cases EcoRI- digested chromosomal DNA from resistant strains hybridized with the used tet-gene probe [ATCC 37234] of Kpnl/Hpal 0.39 [Kb] fragment. No differences were detected between GBS strains of various origin. No resistance to penicillin or ampicillin was found, nor was penicillinase production demonstrated. Yet tolerace to penicillin was found among GBS strains as tested by penicillinase-disk diffusion, penicillin-gradient replica plating and quantitative killing curves methods. Data of the latter method showed that 21 strains [14 percent] were tolerant to penicillin. Results suggest that penicillin tolerance is not rare among strains of GBS isolated in our hospitals and its routine testing may be warranted