RESUMO
BACKGROUND: Group B streptococcus, or Streptococcus agalactiae, is a grampositive coccus related to infections in the mother and the newborn during peri and postnatal period. OBJECTIVE: To describe the prevalence of S. agalactiae serotype III and the susceptibility to antimicrobials in strains isolated from pregnant women. MATERIAL AND METHODS: Cultures from vagina, rectum, and urine were taken from 123 high risk pregnant women, who attended to a Gynecology and obstetrics hospital from June 1st to August 30, 2000. Samples were cultured on 5% sheep blood agar and selective broth. For comparison purposes, we also studied 25 S. agalactiae strains from non-pregnant women isolated from January 2000 to August 2001. Serotyping was performed by latex agglutination and susceptibility testing by Kirby Bauer method. RESULTS: The prevalence of S. agalactiae carriers in pregnant women was 13% and the serotypes were: I (58.8%), II (29.4%), III (5.9%) and non typeable (5.9%). Serotypes from non-pregnant women were: I (68%), II (4%), and III (28%). In both groups, the intermediate resistance to penicillin was 17.6 and 12%, whereas for ceftriaxione was 17.6 and 20% respectively. Resistance to both clindamycin and erythromycin was lower than 4%. CONCLUSIONS: The prevalence of S. agalactiae in pregnant women was low and similar to other studies reported in Mexico. Serotype I was the most frequently isolated. Resistance to clindamycin and erythromycin was low, whereas intermediate resistance to penicillin and ceftriaxone was high. The low prevalence of both Streptococcus agalactiae and associated infections in Mexico could be related to racial factors or immunity due to early exposure to that bacterium.