Frequency of antimicrobial resistance among invasive and colonizing Group B streptococcal isolates.

BACKGROUND: Group B Streptococcus (GBS) remains susceptible to penicillin, however, resistance to second-line antimicrobials, clindamycin and erythromycin, has increased since 1996. We describe the age-specific antibiotic susceptibility profile and capsular type distribution among invasive and colonizing GBS strains. METHODS: We tested 486 invasive GBS isolates from individuals of all ages collected by a Wisconsin surveillance system between 1998 and 2002 and 167 colonizing strains collected from nonpregnant college students during 2001 in Michigan. Antimicrobial susceptibility testing was performed by disk diffusion or Etest and capsular typing was performed using DNA dot blot hybridization RESULTS: 20.0% (97/486) of invasive and 40.7% (68/167) of colonizing isolates were resistant to clindamycin (P < .001) and 24.5% (119/486) of invasive and 41.9% (70/167) of colonizing isolates were resistant to erythromycin (P < .001). Similarly, 19.8% (96/486) of invasive and 38.3% (64/167) of colonizing isolates were resistant to both antimicrobial agents (P < .001). 29.4% (5/17) of invasive isolates from persons 18-29 years of age and 24.3% (17/70) of invasive isolates from persons 30-49 years of age were resistant to clindamycin. Similarly, 35.3% (6/17) of invasive isolates from persons 18-29 years of age and 31.4% (22/70) of invasive isolates from persons 30-49 years of age were resistant to erythromycin. 34.7% (26/75) of invasive isolates from persons < 1 year of age were capsular type Ia, whereas capsular type V predominated among isolates from adults. CONCLUSION: Clindamycin and erythromycin resistance rates were high among isolates colonizing nonpregnant college students and invasive GBS isolates, particularly among the colonizing isolates. Susceptibility profiles were similar by age although the proportion of clindamycin and erythromycin resistance among invasive isolates was highest among persons 18-49 years of age. Increasing antimicrobial resistance has implications for GBS disease treatment and intrapartum prophylaxis among penicillin intolerant patients.

Prevalence of group B streptococcus colonization and potential for transmission by casual contact in healthy young men and women.

Group B Streptococcus (GBS) causes disease in newborns, pregnant women, and adults with underlying medical conditions, but it is also a commensal organism that commonly colonizes the bowel. In this study, the prevalence of colonization was high among 241 women (34%) and 211 men (20%) living in a college dormitory; sexually experienced subjects had twice the colonization rates of sexually inexperienced participants. Other predictors of colonization varied by colonization site. Only 10 of the 142 roommate pairs had roommates who were both colonized with GBS, and 20% of these pairs shared identical strains, which is the same rate predicted by the population distribution. By contrast, a previous report found that 86% of co-colonized sex partners shared identical strains. GBS is likely transmitted by intimate contact, but transmission modes may vary by colonization site. Large prospective studies are needed to better understand colonization site-specific factors for GBS and to clarify potential transmission modes.

Comparison of DNA dot blot hybridization and lancefield capillary precipitin methods for group B streptococcal capsular typing.

Group B streptococci (GBS) (Streptococcus agalactiae) are a major cause of sepsis and meningitis in neonates and infants and of invasive disease in pregnant women, nonpregnant, presumably immunocompromised adults, and the elderly. Nine GBS serotypes based on capsular polysaccharide antigens have been described. The serotype distributions among invasive and colonizing isolates differ between pediatric and adult populations and have changed over time. Thus, periodic monitoring of GBS serotype distributions is necessary to ensure the proper formulation and application of an appropriate GBS vaccine for human use and to detect the emergence of novel serotypes. Since the mid-1990s, the proportion of GBS isolates that are nontypeable by standard serologic methods has increased, creating a need for more sensitive typing methods. We describe a typing method that uses DNA dot blot hybridization with probes generated by PCR from the GBS capsular genes for serotypes Ia, Ib, and II to VIII. PCR primers were designed to amplify type-specific GBS capsular gene sequences. Gene probes were constructed from the PCR products and used to classify isolates based on hybridization profiles. A total of 306 previously serotyped invasive and colonizing isolates were used to compare our dot blot capsular typing (DBCT) identification method with Lancefield serotyping (LS). A dot blot capsular type was assigned to 99% (303 of 306) of the isolates, whereas 273 of 306 isolates (89%) were assigned a Lancefield serotype. The overall agreement between the methods was 95% (256 of 270 isolates typeable by both methods). We conclude that the DBCT method is a specific and useful alternative to the commonly used LS method.