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.

Incidence and duration of group B Streptococcus by serotype among male and female college students living in a single dormitory.

Group B Streptococcus causes a variety of morbid and sometimes fatal conditions affecting individuals of all age groups. There are nine known serotypes of this Gram-positive coccus but few estimates of the incidence and duration of its colonization and none by serotype in the literature. In 2001, the authors conducted a prospective cohort study among 257 men and women living in a single dormitory in Ann Arbor, Michigan. The 3-week incidence with any serotype was 11.3% (+/-3.9%) among women and 8.8% (+/-3.0%) among men; 3-week incidence rates were highest for serotype V (4.7% for women and 3.5% for men) and type Ia (2.3% for women and 2.4% for men), with no significant differences by gender. The estimated average duration of any group B Streptococcus colonization was longer for women (13.7 weeks) than men (8.5 weeks); serotype Ia was carried an average of 6.5 weeks longer in women, and serotype III was carried 4.9 weeks longer. Colonization with more than one serotype occurred significantly less than would be expected by chance (p <<< 0.001). Based on the overall incidence, transmission occurred between roommate pairs at the rate expected. Group B Streptococcus colonization is frequent and dynamic, but it is not transmitted by casual contact.

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.

Correlates of antibiotic-resistant group B streptococcus isolated from pregnant women.

Despite antibiotic prophylaxis for at-risk mothers during labor and delivery, group B streptococcus still causes substantial morbidity and mortality among newborns. Resistance to antibiotics recommended for penicillin-allergic pregnant women, such as erythromycin and clindamycin, has increased. A better understanding of factors associated with group B streptococcus resistance is essential to effectively prevent group B streptococcus disease.A total of 117 sequential group B streptococcus isolates were obtained between August 1999 and March 2000 from pregnant women at the University of Michigan Medical Center. Serotype and susceptibility to ten antimicrobials using disk diffusion with E-test for confirmation were determined, and the association between several host factors and colonization with a resistant strain was evaluated. Group B streptococcus was frequently resistant to erythromycin (29%) and clindamycin (21%) but was susceptible to all other antimicrobials tested. A stepwise logistic regression model revealed that black ethnicity (P =.02) and carriage of a serotype V strain (P =.01) were associated with group B streptococcus resistance. Among this population of pregnant women, black ethnicity and serotype V were the strongest predictors of colonization with an erythromycin- or clindamycin-resistant group B streptococcus strain. A better understanding of factors associated with antibiotic resistance is needed to minimize group B streptococcus disease risks and to maximize effective chemoprophylaxis.

Uropathogenic Escherichia coli are more likely than commensal E. coli to be shared between heterosexual sex partners.

Because uropathogenic Escherichia coli are better adapted than other E. coli to the urethra, periurethra, and vagina, the authors reasoned that uropathogenic E. coli would be more likely than commensal E. coli to be shared between sex partners. In this 1996-1999 Michigan study, the genetic identity of E. coli isolated from 166 women with E. coli urinary tract infection (UTI) and 94 women without UTI and their sex partners was determined by pulsed-field gel electrophoresis. Rectal isolates were considered uropathogenic E. coli if genetically identical to the urinary isolate causing UTI. All eight urinary isolates from men with UTI partners were identical to the E. coli found in the urine or vagina of their sex partner. When the 550 unique rectal E. coli isolates from couples were considered the unit of analysis, E. coli that caused UTI were nine times (odds ratio (OR) = 8.87, 95% confidence interval (CI): 5.41, 14.54) more likely than other E. coli to be shared between sex partners. Sharing occurred twice as frequently (OR = 1.87, 95% CI: 1.13, 3.08) if the E. coli had P pili or if the couples engaged in oral sex (OR = 2.09, 95% CI: 1.09, 4.00). Uropathogenic E. coli are more likely than commensal E. coli to be shared with a current heterosexual sex partner. Both sexual behaviors and a bacterial virulence factor, P pili, modified sharing.

Determinants of co-colonization with group B streptococcus among heterosexual college couples.

BACKGROUND: Group B causes morbidity and mortality among newborns, pregnant women, and nonpregnant adults. Among adults, sexual and fecal-oral routes of transmission are hypothesized; this study addresses whether sexual transmission occurs. METHODS: Our outcome of interest was group B. From our investigation of the heterosexual transmission of urinary tract infections among college students at the University of Michigan, conducted in 1996-1999, we identified 120 couples in which one or both partners carried group B. Each partner completed a questionnaire regarding potential risk factors for colonization. RESULTS: Co-colonization with the identical group B strain (as determined by pulsed-field gel electrophoresis) occurred in 86% of the 57 co-colonized couples. When the male sex partner carried group B, 64% of female partners also were colonized; conversely, 49% of male partners of colonized females were colonized with identical strains. Among behaviors predicting co-colonization within the partnership, male-to-female oral sex was a risk factor among both women (odds ratio [OR] = 2.9; 95% confidence interval [CI] = 1.2-6.9) and men (OR = 2.5; CI = 1.1-5.6). First sex at age 20 years or older was associated with an increased risk among women (OR = 2.1; CI = 0.7-6.4) and among men (OR = 3.0; CI = 1.0-9.3), and four or more lifetime sex partners was associated with a decreased risk of co-colonization among women (OR = 0.6; CI = 0.2-1.5) and among men (OR = 0.4; CI = 0.2-1.0). CONCLUSIONS: Among heterosexual college couples, sexual activity, particularly male-to-female oral sex, increases the risk of co-colonization with an identical group B strain. Future studies should evaluate the role of the pharynx and examine the effects of both bacterial characteristics and host response on transmission.

Variations in 10 putative uropathogen virulence genes among urinary, faecal and peri-urethral Escherichia coli.

A total of 868 isolates was screened from seven different collections of organisms from previous studies - pyelonephritis in children aged 1-24 months; first, second and recurring urinary tract infection (UTI) in women aged 18-39 years; UTI in women aged 40-65 years and peri-urethral and faecal isolates from women aged 18-39 years - for the presence of 10 potential Escherichia coli UTI virulence genes. Previously reported differences between the frequency of these genes in UTI compared with faecal isolates were confirmed and extended. A single virulence signature (strains containing aer, kpsMT, ompT, fim and papGAD) occurred in 29% of the pyelonephritic isolates, but in no more than 11% of the other collections. Peri-urethral isolates were found to have frequencies of these 10 genes that differed from those found for both UTI and faecal isolates.

Group B Streptococcus colonization in male and nonpregnant female university students: a cross-sectional prevalence study.

We describe the prevalence of colonization with group B Streptococcus species in a random sample of otherwise healthy male and nonpregnant female college students. Colonization with group B Streptococcus species occurs at a high frequency among healthy students, and there was a suggestion that it is associated with having engaged in sexual activity, tampon use, milk consumption, and hand washing done < or =4 times per day. However, larger studies are needed to verify these findings.