Detection Of Group B Streptococcus Research Articles

Use of Granada medium to detect group B streptococcal colonization in pregnant women.

Direct inoculation onto Granada medium (GM) in plates and tubes was compared to inoculation into a selective Todd-Hewitt broth (with 8 microg of gentamicin per ml and 15 microg of nalidixic acid per ml) for detection of group B streptococci (GBS) in pregnant women with 800 vaginal and 450 vaginoanorectal samples. Comparatively, GM was found to be as sensitive as the selective broth for the detection of GBS in vaginal specimens and more sensitive than selective broth for the detection of GBS in vaginoanorectal samples (96 versus 82%). The use of GM improved the time to reporting of a GBS-positive result by at least 24 h and reduced the direct cost of screening. We have also found that the inconvenience of anaerobic incubation of GM plates can be avoided when a cover slide is placed upon the inoculum, because aerobic incubation in GM plates with cover slides causes GBS to develop the same pigmentation that it develops with incubation under anaerobic conditions. These data support the routine use of GM plates or tubes as a more accurate, easier, and cheaper method of identification of GBS-colonized women compared to the enrichment broth technique.

Screening Pregnant Women for Group B Streptococcal Colonization

The recovery rates of group B streptococcus (GBS) from anorectal swabs (RS) and vaginal swabs (VS) that were enriched were compared to the routine method to determine the optimal procedure. Separate RS and VS were collected from women attending antenatal clinics. RS and VS were placed in 2 ml enrichment and selective broth. Swabs were inoculated onto colistin/nalidixic acid agar (CNA) upon arrival in the laboratory and onto 5% sheep blood agar (SBA) and CNA after 24 h enrichment. The routine method consisted of a VS sent in transport medium and inoculated in the laboratory onto SBA (no enrichment). The overall GBS colonization rate was 24% (64/264). Of the 64 GBS carriers, 77% were colonized in the vagina and 89% were colonized in the anorectum. The anorectum was the only site of colonization in 24% of the women, whereas the vagina was the only site of colonization in 11% of cases. Enrichment increased the detection of GBS from both RS (55 versus 42; P < 0.025) and from VS (49 versus 27; P < 0.001). Of the 64 cases, enriched RS detected 86%, enriched VS detected 77% and the standard VS detected only 41%. Enriched RS and enriched VS collectively detected 99% of cases. SBA was better than CNA for subculture of the enrichment broth because of a higher recovery rate (98–100% versus 80–82%; P < 0.01) and the fact that the hemolysis on SBA made it easier to differentiate GBS from enterococci. The data confirm that optimal screening of pregnant women for GBS should include a combined RS/VS swab placed in enrichment broth that is then subcultured onto SBA after 24 h incubation.

Screening pregnant women for group B streptococcal colonization.

The recovery rates of group B streptococcus (GBS) from anorectal swabs (RS) and vaginal swabs (VS) that were enriched were compared to the routine method to determine the optimal procedure. Separate RS and VS were collected from women attending antenatal clinics. RS and VS were placed in 2 ml enrichment and selective broth. Swabs were inoculated onto colistin/nalidixic acid agar (CNA) upon arrival in the laboratory and onto 5% sheep blood agar (SBA) and CNA after 24 h enrichment. The routine method consisted of a VS sent in transport medium and inoculated in the laboratory onto SBA (no enrichment). The overall GBS colonization rate was 24% (64/264). Of the 64 GBS carriers, 77% were colonized in the vagina and 89% were colonized in the anorectum. The anorectum was the only site of colonization in 24% of the women, whereas the vagina was the only site of colonization in 11% of cases. Enrichment increased the detection of GBS from both RS (55 versus 42; P < 0.025) and from VS (49 versus 27; P < 0.001). Of the 64 cases, enriched RS detected 86%, enriched VS detected 77% and the standard VS detected only 41%. Enriched RS and enriched VS collectively detected 99% of cases. SBA was better than CNA for subculture of the enrichment broth because of a higher recovery rate (98-100% versus 80-82%; P < 0.01) and the fact that the hemolysis on SBA made it easier to differentiate GBS from enterococci. The data confirm that optimal screening of pregnant women for GBS should include a combined RS/VS swab placed in enrichment broth that is then subcultured onto SBA after 24 h incubation.

Effect of specimen storage, antibiotics, and feminine hygiene products on the detection of Group B Streptococcus by culture and the STREP B OIA test

Agar culture from vaginal swabs is the routine method for diagnosis of maternal Group B Streptococcus (GBS) colonization. Swab specimens are often transported to a clinical laboratory for processing. In these studies, specimen transport was simulated by inoculating swabs with GBS and storing them at selected temperatures and with or without transport medium. The recovery of viable GBS was assessed by agar culture. GBS antigen was detected immunologically with an Optical ImmunoAssay (OIA®) method. Swabs that were stored with transport medium harbored viable but rapidly declining numbers of GBS. In contrast, a strong OIA signal was maintained. Recovery of viable GBS organisms declined more quickly when swabs were stored in the absence of transport medium, whereas detection of GBS antigen remained consistent. Both methods were tested for interference from either antibiotics or feminine hygiene products. These compounds inhibited the detection of GBS by culture but had no detrimental effect on the OIA result.

Detection of group B Streptococcus comparison of solid and liquid culture media with and without selective antibiotics

A total of 952 consecutive vaginal swabs were obtained from patients who attended obstetric or gynecologic clinics affiliated with the Children's Hospital of Buffalo, New York. Swabs were cultured comparatively on 5% sheep blood agar (BA), selective sheep blood agar containing 1.25 μ g/ml trimethoprim-23.75 μ g/ml sulfamethoxazole (SXT), and Lim broth (Todd-Hewitt broth containing 1% yeast extract, 10)μ g/ml colistin, and 15 μ g/ml nalidixic acid). A total of 168 swabs (18%) were positive (by at least one method) for group B Streptococcus (GBS). The overall agreement among the three techniques was 90% (858 of 952); 94 specimens (10%, 94 of 952) had discrepant results, and 74 of these (44%, 74 of 168) were positive, only by Lim as opposed to two (1%) and 0 by BA and SXT, respectively. There were only two (2%, 2 of 168) false negative for Lim as compared with 82 (49%) for BA and 86 (51%) for SXT. Thus, the sensitivity of GBS detection by BA, SXT, and Lim is 51%, 49%, and 99%, respectively. These data suggest that the use of Lim broth increases the recovery rate of GBS by 48% after 48 h while the use of the SXT plate reduced the recovery rate by 2% as compared with the conventional BA plate.

Comparison of Culture and Rapid Enzyme Immunoassay for the Detection of Group B Streptococcus in High-Risk Pregnancies

Objective: The purpose of this study was to evaluate the Equate Strep B® test for clinical use in patients at high risk for complications from group B streptococcus (GBS) disease. Methods: Vaginoperineal swabs were obtained from patients with preterm premature rupture of the membranes and/or preterm labor and semiquantitative GBS cultures and Equate® assay were performed. Results: From May 14, 1990, to April 30, 1992, 650 patients were enrolled; 626 had both culture and Equate® results available, of whom 24% were colonized with GBS. The sensitivity, specificity, positive predictive value, and negative predictive value of the rapid assay were 28%, 84%, 35%, and 79%, respectively. Although the prevalence of GBS was higher in patients with ruptured membranes compared with those with intact membranes, rupture of membranes did not affect test sensitivity or specificity. Conclusions: We conclude that the Equate® rapid assay is not a sensitive method of GBS detection in high-risk patients.

Rapid detection of group B streptococcal antigen in human amniotic fluid.

Infants exposed in utero to group B streptococcus (GBS)-infected human amniotic fluid (HAF) are at high risk for serious infection. Latex particle agglutination (LPA) tests are not approved for detection of GBS in HAF. Two LPA systems, Patho-Dx Strep B and Wellcogen Strep B, were used to test unfiltered sterile HAF and filtered HAF containing concentrations of GBS carbohydrate from 0.2 to 100 micrograms/ml. Four different processing techniques were used to prevent nonspecific LPA: EDTA, nitrous acid, enzyme, and nitrous acid-heat. GBS (10(2) CFU/ml) was inoculated into filtered HAF, incubated, sampled serially, processed with enzyme, and tested by LPA. Unprocessed, unfiltered HAF showed 33% nonspecific agglutination when tested by LPA. Processing of HAF removed nonspecific agglutination and improved GBS antigen detection. Without processing, LPA could not detect less than 100 micrograms of GBS carbohydrate per ml. With nitrous acid or enzyme processing, as little as 0.2 microgram/ml could be detected. Results were easier to read after enzyme processing than after nitrous acid processing. Although both LPA systems were equally efficient, testing was easier with the Patho-Dx system. After enzyme processing, LPA could detect as few as 10(4) CFU/ml when agglutination was read with a 4 X hand lens. Substances in HAF induce false-positive reactions during LPA testing. Processing removes the interference and improves the detection of GBS. LPA testing of HAF may allow earlier identification and treatment of infants at risk for serious GBS infection.

Rapid detection of group B streptococcal antigen by monoclonal antibody sandwich enzyme assay.

Group B Streptococcus (GBS) is the most common cause of neonatal sepsis and meningitis. Infants at greatest risk to develop invasive disease are delivered to women colonized with GBS in their birth canals and lacking immunity to the colonizing serotype. We have investigated the sensitivity and specificity of a recently developed monoclonal antibody sandwich enzyme immunoassay for detection of GBS antigen. The sandwich enzyme immunoassay detected types II and III GBS at a concentration of 5 X 10(4) CFU/ml and types Ia and Ib GBS at 5 X 10(5) CFU/ml. No cross-reactions were noted when each of the GBS serotypes was reacted with antibodies of differing serotypes specificities. Type III GBS native antigen was detected at a concentration of 1 ng/ml. The sandwich enzyme assay is more sensitive than other methods currently in use for rapid detection of GBS and is serotype specific. This assay system should prove useful for the detection of GBS colonization during labor and for identification of neonates with invasive disease.

Granada medium for detection and identification of group B streptococci.

A new starch serum medium, Granada medium, for isolation and identification of group B streptococci (GBS) anaerobically as red colonies is described. The medium contains 3.8% Proteose Peptone no. 3 (Difco), 15% soluble starch 1252 (Merck), 10% coagulated horse serum, 15 micrograms of trimethoprim per ml, and 0.06 M phosphate buffer (pH 7.8; medium pH 7.4). This medium inhibited fecal flora and at the same time supported growth of GBS. A new pigment-enhancing effect of folate inhibitors on GBS is reported and used in the formulation of the medium. The good selective and differential properties of the Granada medium favor quicker and easier detection of GBS in heavily contaminated specimens. Since the medium is convenient to use and requires only 18 h of incubation to detect and identify GBS, it should be useful in any clinical microbiology laboratory and would assist in the early detection of GBS in clinical specimens.

Detection and identification of group B streptococci by use of pigment production.

Pigment production by group B streptococci (GBS) is a useful test for identification of the organisms. The test is positive in 99.5% of beta-haemolytic strains. No false-positives are noted. Non-haemolytic strains do not produce pigment. Islam's media less agar can be used as a one-step broth detector of GBS in mixed cultures. This may have application for the detection of GBS in women in labour. When used as an identification system for GBS, serum-starch broth can be further modified by reduction of serum and starch concentrations by at least 80%.