Evaluation of four methods for detection of group B streptococcal colonization.

Four methods (streak plate, pour plate, selective broth, and direct fluorescent-antibody staining) were evaluated for their ability to detect group B streptococcal colonization in parturient women and their offspring. When colonization was defined as a positive culture by any method from any site, selective broth was the most sensitive method, detecting 100% of colonized mothers and infants at birth and 48 h of age. This method failed to detect only one colonized individual (infant at 24 h of age). The other three methods detected from 20 to 56% of colonized individuals.     

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.     

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.     

Enzyme immunoassay for the detection of group A streptococcal antigen.

A competitive inhibition enzyme immunoassay for the detection of Streptococcus pyogenes directly from throat specimens or from solid bacteriological medium is described. Group A-specific polysaccharide adsorbed onto treated polystyrene beads, in conjunction with rabbit antibody to S. pyogenes, was used to determine the presence of the polysaccharide antigen. Inhibition values in excess of 65% were observed with 10(4) or more CFU of S. pyogenes per test. An inhibition of 25% was demonstrated with as few as 10(3) CFU per test. Heterologous microorganisms tested at 10(6) CFU per test reacted at levels of inhibition less than 25%. Two types of bacterial transport medium and swabs of different fiber compositions did not alter the assay performance. Accurate identification of S. pyogenes was achieved by testing single colonies picked directly from blood agar plates which had been incubated for 18 to 24 h. In addition, the assay was performed on throat specimens from children and adults having pharyngitis. A single-swab, blind study was conducted in which enzyme immunoassay reactivity was compared with results of blood agar culture and bacitracin sensitivity. When there were discordant results, serological identification was used as the confirmatory test. At an optimal cutoff value of 40% inhibition, sensitivity and specificity by enzyme immunoassay were 97.0% and 97.9%, respectively, as compared with confirmed culture results. The assay has an incubation time of 3 h and is a sensitive and specific method for the detection of S. pyogenes antigen.     

Rapid detection of Shiga toxin-producing Escherichia coli by optical immunoassay

In a multi-health center study, a new rapid optical immunoassay (OIA) for the detection of Shiga toxin types 1 and 2, the BioStar OIA SHIGATOX kit (Inverness Medical Professional Diagnostics, Inc.), was used to prospectively screen 742 fresh fecal samples for Shiga toxins in parallel with the Premier enterohemorrhagic Escherichia coli (EHEC) kit (Meridian BioScience, Inc.) with and without enrichment of the specimens by incubation in MacConkey broth. Additionally, 85 previously tested frozen fecal samples were assessed as described above. All positive immunoassay results were confirmed by the Vero cell cytotoxicity assay. A further modification of the screening procedure was evaluated on 470 of the prospectively screened specimens. Swabs of growth from conventionally plated stool culture media were subjected to the OIA SHIGATOX, and results were compared with those obtained with the Premier EHEC kit following broth enrichment. Overall, the OIA SHIGATOX kit was significantly more sensitive than the Premier EHEC kit on fresh direct stool specimens (sensitivities, 96.8% and 83.9%, respectively; P < 0.05). The two assays performed equally well with each other on frozen and broth-enriched samples. The colony sweep method used in conjunction with the OIA kit was somewhat more effective at detection of Shiga toxins from growth on agar than the overnight broth enrichment procedure used with the Premier EHEC assay (sensitivities, 100% and 92%, respectively; P < 0.09). Overall, the OIA SHIGATOX kit provided rapid, easy-to-interpret results and was highly effective at detection of Shiga toxin-producing E. coli in fecal samples and overnight cultures.     

Comparison of two antigen assays for rapid intrapartum detection of vaginal group B streptococcal colonization.

As part of a clinical investigation evaluating the efficacy of intrapartum antigen detection for screening for heavy vaginal colonization with group B streptococci (GBS), we compared the performance of modified Bactigen and Directigen GBS latex particle agglutination (LPA) kits. Paired vaginal swabs obtained from women in labor were rapidly transported to the laboratory and used for culturing (both swabs) and LPA testing (one swab by each method). GBS growth was estimated semiquantitatively and further designated as light or heavy growth. Performance specifications for each method were determined by comparing LPA and culture results from the same swab. A total of 4,251 paired swabs were evaluated during the study period. The performance specifications for detecting GBS growth of any degree for Bactigen and Directigen, respectively, were as follows: sensitivity, 20 and 24%; specificity, 99 and 99%. The performance specifications for heavy colonization for Bactigen and Directigen, respectively, were as follows: sensitivity, 57 and 62%; specificity, 99 and 99%. Neither LPA kit was a sensitive indicator of vaginal colonization with GBS or neonatal infection.     

Rapid detection of respiratory syncytial virus in nasopharyngeal aspirates by a commercial enzyme immunoassay.

A commercial enzyme immunoassay (EIA) for the rapid detection of respiratory syncytial virus (RSV) in respiratory secretions was evaluated by comparison with both virus isolation in HEp-2 cells and indirect immunofluorescence (IFA) staining of exfoliated respiratory cells. Initial examination of 80 nasopharyngeal aspirates collected from infants with acute respiratory illness showed that the RSV EIA was positive for 21 of 24 specimens positive by virus isolation or IFA (87.5% sensitivity) and negative for 53 of 56 specimens negative by virus isolation and IFA (95% specificity). The EIA appears to be an acceptable and more rapid test than virus isolation for the detection of RSV, especially for laboratories in which prompt inoculation of specimens is not always possible. IFA staining with commercial bovine anti-RSV serum was found to be the most sensitive and rapid test for the detection of RSV. However, three of four specimens positive by IFA and negative by virus isolation were not cultured under optimal conditions. In addition, the IFA test requires a highly trained technologist to interpret the staining results.     

In vitro evaluation of the performance of Granada selective enrichment broth for the detection of group B streptococcal colonization

A broth for the screening of group B streptococcal (GBS) carriage during pregnancy is about to be introduced. Simulating conditions in everyday practice, we have compared the sensitivity of this Granada tube broth (GT) with that of classical Amies transport medium (AT) in vitro. A total of 1,485 GT and 1,485 AT were tested with 33 well-characterized GBS strains in three different concentrations, five different incubation times, and three different temperatures. After initial incubation at room temperature (RT) or 4°C, GT were placed at 37°C. GT were scored for the presence of orange pigment. GT and AT were subcultured on blood agar (BA). Pigment was observed in 98% of GT incubated at 37°C. GBS could be cultured in 91%, 73%, and 55% of GT incubated at 37°C, RT, or 4°C, respectively. For AT, these percentages were only 20% at 37°C, 52% at RT, and 59% at 4°C. When GT initially incubated at RT or 4°C were subsequently incubated at 37°C, the sensitivity improved significantly. We conclude that GT is a more sensitive GBS transport and culture medium than the conventional method, especially for low inocula and prolonged transport/incubation times. GT does not exclude the presence of GBS, and should always be incubated at 37°C and subcultured on solid agar for optimal sensitivity.     

Source of group B streptococci in the female genital tract.

Swabs were taken from the posterior fornix, perineum, and anorectum of 135 patients on three occasions during their pregnancy. Multiple isolates of beta-haemolytic streptococci of group B were obtained from 24 women, in 21 of whom the strains were examined by a highly discriminative serotyping and phage typing method. In 18 of these patients their own isolates were indistinguishable but different from those of other women with multiple isolates. Women yielding group B streptococci from the posterior fornix usually carried an indistinguishable strain in the anorectum.     

Prevalence of group B streptococcal colonization in the healthy non-pregnant population: a systematic review and meta-analysis

BackgroundColonization and transmission precede invasive group B streptococcal (GBS) disease. Data on GBS colonization prevalence, detection methods and risk factors for carriage are relevant for vaccine development and to understand GBS pathogenesis.ObjectivesTo evaluate GBS colonization prevalence after the first week of life in the healthy non-pregnant population.Data sourcesPubmed/Medline, Embase, Latin American and Caribbean Health Sciences Literature, World Health Organization Library Information System, and Scopus. Search performed 12 January 2021 with search terms related to ‘GBS’ and ‘colonization, epidemiology, prevalence or screening’ without restrictions.Study eligibility criteriaAll studies that reported prevalence of GBS colonization (any site) in the healthy population.ParticipantsAll individuals (>6 days of age), with no indication of pregnancy, invasive disease or severe underlying immunological co-morbidities.MethodsLogit transformation and a random effects model (DerSimonian and Laird) were used to pool colonization estimates. Subgroup analysis and meta-regression on a priori determined subgroups were performed.ResultsWe included 98 studies with 43 112 participants. Our search identified 9309 studies of which 8831 were excluded based on title and abstract and 380 after reading the full text. Colonization rates varied considerably between studies (I² = 97%), which could be partly explained by differences in culture methods (R² = 27%), culture sites (R² = 24%), continent (R² = 10%) and participant's age (R² = 6%). Higher prevalence was found with selective culture methods (19%, 95% CI 16%–23% versus non-selective methods 8%, 95% CI 6%–9%; p < 0.0001). Colonization rates were highest in rectum (19%, 95% CI 15%–24%), vagina (14%, 95% CI 12%–17%) and urethra (9%, 95% CI 5%–18%). In participants with negative rectal cultures, 7% (95% CI 5%–9%) had GBS cultured from another niche. Colonization prevalence was lower in children (6 months to 16 years; 3%, 95% CI 2%–5%) compared with adults (16%, 95% CI 14%–20%; p < 0.0001). Using selective culture methods in adults resulted in a prevalence of 26% (95% CI 19%–33%) rectal, 21% (95% CI 17%–25%) vaginal and 9% (95% CI 6%–14%) urethral colonization.ConclusionThe rectum is the most common body site colonized by GBS. The best approach to screen for any GBS colonization is to screen multiple body sites using selective culture methods.     

Infections in international pregnancy study: performance of the optical immunoassay test for detection of group B streptococcus

We evaluated the Strep B optical immunoassay (OIA; ThermoBiostar, Inc.) for detecting light and heavy group B streptococcus colonization in 1,306 pregnant women. The women were examined at 20 to 32 weeks gestation and were from six countries. Compared to culture, the sensitivity and specificity of OIA were 13.3 and 98.4%, respectively, for light colonization and 41.5 and 97.7%, respectively, for heavy colonization.     

Lactate acquisition promotes successful colonization of the murine genital tract by Neisseria gonorrhoeae

Previous studies on Neisseria gonorrhoeae have demonstrated that metabolism of lactate in the presence of glucose increases the growth rate of the bacterium and enhances its resistance to complement-mediated killing. Although these findings in vitro suggest that the acquisition of lactate promotes gonococcal colonization, the significance of this carbon source to the survival of the gonococcus in vivo remains unknown. To investigate the importance of lactate utilization during Neisseria gonorrhoeae genital tract infection, we identified the gene lctP, which encodes the gonococcal lactate permease. A mutant that lacks a functional copy of lctP was unable to take up exogenous lactate and did not grow in defined medium with lactate as the sole carbon source, in contrast to the wild-type and complemented strains; the mutant strain exhibited no growth defect in defined medium containing glucose. In defined medium containing physiological concentrations of lactate and glucose, the lctP mutant demonstrated reduced early growth and increased sensitivity to complement-mediated killing compared with the wild-type strain; the enhanced susceptibility to complement was associated with a reduction in lipopolysaccharide sialylation of the lctP mutant. The importance of lactate utilization during colonization was evaluated in the murine model of lower genital tract infection. The lctP mutant was significantly attenuated in its ability to colonize and survive in the genital tract, while the complemented mutant exhibited no defect for colonization. Lactate is a micronutrient in the genital tract that contributes to the survival of the gonococcus.     

Experimental group B streptococcal infections in mice: hematogenous virulence and mucosal colonization.

A group B streptococcus recovered from a blood specimen from a neonate with sepsis was used to evaluate the use of mice for studies characterizing the hematogenous virulence and the asymptomatic mucosal colonization of the vagina or of the respiratory tract by these bacteria. When injected intravenously, the 50% lethal dose for mice was 10(6); however, as few as 10(2) organisms produced septic deaths. In mice undergoing water diuresis, bacteriuria and pyelonephritis were not produced after direct bladder inoculation of the streptococci. Asymptomatic vaginal colonizations that persisted for 12 days were produced in both pregnant and virgin mice. Vaginal colonization before delivery did not result in transmission of infection to litters or in protection against subsequent oropharyngeal colonization in the suckling mice. In mice born of nonexposed mothers, oropharyngeal colonization was produced in both suckling and 3-week-old weaned mice. Whereas infection persisted for 14 days in all suckling mice, clearance occurred in over 50% of the weaned mice by day 14. The use of mice for studies on the virulence of the group B streptococci as well as for studies on the pathogenesis of disease by virulent strains is discussed.     

Rapid identification of material colonization with group B streptococci by use of fluorescent antibody.

To identify women colonized with group B streptococci during parturition, we used pooled type-specific fluorescent antibody to examine vaginal swabs enriched by preincubation in selective broth medium. In preliminary experiments, group B streptococcus strain III-Bell was reliably detectable with fluorescent antibody at concentrations of greater than 10(5) colony-forming units per ml, achieved after 6 h of incubation of small inocula (18 to 26 colony-forming units). Of the vaginal swabs from 924 parturient women examined prospectively by both fluorescent antibody and selective bacteriology techniques, group B streptococci were isolated in 154. The sensitivity of the fluorescent antibody technique increased with increasing incubation time and ranged from 49% (3 to 6 h) to 81% (7 to 12 h) to 83% (13 to 18 h) to 93% (greater than 18 h). Colonized mothers identified within 6 h by the fluorescent antibody technique had higher rates of vertical transmission to their newborn infants (61%) than colonized mothers whose fluorescent antibody examinations were negative within this time interval (32%; P = 0.027). However, because of the timing of their admissions, none of the colonized mothers of the four infants who developed early-onset group B streptococcal sepsis were identified with fluorescent antibody until after delivery. Although its sensitivity approaches selective culture methods after 6 h of incubation, fluorescent antibody examination of vaginal swabs does not appear to offer a practical approach to identifying colonized parturient women for intrapartum antibiotic prophylaxis of group B streptococcal infection.     

Comparative evaluation of commercial enzyme immunoassay kits for detection of hepatitis B seromarkers.

The commercial hepatitis B enzyme immunoassay kits of Abbott Laboratories and Organon Teknika were compared for their sensitivity, specificity, and reproducibility in detecting the hepatitis B seromarkers hepatitis B surface and e antigens and antibodies to hepatitis B core, e, and surface antigens. With the exception of the Organon kit for antibodies to hepatitis B surface antigen, the specificity and reproducibility were about the same for both products, but the level of sensitivity was generally lower for the Organon kits; this, however, may not be critical in routine clinical application. The Organon kits have a longer shelf life and are cheaper.     

Rapid detection ofBrucella melitensis from blood cultures by a commercial system

To assess the capability of the Peds Plus medium of the Bactec 9240 blood culture system to recoverBrucella melitensis within the routine seven-day protocol used by most clinical microbiology laboratories, inoculated blood culture bottles were monitored by the Bactec 9240 instrument for four weeks, and blind subcultures were performed once a week. A total of 2579 blood cultures were drawn, 42 (1.6%) of which were positive forBrucella melitensis. Forty-one of the 42 (97.6%) positive cultures were detected by the Bactec 9240 instrument within two to six days; a single positive culture was missed by the instrument and detected by blind subculture performed on day 7.