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

Molecular and phenotypic identification of bacterial species isolated from cows with mastitis from three regions of Poland

BACKGROUND

Bovine mastitis is a widespread disease affecting dairy cattle worldwide and it generates substantial losses for dairy farmers. Mastitis may be caused by bacteria, fungi or algae. The most common species isolated from infected milk are, among others, Streptococcus spp., Escherichia coli, Staphylococcus aureus and non-aureus staphylococci and mammaliicocci. The aim of this paper is to determine the frequency of occurrence of bacterial species in milk samples from cows with mastitis from three regions of Poland: the north-east, the south-west and the south. To this end 203 milk samples taken from cows with a clinical form (CM) of mastitis (n = 100) and healthy animals (n = 103) were examined, which included culture on an appropriate medium followed by molecular detection of E. coli, S. aureus, Streptococcus agalactiae and Streptococcus uberis, as one of the most common species isolated from mastitis milk.

RESULTS

The results obtained indicated that S. uberis was the most commonly cultivated CM species (38%, n = 38), followed by S. aureus (22%, n = 22), E. coli (21%, n = 21) and S. agalactiae (18%, n = 18). Similar frequencies in molecular methods were obtained for S. uberis (35.1%) and S. aureus (28.0%). The variation of sensitivity of both methods may be responsible for the differences in the E. coli (41.0%, p = 0.002) and S. agalactiae (5.0%, p = 0.004) detection rates. Significant differences in composition of species between three regions of Poland were noted for E. coli incidence (p < 0.001), in both the culture and molecular methods, but data obtained by the PCR method indicated that this species was the least common in north-eastern Poland, while the culture method showed that in north-eastern Poland E. coli was the most common species. Significant differences for the molecular method were also observed for S. uberis (p < 0.001) and S. aureus (p < 0.001). Both species were most common in southern and south-western Poland.

CONCLUSIONS

The results obtained confirm the need to introduce rapid molecular tests for veterinary diagnostics, as well as providing important epidemiological data, to the best of our knowledge data on Polish cows in selected areas of Poland is lacking.

Use of Recombinant Endolysin to Improve Accuracy of Group B Streptococcus Tests

Group B Streptococcus (GBS) causes serious neonatal infection via vertical transmission. The prenatal GBS screening test is performed at the late stage of pregnancy to avoid risks of infection. In this test, enrichment culture is performed, followed by GBS identification. Selective medium is used for the enrichment; however, Enterococcus faecalis, which is a potential contaminant in swab samples, can interfere with the growth of GBS. Such bacterial contamination can lead to false-negative results. Endolysin, a bacteriophage-derived enzyme, degrades peptidoglycan in the bacterial cell wall; it is a promising antimicrobial agent for selectively eliminating specific bacterial genera/species. In this study, we used the recombinant endolysin EG-LYS, which is specific to E. faecalis; the endolysin potentially enriched GBS in the selective culture. First, in the false-negative model (coculture of GBS and E. faecalis, which disabled GBS detection in the subsequent GBS identification test), EG-LYS treatment at 0.1 mg/ml improved GBS detection. Next, we used 548 vaginal swabs to test the efficacy of EG-LYS treatment in improving GBS detection. EG-LYS treatment (0.1 mg/ml) increased the GBS-positive ratio to 17.9%, compared to 15.7% in the control (phosphate-buffered saline [PBS] treatment). In addition, there were an increased number of GBS colonies under EG-LYS treatment in some samples. The results were supported by the microbiota analysis of the enriched cultures. In conclusion, EG-LYS treatment of the enrichment culture potentially improves the accuracy of the prenatal GBS screening test. IMPORTANCE Endolysin is a bacteriophage-derived enzyme that degrades the peptidoglycan in the cell wall of host bacteria; it could be used as an antimicrobial agent for selectively eliminating specific bacterial genera/species. Group B Streptococcus (GBS) causes neonatal infection via vertical transmission; prenatal GBS screening test, in which enrichment culture is followed by bacterial identification, is used to detect the presence of GBS in pregnant women. However, the presence of commensal bacteria such as Enterococcus faecalis in clinical specimens can inhibit GBS growth in the selective enrichment culture, resulting in false-negative result. Here, we demonstrated that the application of originally isolated endolysin in the enrichment culture improved the test accuracy by inhibiting unwanted E. faecalis growth and therefore avoiding false-negative results, not only in experimental settings, but also in tests using vaginal swabs.

Diagnostic performance of direct latex agglutination, post-enrichment latex agglutination and culture methods in screening of group B streptococci in late pregnancy: a comparative study

Background

Group B streptococcus (GBS) is one of the main causes of neonatal sepsis.

Purpose

Evaluation of the diagnostic performance of direct latex agglutination test (DLA), post-enrichment latex agglutination (LA) test, and direct culture on chromogenic media in rapid identification of GBS carrier in pregnant women in comparison with the conventional post-enrichment CDC-recommended culture method and further to estimate GBS carriage prevalence and its antimicrobial susceptibility.

Methods

Two hundred pregnant women at gestational age (35–37 weeks) were enrolled. Three low vaginal swabs were obtained from each participant. One swab was directly inoculated into Strep B Select (SBS) agar. The second swab was inoculated in enrichment Lim broth for immunological antigen detection by post-enrichment latex agglutination (5 h and 24 h) and subculture for bacteriological detection. The third swab was used for immunological detection of GBS antigen by direct latex agglutination. The isolated GBS was subjected to antimicrobial susceptibility testing.

Results

Among 200 pregnant women, 47 (23.5%) were GBS carriers. Considering post-enrichment subculture on SBS medium as a gold standard, the sensitivities for post-enrichment 5 h and 24 h LA were 66% and 95.7%, respectively. However, direct cultivation of the vaginal swabs on SBS medium and DLA recorded 83% and 4.3%, respectively, for sensitivity. All GBS isolates (100%) were sensitive to penicillin G, ampicillin, ceftriaxone, and vancomycin. In contrast, 21.3% and 12.8% of isolated GBS were resistant to erythromycin and clindamycin, respectively.

Conclusion

Group B streptococcal antigen detection by latex agglutination after 5 h enrichment is a reliable, easy, and relatively rapid method for screening of GBS carriage in pregnant woman not in labor. Latex agglutination after 18–24 h enrichment can be used alternative to standard subculture method for screening GBS carriage.

Comparison of Three Nucleic Acid Amplification Tests and Culture for Detection of Group B Streptococcus from Enrichment Broth

Colonization of the gastrointestinal and genitourinary tracts of pregnant women with group B Streptococcus (GBS) can result in vertical transmission to neonates during labor/delivery. GBS infections in neonates can cause severe complications, such as sepsis, meningitis, and pneumonia. Accurate detection is critical because administration of intrapartum antibiotics can significantly reduce transmission. We compared the clinical sensitivities of three nucleic acid amplification tests (NAATs), the Hologic Panther Fusion GBS, Luminex Aries GBS, and Cepheid Xpert GBS LB assays, to that of the standard of care culture method recommended for GBS screening using 500 vaginal-rectal swab specimens after 18 to 24 h of broth enrichment. We identified 108 positive specimens (21.6%) by culture, while at least 1 of the 3 NAATs was positive for GBS in 155 specimens (31.0%). All 108 specimens positive by culture were also detected by the Panther Fusion assay, while 107/108 (99.1%) were detected by the Cepheid Xpert and Luminex Aries assays. Of the 61 specimens positive by at least 1 NAAT but negative by culture, 24 (39.3%) were positive by all 3 NAATs, suggesting that they represent true positives (TPs). NAATs offer less hands-on time, greater throughput, faster time to result, and potentially greater sensitivity than culture methods, and they should be considered the new gold standard for intrapartum GBS screening.

[Colonization rates by Streptococcus agalactiae in Spanish and foreign pregnant women in the Fuenlabrada University Hospital]

OBJECTIVE

In pregnant women, the rectovaginal colonization by Streptococcus agalactiae (GBS) is related with geographic area of origin (6.5% to 36%). It was analysed GBS carriage in pregnant women in 2012-2014 in our hospital.

METHODS

Observational retrospective study about GBS isolates from rectovaginal samples (RVS) and urine cultures of Spanish and immigrant pregnant women in 2012-2014. It was considered only a single isolation for patient. There were excluded women with GBS in urine samples of RVS study.

RESULTS

A total of 4,648 Spanish and 1,405 immigrant women were analysed. GBS was detected in urine samples in 231 Spanish (5%) and 106 immigrant (7.6%). A total of 5,716 RVS were analysed, GBS was detected in 10.5% of Spanish women and in 18.9% of immigrant women.

CONCLUSIONS

The overall colonization in immigrant women is higher than in Spanish with the exception of Asian women. Cases of GBS detected in urine samples might serve as a possible explanation for the high rate of GBS carriage.

Reliable Detection of Group B Streptococcus in the Clinical Laboratory

Group B streptococcus (GBS) is a leading cause of invasive neonatal infections and a significant pathogen in immunocompromised adults. Screening to detect GBS colonization in pregnant women determines the need for antibiotic prophylaxis in that pregnancy. Efficient determination of the GBS colonization status of pregnant women is crucial. Methods that maximize the probability of GBS recovery are needed. The availability of technologies such as matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), molecular techniques, and chromogenic culture media, including Granada-type media, have changed the scenario for GBS detection and identification. This review presents and evaluates novel diagnostic tools, as well as classic identification techniques, for GBS species determination.

Molecular characterization and antimicrobial susceptibility of hemolytic Streptococcus agalactiae from post-menopausal women

PURPOSE

Streptococcus agalactiae (Group B streptococcus, GBS) is increasingly recognized as a pathogen in adult populations, including the elderly. Appropriate treatment involves antibiotics. An alternative to this strategy would be the administration of a polysaccharide vaccine therefore the capsular serotypes and molecular characterization of circulating strains needs to be known. Few studies have been conducted in this population.

METHODS

One hundred and seven GBS isolates collected from vagino-rectal swabs from 600 post-menopausal women were analysed for their capsular type, antimicrobial resistance and genetic relatedness (multilocus sequence typing, MLST).

RESULTS

The colonization rate was 17.8%. Capsular type III was predominant (34.6%), followed by type V (22.4%). The most frequent sequence type (ST) was 19 (23.3%), followed by 23 (18.7%), 1 (16.8%) and 17 (12.1%). Isolates were assembled into three phylogenetic groups from ST-19, ST-23 and ST-17 founders. All isolates were susceptible to penicillin, whereas resistance to erythromycin and clindamycin was recorded in 23.4% and 20.6% of isolates, respectively.

CONCLUSIONS

In our setting, the GBS colonization rate in postmenopausal women is similar to that reported in others populations studied. The population structure of these isolates is highly diverse and contains different STs. These data can contribute to the future development of a polysaccharide vaccine for preventing GBS infection in older adults.

Group B streptococcal haemolysin and pigment, a tale of twins

Group B streptococcus [(GBS or Streptococcus agalactiae)] is a leading cause of neonatal meningitis and septicaemia. Most clinical isolates express simultaneously a β-haemolysin/cytolysin and a red polyenic pigment, two phenotypic traits important for GBS identification in medical microbiology. The genetic determinants encoding the GBS haemolysin and pigment have been elucidated and the molecular structure of the pigment has been determined. The cyl operon involved in haemolysin and pigment production is regulated by the major two-component system CovS/R, which coordinates the expression of multiple virulence factors of GBS. Genetic analyses indicated strongly that the haemolysin activity was due to a cytolytic toxin encoded by cylE. However, the biochemical nature of the GBS haemolysin has remained elusive for almost a century because of its instability during purification procedures. Recently, it has been suggested that the haemolytic and cytolytic activity of GBS is due to the ornithine rhamnopolyenic pigment and not to the CylE protein. Here we review and summarize our current knowledge of the genetics, regulation and biochemistry of these twin GBS phenotypic traits, including their functions as GBS virulence factors.

Evaluation of chromogenic medium and direct latex agglutination test for detection of group B streptococcus in vaginal specimens from pregnant women in Lebanon and Kuwait

This study was undertaken to evaluate chromogenic medium and a direct latex agglutination test (DLA) for detection of Group B Streptococcus (GBS) in the vaginal specimens of pregnant women, and to ascertain the prevalence of GBS in this population in Kuwait and Lebanon. Vaginal swabs, collected from women at 35-37 weeks of gestation, were cultured on 5 % sheep blood agar (SBA), colistin nalidixic acid agar (CNA), Strept B Select chromogenic agar (SBS) as well as Lim enrichment broth in 168 cases in Lebanon while only SBA was used for 1391 samples in Kuwait. In addition, vaginal samples from 102 GBS-positive and 20 GBS-negative women near the time of delivery were collected in Kuwait for evaluation of the DLA test. During the study period, the prevalence of GBS colonization was determined to be 20.7 % (288/1391) in Kuwait while 18.4 % (31) of 168 pregnant women in Lebanon had vaginal cultures positive for GBS. By direct plating of vaginal swabs on the three media used, the isolation rates of GBS were 51.6, 64.5 and 77.4 % on SBA, CNA and SBS, respectively, which increased to 90.35, 93.1 and 96.8 %, respectively, following subculture in Lim broth after 18 h of incubation. The sensitivity of the DLA test was found to be dependent on the density of GBS colonization, resulting in 100 % sensitivity and 100 % specificity for heavy (>10(2) c.f.u. per swab) and moderately heavy (50-100 c.f.u. per swab) growth of GBS. However, for vaginal specimens yielding <50 c.f.u. per swab, the sensitivity, specificity, positive and negative predictive values of the DLA test were 100, 55.5, 63.6 and 100 %, respectively. In conclusion, a chromogenic agar, such as SBS, and a DLA test can be used for rapid detection of GBS in pregnant women. The DLA test, in particular, could prove to be a useful tool for immediate detection of GBS in women near delivery so that intrapartum antibiotic prophylaxis can be initiated.

Evaluation of chromID strepto B as a screening media for Streptococcus agalactiae

Background

Streptococcus agalactiae (Group B Streptococcus, GBS), a leading cause of sepsis and meningitis in infants, can be transmitted vertically from mother to infant during passage through the birth canal. Detection of GBS colonization in perinatal women is a major strategy for the prevention of postpartum neonatal disease. The U.S. Centers for Disease Control and Prevention recommends that all women undergo vaginal-rectal screening for GBS colonization at 35-37 weeks of gestation. ChromID Strepto B (STRB) is a chromogenic GBS screening media on which GBS colonies appear pink or red, while other bacteria are either inhibited or form colonies in other colors. In this study, we compared STRB with a conventional GBS detection method using 5% sheep blood agar (BA) followed by a selective enrichment broth.

Methods

Anovaginal swabs were collected from 1425 women during weeks 35 to 37 of their pregnancies. The swabs were used to inoculate both STRB and BA plates after enrichment with selective Todd Hewitt Broth (THB). A GBS latex agglutination test was used to confirm the identity of isolates from each plate.

Results

GBS was recovered from 319 (22.4%) samples with one or both media: 318 on STRB compared to 299 using BA. One false negative was observed on STRB, and 20 false negatives were observed on BA. In addition, non-hemolytic GBS was recovered from 19 (6.0%) samples using STRB.

Conclusions

STRB offers effectiveness and convenience over BA for GBS screening in clinical laboratories. STRB produces fewer false negatives, has a higher detection rate and uses a simple color screen that is ideal for technician-level applications. We recommend STRB as the media of choice for GBS screening.

Infection and cellular defense dynamics in a novel 17β-estradiol murine model of chronic human group B streptococcus genital tract colonization reveal a role for hemolysin in persistence and neutrophil accumulation

Genital tract carriage of group B streptococcus (GBS) is prevalent among adult women; however, the dynamics of chronic GBS genital tract carriage, including how GBS persists in this immunologically active host niche long term, are not well defined. To our knowledge, in this study, we report the first animal model of chronic GBS genital tract colonization using female mice synchronized into estrus by delivery of 17β-estradiol prior to intravaginal challenge with wild-type GBS 874391. Cervicovaginal swabs, which were used to measure bacterial persistence, showed that GBS colonized the vaginal mucosa of mice at high numbers (10(6)-10(7) CFU/swab) for at least 90 d. Cellular and histological analyses showed that chronic GBS colonization of the murine genital tract caused significant lymphocyte and PMN cell infiltrates, which were localized to the vaginal mucosal surface. Long-term colonization was independent of regular hormone cycling. Immunological analyses of 23 soluble proteins related to chemotaxis and inflammation showed that the host response to GBS in the genital tract comprised markers of innate immune activation including cytokines such as GM-CSF and TNF-α. A nonhemolytic isogenic mutant of GBS 874391, Δcyle9, was impaired for colonization and was associated with amplified local PMN responses. Induction of DNA neutrophil extracellular traps, which was observed in GBS-infected human PMNs in vitro in a hemolysin-dependent manner, appeared to be part of this response. Overall, this study defines key infection dynamics in a novel murine model of chronic GBS genital tract colonization and establishes previously unknown cellular and soluble defense responses to GBS in the female genital tract.

[Prevention of Neonatal Group B Sreptococcal Infection. Spanish Recommendations. Update 2012. SEIMC/SEGO/SEN/SEQ/SEMFYC Consensus Document]

Group B streptococci (GBS) remain the most common cause of early onset neonatal sepsis. In 2003 the Spanish Societies of Obstetrics and Gynaecology, Neonatology, Infectious Diseases and Clinical Microbiology, Chemotherapy, and Family and Community Medicine published updated recommendations for the prevention of early onset neonatal GBS infection. It was recommended to study all pregnant women at 35-37 weeks gestation to determine whether they were colonised by GBS, and to administer intrapartum antibiotic prophylaxis (IAP) to all colonised women. There has been a significant reduction in neonatal GBS infection in Spain following the widespread application of IAP. Today most cases of early onset GBS neonatal infection are due to false negative results in detecting GBS, to the lack of communication between laboratories and obstetric units, and to failures in implementing the prevention protocol. In 2010, new recommendations were published by the CDC, and this fact, together with the new knowledge and experience available, has led to the publishing of these new recommendations. The main changes in these revised recommendations include: microbiological methods to identify pregnant GBS carriers and for testing GBS antibiotic sensitivity, and the antibiotics used for IAP are updated; The significance of the presence of GBS in urine, including criteria for the diagnosis of UTI and asymptomatic bacteriuria in pregnancy are clarified; IAP in preterm labour and premature rupture of membranes, and the management of the newborn in relation to GBS carrier status of the mother are also revised. These recommendations are only addressed to the prevention of GBS early neonatal infection, are not effective against late neonatal infection.

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.

Temporal characterization of carrot broth-enhanced real-time PCR as an alternative means for rapid detection of Streptococcus agalactiae from prenatal anorectal and vaginal screenings

Analysis of overnight carrot broth culture using the BD GeneOhm StrepB assay (carrot broth-enhanced PCR) yields increased sensitivity compared to that of carrot broth culture alone for the detection of Streptococcus agalactiae. We investigated the prospect of reducing the carrot broth incubation time prior to PCR performance. In vitro experimentation demonstrated that carrot broth-enhanced PCR nominally detected 10 CFU S. agalactiae after 4 h of carrot broth incubation with competitive flora. Detection rates improved with inocula of 100 and 1,000 CFU S. agalactiae, with the majority of these aliquots demonstrating detection after 2 h of carrot broth incubation. Carrot broth was prospectively inoculated with clinical vaginal/anorectal swabs, with 500-μl aliquots collected. Early aliquots from 227 specimens were subjected to carrot broth-enhanced PCR (early-aliquot carrot broth-enhanced PCR) in instances of subsequent positive carrot broth culture or positive overnight clinical carrot broth-enhanced PCR. The S. agalactiae detection rate by early-aliquot carrot broth-enhanced PCR (66.1%) exceeded that observed for 227 remnant swabs retrospectively tested by direct swab PCR (56.4%; P=0.03). Early-aliquot carrot broth-enhanced PCR detection rate differences were most pronounced in aliquots from 83 carrot broth aliquots collected after 6 h (84.3%) compared to detection rates from either direct swab PCR of these samples (51.8%; P<0.0002) or early-aliquot carrot broth-enhanced PCR of 144 carrot broth aliquots collected after fewer than 6 h of incubation (55.6%; P<0.0002). Enhanced sensitivity of early-aliquot carrot broth-enhanced PCR versus direct swab PCR suggests that this assay could serve as a surrogate rapid detection method facilitating the prevention of group B streptococcal disease.

Comparison of different sampling techniques and of different culture methods for detection of group B streptococcus carriage in pregnant women

Background

Streptococcus agalactiae (group B streptococcus; GBS) is a significant cause of perinatal and neonatal infections worldwide. To detect GBS colonization in pregnant women, the CDC recommends isolation of the bacterium from vaginal and anorectal swab samples by growth in a selective enrichment medium, such as Lim broth (Todd-Hewitt broth supplemented with selective antibiotics), followed by subculture on sheep blood agar. However, this procedure may require 48 h to complete. We compared different sampling and culture techniques for the detection of GBS.

Methods

A total of 300 swabs was taken from 100 pregnant women at 35-37 weeks of gestation. For each subject, one rectovaginal, one vaginal and one rectal ESwab were collected. Plating onto Columbia CNA agar (CNA), group B streptococcus differential agar (GBSDA) (Granada Medium) and chromID Strepto B agar (CA), with and without Lim broth enrichment, were compared. The isolates were confirmed as S. agalactiae using the CAMP test on blood agar and by molecular identification with tDNA-PCR or by 16S rRNA gene sequence determination.

Results

The overall GBS colonization rate was 22%. GBS positivity for rectovaginal sampling (100%) was significantly higher than detection on the basis of vaginal sampling (50%), but not significantly higher than for rectal sampling (82%). Direct plating of the rectovaginal swab on CNA, GBSDA and CA resulted in detection of 59, 91 and 95% of the carriers, respectively, whereas subculturing of Lim broth yielded 77, 95 and 100% positivity, respectively. Lim broth enrichment enabled the detection of only one additional GBS positive subject. There was no significant difference between GBSDA and CA, whereas both were more sensitive than CNA. Direct culture onto GBSDA or CA (91 and 95%) detected more carriers than Lim broth enrichment and subculture onto CNA (77%). One false negative isolate was observed on GBSDA, and three false positives on CA.

Conclusions

In conclusion, rectovaginal sampling increased the number GBS positive women detected, compared to vaginal and/or rectal sampling. Direct plating on CA and/or GBSDA provided rapid detection of GBS that was at least as sensitive and specific as the CDC recommended method of Lim broth subcultured onto non chromogenic agar.

Evaluation of three commercial broth media for pigment detection and identification of a group B Streptococcus (Streptococcus agalactiae)

Detection of group B Streptococcus (GBS) strains at various bacterial concentrations was evaluated using three pigment-producing broth media. At 10(3) CFU/ml, StrepB carrot broth (SBCB), Granada instant liquid biphasic (IGLB), and Northeast Laboratory GBS screening medium (NEL-GBS) showed 100% detection, but at the lower bacterial counts, SBCB and IGLB were more sensitive than NEL-GBS after 24 h.

[Evaluation of the new chromogenic medium StrepB Select for screening of group B Streptococcus in pregnant women]

OBJECTIVES

To compare and evaluate the new chromogenic StrepB Select (BioRad) medium to the Granada (bioMérieux) and Columbia horse blood agar plates (CH-BAP) for screening of Group B Streptococcus (GBS) vaginal colonization in pregnant women.

METHODS

One hundred and ninety vaginal swabs were processed and the three media inoculated. All plates were examined after 18-24h incubation at 37 degrees C and reincubated for an additional 24h. All suspected colonies were identified as GBS by using a commercial Lancefield group-specific latex agglutination test.

RESULTS

GBS were isolated in 32 samples (16.8%) by at least one medium. After 24h of incubation, GBS were recovered on CH-BAP in 16 samples (50%) compared to 28 (87.5%) for StrepB Select, and 27 (84.5%) for Granada. After 48h of incubation, 30 (93.7%) out of the 32 GBS vaginal carriers were positive with CH-BAP, StrepB Select and Granada. Other streptococcal and enterococcal species gave GBS-like colonies on StrepB Select medium implying the use of other tests to confirm GBS identification. We demonstrated that direct agglutination of GBS isolated all media with Pastorex StrepB accurately identified GBS. The two StrepB Select false-negative results corresponded to a very low colonisation rate. Two Granada false-negative results corresponded to non-haemolytic and non-pigmented GBS strains which were correctly identified on StrepB Select. Both selective media inhibit the growth of associated saprophytic flora.

CONCLUSION

The use of the new StrepB Select chromogenic medium in routine laboratories may therefore markedly facilitate the rapid and accurate detection of GBS in vaginal samples.

Comparison of carrot broth- and selective Todd-Hewitt broth-enhanced PCR protocols for real-time detection of Streptococcus agalactiae in prenatal vaginal/anorectal specimens

The reporting of accurate Streptococcus agalactiae screening results in a short time frame is of tremendous clinical benefit. A total of 203 consecutive primary vaginal/anorectal specimens were cultured in selective Todd-Hewitt broth (LIM broth) and with the StrepB carrot broth kit (carrot broth). One-day broth cultures were subjected to both centrifugation and clarification of a 500-mul aliquot prior to sample lysis (protocol A) and direct lysis of a 50-mul aliquot (protocol B). The lysates were subsequently analyzed by the BD GeneOhm StrepB assay. The results were compared to the carrot broth culture results derived from visualization of pigment on day 1 or from a subculture of carrot broth. Thirty-four carrot broth cultures (16.7%) generated diagnostic pigment following overnight incubation; an additional 26 (12.8%) were positive for S. agalactiae upon subculture. Carrot broth-enhanced PCR by the use of either protocol A or protocol B trended toward a higher rate of positive results (33.0%) than the rate observed by either the LIM broth-enhanced PCR (30.5%) or full carrot broth culture analysis (29.6%). In the context of the result on day 1, both carrot broth- and LIM broth-enhanced PCRs generated more true-positive results (P < 0.001) than carrot broth culture visualization. The predictive values for both protocols of carrot broth- or LIM broth-enhanced PCR were >/=95.4%. Whereas protocol A resolved the results for 99.8% of the specimens in the evaluation upon initial testing, a 5.7% initial unresolved rate and a 1.5% final unresolved rate were determined by the use of protocol B. The use of carrot broth within a rapid and highly accurate molecular reflex testing algorithm can limit follow-up testing to cultures without evidence of pigmentation.

Evaluation of liquid biphasic Granada medium and instant liquid biphasic Granada medium for group B streptococcus detection

INTRODUCTION

Group B streptococci (GBS) are transmitted from the mother to the newborn. Prevention of neonatal infection is achieved by intrapartum prophylaxis given to mothers colonized with GBS at 35 to 37 weeks of pregnancy.

MATERIALS AND METHODS

Liquid biphasic Granada medium (LB) and instant liquid biphasic Granada medium (ILB) were evaluated for GBS detection. Vaginal swabs obtained from 300 women were inoculated onto LB or ILB, or onto Todd-Hewitt broth and analyzed with the ATB system (comparison method).

RESULTS

Prevalence of GBS was 20% (61/300). LB and Todd-Hewitt with ATB detected GBS in 20% of women, and ILB in 19% of women. No growth was observed at four hours in any of the media studied. At 10 h and 14 h, identification of GBS was possible in 43/300 (14%) and 53/300 (18%) of ILB cultures, respectively, and in 32/300 (11%) and 46/300 (15%) of LB cultures.

CONCLUSION

All the media used are suitable for GBS detection. The majority of GBS were identified in ILB and LB cultures at 10 h and 14 h.

Evaluation of a new chromogenic agar medium for isolation and identification of Group B streptococci

AIMS

To evaluate a new chromogenic agar as a screening medium for the isolation of Group B streptococci from high vaginal swabs from pregnant women.

METHODS AND RESULTS

The medium was evaluated with 195 high vaginal swabs referred for antenatal screening and compared with blood agar and Granada medium. The new chromogenic medium showed 100% sensitivity for the detection of Group B streptococci, and also showed a positive predictive value of 100%. Granada medium also showed excellent sensitivity and specificity and both media were superior to blood agar.

CONCLUSIONS

The new chromogenic medium showed excellent performance for the detection of Group B streptococci from clinical samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first chromogenic medium described for the detection of Group B streptococci. The medium offers an effective and convenient alternative to conventional media, currently used in clinical laboratories.

The putative glycosyltransferase-encoding gene cylJ and the group B Streptococcus (GBS)-specific gene cylK modulate hemolysin production and virulence of GBS

Group B streptococcus (GBS) expresses a hemolysin/cytolysin that plays an important role in pathogenesis. Using the Himar1 transposon mutagenesis system, a hypohemolytic mutant carrying an interrupted cylJ gene was characterized. cylJ, encoding a putative glycosyltransferase, and cylK, whose product is unknown, are both required for the full hemolytic/cytolytic activity, pigment formation, and virulence of GBS.

Erythromycin resistance and genetic elements carrying macrolide efflux genes in Streptococcus agalactiae

The macrolide resistance determinants and genetic elements carrying the mef(A) and mef(E) subclasses of the mef gene were studied with Streptococcus agalactiae isolated in 2003 and 2004 from 7,084 vaginorectal cultures performed to detect carrier pregnant women. The prevalence of carriage was 18% (1,276 isolates), and that of erythromycin resistance 11.0% (129 of the 1,171 isolates studied). erm(B), erm(A) subclass erm(TR), and the mef gene, either subclass mef(A) or mef(E), were found in 72 (55.8%), 41 (31.8%), and 12 (9.3%) erythromycin-resistant isolates, while 4 isolates had more than 1 erythromycin resistance gene. Of the 13 M-phenotype mef-containing erythromycin-resistant S. agalactiae isolates, 11 had the mef(E) subclass gene alone, one had both the mef(E) and the erm(TR) subclass genes, and one had the mef(A) subclass gene. mef(E) subclass genes were associated with the carrying element mega in 10 of the 12 mef(E)-containing strains, while the single mef(A) subclass gene found was associated with the genetic element Tn1207.3. The nonconjugative nature of the mega element and the clonal diversity of mef(E)-containing strains determined by pulsed-field gel electrophoresis suggest that transformation is the main mechanism through which this resistance gene is acquired.

Evaluation of Group B Streptococcus Differential Agar for detection and isolation of Streptococcus agalactiae

In total, 320 vaginal or rectal swabs were cultured on Granada medium (GM) or Group B Streptococcus Differential Agar (GBSDA), and were also inoculated into LIM broth (Todd-Hewitt broth supplemented with selective antibiotics), for detection of group B Streptococcus (GBS). Overall, GBS isolates were detected on 53 of the 320 swabs; 47 of these isolates grew on both GM and GBSDA, five only on GBSDA, and one only following subculture from LIM broth. GBSDA appears to be a valid alternative to GM for the growth of GBS isolates from pregnant women.

Use of unmodified starches and partial removal of serum to improve Granada medium stability

The use of 1% unmodified rice starch and 1% horse serum instead of 2% soluble starch and 5% serum in Granada medium is described. These components result in a medium of increased stability, preventing spoilage after a few days of storage at room temperature.

Specimen storage in transport medium and detection of group B streptococci by culture

Recovery of group B streptococci (GBS) was assessed in 1,204 vaginorectal swabs stored in Amies transport medium at 4 or 21 degrees C for 1 to 4 days either by direct inoculation onto Granada agar (GA) or by culture in blood agar (BA) and GA after a selective broth enrichment (SBE) step. Following storage at 4 degrees C, GBS detection in GA was not affected after 72 h by either direct inoculation or SBE; however, GBS were not detected after SBE in the BA subculture in some samples after 48 h of storage and in GA after 96 h. After storage at 21 degrees C, loss of GBS-positive results was significant after 48 h by direct inoculation in GA and after 96 h by SBE and BA subculture; some GBS-positive samples were not detected after 24 h of storage followed by SBE and BA subculture or after 48 h of storage followed by SBE and GA subculture. Storage of swabs in transport medium, even at 4 degrees C, produced after 24 h an underestimation of the intensity of GBS colonization in most specimens. These data indicate that viability of GBS is not fully preserved by storage of vaginorectal swabs in Amies transport medium, mainly if they are not stored under refrigeration.

Comparison of two culture media and three sampling techniques for sensitive and rapid screening of vaginal colonization by group B streptococcus in pregnant women

The Centers for Disease Control and Prevention (CDC) recommend universal screening of all pregnant women between 35 and 37 weeks of gestation for group B streptococci (GBS) by use of a selective broth medium. Recent reports suggest that Granada medium can be used for rapid and direct visual identification of GBS colonies. However, studies comparing the Granada medium method to the selective broth method are few, and while some report comparable sensitivities, others have found significant differences in detection rates between the two methods. This prospective study compared a method using Granada agar to a Todd-Hewitt broth method with subculture to blood agar in order to determine which GBS detection method is more sensitive and less labor-intensive and has a more rapid turnaround time. Detection rates for three sampling techniques (rectovaginal, vaginal only, and cervical only) were also compared. Consecutive specimens for GBS screening received over a 6-month period from 1,635 pregnant women were included. Overall, GBS was detected in 390 (23.8%) women. The Granada medium gave positive results for 348 of these women, and the selective broth gave positive results for 385, indicating sensitivities of 89.2% for the Granada medium and 98.7% for the selective broth. These findings show that the Granada medium method is less sensitive than the selective broth method and should not replace it as the only method for screening pregnant women for GBS. However, the Granada medium method reduced detection time to 1 day and also reduced the use of ancillary tests in approximately 90% of positive cases. Additionally, no significant differences were noted in the detection rates with rectovaginal, vaginal, and cervical specimens.

Evaluation of Granada agar plate for detection of Streptococcus agalactiae in urine specimens from pregnant women

The Granada agar plate (GAP; Biomedics SL, Madrid, Spain) was evaluated for the detection of group B streptococci (GBS) in urine specimens from pregnant women submitted for testing for asymptomatic bacteriuria and was compared with blood agar (BA [Columbia agar with 5% sheep blood]; bioMérieux, Marcy l'Etoile, France). The GAP detected 103 out of 105 GBS, whereas BA detected only 50. Use of the GAP could be a good method for the detection of GBS in urine specimens from pregnant women.

[Comparative study of three culture media for detecting group B Streptococcus colonization in pregnant women]

OBJECTIVE

To compare the efficacy of three culture media to detect vaginal and rectal colonization by group B streptococci (GBS) in pregnant women.

METHODS

We processed 1334 samples from 861 pregnant women: in 388 patients only vaginal swab was cultured (Group A) and in 473 vaginal and rectal swabs were cultured (Group B). Samples were inoculated on blood agar with colistin-nalidixic acid (BA-CNA), on plates with Granada medium, and on Todd-Hewitt broth (THB) with amikacin followed by subculture in BA-CNA.

RESULTS

GBS was isolated in 181 samples (13.6%): 114 vaginal swabs (13.2%) and 67 rectal swabs (14.2%). Among the positive samples, GBS was isolated on BA-CNA in 60.5% of vaginal swabs and in 59.7% of rectal swabs, on Granada medium in 80.7% of vaginal swabs and in 91% of rectal swabs, and on THB in 97.4% of vaginal swabs and in 97% of rectal swabs.We detected 130 GBS carriers, 54 (13.9%) in Group A and 76 (16.1%) in Group B. The percent of carriers detected in groups A and B, respectively, was 59.3% and 75% with BA-CNA, 77.8% and 93.4% with Granada medium, and 96.3% and 97.4% with THB.

CONCLUSIONS

THB was the most reliable medium for the detection of GBS. Use of Granada medium allows fast detection of about 87% of carriers. The combination of THB and an initial plate of Granada medium or BA-CNA allows detection of more than 99% of GBS carriers.

Optimisation of prenatal group B streptococcal screening

The purpose of the study presented here was to confirm the high yield of group B streptococci (GBS) on Granada medium for the detection of pregnant GBS carriers and to compare the results with those obtained using standard Columbia blood agar at two participating centers in Belgium. Culture results of the vaginorectal swabs obtained at the two centers were also compared. A total of 1,142 samples (838 in Leuven and 304 in Bonheiden) obtained from consecutive pregnant women were cultured onto both media. Of all GBS carriers 84.7% were detected on Columbia blood agar and 93.4% on Granada agar ( P<0.01, McNemar test). The addition of Granada agar was responsible for a 15% higher rate of detection of GBS carriers. As a result of this study, both participating hospitals will use a combination of Granada agar with Columbia blood agar for optimal GBS screening in the future.

Comparison of direct selective versus nonselective agar media plus LIM broth enrichment for determination of group B streptococcus colonization status in pregnant women

CONTEXT

Group B streptococcus (GBS) is the most common cause of early-onset neonatal sepsis in developed countries, and determination of the GBS colonization status in pregnant patients near term is essential for the provision of prophylactic measures to prevent early-onset disease.

OBJECTIVES

To determine if GBS recovery rates and/or result turnaround times for vaginal or combined vaginal/rectal swab specimens from pregnant patients near term are enhanced if swabs are inoculated initially onto selective versus nonselective agar media, in addition to the standard Centers for Disease Control and Prevention method.

DESIGN

Prospective laboratory analysis.

SETTING

Urban health region/centralized diagnostic microbiology laboratory.

PATIENTS

Pregnant women presenting for routine obstetrical care and collection of vaginal or combined vaginal/rectal swab specimens for GBS testing at 35 to 37 weeks' gestation.

INTERVENTION

Culture of specimens directly onto selective (5% sheep blood with colistin and nalidixic acid) or nonselective (5% sheep blood) agar media, in addition to LIM broth enrichment and terminal subculture.

MAIN OUTCOME MEASURES

Group B streptococcus recovery rate and culture result turnaround time.

RESULTS

A total of 639 specimens were tested, with 128 (20%) positive for GBS. Sixty-three isolates were recovered on direct agar media at 24 hours, of which 16 (12.5%) were isolated on selective plates only. An additional 38 isolates were recovered at 48 hours from direct plates. Twenty-seven (21.1%) isolates that failed to grow on direct plates were recovered from the LIM broth subculture only. Three (2.3%) isolates not recovered from LIM broths were detected at 48 hours on the direct selective (2 isolates) and nonselective (1 isolate) agar plates. A 24-hour result turnaround time was achieved for 63 (49.2%) and 47 (36.7%) of the 128 culture-positive specimens for direct selective and nonselective plates, respectively (chi2 = 76.63, P <.001).

CONCLUSIONS

Use of direct selective agar media, in addition to LIM broth enrichment, for the determination of the GBS colonization status in pregnant patients near term results in decreased turnaround time for reporting positive results.

Evaluation of methods to increase the sensitivity and timeliness of detection of Streptococcus agalactiae in pregnant women

Direct culture of rectovaginal specimens on Granada agar was compared to culture on sheep blood agar plate (SBAP) and AccuProbe detection of group B streptococcus from overnight LIM broth enhancement cultures (LIM-SBAP). Both broth-enhanced methods demonstrated excellent sensitivity (97.5% for LIM-SBAP and 93.5% for AccuProbe), while Granada agar demonstrated a sensitivity of only 40.3%.

Molecular methods for rapid detection of group B streptococci

Group B streptococci (GBS) are an important cause of neonatal sepsis and meningitis. Implementation of selective intrapartum chemoprophylaxis based on either a screening-based approach or a risk-based approach has led to a substantial decrease in the morbidity and mortality of GBS disease. Current 'gold-standard' detection methods for GBS are selective broth cultures of combined vaginal and anal specimens collected at 35-37 week's gestation. Rapid immunological detection methods, including latex agglutination test, enzyme immunoassay and optical immunoassay, as well as hybridization-based test, are available. These methods are useful in rapid identification of heavily colonized women, but are unable to detect light GBS colonization due to poor sensitivity. Recent development of real-time PCR and fluorescence labeling technologies has provided new detection platforms for bacterial identification. GBS-specific PCR assays using these new technologies offer promising tools for sensitive and specific detection of GBS directly from clinical specimens. The application of these assays in the current prevention strategy will simplify the prevention practice and rationalize antibiotic use.

Pigment production by Streptococcus agalactiae in quasi-defined media

A quasi-defined medium that supports the growth of Streptococcus agalactiae as pigmented colonies has been developed. The medium contains starch, a peptic digest of albumin, amino acids, nucleosides, vitamins, and salts. The presence of free cysteine, which could be replaced with other sulphur-containing compounds and to a lesser degree by reducing agents, was required for pigment formation.

Modified Granada Agar Medium for the detection of group B Streptococcus carriage in pregnant women

OBJECTIVES

To improve the detection rate of group B streptococci (GBS) in pregnant women, aiming at the prevention of early-onset septicemia in the newborn.

METHODS

The yield from culturing two sites, vaginal and anorectal, on a Modified Granada Medium (MGM) was compared with our standard approach of culturing a vaginal swab on blood agar (BA).

RESULTS

Samples were processed from 430 consecutive pregnant women. GBS was isolated from the vagina in 11.6% with BA, and in 13.7% with MGM. In 17.0% of anorectal samples, GBS was identified with MGM. The combination of both sites and media had a yield of 20.0%. MGM identified all but six (2%) of 310 GBS strains after aerobic incubation, with use of a cover slide, and missed only three strains (1%) after anaerobic incubation.

CONCLUSIONS

Separate culture of vaginal and anorectal samples using the same MGM agar plate resulted in an increase in detection rate for GBS of 76% as compared to BA alone. The technique is simple and results are available after overnight incubation. MGM was confirmed as a specific medium for the identification of GBS, with a sensitivity of 98-99%.