Comparative study of group B Streptococcus differential agar versus LIM broth for detection and identification of Streptococcus agalactiae in pregnant women
Abstract number: 1734_115
Adler A., Block C., Engelstein D., Hochner-Celnicier D., Drai-Hasid R., Moses A.E.
Objectives: Our goal was to compare BD Group B Streptococcus Differential Agar (GBSDA, Becton Dickinson), a commercially available modification of Granada medium, with inoculation into LIM broth and subculture onto blood agar plates (LIM-BAP) as a method for GBS screening in pregnant women.
Methods: First, we compared the detection threshold and the ease of use of GBSDA with LIM-BAP by inoculating known numbers of GBS mixed with approximately 107 colony-forming units (cfu)/mL of other bacteria (E. faecalis ATCC 29212, S. epidermidis ATCC 12228, P. mirabilis ATCC 7002 and a clinical isolate of LactoBacillus sp.). Second, we tested the production of carotenoid pigment in 159 GBS blood culture isolates. Finally, we compared GBSDA, LIM broth with direct GBS antigen detection (LIM-AG) and LIM-BAP as methods for GBS screening in pregnant women presenting in labour to the delivery room. Suspect colonies were identified as GBS by a commercial agglutination test. Identification of non-haemolytic GBS included a positive CAMP test and failure to hydrolyse esculin on bile-esculin agar.
Results: GBS colonies were easily detected on GBSDA (figure) at a threshold of 2000 cfu/mL in a mixed culture. In contrast, GBS was not detected in a mixed culture on BAP subcultured from LIM broth with initial inocula of up to 104 cfu/mL. Orange pigment was produced in 149 of 159 GBS blood culture isolates, including one non-haemolytic isolate. Pigment was not produced in 8 non-haemolytic and 2 haemolytic strains. GBS was detected by GBSDA in 49 out of 226 women (21.6%) but in only 42 (18.5%) and 36 (16%, p < 0.05) women by using LIM-BAP and LIM-AG, respectively.
Conclusion: GBSDA was faster, easier to use and more sensitive for the detection of GBS from vaginal swabs, compared with LIM-BAP. Although non-haemolytic strains are usually missed by this method, it appears that enrichment in LIM broth offers no advantage for detection of these strains. Therefore, GBSDA may be the culture method of choice for GBS screening in pregnant women.
|Session name:||European Society of Clinical Microbiology and Infectious Diseases|
|Location:||ICC, Munich, Germany|
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