Objectives:

Routine screening of pregnant women for group B Streptococci (GBS) rather than risk-based approach is now recommended. We evaluated five media for the detection of GBS in pregnant women 35–367 weeks gestation.

Methods:

Vaginal/rectal swabs transported in Amies media (Starplex Scientific, Canada. In the laboratory, the swabs were transferred to tubes containing 0.8 mL sterile saline and vortexed. One hundred microlitres of the bacterial suspension was used to inoculate each of the following media, CNA agar with 5% sheep blood (Oxoid Canada), selective Todd Hewitt broth with 5% sheep blood (THB, Oxoid Canada), LEN GBS agar (GBSA, Northeastern Laboratory Services, Winslow, ME), NEL GBS broth (GBSB), and Instant Granada broth (IGB, Biomedics, Madrid, Spain). CNA, GBSB, GBSA, and IGB were examined after 24 and 48 h of incubation. Development of orange to red colouration in GBSA, GBSB, and IGB was considered to be an indication of GBS growth. GBSB, IGB if negative and THB were subcultured onto CNA after 24 h incubation.

Results:

Specimens from 405 women were processed, 97 (24%) of these were found to be positive for GBS. Seven (7.2%) of 97 GBS were non-haemolytic and non-pigment producing and were not detected in GBSB, GBSA, and IGB. Detection of GBS after 24 and 48 h incubation was achieved in 79 (81.4%) and 80 (82.6%) specimens, respectively, by CAN, 84 (86.6%) and 86 (88.7%) specimens by GBSA, 82 (84.5%) and 86 (88.7%) specimens by GBSB and 86 (88.7%) and 88 (90.7%) specimens by IGB. Ninety-one (93.8%) GBS were isolated from IGB subcultures and 90 from GBSB and IGB subcultures.

Conclusions:

All media, except CNA performed well. THB subcultures had the least overgrowth with commensal organisms. Broth media performed better than plate media. For most strains, results from GBSA, GBSB, IGB were available earlier than those of THB. However, more GBS were identified on subcultures from GBSB and IGB than could be identified in these media after 48 h incubation. Consequently turn-around time for broth media was the same.