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Infectious Diseases in Obstetrics and Gynecology
Volume 11 (2003), Issue 4, Pages 199-202
http://dx.doi.org/10.1080/10647440300025521

Screening Protocols for Group B Streptococcus: Are Transport Media Appropriate?

Department of Microbiology and Infectious Diseases, The Royal Women's Hospital, Women's and Children's Health, Flemington Road, Parkville, Victoria 3053, Australia

Received 3 March 2003; Accepted 16 July 2003

Copyright © 2003 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objective: To evaluate group B streptococcus (GBS) detection in an in vitro setting, using a low and controlled inoculum from swabs directly inoculated into a selective medium, as compared to delayed inoculation following a period in a commercial Amies transport medium with charcoal (Venturi Transystem Copan, Italy).

Study design: Clinical isolates of GBS (n = 103), were inoculated into the Amies transport medium with charcoal in a concentration of 100 colony-forming units (cfu)/ml (10 cfu/swab). Swabs were then transferred to an enrichment broth (NPC) at time intervals of 0, 2, 4, 6 and 24 hours. Broths were then incubated for 18–24 hours at 35C° in air, before being transferred to New Granada Medium Modified (NGM) for GBS detection and incubated for a further 18–24 hours at 35C°in air. If the characteristic orange pigmented colonies were observed after this period, the specimen was recorded as + (1–10 colonies) or ++ (more than 10 colonies).

Results: Overall 92.2% (95/103) of isolates were detected in all tubes and at all times. An additional two isolates were non-hemolytic, non-pigment forming GBS. Of note, 3.9% (4/103) were negative until 2 hours delayed inoculation and 1.9% (2/103) gave inconsistent results, likely due to the low inoculum used.

Conclusion: Delayed inoculation into selective enrichment broth following a period in transport medium, even with a low inoculum, gave a similar and acceptable GBS detection rate to direct inoculation. Hence, Amies transport medium with charcoal is an appropriate transport medium to use, where it is not practical for clinical specimens to be directly inoculated into selective enrichment broth and as endorsed in the Centers for Diseases Control (CDC) Guidelines, 2002.