Screening protocols for group B streptococcus: are transport media appropriate?
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).


METHODS
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 35 degrees C in air, before being transferred to New Granada Medium Modified (NGM) for GBS detection and incubated for a further 18-24 hours at 35 degrees C 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.


CONCLUSIONS
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.
Teese
Nicolette
N
Department of Microbiology and Infectious Diseases, The Royal Women's Hospital, Women's and Children's Health, Farmington Road, Parkville, Victoria, Australia.
Henessey
Daneeta
D
Pearce
Christopher
C
Kelly
Nigel
N
Garland
Suzanne
S
D000362:Agar; D001431:Bacteriological Techniques; D002606:Charcoal; D015169:Colony Count, Microbial; D017077:Culture Media, Conditioned; D005260:Female; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D012680:Sensitivity and Specificity; D013290:Streptococcal Infections / Q000175:diagnosis; D013292:Streptococcus agalactiae / Q000254:growth & development* / Q000302:isolation & purification
D017077:Culture Media, Conditioned; D002606:Charcoal; D000362:Agar