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

Area of Science:

• Microbiology
• Clinical Diagnostics
• Bacterial Pathogenesis

Background:

• Group B Streptococcus (GBS) is a significant cause of neonatal infections.
• Accurate and timely detection of GBS is crucial for effective prevention and treatment strategies.
• Current diagnostic protocols often involve direct inoculation of clinical specimens into selective media.

Purpose of the Study:

• To compare the detection rate of GBS using direct inoculation versus delayed inoculation into selective enrichment broth after transport in Amies medium with charcoal.
• To evaluate the suitability of Amies transport medium for maintaining GBS viability and detectability.

Main Methods:

• Clinical GBS isolates (n=103) were inoculated into Amies transport medium with charcoal at a low concentration (10 colony-forming units/swab).
• Swabs were subsequently transferred to enrichment broth (NPC) at various time intervals (0, 2, 4, 6, 24 hours).
• Detection of GBS was performed using New Granada Medium Modified (NGM) after incubation, with results recorded based on characteristic orange pigmented colonies.

Main Results:

• An overall GBS detection rate of 92.2% was achieved across all time points and conditions.
• A small percentage of isolates (3.9%) required up to 2 hours of delayed inoculation for detection.
• Two isolates (1.9%) yielded inconsistent results, potentially due to the very low inoculum used.

Conclusions:

• Delayed inoculation into selective enrichment broth following transport in Amies medium with charcoal demonstrates comparable GBS detection rates to direct inoculation.
• Amies transport medium with charcoal is validated as an appropriate medium for GBS transport when immediate inoculation is impractical.
• The findings align with recommendations from the Centers for Disease Control (CDC) Guidelines, 2002, supporting the use of this transport method.