12. Evaluation of Optimal Storage and Transport Medium for the Detection of Group B Streptococcus in StrepB Carrot Broth

Abstract

Group B streptococcus (GBS) is the leading infectious cause of morbidity and mortality among newborns in the USA and optimal detection of GBS colonization in pregnant women is paramount. In 2010, the Centers for Disease Control and Prevention (CDC) revised consensus guidelines for the prevention of GBS disease to include identification by chromogenic media such as StrepB Carrot Broth (CB). However, limited data are available to determine the optimal storage and transport medium (TM) required to optimize GBS survival. We compared ESwab and Amies TM to recover GBS in CB for up to 144 h at 4oC, 21oC and 24oC. 50 isolates of GBS from vaginorectal swabs were evaluated. 100 μL aliquots of 103 CFU/mL suspensions were inoculated onto Amies and ESwab TM and stored at the evaluated times and temperatures. At 24 h time periods, Amies and ESwab TM were inoculated into CB and incubated for 24 h. Results were quantified as 0, 1+, 2+, 3+, and 4+ with the degree of pigmentation correlating with the recovery of GBS. ESwab was superior to Amies at all temperatures but was optimal at 21ºC and 24ºC, whereas recovery in Amies was significantly decreased at these temperatures. Results support the use of CB to facilitate detection of GBS. Furthermore, this demonstrates that ESwab TM is superior to Amies TM for recovery of GBS, particularly when stored at 21ºC and 24ºC. In light of these findings, the CDC may consider expanding the recommendations to include alternate transport systems in addition to non-nutritive medium.