Oral Presentations - Pathology and Laboratory Medicine - University ...

OtherAbstract # 69Laura Book 1 , Ghada N. Al-Rawahi 1,2 , Eva Thomas 1,21Department of Pathology and Laboratory Medicine, BC Children’s Hospital, 2 Department ofPathology and Laboratory Medicine, University of British ColumbiaGhada Al-Rawahievaluation of two chromogenic media for screening ofgroup b streptococcus in pregnant womenBackround/ObjectivesTo compare the performance of StrepB Select (SBB) (Bio-Rad) and chromID Strepto B agar (STRB) (BioMerieux)media to that of our routine method for group B Streptococcus (GBS) detection in women at 35 to 37 weeksgestation.MethodsFive hundred consecutive vaginal/anal swabs were submitted directly to our microbiology laboratory for routineGBS screen between January and July 2009. The swabs were immediately emulsified in 0.5 ml of sterile saline andprocessed as follows:• Routine: Blood agar plate (BAP) (PML) + Group B Strep (GBS) Broth (PML).The BAPs and the GBS broths were inoculated, then incubated at 35oC for 18-24 hours. BAPs were examinedfor colonies with typical GBS morphology. Negative BAPs were re-incubated for an additional 24 hrs and thecorresponding GBS broths were sub-cultured to BAPs. All suspect colonies were confirmed by Prolex Streptococcalgrouping latex reagents (Group B) (Pro-Lab Diagnostics).• Study: SBB + STRB + GBS broth.The SBB, STRB plates and GBS broths were incubated for 24 hours at 35oC, then processed as follows: all plateswere examined for the presence of GBS colonies (SBB: blue colonies; STRB: pale pink/red colonies) followed by latexagglutination confirmation. Negative SSB/STRB plates were re-incubated for an additional 24 hours and the GBSbroth was sub-cultured to SBB and STRB. Confirmation by latex agglutination was considered the gold standard.ResultsA total of 109/500 samples (22%) were positive for GBS as follows: routine method detected 88/109 (80%); SBBdetected 90/109 (83%) at 24 hours, 99/109 (91%) at 48 hrs, 107/109 (98%) after selective broth culture; STRBdetected 85/109 (78%) at 24 hrs, 95/109 (87%) at 48 hours, 104/109 (95%) after selective broth culture.ConclusionBoth chromogenic media were more sensitive than our routine method for detection of GBS. The SBB was easier toread and more sensitive whilst the STRB was more specific after direct reading. However, the specificity becomes less ofan issue if all suspect colonies are confirmed by latex agglutination.80 2 0 1 0 * P o s t e r P r e s e n t a t i o n s