Comparison of various methods for Group B Streptococcus Identification and Cost Comparison

Abstract

Objectives To verify the utility, cost and feasibility of various methods for Group (Gp) B Streptococcus (GBS) identification; To elucidate the prevalence and resistance patterns of GBS in a clinic population. Design and Methods Isolates were collected from pregnant patients by culturing lower vaginal swabs (LVS) and rectal swabs (RS) from May to September 2015 at Sangre Grande Hospital, Trinidad. These were screened in Carrot Broth (CB), Gram stained and isolated on Blood Agar (BA) and Streptococcus Selective Agar (SSA) simultaneously. Identification was done simultaneously with the Microscan Autoscan® and Streptex® – Streptococcal Grouping kit, to establish concordance. The Microscan Autoscan® panel identified various Streptococcus spp. and Streptex® identified Lancefield Gps A-G. Antimicrobial susceptibility was determined with the Microscan Autoscan® for Gp B Streptococcus only. Discordant isolate identifications between Microscan and Streptex were retained for further analysis. Gram staining was also carried out on negative CB. The total cost of identification of isolates was calculated in Trinidad and Tobago dollars. Results 36 LVS & RS samples were collected: 16 Gp B, 1 Gp C, 11 Gp D & 8 with no Streptococci Gp identification. Prevalence of Gp B Streptococci: 44.4%. Concordance between CB and other methods was 86.1%. Sensitivity: 100%; CI (72% – 100%), Specificity: 80%; CI (59% – 93%). Accuracy: 86.1%; CI (70% – 96%). Microscan Autoscan® and Streptex® identified 100% of isolates correctly. Penicillin resistance was 12.5%, Vancomycin and Clindamycin sensitivity were 100% each. The costs for isolation media plates were – SSA: $ 26 per plate and BA: $18 per plate. Streptococcus identification and sensitivity using Microscan Autoscan® Panel 33: $114 per isolate (with blood agar). Streptococcus identification using Streptex®: $193 per isolate (with blood agar) and Carrot Broth: $49 per isolate. Key Words: Group B Streptococci, Carrot Broth, Microscan, Streptex, SSA, Cost