Culture-Based Method with Performance Comparable to That of PCR-Based Methods for Detection of Group B Streptococcus in Screening Samples from Pregnant Women

Abstract

We compared five approaches for group B streptococcus (GBS) detection: three culture-based methods and two methods using broth-enhanced real-time PCR. Carrot broth-enhanced subculture to GBS Detect (Hardy Diagnostics, Santa Maria, CA) exhibited sensitivity and specificity comparable to carrot broth-and LIM broth-enhanced real-time PCRs. G roup B streptococcus (GBS) colonization during pregnancy has been implicated as a major risk factor for severe neonatal infections, including sepsis, pneumonia, and meningitis (1, 2). In the United States, the Centers for Disease Control and Prevention recommend screening women between 35 and 37 weeks of pregnancy to determine GBS carrier status and prophylactic antibiotic treatment during labor for women at risk of transmitting this organism (2).Several published studies have demonstrated the usefulness of culture-based (3, 4) and PCR-based (5-10) methods for detecting GBS. We compared five approaches for GBS detection: chromogenic culture detection by Northeast Laboratory GBS agar (NEL; Northeast Laboratory Services, Winslow, ME) and StrepB carrot broth (carrot broth; Hardy Diagnostics, Santa Maria, CA), carrot broth-enhanced subculture to GBS Detect (Detect; Hardy Diagnostics, Santa Maria, CA), and carrot broth-enhanced and LIM broth-enhanced (Remel, Lenexa, KS) real-time PCRs.A total of 211 vaginal/rectal swabs submitted for routine prenatal GBS screenings were evaluated, including 104 BactiSwab double swab transports (Remel, Lenexa, KS) and 107 Eswabs (Copan Diagnostics, Inc., Murrieta, CA). All specimens were directly inoculated on NEL plates using the specific transport swab (Fig. 1). When a BactiSwab double-swab transport was received, both swabs were used to inoculate NEL plates. One swab was placed in the carrot broth (according to the manufacturer's instructions), and the second swab was placed in the LIM broth. When an Eswab was received, both the carrot and LIM broths were each inoculated with approximately 500 l of the Eswab modified Liquid Amies transport solution and the swab was placed in the carrot broth (according to the manufacturer's instructions). NEL plates were incubated anaerobically at 35°C and examined at 18 to 24 h and 48 h for orange colonies (indicative of GBS). Carrot and LIM broths were incubated aerobically at 35°C for 18 to 24 h. Prior to PCR, all carrot broths were examined for any orange color in the broth, which is indicative of GBS, and were subcultured to Detect plates. Detect plates were incubated aerobically at 35°C for 18 to 24 h and examined for any beta-hemolytic colonies, which is a specific characteristic of GBS on Detect regardless of hemolysis exhibited on sheep blood agar. Real-time PCR was performed on the Cepheid SmartCycler system (Cepheid, Sunnyvale, CA) using the BD GeneOhm StrepB assay (Becton, Dickinson, Franklin Lakes, NJ) as described previously for 50 l aliquots of carrot and LIM broths (5). All NEL, carrot broth, and Detect isolates were confirmed GBS positive by performing CAMP tests. CAMP negative isolates were confi...

Multicenter Clinical Evaluation of the Xpert GBS LB Assay for Detection of Group B Streptococcus in Prenatal Screening Specimens

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Evaluation of StrepB Select Chromogenic Medium and the Fast-Track Diagnostics Group B Streptococcus (GBS) Real-Time PCR Assay Compared to Routine Culture for Detection of GBS during Antepartum Screening

“…Performance of qPCR directly with rectovaginal samples missed 3% of the cases that were detected by using pre-enrichment prior to either CM culture or qPCR, although the bacterial inoculum size was small for these women. Berg et al compared five different methods of genital GBS detection that included three culture-based methods, including chromogenic culture with Northeast Laboratory GBS agar (Northeast Laboratory Services, Winslow, ME), carrot broth-enhanced subculture to GBS Detect (Hardy Diagnostics), and carrot broth-and Lim broth-enhanced real-time PCRs, as well as routine Strep B Carrot Broth culture (22). Carrot broth-enhanced subculture to GBS Direct chromogenic medium had performance comparable to that of broth-enhanced qPCR, and either method had a higher sensitivity than routine culture.…”

Prevención de la infección por Streptococcus del grupo B en gestantes

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