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...

Previous published reports have shown that group B Streptococcus (GBS) isolates were 100% susceptible to both penicillin (1, 2) and vancomycin (1); however, reduced susceptibilities to penicillin have been documented (3)(4)(5)(6)(7)(8). GBS susceptibilities to clindamycin and erythromycin have varied (2,(9)(10)(11)(12), and data regarding inducible clindamycin resistance are not always reported (2). We examined GBS susceptibilities to clindamycin, erythromycin, penicillin, and vancomycin from isolates obtained from prenatal screening samples.Vaginal/rectal ESwab (Copan Diagnostics Inc., Murrieta, CA) samples submitted for routine prenatal GBS screenings were evaluated. GBS was isolated and identified using Strep B Carrot Broth (Hardy Diagnostics, Santa Maria, CA) subcultured to GBS Detect (Hardy Diagnostics, Santa Maria, CA) as previously described (13). GBS Detect is a selective medium, and it allows for the isolation of GBS, including strains that are typically nonhemolytic on sheep blood agar. Immediately following isolation, GBS isolates were subcultured to sheep blood agar plates (Remel, Lenexa, KS) and incubated aerobically for 18 to 20 h at 35°C. Antimicrobial susceptibility testing (AST) was performed according to 2013 CLSI guidelines (14) on 102 GBS isolates using vancomycin and benzylpenicillin G (0.016 to 256 g/ml) Etest strips (bioMérieux, Durham, NC) and on 387 GBS isolates using clindamycin (2 g) and erythromycin (15 g) BBL Sensi-Discs (Becton, Dickinson, and Company, Sparks, MD) placed 12 mm apart to detect inducible clindamycin resistance.A total of 102/102 (100%) GBS isolates examined were susceptible to penicillin and vancomycin (Table 1). Both the MIC 50 and MIC 90 for penicillin were 0.064 g/ml, and both the MIC 50 and MIC 90 for vancomycin were 1.0 g/ml (data not shown). GBS isolates were susceptible to both clindamycin and erythromycin in 195/387 (50.4%) isolates and resistant to both clindamycin and erythromycin in 106/387 (27.4%) isolates (data not shown). An additional 8% (31/387) of isolates had a positive D-test, indicating inducible clindamycin resistance. The overall susceptibilities of GBS isolates to clindamycin were 62.8% (243/387) or 70.8% (274/ 387), accounting for or not accounting for inducible clindamycin resistance, respectively. The overall susceptibility of GBS isolates to erythromycin was 51.7% (200/387) ( Table 1).Current recommendations for GBS in pregnant women include AST of GBS strains isolated from penicillin-allergic women at high risk for anaphylaxis, screening for inducible clindamycin resistance when AST is performed, and reporting GBS isolates with inducible clindamycin resistance as clindamycin resistant (15). However, penicillin allergy may not always be known at the onset of labor. Our laboratory routinely performs clindamycin and erythromycin susceptibility testing on all GBS strains isolated from prenatal screening samples. Here we report rates of susceptibility of GBS to clindamycin, erythromycin, penicillin, and vancomycin that are very similar to those ...

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