Evaluation of chromID strepto B as a screening media for Streptococcus agalactiae
Toyohisa Morita, Dongyun Feng1, Yoko Kamio
1Department of Scientific Research, Division of Scientific Affairs, Sysmex Corporation, 1-3-2 Murotani, Nishi-ku, Kobe 651-2241, Japan. Feng.Dongyun@sysmex.co.jp.
Insights
ChromID Strepto B (STRB) media is more effective for detecting Group B Streptococcus (GBS) colonization in pregnant women than traditional blood agar. STRB offers higher detection rates and fewer false negatives, simplifying GBS screening.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Public Health
Background:
- Group B Streptococcus (GBS) causes infant sepsis and meningitis, preventable by maternal screening.
- Maternal GBS colonization is detected via vaginal-rectal screening at 35-37 weeks gestation.
- Chromogenic media like ChromID Strepto B (STRB) offer a visual method for GBS detection.
Purpose of the Study:
- To compare the efficacy of ChromID Strepto B (STRB) with conventional blood agar (BA) for GBS screening.
- To evaluate GBS detection rates and false negative occurrences between the two methods.
- To assess the suitability of STRB for clinical laboratory use.
Main Methods:
- Anovaginal swabs from 1425 pregnant women (35-37 weeks gestation) were analyzed.
- Samples were cultured on both STRB and BA plates after enrichment in Todd Hewitt Broth (THB).
- Isolates were confirmed using GBS latex agglutination testing.
Main Results:
- GBS was detected in 319 (22.4%) samples.
- STRB identified 318 GBS cases versus 299 with BA.
- STRB exhibited one false negative, while BA had 20; STRB also detected non-hemolytic GBS.
Conclusions:
- STRB demonstrates superior performance compared to BA for GBS screening.
- STRB offers a higher detection rate and fewer false negatives, enhancing diagnostic accuracy.
- The simple colorimetric result of STRB makes it ideal for clinical laboratory technicians.
Background:
Streptococcus agalactiae (Group B Streptococcus, GBS), a leading cause of sepsis and meningitis in infants, can be transmitted vertically from mother to infant during passage through the birth canal. Detection of GBS colonization in perinatal women is a major strategy for the prevention of postpartum neonatal disease. The U.S. Centers for Disease Control and Prevention recommends that all women undergo vaginal-rectal screening for GBS colonization at 35-37 weeks of gestation. ChromID Strepto B (STRB) is a chromogenic GBS screening media on which GBS colonies appear pink or red, while other bacteria are either inhibited or form colonies in other colors. In this study, we compared STRB with a conventional GBS detection method using 5% sheep blood agar (BA) followed by a selective enrichment broth.
Methods:
Anovaginal swabs were collected from 1425 women during weeks 35 to 37 of their pregnancies. The swabs were used to inoculate both STRB and BA plates after enrichment with selective Todd Hewitt Broth (THB). A GBS latex agglutination test was used to confirm the identity of isolates from each plate.
Results:
GBS was recovered from 319 (22.4%) samples with one or both media: 318 on STRB compared to 299 using BA. One false negative was observed on STRB, and 20 false negatives were observed on BA. In addition, non-hemolytic GBS was recovered from 19 (6.0%) samples using STRB.
Conclusions:
STRB offers effectiveness and convenience over BA for GBS screening in clinical laboratories. STRB produces fewer false negatives, has a higher detection rate and uses a simple color screen that is ideal for technician-level applications. We recommend STRB as the media of choice for GBS screening.
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