CHROMagar™ StrepA Chromogenic Medium

For Screening of Group A Streptococci (GAS) in Throat Samples

CHROMagar™ StrepA is a selective chromogenic culture medium designed for the detection and presumptive identification of Streptococcus pyogenes (Group A Streptococcus, GAS) directly from throat swabs. Colonies of S. pyogenes appear intense orange to red, while most commensal streptococci appear colorless or blue, allowing for rapid visual differentiation within 18–24 hours.

This medium was developed to support rapid diagnosis of streptococcal pharyngitis, complementing or confirming rapid antigen and molecular test results, while preserving the advantages of traditional culture—including susceptibility testing and epidemiological tracking.

Colony Appearance

• Group A Streptococcus (S. pyogenes): Orange to red
• Other oral streptococci: Colorless or blue

Performance

Streptococcus pyogenes accounts for approximately 20–30% of bacterial pharyngitis in children and 5–15% in adults. While many sore throat cases are viral and self-limiting, untreated GAS infections can lead to complications including rheumatic fever, glomerulonephritis, and invasive disease.

Because clinical signs are not reliable in differentiating GAS from viral infections, especially in pediatric patients, laboratory confirmation is necessary. Although rapid tests and molecular methods are increasingly used, culture remains the gold standard, as it allows for:

• Confirmation of positive or questionable rapid test results
• Antimicrobial susceptibility testing
• Strain typing and surveillance

CHROMagar™ StrepA provides a faster and more interpretable alternative to blood agar, reducing false negatives and improving visualization of colonies even in polymicrobial samples.

Intended Use

CHROMagar™ StrepA is intended for the qualitative detection and presumptive identification of Streptococcus pyogenes from throat swab specimens to assist in diagnosing streptococcal pharyngitis. It can also support:

• Surveillance of asymptomatic carriers
• Epidemiological investigations
• Confirmation of GAS in pediatric and adult patients presenting with sore throat

The test should be performed with 18–24 hours of incubation at 35–37 °C in a CO₂-enriched atmosphere.

This medium is not intended to diagnose infection or guide therapy, and should be used in conjunction with other clinical information and confirmatory tests.

Advantages

1. First chromogenic medium specifically developed for Group A Streptococcus
2. Easy colony identification: Orange-red color clearly distinguishes S. pyogenes from other flora
3. High sensitivity and specificity compared to traditional blood agar methods
4. Compatible with automation: Suitable for integration into WASPLab™ and other digital microbiology platforms
5. Supports downstream testing: Cultures can be used for susceptibility tests or MALDI-TOF identification

Test Procedure

• Sample type: Throat swab
• Inoculation: Direct plating
• Incubation: 18–24 hours at 35–37 °C in CO₂
• Interpretation:
  • Orange to red colonies = presumptive S. pyogenes
  • Colorless or blue colonies = non-GAS streptococci

Ordering Information

Each pack includes:

• Base medium
• Supplements SP372(S1) and SP372(S2)

Storage and Shelf Life

• Storage: 2–8 °C, dry and protected from light
• Shelf life: Up to 24 months from the date of manufacture
• Prepared media: Use within validated shelf-life as indicated in product instructions

Scientific Publications

• Gaskin et al., 2019 – Implementation of CHROMagar™ StrepA on WASPLab™ using ESwab™
• Kayak, 2019 – Artificial intelligence-assisted detection of S. pyogenes
• Van et al., 2019 – Automated GAS detection with CHROMagar™ and digital imaging systems
• All studies presented at ASM and J. Clin. Microbiol.

CHROMagar™ StrepA provides a reliable, rapid, and visually clear solution for the screening of Group A Streptococcus in throat swabs. With its high specificity, easy-to-interpret color reactions, and compatibility with modern automation platforms, it is an ideal tool for clinical microbiology laboratories, particularly those serving pediatric, emergency, or outpatient settings.