Features

BBL™ CHROMagar™ O157

BBL™ CHROMagar™ O157 medium is a selective medium for the isolation and presumptive identification of Escherichia coli O157 using clinical, food, veterinary and environmental sources. Current methods can take 24-72 hours and there are many health risk concerns in delayed detection of E. coli 0157:H7.

CHROMagar™ O157 provides:

• AOAC- RI approved
• Time to results 24 hours
• Confirmation of E. coli O157:H7 of the serotype and/or toxin
• Colonies of E. coli 0157:H7 produce a mauve color
• High Sensitivity and Specificity

Results

After proper incubation, read plates against a white background. E. coli O157 will produce mauve-colored colonies on CHROMagar O157 medium. Gram-positive organisms should be completely inhibited. Gram-negative organisms, other than E. coli O157, will either be inhibited or produce colorless, blue, green or blue-green (aqua) colonies.

Principles

Specially selected peptones supply the nutrients. The addition of potassium tellurite, cefixime and cefsulodin reduces the number of bacteria other than E. coli O157 that grow on this medium. The chromogen mix consists of artificial substrates (chromogens), which release an insoluble colored compound when hydrolyzed by a specific enzyme. E. coli O157 uses one of the chromogenic substrates and produces mauve colonies on this medium. Bacteria, other than E. coli O157, may utilize other chromogenic substrates resulting in blue to blue-green colored colonies or, if none of the chromogenic substrates are utilized, appear as their natural color. This permits the differentiation of E. coli O157 rather than other organisms.

Procedure

1. Enrich sample in enrichment broth i.e. E.coli pre-enrichment broth, Phosphate buffered (butterfield) diluent at 35 degrees C. for 24 hours.

2. Inoculate CHROMagar^TM O157 plate with 0.1ml of the enrichment broth and streak for isolation. Incubate at 35 degrees C. for 24 hours. If the specimen is cultured out of a swab, roll the swab over a small area and streak starting in this area with a loop.

3. Observe plates for characteristic colonial morphology and color at 18-24 hours. If negative for E.coli re-incubate for an additional 12-24 hours and read again.

AOAC is a trademark and Performance Tested Methods Program is a service mark of AOAC International. CHROMagar is a trademark of Dr. A. Rambach. BD, BD Logo and BBL are trademarks of Becton, Dickinson and Company. ©2005 BD

Literature

Bdchromagar0157 (1.92 MB)

Ecoliflowchart (75.06 kB)

GeneralbrochureBDchromagar (701.15 kB)

Specs