MUG EC O157 Agar is recommended for isolation and differentiation of enterohaemorrhagic Escherichia coli O157:H7 from foodstuffs, water and clinical samples by a fluorogenic method.
PRINCIPLE AND INTERPRATATION
MUG EC O157 Agar is recommended for isolation and enumeration of enterohaemorrhagic Escherichia coli (EHEC) from foodstuffs, water and clinical samples based on sorbitol utilization and formation of beta-glucuronidase enzyme. The enterohaemorrhagic E. coli O157:H7 strains produce toxins, which can result in life threatening extra intestinal complications in the form of the hemolytic uremic syndrome and thrombotic-thrombocytopenic purpura. Due to severe clinical implications, the isolation and detection of E. coli O157:H7 strains are of importance.
Sodium deoxycholate inhibits the growth of gram-positive microbes. Sorbitol provides carbon and energy source. Bromothymol blue is the pH indicator. Microorganisms utilizing sorbitol exhibit yellow colonies whereas sorbitol-negative strains (such as E. coli O157:H7) grow as greenish colonies. Hydrogen suphide production is detected as black-brown colony colouration due to presence of sodium thiosulphate and ferric ammonium citrate. Thus, Proteus mirabilis having similar biochemical characteristics as that of E. coli O157:H7 can easily be differentiated. 4-Methylumbelliferyl b-D-glucuronide (MUG) is converted into 4-methylumbelliferone by beta-D-glucuronidase-forming pathogens. 4-methylumbelliferone fluoresces under UV light. All commensal E. coli produce beta-glucuronidase. E. coli O157:H7 is not capable of forming b-glucuronidas, thus when exposed under long-wave UV light, no fluorescence is observed. The plates were exposed to ammonia fumes to increase fluorescence as suggested by Freir and Hartman.