BS ISO 16649-1:2018

Microbiology of the food chain. Horizontal method for the enumeration of beta-glucuronidase-positive Escherichia coli. Colony-count technique at 44 ° C using membranes and 5-bromo-4-chloro-3-indolyl beta-D-glucuronide | Status: Confirmed, Current

1 Scope This document specifies a horizontal method for the enumeration of β-glucuronidase-positive Escherichia coli by colony-count technique after resuscitation using membranes and incubation at 44 °C on a solid medium containing a chromogenic ingredient for detection of the enzyme β-glucuronidase[9][10][13][14][17][18][19][20]. It is applicable to

• — products intended for human consumption,
• — products intended for feeding animals,
• — environmental samples in the area of food production and food handling, and
• — samples from the primary production stage such as animal faeces, dust, and swabs.

WARNING Some strains of Escherichia coli may grow poorly or not at all in media incubated at 44 °C. This includes strains of E. coli O157:H7 and O157:H-. Additionally, some strains of Escherichia coli, notably those belonging to serotype O157:H7, are mostly β-glucuronidase negative[11]. Consequently, some strains of E. coli, including pathogenic ones, will not be detected by this method. β-glucuronidase activity may also be exhibited at 44 °C by certain other members of the Enterobacteriaceae, notably Shigella[15] and Salmonella[16].