Microbiology of the food chain - Horizontal method for the enumeration of beta-glucuronidase-positive Escherichia coli - Part 3: Detection and most probable number technique using 5-bromo-4-chloro-3-indolyl-ß-D-glucuronide (ISO 16649-3:2015)
This International Standard specifies a horizontal method for the detection and enumeration of ß-glucuronidase positive Escherichia coli, by means of the liquid medium culture technique and calculation of the most probable number (MPN) after incubation at 37 °C, then at 44 °C. This International Standard is applicable to:
- products intended for human consumption and the feeding of animals, and
- environmental samples in the area of food production and food handling
The method is suitable for the enumeration of cells of Escherichia coli that may have been subjected to stress arising from dehydration, freezing, exposure to a saline (such as marine) environment or damage by disinfectants such as chlorine-containing products.
A limitation of the applicability of this International Standard is imposed by the susceptibility of the method to a large degree of variability.
This method has not been fully evaluated for all matrices, e.g. for milk and milk products. ISO 7251 should be used for milk and milk products.
WARNING – Strains of Escherichia coli that do not grow at 44 °C and, in particular, those that are ß glucuronidase negative, such as Escherichia coli O157 and some other strains of pathogenic E. coli, will not be detected by the method described in this International Standard.