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Title: An investigation of the use of β-glucuronidase activity for the enumeration of Escherichia coli
Author: Grubb, Susan Mary
ISNI:       0000 0001 3521 4138
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1991
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beta-Glucuronidase activity was investigated as a method of enumerating Escherichia coli in food and water more rapidly than traditional methods. As approximately 95% of E. coli strains and very few other microbial species are reported to produce the enzyme this may provide a convenient marker for the organism. A liquid medium has been developed containing the substrate p-nitrophenol-beta-D-glucuronide which is hydrolysed by beta-glucuronidase releasing the coloured product p-nitrophenol. In this medium there was a direct inverse linear relationship between the log E. coli concentration in the inoculum and the length of incubation required for colour to reach a threshold optical density of 0.05, the "detection time". This relationship was maintained at 37 and 44°C for a single E. coli strain and a mixed E. coli inoculum containing approximately 5% beta-glucuronidase-negative cells and could be used as the basis for a calibration curve. At 44°C colour development was achieved more quickly as a result of increased enzyme activity. This temperature was also sufficiently selective to allow the procedure to be used in the presence of a competitive microflora that outnumbered E. coli by a factor of up to 10e4. The method gave a good correlation with a standard cultural method for the enumeration of E. coli in water samples. The medium was also used as the basis of a simpler pass/fail test using the Lovibond comparator to assess colour development and hence beta-glucuronidase activity following 15 hours incubation at 44°C. This method is of greater potential as a simple test of compliance with guideline values for E. coli rather than direct enumeration of the organism. Both methods are able to generate results more rapidly than traditional methods using a minimum of laboratory equipment and as such could be applied to food and water testing in the field.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Food preservation/microbiology