Original scientific paper
Evaluation of PetrifilmTM Escherichia coli method for bacterial count of Escherichia coli in raw milk
Karmen Godič Torkar
; Biotehniška fakulteta, Oddelek za zootehniko, Institut za mlekarstvo, Groblje 3, 1230 Domžale, Slovenija
Slavica Golc Teger
; Biotehniška fakulteta, Oddelek za zootehniko, Institut za mlekarstvo, Groblje 3, 1230 Domžale, Slovenija
Abstract
The presence and number of bacteria Escherichia coli in bulk milk from farms, samples of raw milk and samples taken from collection points and transporting tanks were stated by the experiment. Four methods were applied. Two methods based on standard principle of counting colonies on Petridishes using selective mediums called Coli ID and VRB-MUG, to which flourescent component 4-methyl-umbellypheryl-beta-D-glucuronide (MUG) was added. There was used also PetrifilmTM E. coli plate method and the most probable number (MPN) method with lauryl-sulphate broth with MUG was taken as a standard. Among 100 samples of raw milk 31 (31%) contained less than 30 bacteria in 100 ml. Statistical proceeding of logarithmic transformation of remaining 69 samples showed, that the correlation coefficient between methods with Petrifllm and MPN method was the best (r=0.83) while it was slightly lower when comparing methods of Coli ID (r-0.80) or the method with VRB-MUG (r=only 0.65) and the mentioned standard method. Comparision of methods with Petrifilin and Coli ID shows better correlation r=0.90). The comparison between methods was better when the results of samples with high level of contamination were calculated. The results of analysis of variance show, that the difference between the standard (MPN) and other three methods, basing on colonies count on solid mediums, was statistically significant (P<0.05). The statistically characteristic difference is mostly due to large variability of data within particular methods (0-3000 bacteria/ml) and various evaluation of results for the method of the most probable number and other methods. The Duncan's test namely showed statistically significant similarity of methods Coli ID, Petrifilm and MPN method. The Coli ID method gives similar results as the standard method in 68% of cases while Petrifilm methods shows 65% and the method using VRB-MUG medium only 55%, all plotted on MPN 95% confidence intervals. For the Petrifilm method, the standard deviation for repeatability was 0.029 log units and the repeatability was 0.082 log units.
Keywords
milk; PetrifilmTM E. coli; Escherichia coli; methods
Hrčak ID:
94896
URI
Publication date:
12.5.1997.
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