Comparison between Colifast® Milk and the standard method for the detection of coliforms in pasteurised milk

Abstract

-Colifast ® Milk is a rapid screening test for the detection of total coliforms in milk based upon the measurement of change in fluorescence during an incubation period, due to the targeted b-D-galactosidase activity on 4-methyl-umbelliferone-b-D-galactoside contained in a selective growth medium. In this work, 800 samples of homogenised pasteurised milk, with different fat content (1.5 and 3.5%) and contaminated with various concentrations of coliforms (from 0.03 to > 10000 CFU·mL -1 ), were analysed in order to compare the results obtained by Colifast ® Milk with those by the standard method. The effect of the incubation temperature (30 and 39 °C) was also investigated. For the totality of samples the correspondence between coliform counts obtained by the two methods was 64% (r 2 = 0.743; P = 0.88). The performance of Colifast ® Milk was notably affected by the level of contamination, since for samples with coliforms > 10 CFU·mL -1 the correspondence between the two methods achieved 86% (r 2 = 0.837; P = 0.94) whereas for samples with coliforms £ 10 CFU·mL -1 it fell to 42% (r 2 = 0.073; P = 0.33). Fat content also influenced the response of the Colifast ® system since the correspondence decreased from 80% (r 2 = 0.767; P = 0.91) for semi-skimmed milk to 48% (r 2 = 0.724; P = 0.63) for whole milk. Incubation at 30°C improved the recovery of coliforms by Colifast ® Milk as the correspondence between values obtained with the two methods reached 72% (r 2 = 0.760; P = 0.89) if compared with 56% (r 2 = 0.735; P = 0.87) when the incubation temperature was 39 °C. Under these operating conditions the sensitivity showed by the fluorometric method appeared to be not sufficient for the detection of coliforms in pasteurised milk.

Comparison of Standardized X-gal, ONPG and MUG Assay Methods with IS Methods by Analyzing Milk Samples

“…Foschino et al [19] developed Colifast® Milk, a fluorescence based rapid screening test for the detection of total coliforms in milk. In this, 800 samples of homogenized pasteurized milk, with different fat content (1.5 and 3.5%) and contaminated with various concentrations of coliforms (from 0.03 to > 10000 cfu/ml), were analyzed by Colifast® Milk method and compared with the standard method.…”

Selective colorimetric detection of Gram-negative re-contaminants in pasteurised milk products by a novel application of the BacT/ALERT 3D system

“…They often can be partly automated or integrated in existing laboratory information management systems. Different microbiological parameters have been analysed using novel cultural techniques in pasteurised milk: coliforms (Foschino, Colombo, Crepaldi, & Baldi, 2003;Kang & Gray, 2002;Madden & Gilmour, 1995;Raybaudi, Zea, Curini, & Martínez, 2005), Pseudomonas species (Van Tassell et al, 2012), Escherichia coli and coliforms (Beloti, Barros, Nunes, De Santana, & Nero, 2002;Feldsine et al, 2005), total bacterial counts and coliforms (Ginn, Packard, & Fox, 1986), standard plate counts, psychrotrophic bacterial counts, and coliforms (Senyk, Kozlowski, Noar, Shipe, & Bandler, 1987) and total viable counts, coliforms, and Enterobacteriaceae (Firstenberg-Eden, Foti, McDougal, & Baker, 2002). Furthermore, novel detection techniques and procedures have been presented for the detection of recontaminants in pasteurised milk, such as the determination of microbial activity using a microrespirometer (Ren & Hsieh, 2005), the detection of coliforms by menadione-catalysed luminol chemiluminescence (Kawasaki et al, 2007), the detection of microbial spoilage of milk using Fourier transform infrared spectroscopy and chemometrics (Nicolaou & Goodacre, 2008), the application of a matrix-assisted laser desorption/ionisation timeof-flight mass spectrometry (MALDI-TOF-MS) and multivariate analysis (Nicolaou, Xu, & Goodacre, 2012), and finally the specific detection of total viable coliforms, as well as viable Enterobacteriaceae, by PCR-based techniques (Soejima, Minami, Ayeshima, & Iwatsuki, 2012a;Soejima, Minami, Yaeshima, & Iwatsuki, 2012b).…”