ABSTRACT
AIMS: To reduce the analysis time needed for the enumeration of Escherichia coli, a rapid fluorogenic method (MUG) which takes only 48 h was compared with the standard most probable number (MPN) method which takes 6 days as described in the International Standards Organization (ISO). This study provides reliability data for the fluorogenic method applied to certain foods. METHODS AND RESULTS: Both methods were applied to 500 food samples which were analysed for E. coli enumeration. Agreement between the two methods was found in 409 (81 x 8%) samples; 81 (16 x 2%) samples gave higher values by the fluorogenic method, and only 10 (2 x 0%) samples were more effectively assayed by the ISO method. According to statistical analysis, the reliability between the methods was r = 0 x 9706, r(2) = 0 x 9421 and Cronbach's alpha = 0 x 9851. While all three values showed a high degree of correlation (P < 0 x 0001) between the two methods, McNemar's test demonstrated a significant difference between them, indicating that the MUG method was more reliable than the ISO method. CONCLUSIONS: The data suggest that the fluorogenic method is more reliable and shorter to perform than the standard ISO method. SIGNIFICANCE AND IMPACT OF THE STUDY: Comparison of the two methods may provide a rapid and more reliable alternative for the enumeration of E. coli in food samples.
Subject(s)
Escherichia coli/isolation & purification , Fluorometry/methods , Food Microbiology , Bacteriological Techniques/methods , Bacteriological Techniques/standards , Culture Media , Fluorescent Dyes/chemistry , Meat Products/microbiology , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
An assay to screen Escherichia coli in foods using MUG supplemented lauryl sulfate tryptose (LST) broth instead of tryptone water (TW) medium was evaluated. The results presented in this paper suggest that this method is more sensitive for lower levels of E. coli, faster (16-18 h vs. 6-10 days) and less expensive (2.454 vs. 2.887 EURO/sample) than the standard ISO procedure. Thus, this method may be beneficial for use when both fecal coliforms and E. coli analyses are required in food systems.
Subject(s)
Colony Count, Microbial/methods , Enterobacteriaceae/growth & development , Escherichia coli/growth & development , Food Microbiology , Colony Count, Microbial/economics , Costs and Cost Analysis , Culture Media , Enterobacteriaceae/isolation & purification , Escherichia coli/isolation & purification , Feces/microbiology , Fluorescent Dyes/metabolism , Hymecromone/analogs & derivatives , Hymecromone/metabolism , Sensitivity and Specificity , Time FactorsABSTRACT
255 minced beef, 101 soudjouk and 50 uncooked hamburger samples were analyzed for the presence of Escherichia coli O157:H7 serotype. m-EC and LST broths were used as selective enrichment media and SMAC agar was used as a selective isolation medium. A total of 3 E. coli O157 were isolated by conventional culture techniques; one from each of minced beef, uncooked hamburger and soudjouk but none were identified as the H7 serotype. For determination of selective media-growing cohabitant bacteria, 2645 isolates were obtained from SMAC agar. Results showed that E. coli type 1, Hafnia alvei and Citrobacter freundii were dominant competitive flora. As selective enrichment broth-growing cohabitant microflora existed at higher levels, it was too difficult to isolate E. coli O157 from these mixed flora. Therefore, conventional methods are not suitable for these types of products, because of isolation difficulties and failure to confirm.
