Summary This study characterised the phylogenetic groups, pathotypes, antibiotic resistance and stress response of Escherichia coli isolates recovered from dairy and dried milk‐related products. A total of 54 isolates of E. coli were recovered from thirty‐three of 180 samples (18%) of these products. Representatives from all the four phylogenetic groups of the organism were identified, although groups A and B1 dominated groups B2 and D. Enterotoxigenic E. coli (ETEC) strains producing heat‐labile toxin (LT) could be detected among the isolates and were found to be associated with the Kariesh cheese. Escherichia coli isolates showed single‐drug and multiple‐drug resistance to ß‐lactams and other antibiotic classes. The blaTEM‐1 gene was found to be associated with resistance to ampicillin but not to cephalothin. Escherichia coli survived heating at 50 and 55 °C for 60 min, but was undetectable after only 10 min of exposure to 60 °C. It also survived in the presence of 6% and 8% salt for 96 h and in pH 4.0 for 72 h.

Escherichia coli is a frequent foodborne contaminant that negatively affects the quality and safety of dairy products. The present study aimed to examine the presence of E. coli in dairy and milk-related products using two detection methods namely, "direct plating" and "3-stage method". Sixty-nine samples of yoghurt, Domiati cheese, Kariesh cheese, UHT milk, dried skim milk, dried ice-cream, dried whey proteins, creamchantee, infant milk formulas, and "sahlab" were collected from 3 Egyptian governorates and examined for the presence of E. coli. A total of 250 suspected E. coli isolates could be cultured from these samples and subjected to biochemical identification that characterized 35 of these isolates as potential E. coli cultures. Further biochemical testing of these 35 cultures using the Microbact MGNB-12A miniaturized identification system confirmed their belonging to the E. coli species. These isolates were variably recovered from yoghurt (8 isolates), Kariesh cheese (12 isolates), UHT milk (1 isolate), dried ice-cream (2 isolates), creamchantee (1 isolate), infant milk formulas (5 isolates), and sahlab (6 isolates). The 3-stage method showed higher efficiency in detecting E. coli in these products than direct plating. This was attributed to the ability of the 3-stage method to detect injured cells generated on exposure to sub-lethal stress factors including those applied during food manufacture and preservation. The 3-stage method outlined in this study is, therefore, recommended for reliable detection of E. coli in dairy and milk-related products.

Enterococcus is one of the most predominant genus in milk, dairy products, and dairy effluents. The present study aimed to study the presence of Enterococcus termitis in dairy effluent (cheese whey) samples which were collected from different Egyptian dairy plants. Samples were surface plated on plates of TSA medium using miles-misra plating method. 13 isolates out of 86 bacterial isolates were suspected to belong to the genus Enterococcus. Suspected isolates were examined morphologically. Additionally, several biochemical tests like catalase, starch hydrolysis, citrate utilization, caseinase, lysine decarboxylase, lysine deaminase, H 2 S production, Esculine hydrolysis and growth on MSA medium were applied on the isolates. Moreover, the suspected isolates were examined for the ability to ferment Lactose, Glucose, Galactose, Fructose, dextrose, Mannose, Ribose, Xylose, and Manitol. Results of morphological and biochemical testes indicated that the examined isolates are Enterococcus termitis. Results of 16s RNA sequencing indicated that the examined strains are Enterococcus termitis strain LMG 8895.

Injured cells of foodborne bacteria are generated by exposure to sub-lethal doses of food preservation factors. These cells maintain viability but loss resistance to selective agents in differential media used for their detection in foodstuffs, and could thus lead to false negative results. Injured cells can be reliably recovered using a 3stage method that requires at least 4 days of lengthy culture. This study was therefore designed to develop a time and effort-effective protocol for detecting injured cells of Escherichia coli in milk. Heat-injured cells of E. coli could be generated in reconstituted skim milk (RSM) by exposure to 55 ºC for 50 min. Heat-injured cells of E. coli could be recovered using direct plating on the nonselective media of tryptone soy agar (TSA), tryptone glucose extract (TGE), and plate count agar (PCA) with TSA supplemented with 1% sodium pyrurvate (NaPyr) showing the highest recovery efficiency. None of 3 selective media of MacConkey agar (Mac), eosin methylene blue agar (EMB) and violet red bile agar (VRB) was able to recover heat-injured cells of E. coli from RSM. However, supplementing these selective media with 1% NaPyr allowed the detection of heat-injured cells of E. coli with limited recovery rates. Overlaying a thin layer of a nonselective agar over another layer of a selective medium (the thin agar layer method) improved the recovery of heat-injured cells from RSM, compared to recovery by selective media only. Supplemented TSA (TSA+) combined with EMB showed the highest recovery of injured cells from RSM, compared to other combinations of nonselective and selective media. The TSA+/EMB combination could also successfully recover heat-injured E. coli from pasteurized buffalo's milk with different fat contents. These results presented the thin agar layer method involving a combination of TSA+/EMB, as a time and effort-effective protocol for the detection of injured E. coli in milk used for preparing different dairy products.