Detection of Shiga Toxin – Producing Escherichia coli in Raw and Pasteurized Milk

Abstract

One hundred random samples of raw buffalo and pasteurized cow milk (50, each) were collected from different localities of Sharkia Governorate for the detection of E. coli. The isolates were screened by PCR for virulence associated genes as well as antibiotic sensitivity test to determine the most effective antimicrobial agent. Furthermore, an experimental study was carried out to detect the influence of pasteurization and processing of kariesh cheese and yoghurt on E. coli O 111 :H 8 inoculated in milk with the concentration of 10 8 CFU/mL. The obtained results showed that the occurrence of E. coli in the examined raw buffalo and pasteurized cow milk samples were 66% and 30%, respectively. Serogrouping of E. coli isolates revealed that O128, O26 and O111 were recorded as the most frequent O-serogroups. The sensitivity test showed that E. coli isolates were more sensitive to gentamicin (79.2%), followed by ciprofloxacin (70.8%) and colistin (68.8%). However, the examined isolates were completely resistant to erythromycin (100%) followed by sulphamethazole-trimethoprim (79.2%). Molecular identification of virulence associated genes revealed stx1, stx2 and eaeA genes. The experimental study showed that milk pasteurization was more effective on E. coli O 111 :H 8 survival at refrigeration temperature compared with processed products such as kariesh cheese and yoghurt.

Genome engineering of Stx1-and Stx2-converting bacteriophages unveils the virulence of the dairy isolate Escherichia coli O174:H2 strain UC4224

“…Along with this, the intrinsic microbiota of raw milk together with the starter cultures are expected to outcompete pathogens by lowering the pH (Baylis, 2009). Nevertheless, raw milk cheeses of different varieties (soft and semi-hard) have been described as sources of contamination or outbreaks of STEC, since they do not undergo pasteurisation and the production process is not effective in counteracting the proliferation of these bacteria (Schlesser et al, 2006;Caro and García-Armesto, 2007;Miszczycha et al, 2013Miszczycha et al, , 2016Peng et al, 2013;Ahmed and Samer, 2017;Celikl et al, 2021). However, STEC have been isolated from pasteurised milk cheese as well, possibly due to crosscontamination (Fereydouni and Darbouy, 2015;Callon et al, 2016;Cardoso and Marin, 2016).…”

“…These outbreaks, as reported by the data collected in the European Union One-Health (2022) report, demonstrate as raw milk cheese and other dairy products are frequently associated to the presence of STEC (2% of analysed dairy products (EFSA and ECDC, 2022)). Thus, in the absence of an effective pasteurisation process, the cheese production and ripening steps have proven to be insufficient to achieve the complete inactivation of these pathogenic E. coli microorganism (Bellio et al, 2018;Ioanna et al, 2018), as shown in studies that investigated the persistence of STEC in raw milk and its derivatives (Miszczycha et al, 2013;Peng et al, 2013;Ahmed and Samer, 2017).…”

Chemical and Bacteriological Assessment of Raw Milk Collected from Some Dairy Farms in El-Behera Governorate, Egypt.

“…The serogroups of 12 representative E. coli isolates which were categorized as O111,O128, O91, and untyped E. coli strains (2 strain each), O26(3 strains), O44 (1 strain) as displayed in Table 4.These findings agreed with Momtaz et al [57]who reported that O26, O111, O91 O128 and O145 serogroups are the most frequent E. coli O-serogroups detected in raw cow's milk. Additionally, Ahmed and Samer [58] reported that E. coliO26, O44, and O111serogroups were identified from raw buffalo's milk samples in Egypt. Ranjbar et al [59] found that O26, O111, and O121serogroups were prevalent in STEC strains detected in raw milk and milk products in Iran.…”

“…On the other hand, Ahmed and Samer [58] proved that E. coli isolates were sensitive to gentamicin, ciprofloxacin and colistin. In China, all E. coli strains were susceptible to gentamicin and exhibited different resistance levels to ampicillin, amoxicillin-clavulanic acid, trimethoprim-sulfamethoxazole, tetracycline, and ciprofloxacin as (46.3%), (16.4%), (13.4%), (13.4%), and (1.5%), respectively [53].…”