Quantitative Detection of Shiga Toxin-Producing and Enteropathogenic Escherichia coli Serotypes O157 and O26 in Bulk Raw Milk

A hurdle strategy based on the combination of non-thermal treatments to control diarrheagenic E. coli in cheese

This study aimed to assess the efficacy of a multi-hurdle process combining mild High Hydrostatic Pressure (HHP) treatments and Thyme Oil (TO) edible films as a non-thermal method to combat pathogenic E. coli (aEPEC and STEC) in raw cow's-milk cheese stored at 7 °C and packaged under modified atmosphere. Changes in headspace atmosphere of cheese packs and treatment effects on Lactic Acid Bacteria (LAB) counts and diarrheagenic E. coli strains (aEPEC and STEC) were evaluated over a 28 d storage period. The results demonstrated that the combined treatment exhibited the most significant antimicrobial effect against both strains compared to individual treatments, achieving reductions of 4.30 and 4.80 log cfu/g after 28 d of storage for aEPEC and STEC, respectively. Notably, the synergistic effect of the combination treatment resulted in the complete inactivation of intact cells for STEC and nearly completed inactivation for aEPEC by the end of the storage period. These findings suggest that the combination of HHP with selected hurdles could effectively enhance microbial inactivation capacity, offering promising alternatives for improving cheese safety without affecting the starter microbiota.

Quantitative Risk Assessment of Hemolytic Uremic Syndrome Associated with Consumption of Bulk Milk Sold Directly from Producer to Consumer in South Africa

This study was conducted to estimate the hemolytic uremic syndrome (HUS) risk associated with consumption of producer-distributor bulk milk (PDBM) contaminated with Shiga toxin-producing Escherichia coli (STEC) in South Africa. Data were obtained from recently completed studies in South Africa taking into account prior collected prevalence data of STEC in raw and pasteurized PDBM and survey information from producer-distributor outlets and households. Inputs for the models were complemented with data from published and unpublished literature. A probabilistic exposure model was developed with Monte Carlo simulation in Excel add-in software using @Risk software. Hazard characterization was based on an exponential dose-response model to calculate the probability of illness from STEC infection in individuals 5 years and younger and individuals older than 5 years. The estimated mean STEC level was 0.12 CFU/mL (95% confidence interval [CI]: 0 to 1.2; σ = 0.34) for raw PDBM and 0.08 CFU/mL (95% CI: 0 to 1; σ = 0.27) for pasteurized PDBM. A higher risk of HUS cases per year was recorded in raw than in pasteurized PDBM and also in individuals younger than 5 years of age. For every 100,000 servings consumed, the expected median numbers of HUS cases per year from raw PDBM were 52 for 5 years and younger and 3.2 for older than 5 years. The median numbers of cases per year for pasteurized PDBM were 47 for 5 years and younger and 2.9 for older than 5 years. Sensitivity analysis revealed that serving volume and time taken to sell PDBM at producer-distributor outlets were the factors with the greatest impact on probability of illness. The models developed in this study are an example of risk assessments for milk produced and marketed from similar scenarios across the globe.

Effectiveness of the Thermal Treatments Used for Curd Stretching in the Inactivation of Shiga Toxin-Producing O157 and O26 Escherichia coli

The kneading treatment of the fresh curd in hot water is a critical control point in the manufacturing of mozzarella. Factors such as the ratio between hot water and curd mass, the rheological properties, and the mixing and kneading activity affect the processing time and the internal temperature of the curd. The aim of this study was to investigate the effect of thermal treatments on the fate of Shiga toxin-producing Escherichia coli (STEC). Nine curd samples (weight 160-270 g) were artificially contaminated with O157 or O26 STEC and stretched in hot water (90-95°C) for 5-10 min. Depending on the heating process and spinning, different nonisothermal profiles were recorded. Observed reductions of O157 and O26 STEC varied between 1.01 and more than 5.38 log⁡MPN (Most Probable Number)/g at the end of the temperature treatments. Further, nonisothermal log-linear tail models were developed to compare observed reductions for O157 and O26 VTEC under variable temperature conditions. Results obtained showed that the comparison of predictions provided by the dynamic model with observations described well the linear inactivation pattern since nonsignificant differences were denoted at all profiles tested. The dynamic model developed can be useful to evaluate the effectiveness of the thermal treatments used in the manufacturing of mozzarella in the inactivation of STEC.

Paediatric HUS Cases Related to the Consumption of Raw Milk Sold by Vending Machines in Italy: Quantitative Risk Assessment Based on Escherichia coli O157 Official Controls over 7 years

A quantitative risk assessment (RA) was developed to estimate haemolytic-uremic syndrome (HUS) cases in paediatric population associated with the consumption of raw milk sold in vending machines in Italy. The historical national evolution of raw milk consumption phenomenon since 2008, when consumer interest started to grow, and after 7 years of marketing adjustment, is outlined. Exposure assessment was based on the official Shiga toxin-producing Escherichia coli O157:H7 (STEC) microbiological records of raw milk samples from vending machines monitored by the regional Veterinary Authorities from 2008 to 2014, microbial growth during storage, consumption frequency of raw milk, serving size, consumption preference and age of consumers. The differential risk considered milk handled under regulation conditions (4°C throughout all phases) and the worst time-temperature field handling conditions detected. In case of boiling milk before consumption, we assumed that the risk of HUS is fixed at zero. The model estimates clearly show that the public health significance of HUS cases due to raw milk STEC contamination depends on the current variability surrounding the risk profile of the food and the consumer behaviour has more impact than milk storage scenario. The estimated HUS cases predicted by our model are roughly in line with the effective STEC O157-associated HUS cases notified in Italy only when the proportion of consumers not boiling milk before consumption is assumed to be 1%. Raw milk consumption remains a source of E. coli O157:H7 for humans, but its overall relevance is likely to have subsided and significant caution should be exerted for temporal, geographical and consumers behaviour analysis. Health education programmes and regulatory actions are required to educate people, primarily children, on other STEC sources.

Enumeration of verocytotoxigenic Escherichia coli (VTEC) O157 and O26 in milk by quantitative PCR

Quantitative real-time polymerase chain reaction (qPCR) can be a convenient alternative to the Most Probable Number (MPN) methods to count VTEC in milk. The number of VTEC is normally very low in milk; therefore with the aim of increasing the method sensitivity a qPCR protocol that relies on preliminary enrichment was developed. The growth pattern of six VTEC strains (serogroups O157 and O26) was studied using enrichment in Buffered Peptone Water (BPW) with or without acriflavine for 4-24h. Milk samples were inoculated with these strains over a five Log concentration range between 0.24-0.50 and 4.24-4.50 Log CFU/ml. DNA was extracted from the enriched samples in duplicate and each extract was analysed in duplicate by qPCR using pairs of primers specific for the serogroups O157 and O26. When samples were pre-enriched in BPW at 37°C for 8h, the relationship between threshold cycles (CT values) and VTEC Log numbers was linear over a five Log concentration range. The regression of PCR threshold cycle numbers on VTEC Log CFU/ml had a slope coefficient equal to -3.10 (R(2)=0.96) which is indicative of a 10-fold difference of the gene copy numbers between samples (with a 100 ± 10% PCR efficiency). The same 10-fold proportion used for inoculating the milk samples with VTEC was observed, therefore, also in the enriched samples at 8h. A comparison of the CT values of milk samples and controls revealed that the strains inoculated in milk grew with 3 Log increments in the 8h enrichment period. Regression lines that fitted the qPCR and MPN data revealed that the error of the qPCR estimates is lower than the error of the estimated MPN (r=0.982, R(2)=0.965 vs. r=0.967, R(2)=0.935). The growth rates of VTEC strains isolated from milk should be comparatively assessed before qPCR estimates based on the regression model are considered valid. Comparative assessment of the growth rates can be done using spectrophotometric measurements of standardized cultures of isolates and reference strains cultured in BPW at 37°C for 8h. The method developed for the serogroups O157 and O26 can be easily adapted to the other VTEC serogroups that are relevant for human health. The qPCR method is less laborious and faster than the standard MPN method and has been shown to be a good technique for quantifying VTEC in milk.