Investigating the Effects of Time and Temperature on the Growth of Escherichia coli O157:H7 and Listeria monocytogenes in Raw Cow's Milk Based on Simulated Consumer Food Handling Practices

Evaluating the effects of temperature and agitation on biofilm formation of bacterial pathogens isolated from raw cow milk

OBJECTIVES

To study the effect of agitation and temperature on biofilm formation (cell aggregates embedded within a self-produced matrix) by pathogenic bacteria isolated from Raw cow milk (RCM).

METHODS

A 40 RCM samples were gathered from eight dairy farms in Riyadh, Saudi Arabia. After bacterial culturing and isolation, gram staining was performed, and all pathogenic, identified using standard criteria established by Food Standards Australia New Zealand (FSANZ), and non-pathogenic bacteria were identified using VITEK-2 and biochemical assays. To evaluate the effects of temperature and agitation on biofilm formation, isolated pathogenic bacteria were incubated for 24 h under the following conditions: 4 °C with no agitation (0 rpm), 15 °C with no agitation, 30 °C with no agitation, 30 °C with 60 rpm agitation, and 30 °C with 120 rpm agitation. Then, biofilms were measured using a crystal violet assay.

RESULTS

Of the eight farm sites, three exhibited non-pathogenic bacterial contamination in their raw milk samples. Of the total of 40 raw milk samples, 15/40 (37.5%; from five farms) were contaminated with pathogenic bacteria. Overall, 346 bacteria were isolated from the 40 samples, with 329/346 (95.1%) considered as non-pathogenic and 17/346 (4.9%) as pathogenic. Most of the isolated pathogenic bacteria exhibited a significant (p < 0.01) increase in biofilm formation when grown at 30 °C compared to 4 °C and when grown with 120 rpm agitation compared to 0 rpm.

CONCLUSION

Herein, we highlight the practices of consumers in terms of transporting and storing (temperature and agitation) can significantly impact on the growth of pathogens and biofilm formation in RCM.

Quantitative microbiological risk assessment for the occurrence of listeriosis in Brazil due to the consumption of milk processed by pasteurization or thermosonication

This study aimed to estimate the risk of listeriosis from the consumption of pasteurized milk in Brazil, comparing conventional treatment with the technology of thermosonication. The Quantitative Microbiological Risk Assessment (QMRA) model was developed, covering the entire milk production chain, from milking to the moment of consumption. In general, higher risks were observed in association with higher initial concentrations of the pathogen and the vulnerable population. The highest risk predicted (3.67 × 10-5) was related to the scenario considering the initial concentration range of L. monocytogenes between 4 and 6 log CFU/mL, with conventional treatment and considering the vulnerable population, resulting in one case of listeriosis every 27,248 servings. When considering thermosonication treatment, lower risks have been predicted. The scenario analysis indicated that the steps related to storage conditions in retail and at the consumer's home (post-processing steps) are the most influential in the associated risk, in all scenarios. The predictive parameters of inactivation related to the applied treatment also have a considerable influence on the risk. The results point to the influence of the stages of the dairy production chain and the thermosonication treatment applied in the food safety of milk, subsidizing information for industrial application and for regulatory agencies.

A novel approach in public health surveillance: searching the illegal dairy trade in Facebook

This paper uses the internet-based biosurveillance to describe the Brazilian e-commerce of non-inspected dairy products and maps its traditional sale in a medium-sized city (Londrina). We searched the sales of illegal dairy products on Facebook Marketplace and conducted a census of street markets and a random sample of formal markets. Although prohibited in Brazil, consumers can easily find informal dairy products on internet and retail sale. In addition, 7% of the food products hold a false label to mimic food inspection. The e-commerce was linked with regions with higher access to technology and Human Development Index (HDI). We believe that our approach shows a step forward in the public health interventions and could be replicated stimulating debates about policies required to improve the public health surveillance.

The Ability of Shiga Toxin-Producing Escherichia coli to Grow in Raw Cow's Milk Stored at Low Temperatures

Despite the lack of scientific evidence, some consumers assert that raw milk is a natural food with nutritional and immunological properties superior to pasteurized milk. This has led to the increased popularity of unpasteurized cow milk (UPM) and disregard for the risks of being exposed to zoonotic infections. Dairy cattle are healthy carriers of Shiga toxin (Stx)-producing E. coli (STEC), and contaminated UPM has caused STEC outbreaks worldwide. The association between STEC, carrying the eae (E. coli attachment effacement) gene, and severe diseases is well-established. We have previously isolated four eae positive STEC isolates from two neighboring dairy farms in the Southeast of Norway. A whole genome analysis revealed that isolates from different farms exhibited nearly identical genetic profiles. To explore the risks associated with drinking UPM, we examined the ability of the isolates to produce Stx and their growth in UPM at different temperatures. All the isolates produced Stx and one of the isolates was able to propagate in UPM at 8 °C (p < 0.02). Altogether, these results highlight the risk for STEC infections associated with the consumption of UPM.

Impact of Freezing on the Microbiological Quality and Physical Characteristics of Buffalo Mozzarella Cheese

Simple Summary

Buffalo Mozzarella cheese from Campania is made from the fresh milk of the Italian Mediterranean buffalo. In 1996, thanks to its distinctive characteristics (specific environmental conditions and production method), Regulation (EC) No. 1107/96 recognized it as a Protected Designation of Origin product. The limited availability of milk and the increased demand for buffalo mozzarella cheese, especially during the spring-summer period (when milk production is lowest), have induced the use of frozen milk or curd for its production. The aim of this research was to provide preliminary results about the effect of freezing on microbial communities of fresh buffalo milk, curd and Buffalo Mozzarella cheese, and on physical properties (whiteness, hardness, and oxidation state) of Buffalo Mozzarella cheese. The preliminary results obtained have allowed us to conclude that the freezing process if properly carried out, does not compromise the microbiological quality of the products but produces only slight changes of some physical properties.

Abstract

Buffalo Mozzarella cheese from Campania is one of the most worldwide appreciated Italian dairy products. The increased demand for buffalo dairy products and the limited availability of the finest buffalo milk has prompted the diffusion of illicit practices, such as the use of milk, curd, or other products that are frozen or bought at low cost. The aim of this research was to provide preliminary results about the trend of the microbial communities of buffalo milk, curd and Buffalo Mozzarella cheese, during freezing storage of eleven months. At the same time, the alterations of physical properties and the presence of the molecular marker “γ4-casein”, have been investigated. The results showed that freezing reduced the concentrations of the total bacterial count, Enterobacteriaceae, coliforms, Escherichia coli and yeasts in fresh milk and, the concentrations of the total bacterial count, coliforms, lactic acid bacteria and yeasts in mature curd. In the finished product, no notable decreases were observed, except for lactic acid bacteria. About the γ4-casein, no increase was observed in all matrices. These preliminary results allow us to conclude that the freezing process if properly carried out, does not compromise the microbiological quality and the physical properties of the Buffalo Mozzarella cheese.

Why knowledge is the best way to reduce the risks associated with raw milk and raw milk products

In an age of flexible conditions about mandatory milk pasteurisation, this opinion-based research reflection supports the view that the knowledge and the awareness of milk-borne infections are key requirements to decrease the risks associated with raw milk. Providing an analysis of the current potential risks related to consumption of raw milk and raw milk products, we discuss the main reasons to continue to be vigilant about milk-borne pathogens and the current scenario in relation to the formal and clandestine sale of raw milk. Finally, we select some highly effective strategies to reduce the risks associated with raw milk in food services. Regardless of whether a country regulation allows or prohibits the trade of raw milk and its products, this is not the time to be negligent.

Growth interferences between bacterial strains from raw cow's milk and their impact on growth of Listeria monocytogenes and Staphylococcus aureus

AIMS

The purpose of this study was to detect growth enhancing or inhibiting activity between bacterial populations from raw milk under different conditions (temperature, medium).

METHODS AND RESULTS

The interference of 24 raw milk isolates on growth of each other and on Listeria monocytogenes, Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus was screened by drop assay and for selected pairs in co-cultivation experiments. By drop assay, antibacterial activity was observed for 40% of the strains. About 30% of the strains showed growth-enhancing activity on other strains. Most of the isolates were well adapted to cold temperatures and showed consistent or even increased inhibiting or enhancing effects on growth of other strains at 10°C. The growth of L. monocytogenes DSM 20600^T and S. aureus DSM 1104^T was significantly (P < 0·05) reduced in co-cultivation with Pseudomonas protegens JZ R-192.

CONCLUSIONS

Growth interferences between bacterial populations have an impact on the structure of raw milk microbiota, especially when it develops under cold storage, and it may have an effect on the prevalence of certain foodborne pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates growth-inhibiting and also growth-enhancing interactions between raw milk bacteria, which must be considered when predicting bacterial growth and spoilage in food. A Ps. protegens strain isolated from raw milk showed an antagonistic effect on growth of L. monocytogenes in refrigerated raw milk.

Transmission Media of Foodborne Diseases as an Index Prediction of Diarrheagenic Escherichia coli: Study at Elementary School, Surabaya, Indonesia

Foodborne diseases (FBDs) have a large disease burden among children. The major type of FBD in children is diarrhea, caused mainly by contaminated food. One of the diarrhea pathogens is Diarrheagenic Escherichia coli (DEC). The aim of this study was to establish a model of microbial prediction (DEC) in stool, caused by the transmission of FBDs in elementary schoolchildren. An observational analytic study was conducted, with a nested case-control study design. In Stage I, the study population was children in a selected elementary school at Surabaya. The sample size for Stage I was 218 children. In Stage II, the case sample was all children with a positive test for DEC (15 children), and the control sample was all children who had tested negative for DEC (60 children). The result of the laboratory tests showed that the proportion of DEC in children was 6.88% (15 of 218 children) and the proportion of Escherichia coli O157:H7 in children was only 0.46%. The most significant mode of transmission included in the model was the snacking frequency at school and the risk classification of food that was often purchased at school. The formulation of the predicting model of DEC in stool can be used as an early warning against the incidence of FBDs in elementary schoolchildren.