Assessment of the Microbiological Quality of Meat Pies from Retail Sale in England 2013

Risk presented to minimally processed chilled foods by psychrotrophic Bacillus cereus

BACKGROUND

Spores of psychrotrophic Bacillus cereus may survive the mild heat treatments given to minimally processed chilled foods. Subsequent germination and cell multiplication during refrigerated storage may lead to bacterial concentrations that are hazardous to health.

SCOPE AND APPROACH

This review is concerned with the characterisation of factors that prevent psychrotrophic B. cereus reaching hazardous concentrations in minimally processed chilled foods and associated foodborne illness. A risk assessment framework is used to quantify the risk associated with B. cereus and minimally processed chilled foods.

KEY FINDINGS AND CONCLUSIONS

Bacillus cereus is responsible for two types of food poisoning, diarrhoeal (an infection) and emetic (an intoxication); however, no reported outbreaks of food poisoning have been associated with B. cereus and correctly stored commercially-produced minimally processed chilled foods. In the UK alone, more than 1010 packs of these foods have been sold in recent years without reported illness, thus the risk presented is very low. Further quantification of the risk is merited, and this requires additional data. The lack of association between diarrhoeal food poisoning and correctly stored commercially-produced minimally processed chilled foods indicates that an infectious dose has not been reached. This may reflect low pathogenicity of psychrotrophic strains. The lack of reported association of psychrotrophic B. cereus with emetic illness and correctly stored commercially-produced minimally processed chilled foods indicates that a toxic dose of the emetic toxin has not been formed. Laboratory studies show that strains form very small quantities of emetic toxin at chilled temperatures.

Listeria monocytogenes in Foods

Listeria monocytogenes causes listeriosis, a rare foodborne disease with a mortality rate of 20%-30%. The elderly and immunocompromised are particularly susceptible to listeriosis. L. monocytogenes is ubiquitous in nature and can contaminate food-processing environments, posing a threat to the food chain. This is particularly important for ready-to-eat foods as there is no heat treatment or other antimicrobial step between production and consumption. Thus, occurrence and control of L. monocytogenes are important for industry and public health. Advances in whole-genome sequence technology are facilitating the investigation of disease outbreaks, linking sporadic cases to outbreaks, and linking outbreaks internationally. Novel control methods, such as bacteriophage and bacteriocins, can contribute to a reduction in the occurrence of L. monocytogenes in the food-processing environment, thereby reducing the risk of food contamination and contributing to a reduction in public health issues.

An assessment of the microbiological quality of lightly cooked food (including sous-vide) at the point of consumption in England

This observational study aims to investigate the microbiological quality of commercially prepared lightly cooked foods with a major component of food of animal origin and collected as would be served to a consumer. A total of 356 samples were collected from catering (92%), retail (7%) or producers (1%) and all were independent of known incidents of foodborne illness. Using standard methods, all samples were tested for: the presence of Campylobacter spp. and Salmonella spp. and enumerated for levels of, Bacillus spp. including B. cereus, Clostridium perfringens, Listeria spp. including L. monocytogenes, Staphylococcus aureus, Escherichia coli, Enterobacteriacea and aerobic colony count (ACC). Results were interpreted as unsatisfactory, borderline or satisfactory according to the Health Protection Agency guidelines for assessing the microbiological safety of ready-to-eat foods placed on the market. Amongst all samples, 70% were classified as satisfactory, 18% were borderline and 12% were of unsatisfactory microbiological quality. Amongst the unsatisfactory samples, six (2%) were potentially injurious to health due to the presence of: Salmonella spp. (one duck breast); Campylobacter spp. (two duck breast and one chicken liver pâté); L. monocytogenes at 4·3 × 103 cfu (colony-forming units)/g (one duck confit with foie gras ballotin) and C. perfringens at 2·5 × 105 cfu/g (one chicken liver pâté). The remaining unsatisfactory samples were due to high levels of indicator E. coli, Enterobacteriaceae or ACC.

An assessment of the microbiological quality of liver-based pâté in England 2012-13: comparison of samples collected at retail and from catering businesses

The purpose of this study was to investigate the microbiological quality of liver pâté. During 2012-13, a total of 870 samples, unrelated to the investigation of food-poisoning outbreaks, were collected either at retail (46%), catering (53%) or the point of manufacture (1%) and were tested using standard methods to detect Salmonella spp. or Campylobacter spp., and to enumerate for Listeria spp., including Listeria monocytogenes, Clostridium perfringens, coagulase-positive staphylococci including Staphylococcus aureus, Bacillus spp., including Bacillus cereus, Escherichia coli, Enterobacteriaceae, and aerobic colony counts (ACCs). Seventy-three percent of samples were of satisfactory microbiological quality, 18% were borderline and 9% unsatisfactory. Salmonella spp. or Campylobacter spp. was not recovered from any sample. The most common causes of unsatisfactory results were elevated ACCs (6% of the samples) and high Enterobacteriaceae counts (4% of samples). The remaining unsatisfactory results were due to elevated counts of: E. coli (three samples); B. cereus (one sample at 2·6 × 105 cfu/g); or L. monocytogenes (one sample at 2·9 × 103 cfu/g). Pâté from retail was less likely to be contaminated with L. monocytogenes than samples collected from catering and samples from supermarkets were of significantly better microbiological quality than those from catering establishments.

An Outbreak of Human Listeriosis in England between 2010 and 2012 Associated with the Consumption of Pork Pies

An outbreak of listeriosis in England affecting 14 people between 2010 and 2012 and linked to the consumption of pork pies was investigated. All 14 individuals were older than 55 years, 12 were men, and 10 reported the presence of an underlying condition. All were resident in or had visited either of two English regions and were infected with the same strain of Listeria monocytogenes. In interviews with 12 patients, 9 reported eating pork pies, and individuals that consumed pork pies were significantly more likely to be infected with an outbreak strain than were individuals with sporadic cases of listeriosis infections in England from 2010 to 2012. Pork pies were purchased from seven retailers in South Yorkshire or the East Midlands, and the outbreak strain was recovered from pork pies supplied by only the producer in South Yorkshire. The outbreak strain was also recovered from samples of finished product and from environmental samples collected from the manufacturer. The likely source of contamination was environmental sites within the manufacturing environment, and the contamination was associated with the process of adding gelatin to the pies after cooking. Inadequate temperature control and poor hygienic practices at one of the retailers were also identified as possible contributory factors allowing growth of the pathogen. Following improvements in manufacturing practices and implementation of additional control measures at the retailers' premises, L. monocytogenes was not recovered from subsequent food and environmental samples, and the outbreak strain was not detected in further individuals with listeriosis in England.