Food and Environmental Safety

The Food and Environmental Safety Programme provides consultancy, research and surveillance on microbiological and chemical food safety issues on farms and their environment to protect public and animal health.

The Food and Environmental Safety Programme, often in conjunction with the Health Protection Agency (HPA), provides consultancy, research and surveillance on food and environmental safety issues on farms and their environment, in support of public and animal health.

Salmonella

Following the successful completion of the EU survey for the prevalence of Salmonella on holdings of layer flocks, a target has been set for the reduction of S.Enteritidis (SE) and S.Typhimurium (ST) on layer farms. 8% of UK layer holdings were infected with these serotypes, which compared favourably with other Member States. The UK target is to reduce this prevalence by 10% each year from 2008. A statutory programme for the control of Salmonella in commercial egg layer flocks was introduced in February 2008 (The Control of Salmonella in Poultry Order 2007). VLA research has contributed to the development of advice on the prevention and control of Salmonella in commercial egg laying flocks and rodent infestation in poultry flocks.

Field research has shown that SE infection is likely to persist in laying houses, unless effective intervention measures are taken. Routine vaccination against SE may not prevent newly placed flocks from becoming infected in typically contaminated houses, although it does reduce within-flock prevalence, level of excretion and infection of eggs. Effective cleansing and disinfection will not prevent infection of newly placed flocks in the presence of infected rodents. However, intensive and targeted baiting using highly palatable bait may lead to flocks becoming SE-negative.

Multi-variable analysis of epidemiological data collected in the EU prevalence survey supports the findings of field studies. Larger holdings were at higher risk of infection, while vaccination was an effective protective factor. Good hygiene and disinfection practices and running the site as all-in/all-out reduced the likelihood of Salmonella and/or SE, while close proximity to neighbouring farms, frequent sighting of rodents, using a company feed source or having caged birds increased the risk of infection.

EU programmes are being developed to reduce Salmonella in other sectors of primary production and statutory control of broiler flocks will commence next year. A recent survey reported a very low level of infection with serotypes of public health significance in broiler holdings. S.Enteritidis, S.Hadar and S.Infantis were not isolated and there were only single isolations of S.Typhimurium and S.Virchow. This reflects the considerable efforts taken to reduce Salmonella and successful control in breeding flocks. An EU target has been set to reduce SE or ST infection to 1% of flocks or less by 2012 and the UK broiler industry is currently within this target. Prevalence surveys of Salmonella in turkeys and slaughter pigs were completed in September.

Two further surveys began in January; Salmonella in breeding pigs (farm-based) and Campylobacter in broilers (abattoir-based). VLA consultants have played an important part in the design of the EU technical specifications, through their participation as invited experts in the EFSA and DG SANCO working groups. The development of the national control programmes is underpinned by a considerable body of research in support of the development of effective control measures. The VLA has led a successful project proposal to develop a quantitative microbiological risk assessment on Salmonella in pigs that will support development of the EU control programme.

Enterohaemorrhagic E.coli

Enterohaemorrhagic E.coli (EHEC) is an important zoonotic pathogen with ruminants as the primary reservoir. Our research has aided the understanding of EHEC colonisation and persistence in animals and how this may impact control strategies. Recent work has focused on sheep as reservoir hosts. Our studies have shown that lambs deprived of colostrum and then challenged with E.coli O157 are highly susceptible to colonisation compared to conventionally reared lambs. Additionally, lambs pre-disposed with Cryptosporidium shed higher numbers of O157 in their faeces and at necropsy were found to be colonised to a higher level than lambs solely inoculated with O157. These findings have contributed to advice given to petting farms with orphan lambs.

Cryptosporidium

Our study to assess the risk of zoonotic transmission of Cryptosporidium showed that pets associated with human cases did not have a greater likelihood of shedding Cryptosporidium oocysts than those of controls. Mathematical models to describe attribution of human cryptosporidiosis showed that pets account for <0.67% of cases per year. Good hygiene is recommended to prevent infection. Analysis of VLA ‘Farmfile’ data to estimate the burden of illness showed that sheep were particularly likely to be associated with human infection. Two ‘high risk’ scenarios (a camping event held on pasture previously grazed by infected cattle and contact with an infected calf on a petting farm) were modelled in a quantitative risk assessment of key environmental routes of C.parvum transmission from farm animals to humans. Approximately 1/1000 visits resulted in infection in both scenarios. Risk was reduced by hand washing after handling the animals and increasing the time between cattle grazing and the camping event.

Antimicrobial Resistance

Surveillance over 18 months of 940 Staphylococcus aureus isolates recovered from mastitic milk samples from cattle, screened by a duplex PCR, did not reveal the presence of methicillin-resistant Staphylococcus aureus (MRSA). Toxin gene characterisation revealed that 52% of isolates possessed at least one toxin, mainly enterotoxins and all isolates were negative for Panton-Valentine Leukotoxin. The findings are encouraging for the UK livestock industry, given the emergence of MRSA in some food-producing animals in Europe.

All Salmonella isolates recovered from animals are screened phenotypically for extended-spectrum beta-lactamases (ESBL) and none have been detected. Since 2006, VLA has screened E.coli recovered from clinical diagnostic submissions (mainly cattle) for ESBLs. E.coli containing CTX-M-1, 3, 14, 15 and 20 have been detected in a small proportion of cattle samples, mostly faecal or intestinal samples from calves. The E.coli carrying ESBLs were clinically relevant in some cases. Abattoir-based surveillance of poultry for ESBLs in E.coli is underway.

Zoonotic bacteria are becoming increasingly resistant to antibiotics and at the same time there is increased emphasis on cleansing and disinfection as a means to control zoonotic pathogens. Exposure to, and survival against, sub-lethal disinfection may lead to the selection of multiple antimicrobial resistant phenotypes.

A laboratory based project has investigated selection and characteristics of antibiotic and disinfectant resistant mutants of Salmonella in chickens. Mutants with low level resistance were readily selected and one step mutants did not have compromised fitness. The study highlighted the need for adequate and appropriate disinfection regimens and the need to monitor field isolates for low level resistance.

We have developed a novel array technology that detects and differentiates over 60 antibiotic-resistance genes or gene families, which is being used for targeted studies. The array system is called Identibac® and is commercially available. Further information on Identibac® can be found here.