Surveillance and epidemiology of antimicrobial resistant
food-borne pathogens
A national survey of food-borne pathogens in cattle, sheep and pigs began in January 2003, to determine the prevalence of a range of food-borne pathogens and the level of antimicrobial resistance present in a number of important zoonotic and commensal bacteria recovered from animals at slaughter.

The liaison with the HPA is proving to be fruitful as a joint paper comparing levels of resistance in the main salmonella serotypes affecting man and recovered from both humans and animals has been submitted to the journal of ‘Microbial Drug Resistance’.

Presenters at the Food and Environmental Safety seminar on S.Newport at VLA Weybridge

At the European level, VLA is a major partner in a European Concerted Action on antimicrobial resistance in bacteria, which aims to harmonise sensitivity testing across the EU and provide comparative data on levels of resistance detected in farm livestock.

The VLA susceptibility testing report for 2001, compiled from a database containing test results on more than 41,000 organisms, has been completed and published on the Defra website.
The scope of the report has been extended to include data on anaerobic bacteria and bacteria recovered from wild animals.

Multi-drug resistant Salmonella Newport has emerged in the USA as an important zoonotic organism and a cause of disease in cattle. This organism has not yet been detected in animals in Europe but risk assessments relating to its introduction and spread were produced, as well as draft contingency plans detailing suitable response measures. Laboratory instructions for the isolation and provisional identification of multi-resistant strains of S.Newport have been distributed to colleagues in Northern Ireland and Scotland to ensure a common approach throughout the UK. Within VLA a computerised alert system has been put in place in addition to the necessary molecular and phenotypic techniques required to confirm the identity of suspect strains.

Biology and control of food-borne pathogens
Salmonella Enteritidis was found to be the main salmonella in layer houses and, unlike broiler farms, other serotypes were uncommon. The organism was widespread in the environment in non-vaccinated farms but prevalence was generally lower where vaccination had been used. Regular testing of eggs from vaccinated and unvaccinated flocks provided evidence that whilst vaccination reduced the prevalence of contamination by S.Enteritidis it did not eliminate it completely. Molecular typing studies were successfully used to track S.Enteritidis at various stages from breeding through to commercial production and to confirm both long term persistence of particular strains on farms and genetic divergence of organisms whilst resident on those farms.

Recent research has shown that sheep carry many attaching and effacing Escherichia coli (AEEC), a group of which includes E.coli O157. We have demonstrated that O157 can induce specific lesions in a number of sheep models but verocytotoxin E.coli (VTEC) O157 organisms may be associated with lesions induced by other AEEC (non-O157) strains. Current research is investigating at the molecular and cellular level how non-O157 VTECs interact with VTEC O157.

Working with Cambridge University to produce mutants of one of our highly invasive campylobacter strains, VLA’s invasion assay has been adapted to screen large numbers of mutants, some of which have shown reduced invasion in-vitro, compared with the parent strain. The conditions for campylobacter fimbrial expression have been established for the first time and a mutation has been made in one fimbriae-associated gene in collaboration with MGCC, Germany. Mutants will be tested for changes in fimbrial expression as detected by electron microscopy and this should provide novel insights into the mechanisms of colonisation of campylobacters in the chicken gut.

Recent studies have demonstrated that Cryptosporidium parvum genotypes 1 and 2, originating from human samples, are capable of infecting, colonising and being excreted by lambs, calves and piglets although it appears there is some host specificity with genotype 1. During a study of human cryptosporidiosis in South West England, patients were asked about contact with farms and farm animals within the two weeks before illness. The genotype and fingerprint profiles of human strains compared with strains from epidemiologically linked animal faeces have shown that all isolates produced individual fingerprint profiles, but that related isolates have a higher degree of homology. This indicates that the approach can be developed and used to trace the source of outbreaks.

A molecular technique has been developed to type Yersinia enterocolitica strains with the Danish Veterinary Institute. Strains from humans, pigs, cattle and sheep have been typed and we have demonstrated clear relationships between human and pig O9:3 isolates.

Chemical Food Safety
The Radiochemistry Unit (RCU) provides an analytical service for the Food Standards Agency (FSA), whose objective is to ensure that contamination of food by radionuclides does not compromise food safety. In order to maintain its high quality standards, RCU participates in international inter-comparison exercises organised by PROCORAD, France and the National Physical Laboratory.

The Regional Laboratories investigated over 70 potential chemical food safety incidents of which the majority were lead poisoning in cattle, due to ingestion of discarded batteries or lead contaminated soils. The FSA supports VLA in the proactive investigation of bovine copper poisoning and porcine ochratoxicosis. A workshop on copper poisoning was organised at VLA Weybridge in May 2002 and followed up with presentations to stakeholder groups on the identified causes and prevention.