Two cases of Salmonella Java, a serotype rarely isolated from livestock in the UK has become very widespread in some continental poultry organisations and was identified in SW England during the year. With the first case, the organism was isolated from organic wheat bran incorporated into organic finished feeds and was fully susceptible to all antimicrobials tested. Whereas, in the second case the organism was isolated from the premises of a calf dealer in Somerset, and was a multi-drug resistant strain. Further investigations confirmed widespread infection of the premises but no evidence of either clinical disease spread to contiguous premises, or association with human disease. In collaboration with HPA, this strain of S.Java was identified as the first in GB to show this pattern of drug resistance. Although similar to a strain causing disease in humans and associated with fish tanks and feed for ornamental fish, it was different to the strain of S.Java that has become predominant in Europe.

Biology and control of foodborne pathogens

Mixed colonisation with Campylobacter jejuni in chicken models suggests that genetic diversity enhances the capacity for environmental survival of this organism.

The development of taxonomic and typing tools, Multi Locus Sequence Typing, Pulsed Field Gel Electrophoresis, Arbitrarily Primed Fragment Length Polymorphism and Flagellin gene variability, for C.jejuni has resulted in the use of these techniques in numerous collaborative studies including the successful pan-European CAMPYNET project.

Investigations into the colonisation potential of verocytotoxigenic Escherichia coli (VTEC) O157 and other VTEC in farmed animal species has shown that VTEC O157 colonises sheep and forms classic attaching effacing (AE) lesions. These lesions are found mainly in the large intestine but not specifically in the recto-anal junction as suggested for cattle. They are also rare in the older animal. Non-O157 attaching effacing E.coli (AEEC) organisms are very common in sheep, are more competent at AE lesion formation than O157 and appear to inhibit O157 colonisation. However, tissue damage mediated by other gastro-intestinal pathogens appears to enhance O157 colonisation. Similar findings have been made in goats but the transmission of VTEC O157 from nannies to their kids was not readily demonstrated. Colonisation and long-term persistence of VTEC O157 in chickens has been observed experimentally but there is no evidence of it in commercial poultry production.

Field studies on the persistence of Salmonella in egg production systems have focused on quantifying the levels of environmental contamination associated with repeat infections in flocks and the effect of various cleaning, disinfection and vaccination programmes. Even when terminal hygiene and pest control are relatively good, vaccination can fail to prevent infection of flocks placed in contaminated cage houses, whereas those in free-range or barn houses appear to be more resistant.

Antimicrobial resistance

Minimum inhibition concentration (MIC) test being carried out at VLA Bury St Edmunds

VLA became the first anti-microbial resistance reference laboratory for the Office International des Epizooties (OIE), in May 2003, and represented the OIE at the Eighth Conference on Food Microbiology, University of Liège, Belgium. VLA also played a leading role in an expert consultation on non-human Antimicrobial Usage and Antimicrobial Resistance organised jointly by FAO, OIE and WHO in Geneva. The proceedings from this meeting are available on the WHO web-site:

http://www.who.int/foodsafety/publications/micro/nov2003/en/

Veterinary data on antimicrobial resistance was provided to HPA for inclusion in the ‘Antimicrobial Resistance in England and Wales 2002’ publication, the first combined medical/veterinary review of antimicrobial resistance in a range of bacteria recovered from England and Wales.

VLA is also helping to lead a European concerted action entitled ‘Antimicrobial Resistance in Bacteria of Animal Origin II’, which aims to harmonise sensitivity testing of farmed animals across the EU.

Projects designed to assess the prevalence and persistence of resistant bacteria in pig and poultry production have shown a quantitative association when treated with specific antimicrobials. However, resistant organisms were also found in similar situations where no such treatment had been used.

Botulism

The incidence of suspected cattle botulism has increased during the year and many of the incidents reported were circumstantially associated with the spreading of poultry litter on, or close to, land used for grazing or grass conservation. When botulism is suspected in food animals the Food Standards Agency (FSA) requires that milk and meat are withheld from entering the food chain for a two week period after diagnosis of the last clinical case.

Collaborations form an important part of the programme:

University of Liverpool and Institute of Animal Health

• study of the immune response in cattle to endemic and epidemic strains of Salmonella

HPA

• new approaches to detect and differentiate resistance genes by PCR and microarray

HPA and Direct Laboratories Ltd

• studies on antimicrobial resistance in farmed wastes

University of Reading

• studies on antibiotic resistance in pigs and poultry

University of Bristol

• investigation of Salmonella on egg laying flocks

National Public Health Service (Wales)

• investigation of the relationship between isolates of Cryptosporidium in human disease and in animal and environmental contacts
• establishment of the host range of Cryptosporidium species and genotypes

Chemical food safety

VLA’s Radiochemistry unit responded to several incidents, as part of the ad hoc contract with the FSA, where site operators exceeded their authorisation for the emission of radionuclides. None of these incidents were shown to put the food chain at risk.

A new collaborative project with the

Scottish Agricultural College (SAC)

• to establish a response to the FSA’s responsibility for the risk management of food safety throughout the UK. The model for investigation and surveillance of potential chemical contamination incidents in food animals, developed and implemented by VLA for England and Wales, has now been extended to Scotland and will be implemented by SAC.