Foodborne diseases / Campylobacters
CampylobactersCampylobacters are recognised as one of the most important causes of human diarrhoeal disease. Wild birds and domestic animals often carry large numbers of these bacteria in their intestinal tracts, mostly without showing any signs of disease. During slaughter of meat animals, intestinal contents may contaminate the carcass meat. Of the two most important sub-species, Campylobacter jejuni is usually the predominant type isolated from beef, lamb and poultry, Campylobacter coli from pork.
1. Bacteriological characteristics
The genus Campylobacter is a member of the family Spirallaceae and comprises Gram-negative, slender, curved bacteria, that are motile by means of a single, polar flagellum. C. jejuni and C. coli are thermophilic species and are associated with food poisoning. Molecular techniques for differentiating C. jejuni isolates such as AFLP, PFGE and MLST facilitate epidemiological studies.
2. Disease in humans
The most frequent clinical presentation is enteritis, with fever, malaise, abdominal pain and headache frequently preceding the diarrhoeal episode. The incubation period ranges from 2 to 5 days. Acute diarrhoeal disease, which is particularly prevalent in young adults, may last for 2 to 3 days with extended abdominal discomfort. Complications such as reactive arthritis and the Guillain Barré syndrom sometimes occur.
3. Sources of infection and epidemiology
Campylobacteriosis is a multi source disease. The principal reservoirs of thermophilic campylobacters are warm blooded animals whose intestinal contents may contain >10e8 cfu of campylobacters per gram. Although campylobacters are sensitive to the external environment, they can survive fairly well in water, especially at low temperatures.
C. jejuni and C coli can be isolated from red meats sampled throughout the food chain. The highest levels of contamination occur at the abattoir with the prevalence decreasing during distribution. Poultry carcasses are frequently contaminated during processing. Refrigerated storage will reduce the Campylobacter contamination on products although freezing will not eliminate the organisms. Raw milk, seafood and contaminated water have also been associated with foodborne outbreaks of campylobacter enteritis.
4. Growth properties in relation to meat and meat products
C. jejuni and C. coli grow only at temperatures exceeding 30°C with an optimum of 42-43°C. They are microaerophilic and grow optimally in an atmosphere containing 5% oxygen. These two characteristics mean that, under normal circumstances, campylobacters are unlikely to multiply outside the gastrointestinal tract.
The minimum pH value for growth is about 4.9 with an optimum range of 6.5-7.5. Because of their microaerophilic requirements, campylobacters can be expected to survive in Modified Atmosphere Packaged products. Particularly when there is a reduced oxygen concentration, although growth will not occur in conventional storage temperatures. Campylobacters are relatively sensitive to sodium chloride (2% NaCl), but tolerance is greater at higher temperatures.
Campylobacters are susceptible to desiccation and are sensitive to atmospheric oxygen. The use of a resuscitation stage prior to selective isolation may therefore be necessary to allow sublethally injured organisms to recover. Where small numbers of campylobacters are expected, enrichment media may be used, Those presently available contain various antibiotics (e.g. polymyxin B, rifampicin, vancomycin). A number of selective agars is available for isolation of campylobacters from food. These are usually incubated at 42°C under microaerobic atmosphere.
6. Control measures in slaughterhouses and cutting plants
Animals become infected with campylobacters on the farm, but the stress of loading and transportation can exacerbate excretion. There are no specific control measures which can be applied during dressing and further handling of carcasses apart from those general measures aimed at reducing faecal contamination of the meat.
Campylobacters are relatively fragile organisms, which are particularly susceptible to treatments such as drying, as might occur with air chilling, heating and exposure to the disinfectants used routinely in food processing environments. The application of thorough cleaning and disinfection protocols in slaughterhouses and cutting plants should prevent the spread of these organisms from one day’s production to the next.