The Forgotten Pathogen - Geraldine Duffy, The National Food Centre, Dunsinea, Castleknock, Dublin 15. Reproduced from Hygiene Review 1997, the Journal of the Irish Society of Food Hygiene Technology with the permission of the Irish Society and the author.
Over the last decade, the incidence of Campylobacter associated food poisoning has gradually increased and it is now reported to be the leading cause of bacterial gastro-enteritis in the developed world. Campylobacter was first identified as an animal pathogen about 80 years ago, and has been linked to human illness since the 1970s. The symptoms of infection are generally mild diarrhoea and fever but on rare occasions severe side effects, including meningitis, abortion and reactive arthritis syndrome can occur.
Campylobacter species are found in the normal intestinal flora of a wide range of domestic and wild animals and birds. Transmission to humans can result from direct contact with birds and animals and illness associated with this pathogen has been reported in farm and abattoir workers. In addition, foods such as meat and poultry can transmit this pathogen. Red meat carcasses may be contaminated during slaughter with faeces and/or intestinal contents that contain Campylobacter. However, this pathogen is very sensitive to drying and the practice of air chilling meat carcasses results in surface drying which will significantly reduce the number of Campylobacter organisms present. In general, offal is a more likely source of infection because it is not subjected to the same drying procedures as the carcasses. Poultry is considered to be the largest potential source of Campylobacter contamination with some surveys showing that approximately 50% of chickens tested contained the pathogenic strains, C. jejuni and C. coli. This high incidence of Campylobacter is related to differences in poultry and beef processing methods, which allow the pathogen to survive better on poultry. While, Campylobacter is readily killed by conventional cooking methods, there is a risk of cross contamination from raw onto ready to eat foods in the retail or domestic environment. Unpasteurised milk and sewage contaminated water are other potential sources of Campylobacter.
Despite the wide spread occurrence of Campylobacter, few food companies are aware of the presence of this pathogen. Lack of knowledge about the presence of this pathogen is largely related to difficulties in its detection from foods. It is an organism which grows best at 42°C in the presence of low levels of oxygen i.e. a microaerophilic atmosphere (5% 02, 10% CO2, 85% N). It is very sensitive to the effects of drying and requires a high moisture environment for growth. The initial sample enrichment can be carried out in liquid broth at 42°C under aerobic conditions but isolation on agar plates and subsequent confirmation of suspect colonies must be carried out under a microaerophilic atmosphere. This atmosphere can be achieved using gas jars with appropriate gas packs incorporated but isolation tends to be more successful if an anaerobic cabinet connected to a microaerophilic gas mixture is used.
Table
1 Incidence of Campylobacter jejuni/coli in a range of Irish
fresh and processed meat |
Sample |
Number tested |
Number Positive
for Campylobacter jejuni/coli |
Fresh chicken |
53 |
30(56%) |
frozen chicken |
3 |
0(0%) |
turkey |
4 |
0(0 0/0) |
Chicken and ham
roll |
20 |
0(0%) |
Minced beef |
20 |
3(15%) |
pork |
10 |
0(0%) |
Offal (red
meat) |
13 |
7(54%) |
Total |
123 |
49(33%) |
Fig
1. Procedure for the isolation of Campylobacter from food samples |
Enrichment |
|
25
g in 225 ml Campylobacter enrichment broth |
|
|
Incubate 4h at 370C then 44h at 420C |
Detection |
|
Plate
out onto Campylobacter blood free agar |
| |
|
Incubate
48h at 370C under microaerophilic conditions |
Confirmation |
|
Biochemical tests |
A study was carried out by The National Food Centre to
determine the incidence of Campylobacter on a range of retail fresh and frozen
meats in Ireland. A total of 123 samples including fresh and frozen chicken, turkey,
chicken and ham roll, minced beef, pork and offal were purchased from local retail outlets
and examined for the presence of Campylobacter spp. Samples were enriched in Campylobacter
enrichment broth (48h under aerobic conditions) prior to plating out on Campylobacter
selective agar (48h incubation in a microaerophilic cabinet) and then identified
biochemically (Fig 1). Pathogenic Campylobacter spp. i.e. C. jejuni and C.
coli were most commonly isolated from offal (54% positive) and from chicken samples
(56% positive) (Table 1). The pathogen was not detected from turkey, ham or pork but was
detected at a level of 15% on minced beef. These results are similar to those reported
from studies carried out in other countries and indicate the need for HACCP systems in the
meat and poultry industries to control the levels of this pathogen on foods.
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