Most of the microbiological regulatory emphasis from USDA FSIS on the broiler and turkey industries has fallen on salmonella reduction. The next organism in the regulators' cross hairs is campylobacter. Unfortunately, the epidemiology of campylobacter contamination in poultry complexes is not fully understood and effective control measures have not been developed yet, but researchers are making inroads and the poultry industry has made some progress in reducing the incidence rate of carcasses with campylobacter on them.
Campylobacter are able to colonize the intestines of chickens and don't cause morbidty or mortality. Most human illness is caused by Campylobacter jejuni, but sickness can also be caused by other species. C. jejuni grows best at the body temperature of a bird, and seems to be well adapted to birds.
Campylobacter are fragile, cannot tolerate drying, and can be killed by oxygen. They grow only in places that have less oxygen levels than the atmosphere. Freezing reduces the number of viable campylobacter on raw meat.
Sources of campylobacter
For many years, scientists pointed to the possible sources of campylobacter as being feed, wild birds, well water, insects, and rodents. Research has shown that wild birds like starlings are carriers of campylobacter and are a potential source of contamination on the farm if the birds can get into the poultry houses. Campylobacter can't survive longer than an hour in dry conditions, eliminating bird feathers and hatchery transport paper pads from the list of possible sources.
Campylobacter in the reproductive tract
Vertical transmission of campylobacter may take place by primary (contamination of the egg content in the hen's reproductive tract during the egg development) or secondary (contamination of the eggshell via fecal material containing the bacteria with the subsequent penetration of the agent inside the egg) infection of the egg. If vertical transmission of campylobacter through the secondary egg infection occurs, the organism must first penetrate through the eggshell and then maintain its viability inside the egg until hatching.
Campylobacter can be recovered from the ductus deferens of some broiler breeder roosters. Campylobacter-positive semen samples have also been found by researchers. It has been shown that campylobacter from rooster semen can infect hens. Research has also shown that the recovery rate of campylobacter from hen ovarian follicles was reasonably high, suggesting that these breeder hens could be infecting fertile hatching eggs.
Campylobacter infection of chicks
Avian intestinal mucus appears to inhibit campylobacter from interacting with epithelial cell surfaces. This is a possible explanation for why chickens don't get a debilitating infection by colonization with campylobacter. Thus, campylobacter is considered to be a commensal organism in many avian species, such as chickens. As a commensal organism, campylobacter colonizes the mucus layer on the intestinal lining in the crypts of the intestinal epithelium.
Research has shown rapid movement of campylobacter to internal organs following both oral and intracloacal inoculation in chicks. This may be significant, particularly if campylobacter persists in these organs as reservoirs throughout the 65-week life cycle of breeding birds.
Spread among hatch mates is rapid if infected birds are introduced into the population. In a laboratory setting, only three days are required for the majority of the brood to become colonized, because very young chicks (up to two weeks) are highly susceptible to colonization. Once campylobacter positive birds have been introduced into the poultry house, the organisms spread very quickly to other birds, often reaching a prevalence level of 100% by the end of grow out. Additionally, the number of these bacteria in the gut, fecal material, and in the litter can be extremely high with counts as high as 9.0 log10 colony forming units per gram. Because the levels may be very high on birds coming into the plant, it is very difficult to eliminate the pathogen completely from carcasses.
Campylobacter control: Competitive exclusion
Scientists have attempted to use defined competitive exclusion (CE) cultures to reduce campylobacter in chickens. A combination of Citrobacter diversus 22, Klebsiella pneumoniae 23, and E. coli 25 at hatch was the most effective CE treatment.
Researchers also found that only 8% of chicks given just fructo-oligosaccharide supplementation were colonized with campylobacter after challenge. When lactose was fed in combination with the CE culture, colonization was reduced from 80% of controls to only 5% of treated chicks. The CE approach appears to be a successful means for controlling this organism; however, its cost and difficulty in achieving FDA approval may prevent its widespread use.
Campylobacter control: Vaccines
Researchers have developed a formalin-inactivated C. jejuni whole cell vaccine that can be administered orally to broiler chickens. In trials, the overall reductions of C. jejuni colonization in the vaccinated chickens ranged from 16% to 93%, when compared with non-vaccinated controls. Enhanced levels of anti-C. jejuni secretory IgA antibodies were demonstrated in vaccinated chickens. The authors concluded that future development of successful oral vaccines for the control of enteropathogenic campylobacter in poultry is feasible.
Campylobacter control: Bacteriophages
Bacteriophages are naturally occurring viruses that specifically attack and kill bacteria. Researchers have identified two phage candidates with an ability to kill campylobacter. This line of research is very interesting and has great potential in eliminating campylobacter colonization of chickens. However, the cost and consumer concern over feeding viruses to chickens may limit its acceptance as a viable option.
Trend is good for campylobacter
In 1992, a research study found that campylobacter could be isolated from 98% of chicken meat at retail. Additionally, C. jejuni counts on this meat were very high and often exceeded 103 colony forming units per 100 grams.
Since that time, the poultry industry in the U.S. has done an incredible job of lowering the prevalence of this organism on broiler carcasses. Scientists recently conducted a large study to determine campylobacter prevalence on broiler carcasses in the U.S. In this study, 10 of the largest U.S. poultry integrators cooperatively determined the incidence and counts of campylobacter on processed broiler carcasses. Only 26% of carcasses were positive for campylobacter and just 3.6% of the carcasses had more than 105 colony forming units per carcass.
Tough task ahead
The industry faces a daunting task in trying to control campylobacter colonization of poultry. However, as more studies are conducted that identify how campylobacter is able to colonize poultry and novel methods are developed to control campylobacter, the industry will have more tools to work with. Moreover, the poultry industry has accomplished a Herculean task in lowering total prevalence of campylobacter on poultry from 98% in 1972 to 26% today. The industry is to be commended for such efforts to keep food safe for the American public.