Transmission routes of Campylobacter spp. in broilers and possibilities for prevention of infections were studied on two Dutch broiler farms. The occurrence of Campylobacter spp. was studied in successive broiler flocks, in the environment of the farms and in some of the parent flocks involved. Isolates of Campylobacter spp. were typed by using randomly amplified polymorphic DNA (RAPD) analysis. The results indicate that broiler flocks become infected from environmental sources. The typing results suggest that on one farm transmission of Campylobacter spp. occurred from cattle to broilers via the farmer's footwear. After several campylobacter positive broiler cycles hygiene measures, including thorough cleaning and disinfection procedures, change of footwear at the entrance of each broiler house, control of vermin and other hygienic precautions, were introduced on both farms in order to prevent transmission of Campylobacter spp. from the farm environment to the broilers. The results indicate that the application of hygiene measures significantly reduced campylobacter infections of broiler flocks on both farms.

Food-borne pathogens like S. Typhimurium DT104 and E. coli O157 form a serious threat to public health since such strains are able to survive under extreme low pH conditions as present in the human stomach. The emergence these acid-resistant strains suggests the presence of a selection barrier. The intestinal tract of ruminants fed a carbohydrate-rich diet might be such a barrier.

The research described in this contribution provides quantitative data on contamination levels with Salmonella and Campylobacter in chicken and chicken products in The Netherlands at retail level using the most probable number method and direct counting. Most samples contained <10 Salmonella per carcass, both in fresh (89%) and frozen (68%) products, contamination levels with Campylobacter varied from <10 (18%) to more than 5,500 (18%) per fresh carcass. Most frozen samples (57%) contained < 10 Campylobacter per carcass.

From September 1991 until August 1993 an epidemiological study involving 20 Dutch broiler farms was conducted to identify risk factors and risk reducing measures for campylobacter infections in broiler flocks. Campylobacter spp. were detected in 64 (57%) of the 112 broiler flocks and in 25 (63%) of the 40 broiler cycles examined. Univariate analysis of farm management data was performed followed by logistic regression analysis of selected risk and risk reducing factors. The presence of other farm animals, including pigs, cattle, sheep and fowl, other than broilers, was found to be independently associated with an increased risk of campylobacter infections in broiler flocks (odds ratio (OR) = 11.81; P = 0.041). Further, the results indicate that application of specific hygiene measures during the rearing period, such as washing hands before tending the broiler flocks, the use of separate boots for each broiler house and the use of footbath disinfection when entering a broiler house, may significantly reduce the risk of campylobacter infections in broiler flocks.

Broiler flocks are frequently infected with Campylobacterjejuni. The origin of the infection is still unclear. The question of whether colonization of flocks results from transmission of C. jejuni from breeder flocks to progeny (vertical transmission) or from environmental sources (horizontal transmission) remains to be answered. Therefore, in this study samples were taken from successive broiler flocks in two broiler houses (house A on farm A and house Bi on farm B) as well as from the environment of the houses. All C.jejuni isolates were typed by using the Penner serotyping system, and part of the isolates from farm B were typed by using a randomly amplified polymorphic DNA-typing system. In poultry house A, C. jejuni was isolated from the first flock but not from subsequent flocks. In poultry house B1, C. jejuni strains of the same Penner serotypes and exhibiting identical DNA profiles were isolated from successive flocks. Infection of the flocks from a common source via horizontal pathways is suspected, while a vertical route of infection is not likely to exist. Application of measures to control horizontal transmission of C. jejuni on farm B was successful.

The ability of acid-adapted bacteria to survive the human stomach is an important virulence factor. The ability of non-acid adapted E. coli O157 to adapt within a very short period of time under extreme conditions further contributes to the virulence of E. coli O157.

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