Felix Reich
Quantification and prevalence of thermophilic Campylobacter spp. in broiler slaughtering and processing in the course of a longitudinal study
At present thermophilic Campylobacter spp. are the major cause of gastrointestinal disease in man in Europe. Poultry meat has been identified as an important source for human infection. This kind of meat is often highly contaminated with Campylobacter which leads to cross-contamination of ready to eat foods due to improper kitchen hygiene. But also the undercooked meat itself is known as a potential source of infection. Usually the birds do not fall ill but are considered as asymptomatic carriers of Campylobacter. In the course of the highly industrialised slaughter process a wide distribution of these bacteria occurs. Although an eradication of Campylobacter is currently not possible, neither during fattening nor during processing, at least a reduction is the aim. For performing thorough risk assessements and recognising steps for implementing intervention strategies, it is of great importance to have data available on the prevalence and quantitative dimensions of Campylobacter in broiler slaughtering.
In these studies a total of 40 broiler flocks were sampled over a period of 18 months for their Campylobacter status in caecal contents, to acquire the prevalence of broiler flocks upon delivery at the slaughterhouse.
The main focus of this investigation was the quantification of Campylobacter at the slaughterhouse level. Therefore the collection of samples at different points of slaughter and processing was performed every month and changes in the Campylobacter prevalence and counts were determined. The sampling points were:
Scalding/defeathering, evisceration and the chilling operations. Carcasses were collected after the passage of these processing steps. Poultry cuts were collected to
examine the burden of products ready for packaging. Samples of scalding water were collected to show the amount of Campylobacter in the beginning of the slaughter process. Aditionally transport crates were sampled after cleaning and disinfection. The investigation was perrformed in different seasons for examining the influence of seasonality. A comparison of the burden of Campalobacter positive and negative flocks gave information on the amount of cross-contamination.
The combination of qualitative and quantitative methods in the analysis of Campylobacter gave a higher level of confidence in the results of the prevalence and bacterial counts acquired at different steps in the slaughter process. The use of two selective media (mCCDA/Karmali) showed similar results in the enumeration of Campylobater, while the Karmali agar was easier to analyze.
The prevalence studies of broiler flocks gave a positive result for Campylobacter in 70 % (28) of cases.
The results of samples from Campylobacter positive flocks during processing showed a reduction of the Campylobacter counts. The mean Campylobacter count at the beginning was Log10 5.4/5.5 cfu/carcass, after chilling it was reduced to Log10 4.7/4.8 cfu/carcass. The surface contamination of carcasses was reduced by Log10 0.7 and this reduction was statistically significant. The prevalence of Campylobacter in samples from positive flocks was high with over 87 % for all kinds of samples. At the end of the processing the breat meat still showed contamination rates of Log10 2.7/3.0 KbE per pair of fillets. The prevalence was lower in Campylobacter negative flocks with a maximum prevalence of up to 44 % for carcasses. The bacterial counts were lower and the majority of the samples were below the limit of detection of the method for quantitative analysis.
The status of scalding water and transport crates showed a distribution of Campylobacter to the slaughter environment. Scalding water therefore is an important point for contamination of negative flocks passing through the contaminated water. Improper cleaned transport crates posed a risk of introducing Campylobacter to formerly negative flocks.
Seasonal influences were shown, as an accumulation of Campylobacter negative flocks was seen in winter and spring compared to the other seasons. The analysis of the Campylobacter mean counts per slaughter day of positive flocks showed higher contamination of flocks in summer and autumn than in other quarters.
The differentiation of Campylobacter isolates showed that C. jejuni (73.6 %) was dominating in broiler flocks, followed by C. coli (24.9 %). With analysis of isolates from caecal contents it was demonstrated that the majority of flocks was colonised by one Campylobacter species, flocks solely colonised by C. jejuni or C. coli were found.
But mixed colonisation was detected in six flocks.
During slaughtering and processing different amounts of cross-contamination occurred. This was confirmed bei the detection of Campylobacter positive samples at the slaughter of flocks with negative status in caecal contents and by the incidence of Campylobacter species differing from those found in caeca of slaughtered positive flocks.
The combination of media and methods used in these studies for the analsysis of thermophilic Campylobacter resulted in a higher rate of reliability in the estimation of the prevalence and bacterial numbers at the different processing steps. Additionaly, the design as a longitudinal study over 1.5 years, with taking into account seasonal variations and different flock status, allowed for a generalisation of the results for the expected contamination with Campylobacter in intensively fattened broiler flocks in Germany.