Pigs carrying Campylobacter

Context / challenges

Campylobacter is a major cause of foodborne illness in developed countries. Epidemiological studies on the Campylobacter status of pig herds are few and far between. They have established the high frequency of asymptomatic Campylobacter carriage, the very early contamination of the animals and the high amounts excreted (102 to 107 CFU per gram of faeces). However, few studies have described the quantitative variation in the excretion of animals from birth to slaughter. There is also a need to determine the sources and modalities of Campylobacter transmission, both on farms and at slaughter. If the dam appears to play a role in the contamination of piglets, other sources of contamination may be suspected.
The objectives of our work have therefore been to: 

• describe excretion kinetics in order to assess the duration of excretion, the possible existence of intermittency, the variability of the quantity excreted (quantitative data) and the species excreted (qualitative data). Due to the cultural requirements of these bacteria, we have developed a real-time quantitative PCR to identify the major species (C coli and C jejuni) and quantify them directly on samples (faeces, environmental samples, water, al iment).
• to determine the sources and modalities of Campylobacter transmission, which implies "tracing" the strains in order to establish an epidemiological link between them. Validated typing methods are therefore needed to assess the degree of similarity between bacterial strains. However, the high genomic variability of Campylobacter makes the interpretation of genotyping results complex. It therefore appeared necessary, initially, to study this genetic variability by determining the respective share of the different components of the heterogeneity of the profiles observed in the field (spontaneous variability of the strain, animal effect, effect of co-infections, etc.).

Results

Two real-time quantitative PCR assays have been developed: (i) an assay for the quantification of Campylobacter spp with an internal extraction and amplification control (Leblanc Maridor et al. 2011a) and (ii) an assay for the identification and quantification of C coli and C jejuni in pure cultures and complex matrices (including faeces) (Leblanc Maridor et al. 2011b).
The potential for colonisation of the digestive tract of pigs is greater for C coli than for C jejuni in experimental infection of EOPS pigs either with a single strain or with a mixture of strains. These results are consistent with epidemiological studies which show that C coli is the predominant species isolated from pigs. Transmission of C coli between adjacent pens was demonstrated, with animals in contact excreting similar amounts to those inoculated (Leblanc Maridor et al., 2008).
In conventional herds, sows play a major role as a source of early contamination for piglets. The environment (rearing premises, feed, drinking water) is also a potential source of infection although resistance of Campylobacter in the environment seems limited (many environmental samples are negative even in the presence of animals and rearing premises are no longer contaminated after cleaning).
Under experimental conditions, genetic variability is observed in multiple isolates after infection of pigs with a C coli strain of porcine origin, but not in the case of infection with a C. coli strain of avian origin, or with C jejuni. This strain was also the most well established strain in the digestive tract of infected EOPS pigs (quantitatively greater and more durable excretion than the other strains). (Leblanc Maridor et al, 2011c).

Perspectives

Genotyping results obtained under controlled conditions provide information on the spontaneous variability of Campylobacter and will therefore contribute to the interpretation of strain profiles obtained under field conditions to determine the origin of contamination in a herd.
Observations made in conventional herds show that the control of Campylobacter carriage by pigs must first and foremost target the animals that constitute the reservoir of these bacteria in the herd.

Partners

• UMR INRA-Oniris SECALIM
• ANSES Ploufragan-Plouzané

Publications

• Leblanc Maridor M, Denis M, Lalande F, Beaurepaire B, Cariolet R, Fravalo P, Federighi M, Seegers H, Belloc C. 2008. Experimental infection of Specific Pathogen Free pigs with Campylobacter : excretion in faeces and transmission to non-inoculated pigs. Vet Mic 131: 309-317.
• Leblanc Maridor M, Garénaux A, Beaudeau F, Chidaine B, Seegers H, Denis M, Belloc C. 2011a. Quantification of Campylobacter spp in pig faeces by direct real-time PCR with an internal control of extraction and amplification. J. Microb. Methods 85, 53-61.
• Leblanc Maridor M, Beaudeau F, Seegers H, Denis M, Belloc C. 2011b. Rapid identification and quantification of Campylobacter coli and Campylobacter jejuni by real-time PCR in pure cultures and complex samples. BioMed Central Microbiology 11 : 113-128.
• Leblanc Maridor M, Denis M, Rossero A, Beaudeau F, Seegers H, Belloc C. 2011c. Genetic instability of Campylobacter coli in the digestive tract of experimentally infected pigs. Vet Mic (doi:10.1016/j.vetmic.2011.07.002).