Detection and identification by PCR of Clostridium chauvoei in clinical isolates, bovine faeces and substrates from biogas plant

BACKGROUND Clostridium chauvoei causes blackleg, an acute disease associated with high mortality in ruminants. The apparent primary port of entry is oral, during grazing on pasture contaminated by spores. Cases of blackleg can occur year after year on contaminated pastures. A method to determine the prevalence of C. chauvoei spores on pasture would be useful.The standard method for C. chauvoei detection is culture and biochemical identification, which requires a pure culture. In most muscle samples from cattle dead from blackleg the amount of C. chauvoei in samples is high and the bacterium can easily be cultured, although some samples may be contaminated. Detection by PCR would be faster and independent of contaminating flora.Digested residues from biogas plants provide an excellent fertiliser, but it is known that spore-forming baeria such as Clostridium spp. are not reduced by pasteurisation. The use of digested residues as fertiliser may contribute to the spread of C. chauvoei. Soil, manure and substrate from biogas plants are contaminated with other anaerobic bacteria which outgrow C. chauvoei. Therefore, detection by PCR is would be useful. This study applied a PCR-based method to detect of C. chauvoei in 25 muscle and blood samples, 114 manure samples, 84 soil samples and 33 samples from the biogas process. METHODS Muscle tissues from suspected cases of blackleg were analysed both by the standard culture method followed by biochemical identification and by PCR, with and without preculture. To investigate whether muscle tissue samples are necessary, samples taken by swabs were also investigated. Samples from a biogas plant and manure and soil from farms were analysed by culture followed by PCR. The farms had proven cases of blackleg. For detection of C. chauvoei in the samples, a specific PCR primer pair complementary to the spacer region of the 16S-23S rRNA gene was used. RESULTS Clostridium chauvoei was detected in 32% of muscle samples analysed by culture with identification by biochemical methods and in 56% of cases by culture in combination with PCR. Clostridium chauvoei was detected in 3 (out of 11) samples from the biogas plants collected before pasteurisation, but samples taken after pasteurisation and after digestion all tested negative. Clostridium chauvoei was not detected in any soil or silage samples and only one manure samples tested positive. CONCLUSION The diagnostic method used for C. chauvoei was not applicable in estimating the risk of blackleg on particular pastures from manure or soil samples, but found to be highly useful for clinical samples.