Contrary to popular belief, some disease causing bacteria may actually survive the composting process. Researchers from Agriculture and Agri-Food Canada report in the February 2010 issue of the journal Applied and Environmental Microbiology that campylobacter bacteria in cattle manure can survive composting and persist for long periods in the final product.
Campylobacter bacteria are the most common cause of gastroenteritis in the developed world. They are frequently shed by beef cattle in manure and although the impact on human health is undetermined there appears to be a link in areas such as Alberta, Canada where cases of human campylobacteriosis are extremely common and the cattle density is high.
Composting is described as a process in which organic matter in manure is stabilized through water loss, nutrient transmission, alteration of physical structure, elimination of weed seeds, and the inactivation of coliform bacteria, protozoan cysts and oocysts and viruses. Government agencies in both the United States and Canada recommend composting to reduce pathogen levels in manure.
In the study researchers examined the persistence of naturally occurring campylobacter bacteria in compost derived from manure of beef cattle that were administered antibiotics (AS700) and a control group that were not. Bacterial populations were the same in both groups, however, the temperature of the AS700 compost was more viable and not as high as that of the control group. Water content, total carbon, total nitrogen and electrical conductivity varied significantly between groups. Results showed that no reductions in the quantities of Campylobacter jejuni DNA were observed throughout the 10-month composting period. Further testing suggests that Campylobacter DNA examined from compost was extracted from viable cells.
"The findings of this study indicate that campylobacteria excreted in cattle feces persist for long periods in compost and call into question the common belief that these bacteria do not persist in manure," say the researchers.
(G.D. Inglis, T.A. McAllister, F.J. Larney, E. Topp. 2010. Prolonged survival of Campylobacter species in bovine manure compost. Applied and Environmental Microbiology, 76. 4: 1110-1119.)