Animal Waste, Water Quality and Human Health

88Animal Waste, Water Quality and Human HealthThe concentration of E. coli O157:H7 in faeces can vary widely, ranging from10 3 or>10 4 CFU of E. coli O157:H7/g of faeces, depending on the study (Low et al.2005, Naylor et al. 2003, Omisakin et al. 2003). The presence of super-sheddersin herds is associated with a greater number of cattle shedding lower levels ofthe organism, suggesting that the super-shedders enhance transmission of theorganism within the herd (Chase-Topping et al. 2007). Omisakin et al. (2003)reported that as many as 9% of E. coli O157-positive cattle at slaughter inScotland were super-shedders. Chase-Topping et al. (2007) reported that phagetype 21/28 was more frequently associated with supershedding than other E.coli O157 phage types, suggesting both the host and the pathogen may play arole in this phenomenon. In summary, super-shedders are thought to play a keyrole in spreading the organism to other cattle, other species of domestic and wildanimals, contamination of beef, milk and field crops and water. Identificationand treatment or removal of super-shedders from groups of cattle couldsignificantly reduce the environmental load of this dangerous human pathogen.Super-shedders are also likely to play a role in the phenomenon of “clonaldominance” where a single genotype of E. coli O157:H7 predominates in aspecific cattle herd. This characteristic of the organism has the potential to allowspecific sources of food and environmental contamination and human infectionto be traced to specific groups of animals based on the molecular fingerprint ofthe organism (Laing et al. 2009, Cooley et al. 2007).E. coli O157:H7 has been shown to persist in water-trough sediment for at leastfour months (Hancock et al. 1997c) and inoculating calves with 10 6 CFU/L ofwater resulted in several weeks to over a month of faecal shedding of E. coliO157:H7 at concentrations of 10 2 to 10 6 CFU/g faeces (Shere et al. 2002).Livestock manure containing E. coli O157:H7 has been linked to or suspected as