Presence of Extra-intestinal Pathogenic Escherichia coli (ExPEC) in Agricultural Environments

Introduction:   Extra-intestinal pathogenic Escherichia coli (ExPEC) have a combination of virulence factors which allow them to cause disease in both humans and animals.  Little is known about their persistence and survival in agricultural environments.  If present in agricultural environments, it may be possible for ExPEC to contaminate produce commodities and cause human infections through produce consumption.  There is no defined criterion for classification of an E. coli isolate as an ExPEC other than the presence of a single ExPEC virulence factor.

Purpose: This study determined if ExPEC were present in commercial finished compost, indicating their presence in agricultural environments. 

Methods: Seventy-seven E. coli isolates from finished commercial compost were assayed by polymerase chain reaction (PCR) for the presence of nine virulence factors (VF) commonly associated with Avian Pathogenic E. coli (APEC) and ExPEC using previously designed primers:  astA (enteroaggregative toxin), three iss alleles (serum resistance), papC (P fimbriae), iucD (aerobactin), tsh (hemagglutinin), vat (vacuolating toxin), and cvaA/cvi (colicin V plasmid). 

Results:   Only two isolates (3%) of 77 did not contain any ExPEC VF.  Thirty-eight (50%) of the E. coli isolates contained either two or three ExPEC VFs.  Thirty isolates (39%) were positive for at least one adhesin (papC, tsh) and one toxin (astA, vat), indicating a minimum threshold to cause infection.  Twenty-one isolates (27%) were found to be positive for papC or tsh and at least one serum resistance allele (iss types 1, 2, and 3), also indicating their potential to cause human illness.  The two most prevalent virulence factors identified were astA (90%) and iss type 1 (69%).

Significance: These results show that ExPEC are present in commercial composts, which when used in the growing environment may introduce the pathogen to produce commodities.  As more attention is paid to transmission of extraintestinal infections to humans and animals, the presence of ExPEC in agricultural environments deserves attention.