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Applied and Environmental Microbiology, January 2004, p. 356-362, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.356-362.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Occurrence of Genes Associated with Enterotoxigenic and Enterohemorrhagic Escherichia coli in Agricultural Waste Lagoons

Eunice C. Chern,1 Yu-Li Tsai,2 and Betty H. Olson1*

Department of Environmental Analysis and Design, University of California, Irvine, Irvine, California 92697,1 Orange County Sanitation District, Fountain Valley, California 927082

Received 4 June 2003/ Accepted 7 October 2003

The prevalence among all Escherichia coli bacteria of the LTIIa toxin gene and STII toxin gene, both associated with enterotoxigenic E. coli, and of three genes (stxI, stxII, and eaeA) associated with enterohemorrhagic E. coli was determined in farm waste disposal systems seasonally for 1 year. Single- and nested-PCR results for the number of E. coli isolates carrying each toxin gene trait were compared with a five-replicate most-probable-number (MPN) method. The STII and LTIIa toxin genes were present continuously at all farms and downstream waters that were tested. Nested-MPN-PCR manifested sensitivity increased over that of single-MPN-PCR by a factor of 32 for LTIIa, 10 for STII, and 2 for the stxI, stxII, and eaeA genes. The geometric mean prevalence of each toxin gene within the E. coli community in waste disposal site waters after nested MPN-PCR was 1:8.5 E. coli isolates (1:8.5 E. coli) for the LTIIa toxin gene and 1:4 E. coli for the STII toxin gene. The geometric mean prevalence for the simultaneous occurrence of toxin genes stxI, stxII, and eaeA, was 1:182 E. coli. These findings based on total population analysis suggest that prevalence rates for these genes are higher than previously reported in studies based on surveys of single isolates. With a population-based approach, the frequency of each toxin gene at the corresponding disposal sites and the endemic nature of diseases on farms can be easily assessed, allowing farmers and public health officials to evaluate the risk of infection to animals or humans.

* Corresponding author. Mailing address: Department of Environmental Analysis and Design, University of California, Irvine, Irvine, CA 92697. Phone: (949) 824-5281. Fax: (949) 824-2056. E-mail: bholson{at}uci.edu.

Applied and Environmental Microbiology, January 2004, p. 356-362, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.356-362.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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