Cow E. coli ID^TM

Determine quickly if your water source has cattle fecal contamination.

Important Note: The website and the services offered are for environmental professionals. This website is only a cursory overview of the services offered. Source Molecular is not responsible for errors or omissions on the web site. Furthermore, clients must understand the limitations of the services before submitting samples. Please call beforehand to discuss service details and type of samples to be submitted.

Since cattle are known to harbor human pathogens such as Cryptosporidium and E. coli 0157:H7, proper monitoring and remediation of this form of fecal contamination is essential for maintaining viable water systems.

The Cow E. coli ID^TM service is designed around the principle that certain strains of E. coli are specifically pathogenic in cattle. These enterotoxigenic E. coli (ETEC) can be used as indicators of cattle fecal contamination.¹ Enterotoxigenic E. coli have toxin genes that render them pathogenic. These ETEC toxin genes can serve as DNA biomarkers.

It has been shown that the heat labile toxin IIa (LTIIa) gene from enterotoxigenic E. coli can serve as a reliable indicator of cattle fecal contamination.^{2, 5}  Although this toxin gene has on rare occasions been associated with other mammals such as pigs or humans, it is on the whole endemic to cattle.³ As such, the LTIIa toxin gene is used as an indicator of cattle fecal contamination because 1) it is relatively species-specific, 2) its nucleotide sequence is unique to cattle, and 3) LTIIa is relatively non-homologous with other toxin genes, specifically cholera toxin and LTI toxin genes which share some similarities with the  LTIIa gene.⁴

One of the advantages of this method is that the entire population of E. coli of the selected portion of the water sample is screened. As such, this method avoids the randomness effect of selecting isolates off a petri dish.² It has been shown that if the total E. coli count (irrespective of the volume of water) of the sample is equal to or greater than 1,000, the reliability of the analysis is greater, particularly in regards to negative results.

Accuracy of the results is possible because the method uses PCR DNA technology.  PCR allows quantities of DNA to be amplified into large number of small copies of DNA sequences. This is accomplished with small pieces of DNA called primers that are complementary and specific to the genomes to be detected.

Through a heating process called thermal cycling, the double stranded DNA is denatured and inserted with complementary primers to create exact copies of the DNA fragment desired. This process is repeated rapidly many times ensuring an exponential progression in the number of copied DNA. If the primers are successful in finding a site on the DNA fragment that is specific to the genome to be studied, then billions of copies of the DNA fragment will be available for detection by gel electrophoresis.

The gel electrophoresis apparatus uses an electrical field to distinguish different DNA fragments according to their molecular weights. Lighter DNA fragments will move farther along the gel than their heavier counterparts. At the end of the procedure different bands of accumulated DNA fragments will aggregate at different parts of the gel. It is this accumulation of DNA fragments that creates a band on the gel. Researchers use these bands to distinguish certain genomes such as the LTIIa toxin gene from enterotoxigenic E. coli.

These banding patterns confirm or negate the presence of the LTIIa toxin gene from the E. coli of the water sample. As such, the banding patterns provide a good  indicator of cattle fecal contamination. Although the LTIIa biomarker has on rare occasions been associated with other mammals, it is widely accepted that it is an indicator of cattle fecal contamination. To strengthen the validity of the results, the Cow E. coli ID^TM service should nonetheless be combined with other DNA analytical services such as the Cow Bateroidetes IDTM and Cow Fecal Virus IDTM services.

¹ Khatib L, Tsai YL, Olson BH.  2002. A biomarker for the identification of cattle fecal pollution in water using the LTIIa toxin gene from Enterotoxigenic E. coli. Applied Microbiology and Biotechnology.  59:97-104.

² Olson BH, Khatib L, McGee C. 2001. Comparison of DNA Fingerprinting Methods of E. coli, Genotyping Male Specific Phage Serotypes and the Use of Toxin Genes as Biomarkers to Differentiate Human and Animal Waste. American Water Works Association, WQTC Proceedings.

³ Pickett CL, Weinstein DL, Holmes RK (1987) Genetics of type IIa heat-liable enterotoxin of Escherichia coli: operon fusions, nucleotide sequence, and hybridization studies. Journal of Bacteriology. 168:5180-5187.

⁴ Woodward MJ, Kearsley R, Wray C, Roeder PL. 1993. DNA probes for the detection of toxin genes in Escherichia coli isolated from diarrheal disease in cattle and pigs. Veterinary Microbiology 22(2-3):277-90.

⁵ Chern, Eunice C., Tsai, Yu-Li, Olson, Betty H.Occurrence of Genes Associated with Enterotoxigenic and Enterohemorrhagic Escherichia coli in Agricultural Waste Lagoons Appl. Environ. Microbiol. 2004 70: 356-362.