Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2003
Publication Date: 8/1/2003
Citation: BYRNE, C.M., IRFAN, E., CALL, J.E., KASPAR, C., BUEGE, D.R., HIEMKE, C.J., CRAY, P.J., BENSON, A.K., WALLACE, F.M., LUCHANSKY, J.B. CHARACTERIZATION OF ESCHERICHIA COLI O157:H7 FROM DOWNER AND HEALTHY DAIRY CATTLE IN THE UPPER MIDWEST REGION OF THE UNITED STATES. APPLIED AND ENVIRONMENTAL MICROBIOLOGY. 2003. Vol. 69. No. 8. p.4683-4688. Interpretive Summary: Escherichia coli O157:H7 is a pathogen of significant public health concern in the United States, causing an estimated 73,000 cases of infection and 61 deaths per year. Cattle have been identified as a reservoir of the pathogen and ground beef is often implicated in outbreaks of E. coli O157:H7. Cull dairy cows account for approximately 17% of the ground beef produced in the U.S., 1.5% of which comes from downer animals, that is animals with assorted maladies that render them non-ambulatory. Therefore, downer dairy cattle harboring E. coli O157:H7 at slaughter may be an important source of contamination of meat and may contribute appreciably to the health risk associated with ground beef. Hence, the present study was conducted to gain insight on the comparative presence of E. coli O157:H7 in downer compared to healthy dairy cattle. Fecal samples taken in two slaughterhouses in the upper Midwest region of the United States from May to October of 2001 established a 3.3-fold higher prevalence of E. coli O157:H7 in fecal samples of downer than healthy dairy cattle. Analyses of the 57 E. coli O157:H7 isolates by DNA fingerprinting revealed 13 distinct types. In addition, 11 of the 57 isolates were resistant to at least one of 18 antimicrobials tested. However, there was no appreciable difference in the frequency of resistance of isolates recovered from downer and healthy dairy cattle. These results indicate that downer cattle had a 3.3-fold higher prevalence of E. coli O157:H7 than healthy cattle within the time frame and geographic scope of this study. The current study provided further insight into the ecology of E. coli O157:H7 in cattle, which may help in the development of potential interventions to control E. coli O157:H7 on the farm.
Technical Abstract: While cattle in general have been identified as a reservoir of Escherichia coli O157:H7, there are limited data regarding the prevalence and clonality of this pathogen in downer dairy cattle and the potential impact to human health that may occur following consumption of meat derived from downer dairy cattle. In the present study, conducted at two slaughter facilities in Wisconsin between May and October of 2001, we established a 3.3-fold higher prevalence of E. coli O157:H7 in fecal and/or tissue samples obtained aseptically from intact colons of downer (10/203, 4.9%) than in healthy (3/201, 1.5%) dairy cattle. Analyses of 57 isolates, representing these 13 positive samples (1 to 5 isolates per sample), by pulsed field gel electrophoresis (PFGE), revealed 13 distinct XbaI restriction endonuclease digestion profiles (REDP). Typically, isolates from different animals displayed distinct REDP and isolates from the same fecal/colon sample displayed indistinguishable REDP. However, in one sample, two different, but highly related, REDP were displayed by the isolates recovered. Moreover, antimicrobial susceptibility testing indicated that 11 of the 57 isolates, recovered from 3 (1 downer and 2 healthy animals) of the 13 positive samples, were resistant to at least one of 18 antimicrobials tested. There was no appreciable difference in the frequency of resistance of isolates recovered from downer and healthy dairy cattle. In addition, not all isolates with the same REDP displayed the same antimicrobial susceptibility profile. Lastly, it was not possible to distinguish among isolates recovered from downer and healthy cattle based on their XbaI REDP or antimicrobial susceptibility. These results indicate that downer cattle had a 3.3-fold higher prevalence of E. coli O157:H7 than healthy cattle within the time frame and geographic scope of this study.