Food Science and Technology Department


Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Food Science and Technology, Under the Supervision of Professor Samodha C. Fernando. Lincoln, Nebraska: May, 2015

Copyright (c) 2015 Nirosh D. Aluthge


During the past three decades, Shiga toxin-producing E.coli (STEC) have emerged as an important food safety concern. Although initially E. coli O157 was the main focus, recent outbreaks and resulting investigations have shown that certain non-O157 STEC are as much a threat to food safety as their O157 counterparts. To the beef industry, STEC have been of particular concern due to the frequent association of beef and beef products as vehicles of STEC infection. As a result, along with E. coli O157, six non-O157 STEC serogroups (known as the ‘big six’) are now regulated as adulterants in certain raw beef products in the United States. Compared to STEC O157, relatively little is known about the prevalence and pathogenicity of the non-O157 STEC in beef production systems. Fecal shedding of STEC by cattle is considered the main route of entry of these pathogens to the environment.

The main objective of this study was to investigate if differences existed in the fecal bacterial composition of beef cattle based on their level of STEC shedding. In addition, this study also investigated the fecal prevalence of virulent strains of STEC O157 and the ‘big six’ non-O157 STEC (EHEC-7) within a beef cattle population to assess if the fecal microbiota had an influence on the shedding of these virulent STEC strains. A total of 328 cross-bred beef steers from two separate years were fecal sampled and the fecal bacterial composition assessed using high-throughput DNA sequencing. NeoSEEKTM STEC assay was used to determine the prevalence of EHEC-7. No higher order differences were detected that suggests that STEC shedding was associated with changes in fecal bacterial composition. However, some genera and OTUs were associated with a given shedding category. Only 4.08% of the fecal samples yielded a member of the EHEC-7. The low number of samples positive for EHEC-7 prevented an analysis being done to determine the influence of the fecal microbiota on their shedding.

Adviser: Samodha Fernando