Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


Michael W. Black


In the United States, symptoms caused by pathogenic strains of Escherichia coli are on the rise. A major source of these pathogenic strains is the E. coli in the digestive tract of cattle. The purpose of this project was to determine if E. coli are transferred between individuals of the same species and if interspecies transmission is possible. Proximity of cattle was also studied as a contributing factor to the transfer of E. coli. To accomplish this goal, E. coli isolates from cattle and cohabitating ground squirrels were compared through a new method of bacterial strain typing called pyroprinting. Bulls from the Cal Poly Bull Test were sampled every summer from May to September when around 200 bulls from ranches across California are housed together to be tested and eventually auctioned off. The impact of cattle origin (ranch, city) and habitation (pen) on E.coli isolate strain type were evaluated via pyroprinting . The cattle were studied to see if transfer was related to proximity of cohabitation. Since the complete population of intestinal E. coli could not be sampled, transfer could not be directly seen. The probability of sharing E. coli in each time point was used to infer transfer. There was an increase in the probability of sharing E. coli from the May sample date to the September date, indicating that some form of transfer was occurring. There was an even greater increase in the probability of sharing E. coli when the bulls were housed in close proximity. Lastly, ground squirrels cohabitating in the area were found to house some of the same strains as the cattle. This makes transfer between squirrels and cattle a possibility. Overall, this paper shows that the intestinal E. coli composition of bulls may be readily altered by the introduction of new bulls into a population.