Demographics and Transfer of Escherichia coli Within Bos taurus PopulationsJoshua Ryan DillardIn the United States, symptoms caused by pathogenic strains of Escherichia coliare on the rise. A major source of these pathogenic strains is the E. coli in the digestivetract of cattle. The purpose of this project was to determine if E. coli are transferredbetween 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. Toaccomplish this goal, E. coli isolates from cattle and cohabitating ground squirrels werecompared through a new method of bacterial strain typing called pyroprinting. Bullsfrom the Cal Poly Bull Test were sampled every summer from May to September whenaround 200 bulls from ranches across California are housed together to be tested andeventually auctioned off. The impact of cattle origin (ranch, city) and habitation (pen) onE.coli isolate strain type were evaluated via pyroprinting . The cattle were studied to seeif transfer was related to proximity of cohabitation. Since the complete population ofintestinal E. coli could not be sampled, transfer could not be directly seen. Theprobability of sharing E. coli in each time point was used to infer transfer. There was anincrease in the probability of sharing E. coli from the May sample date to the Septemberdate, indicating that some form of transfer was occurring. There was an even greaterincrease 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
v
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.
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