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Scudder, Jennifer M.

Animal Sciences

2009

MS

Bacterial pathogens can enter the mammary gland and cause inflammation and infection known as mastitis. One of the most important species affected is the dairy cow. Gramnegative bacteria, like Escherichia coli, account for nearly 40% of clinical cases of bovine mastitis annually and often do not respond to current control methods. Colicins are proteins produced by E. coli in response to bacterial stress. They are lethal to other strains of E. coli and some other species of bacteria. Their production can be induced in a laboratory setting, and they are currently being researched for use in a number of biotechnological applications. Recently, they have been proven to be effective antimicrobials, both in vitro and in vivo, against E. coli strains responsible for postweaning and edema disease in young pigs. Their previous success suggests they may be effective against mastitis-causing pathogens.
The following thesis investigated the effectiveness of colicin El (ColEl), both in vitro and in vivo, at killing Gram positive and negative mastitis-causing bacterial pathogens. When assessed in growth media in vitro, colicin El was only effective against E, coli strains. Furthermore, it was found that its antimicrobial activity was inhibited in milk. Addition of EDTA to bind the calcium and magnesium ions restored activity of colicin and acted synergistically to kill bacteria. When E. coli were incubated in growth media, combinations of ColE1 less or equal to 100 [mu]g/ml and EDTA less or equal to 10 mM resulted in bacterial killing. In whole milk, combinations of ColEllessor equal to 100[mu]g/ml and 20 mM EDTA resulted in killing of E. coli, while killing also occurred by 4h when 250 [mu]g/m1 ColEl and 20 mM EDTA were added to the growth cult~uesin skim milk. The success of this combination in vitro led to its investigation in vivo, and a rat mastitis model was chosen.