Open Journal of Veterinary Medicine, 2012, 2, 186-190 http://dx.doi.org/10.4236/ojvm.2012.24029 Published Online December 2012 (http://www.SciRP.org/journal/ojvm) Experimental Intramammary Infection with a Strain of Escherichia coli Isolated from a Cow with Persistent E. coli Mastitis Stephen P. Oliver 1 , Susan I. Headrick 1 , Mark J. Lewis 2 , Barbara E. Gillespie 1 , David L. Johnson 3 , Raul A. Almeida 1* 1 Department of Animal Science, The University of Tennessee, Knoxville, USA 2 East Tennessee Research and Education Center, Little River Animal and Environmental Unit, The University of Tennessee, Knoxville, USA 3 Middle Tennessee Research & Education Center, The University of Tennessee, Spring Hill, USA Email: * ralmeida@utk.edu Received August 30, 2012; revised October 11, 2012; accepted October 21, 2012 ABSTRACT Transient E. coli intramammary infections (IMI) are usually associated with rapid onset of clinical signs including mammary gland swelling and abnormal milk with rapid clearance of bacteria from milk. Conversely, reports have de- scribed strains of E. coli showing very different clinical trends. Persistent E. coli IMI are associated with mild clinical symptoms that disappear shortly after the onset of infection, possibly flaring-up intermittently during lactation. In the present study, we evaluated a strain of E. coli isolated from a cow with persistent mastitis to determine if the experi- mental infection model mimics naturally occurring persistent E. coli IMI. Uninfected mammary quarters of 7 Holstein heifers were infused within 10 days of calving with 50 colony-forming units of a persistent E. coli strain. Six of 7 heif- ers developed mild clinical mastitis with elevated rectal temperatures within 9 to 36 h after infusion. The challenge strain was isolated intermittently in milk from all infected mammary quarters during the first two weeks after infusion and 3 animals continued to shed E. coli periodically during the sampling period. One animal shed E. coli intermittently in milk for 172 d after challenge and developed clinical mastitis four times during this period. The isolated strain had an identical pulsed-field gel electrophoresis profile as the E. coli strain used to infuse mammary glands. The experimental IMI model described here mimics very closely naturally occurring persistent E. coli IMI, thus providing an excellent in vivo model to better understand pathogenesis and to facilitate development of control strategies for this important masti- tis pathogen. Keywords: Escherichia coli; Intramammary Experimental Infection; Persistent Mastitis; Dairy Cows 1. Introduction Current mastitis control programs devised in the 1960’s are based on hygiene including teat disinfection, antibi- otic therapy, and culling of persistently infected cows. Acceptance and application of these measures has led to considerable progress in controlling contagious mastitis pathogens. However, these same procedures are less ef- fective against environmental pathogens such as E. coli because of the low susceptibility of E. coli to common mastitis treatments [1], lack of efficacy of teat disinfec- tion for the prevention of new E. coli intramammary in- fections (IMI), and low efficacy of vaccination programs [2]. Therefore, it is not surprising that E. coli mastitis has become a major problem in many well-managed dairy farms that have successfully controlled contagious patho- gens. Transient E. coli mastitis is associated with rapid onset of clinical symptoms including mammary gland swelling and abnormal milk with rapid elimination of bacteria from milk. In some cases, severe systemic involvement occurs and when not properly diagnosed and treated, it could result in the death of the affected animal. Reports have also described strains of E. coli showing very dif- ferent clinical trends. For example, there are reports on E. coli strains associated with persistent IMI which often times start with mild clinical symptoms that disappear soon after the onset of infection only to flare-up again during lactation, usually resulting in mild clinical masti- tis [3-5]. Escherichia coli associated with persistent mas- titis have been isolated in milk for long periods in spite of a high number of somatic cells in milk [3]. Published data suggests that adhesion to and internalization into * Corresponding author. Copyright © 2012 SciRes. OJVM