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Applied and Environmental Microbiology, October 2005, p. 5893-5899, Vol. 71, No. 10
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.10.5893-5899.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
U.S. Department of Agriculture, Agricultural Research Service, Animal Disease Research Unit, Pullman, Washington 99164-6630,1 Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington 99164-7040,2 Field Disease Investigation Unit, Department of Veterinary Clinical Science, Washington State University, Pullman, Washington 99164-6610,3 Department of Microbiology, College of Veterinary Medicine and School of Agricultural Biotechnology, Seoul National University, Seoul 151-742, South Korea4
Received 7 December 2004/ Accepted 3 May 2005
Listeria monocytogenes is a significant food-borne human and veterinary pathogen. Contaminated silage commonly leads to disease in livestock, but the pervasive nature of the bacterium can make it difficult to identify the source of infection. An investigation of bovine listeriosis that occurred on a Pacific Northwest dairy farm ("farm A") revealed that the clinical strain was closely related to fecal strains from asymptomatic cows, and that farm environment was heavily contaminated with a diversity of L. monocytogenes strains. In addition, the farm A clinical strain was closely related to clinical and environmental strains obtained 1 year prior from a second Northwest dairy farm ("farm B"). To investigate the source(s) of contamination on farm A, environmental samples were collected from farm A at two time points. Pulsed-field gel electrophoresis characterization of 538 isolates obtained from that farm identified 57 different AscI pulsovars. Fecal isolates obtained from individual cows were the most genetically diverse, with up to 94% of fecal samples containing more than one pulsovar. The maximum numbers of pulsovars and serotypes isolated from a fecal sample of one cow were 6 and 4, respectively. Serotype 1/2a was isolated most frequently at both time points. Microarray genotyping of bovine listeriosis, fecal, and silage strains from both farms identified four probes that differentiated listeriosis strains from environmental strains; however, no probe was common to both bovine listeriosis strains.
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