29G-9 |
Measurement of competition and fitness in commensal E. coli and E. coli O157:H7 strains |
L. M. DURSO1, G. Vizcaino1, and R. W. Hutkins2. (1) Food Science and Technology, University of Nebraska, 333 FIC - East Campus, Lincoln, NE 68583-0919, (2) Dept. of Food Science & Technology, Univ. of Nebraska, Lincoln, 338 Food Industry Complex, Lincoln, NE 68583-0919 Since its sudden emergence as a pathogen, E. coli O157:H7 has become one of the most widely studied foodborne pathogens. Most natural environments that support growth of E. coli O157:H7 contain not only that strain, but a mixed population of numerous individual E. coli clones. Thus, any individual E. coli clone must compete against other E. coli strains for limited resources in any given habitat. We were therefore interested in characterizing patterns of intra-specific competition, individual fitness, and competitive fitness. The first set of experiments consisted of a series of disk diffusion competition assays performed in a 122 X 122 matrix design, whereby all 122 commensal and O157:H7 E. coli strains were tested for production of and sensitivity to inhibitory agents. The second set of experiments consisted of screening 122 strains of commensal and O157:H7 E. coli for sensitivity to 24 different antibiotics using a standardized NCCLS disk diffusion procedure. In the third set of experiments, we measured growth rates of all 122 strains in various media as a measure of fitness, and then measured growth rates of paired strains grown in the same medium as a measure of competitive fitness. Results indicated that there were distinctive patterns of sensitivity to and production of intraspecific antagonistic agents. The majority of the strains that produced an inhibitory substance were E. coli O157:H7 strains, while the majority of the strains that were sensitive to inhibitory substances were commensal E. coli strains. Most E. coli strains, regardless of commensal or pathogen status, were sensitive to all but two of the antibiotics tested. The individual and competitive fitness assays revealed that both commensal and O157:H7 E. coli strains grew at similar rates in the media used. These results indicate that commensal and O157:H7 E. coli strains have different strategies for competing in natural habitats.
Session 29G, Food Microbiology: General
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