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United States Department of Agriculture

Agricultural Research Service

Title: Characterization of Shiga Toxin-Producing Escherichia Coli Strains Isolated from Swine Feces

Authors
item Fratamico, Pina
item Bagi, Lori
item Cray, Paula
item Bhagwat, Arvind

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 10, 2006
Publication Date: August 13, 2006
Citation: Fratamico, P.M., Bagi, L.K., Cray, P.J., Bhagwat, A.A. 2006. Characterization of shiga toxin-producing escherichia coli strains isolated from swine feces. {Abstract}. International Association of Food Protection. P1-47.

Technical Abstract: Shiga toxin-producing E. coli (STEC) belonging to different serogroups were isolated from swine feces and were characterized to determine the presence of E. coli virulence genes by the PCR, antibiotic resistance profiles, and acid tolerance. Twenty-nine out of 219 (13%) of the isolates harbored the gene for Stx1, 14 (6%) Stx2, 179 (80%) Stx2e, 46 (21%) STa, 14 (6.4%) STb, 10 (4.6%) F18, 94 (42.9%) EAST1, 192 (87.7%) Cdt-II, 1 (0.46%) Cdt-III, and 25 (11.4%) Hly. None of the strains harbored the genes for LT, BFP, F4, F5, F6, F41, CNF1, CNF2, EaeA, Cdt-I, and Cdt-IV. The strains were also examined for antimicrobial susceptibility profiles using 16 antibiotics. The STEC isolates displayed resistance most often to tetracycline (95.4%), sulfamethoxazole (53.4%), kanamycin (38.4%), streptomycin (34.7%), and chloramphenicol (22.4%). An E. coli serotype O20:H42 strain, which was positive for stx2e, astA, and cdtII was resistant to all of the antibiotics tested, except for amikacin. In addition, 52 of the swine isolates were examined for their ability to withstand acid challenge by three types of acid resistance (AR) pathways, AR1 (rpoS-dependent), AR2 (glutamate-dependent) and AR3 (arginine-dependent). None of the strains was defective in the AR1 resistance pathway, while one strain was defective in the AR2 pathway under aerobic growth conditions, but was fully functional under anaerobic growth conditions. However, 8 out of 52 strains were defective in the AR3 pathway. The strain that was defective in AR2 was fully functional in the AR3 pathway. Since acid resistance plays a vital role in the survival and virulence of these strains, differences among the isolates to induce AR pathways may play a significant role in determining their infective dose. This study demonstrates that swine STEC are a heterogeneous group, and the possession of virulence genes, including genes for the Shiga toxins, ST enterotoxins, hemolysin, and cytolethal distending toxins indicate that many swine STEC can potentially cause human illness.

Last Modified: 11/22/2014