T7-10 Multiplex PCR-based Identification of Shiga Toxin-producing Escherichia coli Other Than the Top Seven Serogroups Found in the Feces of Feedlot Cattle

Tuesday, July 11, 2017: 4:15 PM
Room 15 (Tampa Convention Center)
Justin Ludwig , Kansas State University , Manhattan , KS
Xiaorong Shi , Kansas State University , Manhattan , KS
Lance Noll , Kansas State University , Manhattan , KS
Jianfa Bai , Kansas State University , Manhattan , KS
T G Nagaraja , Kansas State University , Manhattan , KS
Introduction: Escherichia coli serogroups O26, O45, O103, O111, O121, O145, and O157 (Top 7) are major STEC foodborne pathogens. Cattle are a reservoir for the Top 7 STEC, which reside in the hindgut and are shed in the feces. Cattle harbor a number of other STEC serogroups (n=108), but not all of them have been shown to be associated with human illness.

Purpose:  Our objective was to develop and utilize several sets of multiplex PCR assays to identify STEC isolates from feedlot cattle feces that were negative for the Top 7 STEC.

Methods: A total of 359 E. coli strains, positive for stx1 (Shiga toxin 1; n=65), stx2 (Shiga toxin 2; n=306), stx1 and stx2 (n=16), and/or eae (intimin; n=68) genes and negative for the Top 7 STEC were used. One hundred eighteen isolates were from fecal samples collected from a single feedlot in 2013 and 241 strains ertr isolated from pen-floor fecal samples collected from eight feedlots in the central United States. Several sets of multiplex PCR assays targeting serogroup-specific genes were used to identify the serogroups.

Results:  Of the 118 strains from the single feedlot, 84 (71.2%) belonged to seven serogroups and 34 (28.8%) were unidentifiable. The seven serogroups included: O168 (29.7%), O109 (20.3%), O171 (9.3%), O104 (4.2%), O2 (4.2%), O8 (2.5%), and O175 (0.8%). Among the 241 strains from eight feedlots, 164 strains (68.0%) belonged to 13 serogroups and 77 (32.0%) were unidentifiable. The 13 serogroups included O168 (29.9%), O109 (16.2%), O2 (8.3%), O104 (5.0%), O8 (2.9%), O171 (1.7%), O136 (1.2%), O178 (0.8%), O76 (0.4%), O113 (0.4%), O118 (0.4%), O175 (0.4%), and O98 (0.4%).

Significance:  Cattle harbor a number of STEC serogroups other than the those included in the Top 7. This illustrates the diversity of STEC shed in the feces. The two most predominant serogroups identified were O168 (107 of 359: 29.8%) and O109 (63 of 359; 17.6%).