Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/27/2017
Publication Date: N/A
Technical Abstract: Cattle are primary reservoirs of Escherichia coli O157:H7 (O157), and super-shedding cattle shed O157 at greater than or equal to 10,000 colony-forming units/g feces. Host, bacteria, and/or the environment reportedly influence the super-shedding phenomenon. We recently demonstrated that a super-shed O157 (SS-O157) strain, SS-17, hyper-adheres to the recto-anal junction (RAJ) squamous epithelial (RSE) cells, which may contribute to SS-O157 persistence at this site in greater numbers. In order to verify if this would be the signature adherence profile of any SS-O157, we tested additional, previously characterized (Arthur et al., AEM, 2013; 79: 4294–4303) SS-O157 isolates (n equals 101; each from a different animal) in the RSE cell adherence assay. Similar to SS-17, all 101 SS-O157 exhibited aggregative adherence on RSE cells, either attaching strongly (greater than 10 bacteria/cell; 56 percent; hyper-adherent) or moderately (1-10 bacteria/cells; 44 percent). Polymorphic Amplified Typing Sequences (PATS) analysis (based on XbaI and AvrII restriction enzyme digestion site-polymorphisms and the presence of specific virulence genes) assigned the 101 SS-O157 into 5 major clades but not to any predominant genotype, or group based on their RSE adherence patterns. Interestingly, of the SS-O157 that shared the top 10 human disease pulsed-field gel electrophoresis (PFGE) patterns on the CDC PulseNet database (Arthur et al.), 69 percent exhibited the hyper-adherence phenotype on RSE cells. Hence, SS-O157 isolates appear to have the potential not only for increased persistence in cattle, but also for causation of human disease. We are presently screening 55/101 SS-O157 isolates, representing the 5 PATS clades or associated with the top 10 human disease PFGE patterns and covering the RSE adherence phenotypes, for the presence of antibiotic resistance (AR) genes in their genomes. AR in SS-O157 could potentially lead to wide spread distribution of resistance on farms to other zoonotic pathogens as well as commensal bacteria. Meta-analysis of three SS-O157 (SS17, SS52 and KCJ1266) and three human outbreak O157 (EDL933, Sakai and Spinach Outbreak EC4115) genomes shows the presence of 29, 33, 22, 22, 21 and 35 AR genes, respectively. We are currently examining a subset of these AR genes, based on their prevalence across these six representative O157 genomes and presence in at least one of the SS-O157genomes. These genes are being evaluated along with genes encoding for colistin resistance and fourteen other standard antibiotics using the Kirby-Bauer disc diffusion method, PCR amplification, and sequencing.