Submitted to: International Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2020
Publication Date: 4/14/2020
Citation: Mir, R.A., Brunelle, B.W., Alt, D.P., Arthur, T.M., Kudva, I.T. 2020. Super-shed Escherichia coli O157:H7 has potential for increased persistence on the recto-anal junction squamous epithelial cells and antibiotic resistance. International Journal of Microbiology. 2020(2368154):1-16. https://doi.org/10.1155/2020/2368154.
Interpretive Summary: Cattle are the primary source of Escherichia coli O157 (O157), a bacteria responsible for bloody diarrhea and other serious symptoms in humans. Although O157 can cause serious disease in humans, cattle carry this bacterium in their intestines without disease and shed this bacterium in their feces. O157 prefers to localize in the recto-anal junction or RAJ of the cattle intestine that is found close to the anal canal. Some colonized animals, referred to as “super-shedders”, are known to shed O157 in large numbers of O157 in feces. Supershedding cattle play a role in the prevalence and transmission of O157, but little is known about the mechanisms causing this phenomenon. The bacteria, host and/or the environment could contribute to the super-shedding phenomenon, and identifying factors contributing to shedding will provide insight to the development of intervention strategies. In this study we evaluated 101 genetically diverse super-shed O157 isolates and confirmed that the binding pattern to RAJ cells was similar for all the super-shed isolates. In addition, many super-shed isolates were resistant to clinically relevant antibiotics and carried genes associated with antibiotic resistance. Understanding the roles of bacteria in the super-shedding phenomenon is important for the development of new methods to reduce/eliminate transmission of super-shed O157 from cattle to the environment.
Technical Abstract: Cattle are primary reservoirs of Escherichia coli O157:H7 (O157), and super-shedding (SS) cattle shed O157 at greater than or equal to 10**4 colony-forming units/g feces. In this study, we tested genetic relatedness and adherence patterns of SS-O157 isolates (n equals 101) using Polymorphic Amplified Typing Sequences (PATS) analysis and in-vitro cell-adherence assays, respectively. PATS analysis grouped the SS-O157 isolates into five major clades and all isolates demonstrated an aggregative adherence phenotype, with 54 percent being hyper-adherent and 46 percent moderately adherent to the bovine recto-anal junction squamous epithelial (RSE) cells. Interestingly, 69 percent of SS-O157 isolates that were identical to human O157 outbreak strains by pulsed-field gel electrophoresis profiles (CDC PulseNet Database) were hyper-adherent on RSE cells and all were grouped into two clades by PATS distinguishing them from the other SS-O157. A subset of the SS-O157 isolates (n equals 53) representing the different PATS and RSE cell adherence profiles were analyzed for antibiotic resistance (AR). Several SS-O157 showed resistance to sulfisoxazole and one isolate was resistant to both sulfisoxazole and tetracycline in antibiotic sensitivity tests (AST). Minimum inhibitory concentration (MIC) tests confirmed the resistance observed using AST. Genes directly associated with AR were rarely amplified from the SS-O157 isolates and confirmed by sequencing. The integrase gene, int, linked with integron-based AR acquisition/transmission, was identified in 92 percent of SS-O157 isolates. Our results indicate that PATS typing can distinguish closely related SS-O157 isolates, RSE cell adherence assay provides better insights into host specific adherence capabilities of SS-O157 and that SS-O157 carry few AR genes that would be of concern for AR dissemination.