Diversity of extended-spectrum cephalosporin-resistant Escherichia coli in feces from calves and cows on Pennsylvania dairy farms

Authors: SALAHEEN, SERAJUS - US Department Of Agriculture (USDA); CAO, HUILIN - US Department Of Agriculture (USDA); Sonnier, Jakeitha - Jackie; KIM, SEON-WOO - University Of Maryland; Del Collo, Laura; HOVINGH, ERNEST - Pennsylvania State University; Karns, Jeffrey; Haley, Bradd; Van Kessel, Jo Ann

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2018
Publication Date: 2/4/2019
Citation: Salaheen, S., Cao, H., Sonnier, J.L., Kim, S., Del Collo, L.P., Hovingh, E., Karns, J.S., Haley, B.J., Van Kessel, J.S. 2019. Diversity of extended-spectrum cephalosporin-resistant Escherichia coli in feces from calves and cows on Pennsylvania dairy farms. Foodborne Pathogens and Disease. https://doi.org/10.1089/fpd.2018.2579.
DOI: https://doi.org/10.1089/fpd.2018.2579

Interpretive Summary: Antimicrobial resistance is a pressing public health concern, and food animal production farms have been implicated as potential sources of resistant bacteria or genetic resistance elements that can be transferred to human pathogens. Some bacteria produce extended-spectrum ß-lactamases (ESBL) and this confers resistance to some antibiotics that are important in human medicine. Escherichia coli are ubiquitous in the guts of healthy mammals and can be used as an indicator of the presence of resistance. We previously studied E. coli that were isolated from different age animals on dairy farms (calves and adult cows) and identified some isolates that were ESBL-producers. Calves have been shown to have more resistance in their fecal E. coli populations, and notably more multi-drug resistance. Our objectives were to determine if certain multi-drug resistant strains of E. coli were persistant in a herd; were E. coli isolates with resistance to the same animicrobial classes that were found in calves and cows the same strains of E. coli or were they different E. coli that carried the same genes that conferred resistance? Based on our analysis, there are specific strains of ESBL-producing E. coli with the same resistance profile that are carried by both the calves and the cows. However there are also different strains of E. coli that are genetically different but carry the same resistance profile. Resistant E. coli are diverse and circulated through different (non-commingled) animal groups on individual farms. This research will be used by scientists to further identify means to reduce antimicrobial resistance in dairy animal-associated bacteria, thereby reducing human exposure to resistant pathogenic bacteria.

Technical Abstract: The global incidence of human infections associated with extended-spectrum ß-lactamase-producing (ESBL) E. coli is increasing. Dairy animals are reservoirs of ESBL-producing E. coli, especially, third generation cephalosporin (3GC)-resistant strains. To further understand the distribution and diversity of 3GC-resistant E. coli across animals of different age-groups (e.g., pre- and post-weaned calves, lactating cows and dry cows) and farms, we used Pulsed-Field Gel Electrophoresis (PFGE) to characterize 70 dairy-associated isolates from 14 farms located in nine Pennsylvania counties by. Results of this analysis indicated that 3GC-resistant E. coli were highly diverse and grouped into 27 PFGE clades (=80 % similarity) and 24 unique antimicrobial resistance patterns were observed amongst the isolates. Several isolates with the same resistance pattern were distributed to different clades, including isolates from different animal age-groups on the same farm, suggesting different strains of E. coli within a farm harbored the same resistance-conferring elements. Additionally, similarly-resistant E. coli grouped within the same clades were isolated from different animal groups on eight farms, indicating that strains were carried in both the calves and the adult cows within the same herd. Results of this analysis indicated 3GC-resistant E. coli were highly diverse, associated with multidrug resistance, and circulated through different (non-commingled) animal groups on individual farms.