biostudies-literatureAvillan JJPoncin Scholarship FundHHS | NIH | National Institute of General Medical SciencesPaul G. Allen School for Global HealthM.J. Murdock Charitable TrustNIGMS NIH HHSe0079122https://www.ebi.ac.uk/biostudies/studies/S-EPMC9361830biostudies-literatureUnknown88(15)At a time when antibiotic resistance is seemingly ubiquitous worldwide, understanding the mechanisms responsible for successful emergence of new resistance genes may provide insights into the persistence and pathways of dissemination for antibiotic-resistant organisms in general. For example, Escherichia coli strains harboring a class A β-lactamase-encoding gene (<i>bla</i>_CTX-M-15) appear to be displacing strains that harbor a class C β-lactamase gene (<i>bla</i>_CMY-2) in Washington State dairy cattle. We cloned these genes with native promoters into low-copy-number plasmids that were then transformed into isogenic strains of E. coli, and growth curves were generated for two commonly administered antibiotics (ampicillin and ceftiofur). Both strains met the definitionApplied and environmental microbiologyExcreted Antibiotics May Be Key to Emergence of Increasingly Efficient Antibiotic Resistance in Food Animal Production.PMC9361830N.A.T32 GM008336T32-GM008336Liu JLofgren EHorton JDavis MAKang CLu SYAhmadvand PCall DRAvillan JJfalseExcreted Antibiotics May Be Key to Emergence of Increasingly Efficient Antibiotic Resistance in Food Animal Production.At a time when antibiotic resistance is seemingly ubiquitous worldwide, understanding the mechanisms responsible for successful emergence of new resistance genes may provide insights into the persistence and pathways of dissemination for antibiotic-resistant organisms in general. For example, Escherichia coli strains harboring a class A β-lactamase-encoding gene (<i>bla</i>_CTX-M-15) appear to be displacing strains that harbor a class C β-lactamase gene (<i>bla</i>_CMY-2) in Washington State dairy cattle. We cloned these genes with native promoters into low-copy-number plasmids that were then transformed into isogenic strains of E. coli, and growth curves were generated for two commonly administered antibiotics (ampicillin and ceftiofur). Both strains met the definition2022-01-01T00:00:00Z2022 Aug2026-06-13T06:20:21.857Z2025-04-19T20:50:17.429ZS-EPMC93618303586758610.1128/aem.00791-22