Transferability of antimicrobial resistance from multidrug-resistant Escherichia coli isolated from cattle in the USA to E. coli and Salmonella Newport recipients

Authors: Poole, Toni; Callaway, Todd; NORMAN, KERI - Texas A&M University; SCOTT, MORGAN - Texas A&M University; LONERAGAN, GUY - Texas A&M University; ISON, SARAH - Texas Tech University; Beier, Ross; Harhay, Dayna; NORBY, BO - Michigan State University; Nisbet, David

Submitted to: Journal of Global Antimicrobial Resistance
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2017
Publication Date: 12/1/2017
Citation: Poole, T.L., Callaway, T.R., Norman, K.N., Scott, M.H., Loneragan, G.H., Ison, S.A., Beier, R.C., Harhay, D.M., Norby, B., Nisbet, D.J. 2017. Transferability of antimicrobial resistance from multidrug-resistant Escherichia coli isolated from cattle in the USA to E. coli and Salmonella Newport recipients. Journal of Global Antimicrobial Resistance. 11:123-132. https://doi.org/10.1016/j.jgar.2017.08.001.
DOI: https://doi.org/10.1016/j.jgar.2017.08.001

Interpretive Summary: Bacteria that cause disease are termed pathogens. They cause a variety of diseases in humans and animals and are problematic; certain diseases once thought well under control are reappearing due to the development of antibiotic resistance. Poultry and livestock producers have long been under pressure to limit the presence of pathogenic bacteria often found in retail meat products. However, with the emergence of pathogens that are resistant to antibiotics, there are new pressures to limit the use of antimicrobial agents in agriculture. Yet, there is evidence that the reduction in antibiotic use alone is not sufficient to reduce antimicrobial resistant bacterial populations. The limitation of antimicrobial use poses an additional dilemma on producers for the maintenance of food animals, as well as for preventing the presence of pathogens in retail meat. There is an effort to determine how antibiotic resistance is transferred among bacteria. This study characterized how antimicrobial resistance was transferred from field strains of E. coli to a field strain of Salmonella and a lab strain of E. coli. It also revealed that extended-spectrum beta-lactamase resistant bacteria that have primarily existed in Europe are now prevalent in the United States as well.

Technical Abstract: The objective of this study was to evaluate conjugative transfer of cephalosporin resistance among (n=100) strains of multi-drug resistant Escherichia coli (MDRE) to Salmonella Newport and E. coli DH5-alpha recipients. To accomplish this, phenotypic and genotypic profiles were determined for MDRE, Salmonella Newport (trSN), and E. coli DH5-alpha (trDH) transconjugants. It was found that twenty-seven percent (n=26) and 28% (n=27) of (n=95) MDR E. coli donor isolates transferred resistance to trSN and trDH recipient isolates, respectively. Twenty-seven percent (n=27) of MDRE were confirmed as extended-spectrum ß-lactamase (ESBL) based on the double disc synergy assay and whole genome sequencing (WGS). WGS was performed on 25 of the ESBLs. Subsequently, two isolates carried blaCTX-M-6, 20 possessed blaCTX-M-32, and three were negative for blaCTX-M genes. Fourteen of the ESBLs sequenced harboured qnrB19. Differential transfer of IncA/C and IncN from MDRE32 was observed between trSN32 and trDH32. IncN positive trDH32 displayed an ESBL phenotype; whereas, IncA/C positive trSN32 displayed an AmpC phenotype. ESBL transfer to SN and DH recipients occurred at 11% and 92% respectively. Twenty-seven MDRE were phenotypically identified ESBLs. WGS of 25 MDRE revealed that two and 20 isolates carried blaCTX-M-6 and blaCTX-M-32 genes, respectively. One multi-drug resistant isolate exhibited a conversion from an AmpC phenotype to an ESBL phenotype with the transfer of only the IncN plasmid. The rate of resistance transfer to Salmonella or E. coli recipients was nearly identical. However, the ESBL phenotype was transferred with significantly greater prevalence to E. coli as opposed to Salmonella Newport, 96% and 11%, respectively.