Can the use of older-generation beta-lactam antibiotics in livestock production over-select for beta-lactamases of greatest consequence for human medicine? An in vitro experimental model

Authors: OGUNRINU, OLANREWAJU - Texas A&M University; NORMAN, KERI - Texas A&M University; VINASCO, JAVIER - Texas A&M University; LEVENT, GIZMEN - Texas A&M University; LAWHON, SARA - Texas A&M University; FAJT, VIRGINIA - Texas A&M University; VOLKOVA, VICTORIA - Kansas State University; GAIRE , TARA - Kansas State University; Poole, Toni; Genovese, Kenneth - Ken; WITTUM, THOMAS - The Ohio State University; SCOTT, HARVEY - Texas A&M University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2020
Publication Date: 11/16/2020
Citation: Ogunrinu, O.J., Norman, K.N., Vinasco, J., Levent, G., Lawhon, S.D., Fajt, V.R., Volkova, V.V., Gaire , T., Poole, T.L., Genovese, K.J., Wittum, T.E., Scott, H.M. 2020. Can the use of older-generation beta-lactam antibiotics in livestock production over-select for beta-lactamases of greatest consequence for human medicine? An in vitro experimental model. PLoS ONE. 15(11). Article e0242195. https://doi.org/10.1371/journal.pone.0242195.
DOI: https://doi.org/10.1371/journal.pone.0242195

Interpretive Summary: Bacteria that cause disease (pathogens) in humans and animals have produced a public health crisis because diseases once thought largely under control are reappearing. Some public health officials blame the food animal industry for the emergence of pathogenic bacteria and downplay the role of human medicine. Poultry and livestock producers have long been under pressure to limit the presence of pathogenic bacteria often present on retail meat products. However, with the emergence of multi-drug resistant pathogens, there are new pressures to limit the use of antimicrobial agents for treatment of food animals. 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 for producers regarding the maintenance of food animals as well as preventing the presence of pathogens on retail meat. There is an effort to find alternatives to antimicrobials that would enhance the growth and health of food animals. Methylsulfonylmethane (MSM), a substance approved for use in humans, horses, and dogs to reduce inflammation caused by arthritis, has been shown by this work to inhibit the growth of some bacteria. This study further characterized the type of bacterial inhibition MSM elicited on Escherichia coli and Salmonella Kinshasa bacteria.

Technical Abstract: Though not licensed for use in food animals, resistance to carbapenems among Enterobacteriaceae has been identified in farm animals and their environments. The objective of our study was to determine the extent to which older-generation ß-lactam antibiotics approved for use in food animals might differentially select for highest priority antibiotic resistance. Escherichia coli (E. coli) strains from humans, food animals, or the environment and bearing a single ß-lactamase gene (n=20 each): that is, blaTEM-1, blaCMY-2, blaCTX-M-*, or blaKPC/IMP/NDM, but not in combination, were identified, along with 20 E. coli strains lacking any known beta-lactamase genes. Baseline estimates of intrinsic bacterial fitness were derived from growth curves. Effects of ampicillin (32 µg/ml), ceftriaxone (4 µg/ml), and meropenem (4 µg/ml) on each strain and group also were assessed. Further, in vitro batch cultures using equal concentration mixtures were prepared with 10 representative E. coli strains (two from each resistance gene group) and each mixture was incubated at 37 deg C for 24 hours in non-antibiotic cation-adjusted Mueller-Hinton II (CAMH-2) broth, ampicillin + CAMH-2 broth (at 2, 4, 8, 16, and 32 µg/ml) and ceftiofur + CAMH-2 broth (at 0.5, 1, 2, 4, and 8µg/ml). Relative and absolute quantitative abundance of bacterial groups were estimated phenotypically via selective antibiotic MacConkey plates. Line plots, non-linear Gompertz models and multilevel mixed-effect linear regression models were generated. The observed strain growth fitness distributions were significantly different across all groups. AmpC strains (i.e., blaCMY-2) had distinctly less robust (p < 0.05) growth in ceftriaxone (4 µg/ml) compared to extended-spectrum beta-lactamase (ESBL) producers harboring blaCTX-M-*. With increasing beta-lactam antibiotic concentrations, relative proportions of ESBLs and CREs were over-represented in mixed bacterial community cultures; importantly, this was more pronounced with ceftiofur than with ampicillin. Aminopenicillins, but especially extended-spectrum cephalosporins, are expected to propagate carbapenemase producing Enterobacteriaceae in food animals if and when they spill over from human health care settings.