Submitted to: Proceedings of American Registry of Professional Animal Scientists
Publication Type: Proceedings
Publication Acceptance Date: 10/11/2007
Publication Date: 10/25/2007
Citation: Rychlik, J.L., Callaway, T.R., Edrington, T.S., Anderson, R.C., Nisbet, D.J. 2007. Darwinian and neo-Darwinian selection mechanisms in bacteria: Effects on antibiotic resistance. In: Proceedings of American Registry of Professional Animal Scientists, October 25-26, 2007, Coalinga, California. p. 1-13. Interpretive Summary: The survival of the fittest concept is as valid amongst bacteria as it is among animals. During the 20th century the role of genes in evolution became more appreciated, and a new biological paradigm appeared; neo-Darwinism. In neo-Darwinistic theory the gene is the ultimate unit of selection rather than the bacteria; meaning that the bacteria is merely a vehicle for genetic reproduction and spread. Antibiotic resistance is a mechanism by which genes can be assured of being carried on into another generation or spread around between bacteria, because they confer a competitive advantage to equipped bacteria. Adding selective pressure via feeding antibiotics helps to select for new antibiotic resistance to develop and provides an environmental opening for resistant strains to fill. Strategies for using new or medically-important antibiotics must be developed and implemented that do not enhance Darwinian and neo-Darwinian selection for antibiotic resistance genes and their host organisms in or near our food supply.
Technical Abstract: Darwin’s concept of survival of the fittest is as critical when applied to bacteria as it is to animals. Bacteria live in a highly competitive environment that is similar to the macrobiological world with its selective pressures. Neo-Darwinism views genes as selfish and as the ultimate unit of natural selection instead of the host organism. Bacteria that carry antibiotic resistance genes are merely vehicles for ensuring the reproduction and dissemination of these genes. Antibiotic resistance genes can be shared horizontally amongst bacteria of the same or different species through conjugation, transduction and transformation. Mobile genetic elements (DNA fragments, transposons, phage and plasmids) are wild cards in the evolution of bacteria and can introduce or combine new genes or groups of genes to bacteria, especially antibiotic resistance genes. The movement of these genes is critical to the further dissemination of the genes by ensuring the survival of the bacterial hosts. Addition of selective pressure via feeding antibiotics helps to select for new antibiotic resistance and provides an environmental niche opening for resistant strains to fill and proliferate. Strategies for using new or medically-important antibiotics must be developed and implemented that do not enhance Darwinian and neo-Darwinian selection for antibiotic resistance genes and their host organisms. The antibiotic resistance gene is as critical as the bacteria itself as related to the dissemination of antibiotic resistance throughout the food animal population.