Antibiotic Resistance and Fitness of Enteric Pathogens

Abstract

This chapter discusses how antimicrobial resistance impacts bacterial fitness and how bacteria adapt to restore fitness in the absence of antibiotic selection pressure. This topic has been studied for many different bacterial pathogens, but in the chapter the authors have reviewed information only on food-borne bacteria, with a particular emphasis on Escherichia coli, Salmonella, and Campylobacter. Mutation-mediated antibiotic resistance often occurs in genes encoding products that are involved in vital cellular processes (e.g., DNA gyrase and 23S rRNA), and the resistance-conferring mutations often affect the normal physiological functions of the products, leading to reduced growth rates. Bacterial resistance to actinonin is usually mediated by mutations in the fmt gene, encoding methionyl-tRNA formyltransferase, or the folD gene, encoding an enzyme involved in the production of 10-formyl-H4-folate. Gene amplification (increased copy number) is also involved in the evolutionary process of fitness restoration. In order to effectively control the persistence and transmission of antimicrobial resistance in food-borne bacteria, we must have a better understanding of if and how antibiotic resistance affects bacterial adaptation and evolution and, in particular, how antibiotic-resistant bacteria interact with their environments and animal hosts in the absence of selection pressure.