Unraveling the Physiological Complexities of Antibiotic Lethality

Abstract

We face an impending crisis in our ability to treat infectious disease brought about by the emergence of antibiotic-resistant pathogens and a decline in the development of new antibiotics. Urgent action is needed. This review focuses on a less well-understood aspect of antibiotic action: the complex metabolic events that occur subsequent to the interaction of antibiotics with their molecular targets and play roles in antibiotic lethality. Independent lines of evidence from studies of the action of bactericidal antibiotics on diverse bacteria collectively suggest that the initial interactions of drugs with their targets cannot fully account for the antibiotic lethality and that these interactions elicit the production of reactive oxidants including reactive oxygen species that contribute to bacterial cell death. Recent challenges to this concept are considered in the context of the broader literature of this emerging area of research. Possible ways that this new knowledge might be exploited to improve antibiotic therapy are also considered.

Generation of reactive oxygen species by lethal attacks from competing microbes

“…To address these concerns, Dwyer et al (27) used a panel of ROS-detection fluorescence dyes, a defined growth medium under stringent anaerobic conditions, and an in vivo H 2 O 2 enzymatic assay to study the effects of antibiotics on cells. The results further support that antibiotics induce ROS generation, which contributes to the efficacy of antibiotics in addition to their primary lethal actions (18,27,28).…”

“…ROS can cause lethal damage to DNA, lipid, and proteins (19,20) and thus can contribute to cell death in combination with the deleterious effects of antibiotics on their primary targets. The idea that antibiotics kill bacterial cells, in part, through the action of ROS has been supported by a number of follow-up studies (18,(21)(22)(23) but has also been challenged by others as a result of observations contradictory to a model where ROS is the sole mediator of antibiotic lethality (24)(25)(26). These observations include the fact that antibiotics kill under anaerobic conditions, oxidation of the hydroxyphenyl fluorescein fluorescence dye used to measure ROS levels is nonspecific, and the extracellular level of H 2 O 2 is not elevated by antibiotic treatment (24,26).…”

“…Collins and coworkers (16)(17)(18) have reported that antibiotic treatment of E. coli elicits the production of reactive oxygen species (ROS) resulting from a series of events involving perturbation of the central metabolic pathway, NADPH depletion, and the Fenton reaction. ROS can cause lethal damage to DNA, lipid, and proteins (19,20) and thus can contribute to cell death in combination with the deleterious effects of antibiotics on their primary targets.…”

Antibiotic treatment enhances the genome-wide mutation rate of target cells

“…Under sustained exposure to norfloxacin, mutation rates revealed by reporter constructs can be elevated 2-9 times (18,23). Norfloxacin is also thought to elevate intracellular reactive oxygen species (ROS) levels (24,25), which may further increase the rate of genomic mutation and the subsequent rate of acquisition of multidrug resistance (23,26).…”

Single-cell, real-time detection of oxidative stress induced in Escherichia coli by the antimicrobial peptide CM15

“…The initial results have been challenged (8)(9)(10), and very recently these challenges have been refuted (11). Evidently, oxidative stress contributes to the lethality of a variety of antimicrobial agents (12,13), including at least some antimicrobial peptides. The methods presented here enable detection of ROS within the cytoplasm of single cells with 12-s time resolution, a capability that should prove useful in many different contexts.…”