Ecogenetics of antibiotic resistance in Listeria monocytogenes

Abstract

The acquisition process of antibiotic resistance in an otherwise susceptible organism is shaped by the ecology of the species. Unlike other relevant human pathogens, Listeria monocytogenes has maintained a high rate of susceptibility to the antibiotics used for decades to treat human and animal infections. However, L. monocytogenes can acquire antibiotic resistance genes from other organisms’ plasmids and conjugative transposons. Ecological factors could account for its susceptibility. L. monocytogenes is ubiquitous in nature, most frequently including reservoirs unexposed to antibiotics, including intracellular sanctuaries. L. monocytogenes has a remarkably closed genome, reflecting limited community interactions, small population sizes and high niche specialization. The L. monocytogenes species is divided into variants that are specialized in small specific niches, which reduces the possibility of coexistence with potential donors of antibiotic resistance. Interactions with potential donors are also hampered by interspecies antagonism. However, occasional increases in population sizes (and thus the possibility of acquiring antibiotic resistance) can derive from selection of the species based on intrinsic or acquired resistance to antibiotics, biocides, heavy metals or by a natural tolerance to extreme conditions. High‐quality surveillance of the emergence of resistance to the key drugs used in primary therapy is mandatory.

Evolutionary Pathways and Trajectories in Antibiotic Resistance

“…The unbeatable strategy occurs because the population is kept in a successful adaptive configuration (the strategy) ensuring an equilibrium with the environment, resulting in ecogenetic stability. This population might have possibilities for acquiring more effective traits leading to higher fitness (for instance, higher antibiotic resistance), but such acquisition implies possible conflicts with other adaptive traits of proven success (545). The minority variants proposing an alternative strategy are prevented from successfully invading the population.…”

The Origin of Niches and Species in the Bacterial World

“…In highly stable environments, predominantly intracellular bacteria such as Chlamydia and Rickettsia also have a predominant core genome. Widespread species such as Pseudomonas aeruginosa, or certain Bacillus, but also Listeria monocytogenes or Legionella pneumophila (that also have intracellular niches), have a relevant core genome, adapted to widespread and/or homeostatized niches (Baquero et al, 2020).…”

Assessment of the Prevalence and Drug Susceptibility of Listeria monocytogenes Strains Isolated from Various Types of Meat

“…Despite relatively high susceptibility to the antimicrobials commonly used in infection treatment, L. monocytogenes has been recently observed to develop increased tolerance to antimicrobials. L. monocytogenes antibiotic resistance can result from the acquisition of resistance genes from other Gram-positive bacteria (e.g., plasmid-mediated transfer), however overuse of antimicrobials in medicine and agriculture can also negatively affect the drug susceptibility of the pathogen [20,27,32,33]. Moreover, L. monocytogenes cell components and mechanisms involved in the adaptation to stress conditions occurring in the food-chain (the alternative sigma factor B (σ B ), two-component signal transduction systems, efflux pump activity) were suggested to contribute to the increased pathogen resistance to ampicillin, penicillin, and cephalosporins [32,34].…”

“…Moreover, L. monocytogenes cell components and mechanisms involved in the adaptation to stress conditions occurring in the food-chain (the alternative sigma factor B (σ B ), two-component signal transduction systems, efflux pump activity) were suggested to contribute to the increased pathogen resistance to ampicillin, penicillin, and cephalosporins [32,34]. On the other hand, high sensitivity of L. monocytogenes to antimicrobials may be due to the origin of these bacteria in the natural environment where they are not exposed to antibiotics [20].…”

“…The risk of L. monocytogenes occurrence in FPE may increase due to the drug resistance of pathogenic strains. Although L. monocytogenes is thought to maintain a relatively high susceptibility to most of the clinically relevant antimicrobials, the anthropogenic activity (extensive use of antibiotics, cross-resistance to molecules used as growth promoters in animal production) can result in spreading antibiotic resistance among L. monocytogenes strains [4,20].…”