title: Survival of Pseudomonas aeruginosa exposed to sunlight resembles the phenom of persistence.
abstract: During exposure of Pseudomonas aeruginosa stationary phase cells to natural solar radiation, a reduction in the rate of loss of bacterial viability was observed when survival fractions were lower than 1/10,000. This reduction was independent of the growth medium used and of the initial bacterial concentration, and was also observed when irradiation was performed with artificial UVA radiation (365nm, 47Wm(-2)). These results indicate the presence of a small bacterial subpopulation with increased tolerance to radiation. Such a tolerance is non-heritable, since survival curves comparable to those of the parental strain were obtained from survivors to long-term exposure to radiation. The radiation response described here resembles the phenomenon called persistence, which consists of the presence of a small subpopulation of slow-growing cells which are able to survive antibiotic treatment within a susceptible bacterial population. The condition of persister cells is acquired via a reversible switch and involves active defense systems towards oxidative stress. Persistence is probably responsible for biphasic responses of bacteria to several stress conditions, one of which may be exposure to sunlight. The models currently used to analyze the lethal action of sunlight overestimate the effect of high-dose irradiation. These models could be improved by including the potential formation of persister cells.
authors.affiliation: Comisión Nacional de Energía Atómica, Departamento de Corrosión, Argentina.
authors.forename: Ana F
authors.initials: AF
authors.lastname: Forte Giacobone
authors.affiliation: Comisión Nacional de Energía Atómica, Departamento de Radiobiología, Argentina. Electronic address: oppezzo@cnea.gov.ar.
authors.forename: Oscar J
authors.initials: OJ
authors.lastname: Oppezzo
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D050296:Microbial Viability / Q000187:drug effects / Q000528:radiation effects; D008962:Models, Theoretical; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000528:radiation effects*; D013472:Sunlight; D014466:Ultraviolet Rays
chemical_list: D000900:Anti-Bacterial Agents