CONICET | Buscador de Institutos y Recursos Humanos

We previously demonstrated that the Gram-negative opportunistic human pathogen Acinetobacter baumannii senses and responds to blue light (Mussi et al., 2010). In particular, we have shown that motility, biofilm formation and virulence against Candida albicans are modulated by blue light. These bacterial responses depend on the expression of the blue-light-sensing A (blsA) gene, which codes for a protein that contains an N-terminal blue-light-sensing-using flavin (BLUF) domain. Interestingly, temperature plays a role in the ability of A. baumannii to sense and respond to light, as the photoregulation is not observed at 37ºC. In addition, we showed that light regulation is not restricted to A. baumannii but is widespread within members of the Acinetobacter genus, showing that light perception is a common trait in the lifestyle of these bacteria (Golic et al., 2013). The first step in the light transduction cascade was thus identified in A. baumannii: the photoreceptor BlsA. In this work, we present evidence on the last step of the light signal transduction cascade, which we have found to be mediated by cyclic second messangers as determined both by overexpression of the corresponding cyclases and phosphodiesterases in wild type and blsA mutants, as well as by external addition of the compounds. We were also interested in evaluating whether light modulates antibiotic resistance in A. baumannii, given its stablished character as a nosocomial pathogen. For this purpose, we performed a systematic analysis using standarized antibiotic susceptibility tests conditions. Our results show that many of the strains analyzed present slight but reproducible differences in antibiotic resistance between light and dark conditions. Moreover, in two strains, A118 and A42, we detected wider differences that could account for a role of light in modulation of antibiotic resistance. These differences were registered mainly with amikacyn, minocyclin and imipenem antibiotics.