Light Modulates Important Pathogenic Determinants and Virulence in Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus ESKAPE Pathogens.

Light sensing has been extensively characterized in the human pathogen Acinetobacter baumannii at environmental temperatures. However, the influence of light on the physiology and pathogenicity of human bacterial pathogens at temperatures found in warm-blooded hosts is still poorly understand. In this work, we show that ESKAPE priority pathogens, such as Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter spp., which have been recognized by the WHO and the CDC as critical, can also sense and respond to light at temperatures found in human hosts. Most interestingly, in these pathogens light modulates important pathogenicity determinants as well as virulence in an epithelial infection model, which could have implications in human infections. In fact, we found that alpha-toxin-dependent hemolysis, motility and growth under iron deprived conditions are modulated by light in S. aureus Light also regulates persistence, metabolism and the ability to kill competitors, in some of these microorganisms. Finally, light exerts a profound effect on the virulence of these pathogens in an epithelial infection model, though the response is not the same in the different species: virulence was enhanced by light in A. baumannii and S. aureus, while in A. nosocomialis and P. aeruginosa it was reduced. Neither the BlsA photoreceptor nor the type VI secretion system (T6SS) are involved in virulence modulation by light in A. baumannii Overall, this fundamental knowledge highlights the potential use of light to control pathogen's virulence, either directly or by manipulating the light regulatory switch toward the lowest virulence/persistence configuration.IMPORTANCE Pathogenic bacteria are microorganisms capable of producing disease. Dangerous bacterial pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumannii are responsible for serious intrahospital and community infections in humans. Therapeutics is often complicated due to resistance to multiple antibiotics, rendering them ineffective. In this work, we show that these pathogens sense natural light and respond to it by modulating aspects related to their ability to cause disease: in the presence of light some of them become more aggressive while others show an opposite response. Overall, we provide new understanding on the behavior of these pathogens, which could contribute to control infections caused by them. Since the response is distributed in diverse pathogens, this notion could prove a general concept.