EFFECT OF TEMPERATURE ON THE SHIFT OF PSEUDOMONAS FLUORESCENS FROM AN ENVIRONMENTAL MICROORGANISM TO A POTENTIAL HUMAN PATHOGEN

Pseudomonas fluoreseens is a Gram-negative bacterium generally considered of scarce clinical significance. However, in the last few years, the isolation of P fluoreseens as causative agent of nosocomial infections has rapidly increased. P. fluorescens is a psychrophile microorganism which grows at an optimal temperature of 25-30 degrees C. In spite of this constraint, it has recently been reported that the human physiological temperature does not appear to be a barrier for this microorganism. In this study we examined the ability of P. fluoreseens, grown at 28 degrees C or at 37 degrees C, to adhere to cultured human A549 pulmonary cells and to form biofilm. The ability of P. fluorescens to induce expression of proinflammatory cytokines, beta-defensin 2 and the intercellular adhesion molecule-1 was also investigated. Our results clearly indicate that inflammatory mediators are induced when the microorganism is grown at a lower temperature, while biofilm is formed only at 37 degrees C. The results presented are consistent with previous reports indicating P fluoreseens as an opportunistic pathogen and underscore the urgent need for further studies to better characterize the virulence of this microorganism.