Ecological paradigm of legionella: a revision. New strategy and its implication in public health

Abstract

Some aspects difficultly explained by the ecological model described by Rowbothan in 1980, as the abnormally low infectious dose, the long distances in which bacteria remains viable in the aerosol, the difficulty of growth in the standard culture media, the low efficiency of the antilegionela disinfectants, in the control of the outbreaks, the reinfection or the absence of 'person to person' transmission, are analyzed from an ecological microbiology standpoint. Focused on the bacterium-protozoo relationship , several studies suggest that bacterial growth might take place in two functionally different phases or stages, according to the proportion or ratio bacterium-amoeba (MOI-multiplicity of infection). In the first phase of rapid growth, in which this relationship is substantially low, the entry of Legionella bacterium in the amoeba would originate a unique vacuole, which after amebian lyses, it would liberate free infectants forms for other amoebae. During the second stage, of dissemination or settling of other ecological niches, with high MOI ratios, several growth vesicles are produced inside the amoeba and are expelled without lyses. The deadlock of the amoeba in this phase, is produced after the massive liberation of the vesicles. Some authors suggest that these vesicles are the infectant nuclei of the legionelosis transmission because of his resistance and alive-legionela packing characteristics. The presence of a specific biofilm might be determinant in this process. Keeping in mind this amoeba-legionela relationship-interaction system, the preventive measures should go directed to supporting the MOI relation low, always in conjunction with low levels of biofilm. In this respect, the addition of in continue antilegionela disinfectants substances seems to be indispensable. Reached the phase of dissemination (only fits) the cleanliness is the unique measure of action. The research on specific mechanisms of legionela-amoeba invasion would be fundamental, in order to find block substances .Regarding the relation with the biofilm (authentic critical point of the system) its elimination or decrease to minimal levels by the utilization of specific materials, the design of devices or systems of easy cleanliness (curved corners, accessible spaces), suitable maintenance of the facilities (inlays, corroded surfaces, etc.) with frequent (physics) cleanliness and the continuously utilization of substances against the film are necessary.