Pseudomonas fluorescens as a potential pathogen: adherence to nerve cells

In order to determine the infectious potential of the psychrotrophic bacter ium Pseudomonas fluorescens, a species closely related to the opportunistic pathogen P. aeruginosa, we investigated the binding activity of this bacte rium on primary cultures of rat neonate cortical neurons and glial cells, a drenal paraneurons and NG108-15 neuroblastoma cells. Incubated at concentra tions of 10(6) and 10(8) CFU/mL, P. fluorescens MF37 exhibited a high bindi ng activity on neurons in the same range as that of P. aeruginosa PAO1. A s ignificant, but lower, adherence of P. fluorescens was also detected on gli al cells and adrenal paraneurons. In contrast, when P. fluorescens MF37 or P. aeruginosa PAO1 were incubated,vith neuroblastoma cells, no binding was observed. In neurons, the association of P. fluorescens with the plasma mem brane occurred both on neurites and cell body. Leakage of the cytoplasmic c ontent was frequently noted. Studies performed using the fluorescent probe Hoechst 33258 revealed that in 10% of neurons, P. fluorescens induced the a ppearance of densely stained clusters of DNA that was typical of an early s tep of apoptosis. In glial cells exposed to P. fluorescens, marked changes in the morphology of the nucleus, including fragmentation into lobular stru ctures and aggregation of DNA, were also reminiscent of the existence of a possible apoptotic mechanism. Taken together, these results reveal that R f luorescens can bind to nerve cells and affect their physiology and, in agre ement with recent clinical observations, suggest that P. fluorescens could behave as a pathogen. (C) 2001 Editions scientifiques et medicales Elsevier SAS.