Characterization of biogenic amine-producing Stenotrophomonas maltophilia strains isolated from white muscle of fresh and frozen albacore tuna

Three strains - one of them psychrotrophic and two mesophilic - of Stenotro phomonas maltophilia, an emerging pathogen involved in an increasing number of clinical syndromes, were isolated from fresh and frozen-stored (6 month s at -25 degrees C) albacore tuna in a routine screening of histamine-formi ng bacteria. All the three strains showed histidine decarboxylase activity when assayed in a 2% histidine-0.0005% pyridoxal-HCl containing trypticase soy broth and further analyzed by HPLC, Although all three strains produced less than 25 ppm of histamine, they showed strong lysine-decarboxylating a ctivity, cadaverine being produced at concentrations ranging from 1736 to 4 821 ppm after 48 h in 0.0005% pyridoxal-HCl-trypticase soy broth supplement ed with 1% lysine. Strong secretion of extracellular lipase and protease wa s also observed in all three strains. The psychrotrophic strain S. maltophi lia 5PC(6) was able to produce both extracellular lipase and protease even at 4 and 7 degrees C, respectively. Phenotyping assays - including the inve stigation of up to 40 biochemical tests and 15 susceptibility assays - reve aled slight differences among the three strains. Genotyping experiments - b ased on RFLP analysis and Southern blot hybridizations - indicated that str ains 15MF and 25MC(6) were closely related but confirmed that all three str ains recovered were different. (C) 2000 Elsevier Science B.V. All rights re served.