FLOW CYTOMETRIC ASSESSMENT OF THE SURVIVAL RATIO OF FRANCISELLA-TULARENSIS IN AEROBIOLOGICAL SAMPLES

Survival of microorganisms in aerobiological samples is often assessed by a survival ratio (SR), which is the ratio between the viable or me tabolic active number (MA) of microorganisms to the total number (TOT) of microorganisms. A method to determine survival ratios with flow cy tometry was developed for Francisella tularensis, the causative agent of tularemia. F. tularensis is a fastidious bacteria that can be trans mitted by aerosol and constitute as such a valid model organism for ae robiological studies. The total number of F. tularensis cells was dete rmined by specific targeting with monoclonal antibodies and detected b y phycoerytrine (PE) conjugated secondary antibodies. The metabolic ac tive part of the targeted F. tularensis cells was quantified by staini ng with rhodamine 123 (Rh123). Application of the presented method sho wed higher precision compared to an earlier developed method for survi val ratios, achieved with plate count (VC) and Coulter Counter (CC) me asurements. The coefficient of variation between samples for the new m ethod was below 5% for the survival ratio. Comparison of VC yield with MA yield showed consistently higher values for MA. The survival ratio s of F. tularensis in samples taken before and after aerosolisation we re analysed. SR for F. tularensis determined with the new method decre ased approximately 19% whereas SR determined with VC and CC decreased 62% after passage through aerosol state. (C) 1998 Federation of Europe an Microbiological Societies. Published by Elsevier Science B.V.