Membrane filter (pore size, 0.22-0.45 μm; thickness, 150 μm) passing-through activity of Pseudomonas aeruginosa and other bacterial species with indigenous infiltration ability

Bacteria growing on MF-Millipore filters (thickness, 150 mum) passed through the underlying membrane by their infiltration activity. Bacillus subtilis, Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli passed through a 0.45-mum pore size filter within 48-96 h. Pseudomonas aeruginosa, Serratia marcescens, and Listeria monocytogenes passed through a 0.3-mum pore size filter. P. aeruginosa passed through a 0.22-mum pore size filter. The membranes which allowed passing-through of bacteria showed normal bubble point values in the integrity test. Studies with isogenic S. marcescens mutants indicated that flagellum-dependent motility or surface-active exolipid were important in the passing-through. P. aeruginosa PAO1 C strain defective in twitching motility was unable to pass through the 0.22-mum filter. Scanning electron microscopy showed bacteria passing-through the 0.22-mum filter. Millipore membrane filters having well-defined reticulate structures will be useful in the study of infiltration activity of microbes. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.