Biocide activity against Legionella and Pseudomonas

Four biocides were tested for their abilities to kill Legionella micdadei and Pseudomona fluorescens in a buffered saline solution. The most effective against both organisms, at concentrations of 50 ppm or above, was a phosphonium compound, but this biocide failed to produce a 99·9% kill of P. fluorescens within 24 h at concentrations below 50 ppm. All chemicals apart from an oxidisingbiocide were more effective against L. micdadei than P. fluorescens. Old cells of Legionella, but not of Pseudomonas, exhibited increased resistance against BNPD. This could be associated with an altered outer envelope, demonstrated by SDS-PAGE analysis.