Toxic activity against alveolar macrophages of products of Pseudomonas aeruginosa isolated from respiratory and non-respiratory sites.

The toxic effect of certain products of Pseudomonas aeruginosa on guinea-pig alveolar macrophages has been studied in an attempt to account for the apparent infrequency with which certain strains of this species are associated with respiratory infection. Texts were carried out on strains derived from the respiratory tract, strains from infection at other sites, and strains from the inanimate hospital environment which were believed not to have been responsible for infection ('environmental' strains). Haemolysin, pigments, enzyme-containing fractions, slime and cell-wall fraction all exhibited toxic activity against macrophages in an in vitro system, although for any given strain of Ps. aeruginosa the haemolysin was by far the most potent factor. The activity of this factor against macrophages was directly proportional to its haemolytic activity against human erythrocytes. The haemolysin fractions of environmental strains, which have previously been found to have little activity on erythrocytes, were also less active against macrophages than haemolysin preparations from 'infective' strains. It is therefore postulated that the ability of a strain of Ps. aeruginosa to initiate respiratory infection may be related to the degree of haemolysin production. The activity of other fractions against macrophages is more variable, but they may contribute in different ways to the development of infection once entry into the lung has been achieved.