a1 Department of Medical Microbiology, University of Sheffield Medical School
One hundred and fifty-six infections or episodes of infection associated with Pseudomonas aeruginosa in six hospitals over 14 months were investigated. Pyocine typing and serotyping suggested that 145 distinct episodes had occurred, caused by 78 different strains. During this period 15 distinct strains were isolated from the environment at one of the hospitals; 12 of these were apparently un-associated with infection in the same ward during the period, and 4 were of types not encountered in infective processes at any hospital. There appeared to be a rather higher proportion of unclassifiable pyocine inhibition patterns among the environmental strains; in general these strains also produced smaller amounts of haemolysin. If failure to produce haemolysin in vitro is correlated with lack of virulence in vivo, this may partially explain the sporadic nature of hospital infection with Ps. aeruginosa, despite the prevalence of strains of this species in the environment.
(Received February 12 1975)