Pseudomonas aeruginosainfection in hospital: a comparison between ‘infective’ and ‘environmental’ strains

Abstract

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 unassociated 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.

Types of Pseudomonas aeruginosa isolated from horses

“…Liu (1966) showed that the organism has the ability to produce lecithinase, lipase and protease, 3 enzymes needed for tissue invasion. Al-Dujaili and Harris (1975) showed that the production of haemolysin by infective strains differentiated them from environmental strains. Liu (1964) showed that the pathological effect of the organism was caused by extracellular toxins and that the production of these toxins was enhanced when colonising damaged tissues.…”

The distribution ofBacteroides fragilisserotypes amongst clinical strains

“…Nevertheless, one cannot exclude the possibility of hospital infection caused by strains of B. fragilis prevalent in the various hospitals. Patients could acquire new hospital strains, similar to Escherichia coli (Cooke, Ewins & Shooter, 1969) and to Pseudomonas aeruginosa (Al-Dujaili & Harris, 1975 …”

Aberrant form of Pseudomonas aeruginosa in sputum and cerebrospinal fluid causing infection in a compromised patient.

“…However, not all colonised patients become infected with these organisms even when they are present in the patient's immediate environment. Al-Dujaili and Harris (1975) have looked at the colony morphology, pyocine typing, and haemolysin production of Ps. aeruginosa in the sputum from hospitalised patients and from their environment to try to discover when Ps.…”