The microcolony mode of growth in vivo — an ecological perspective

Abstract

Pseudomonas aeruginosa is essentially an aquatic micro-organism whose catholic metabolism allows it to colonize a large number of cold oligotrophic aquatic ecosystems. It was once considered to be so reliably non-pathogenic that bandages were soaked in cultures of this aerobic organism before they were used to dress deep wounds (D. W. Lambe, personal communication). Now P. aeruginosa constitutes a serious threat to the health of patients compromised by burns, extensive manipulation, instrumentation, or underlying diseases such as cystic fibrosis. The microbiological approaches that have virtually eradicated most of the acute epidemic bacterial diseases have not been notably successful in the prevention or the treatment of infections caused by this ‘modern’ opportunistic pathogen. Avoidance of contact with this ubiquitous environmental micro-organism is difficult, and immunological measures are contraindicated by the widespread observation that cystic fibrosis patients have high levels of anti-Pseudomonas antibodies but fail to clear their chronic infections. Antibiotic therapy is not particularly effective, especially in chronic infections, because the bacteria often survive within protected niduses and re-establish the infection when therapy is discontinued. Because it is apparent that the group of bacterial diseases caused by P. aeruginosa differs significantly from the classic epidemic bacterial diseases, and because the preventive and therapeutic strategies developed by microbiologists to counteract epidemic diseases have largely failed to prevent or cure these ‘modern’ opportunistic P. aeruginosainfections, we have adopted a radically different approach, viz. that of the microbial ecologist.