Epidemiology of Pseudomonas aeruginosa in agricultural areas

A prevailing opinion is that the strains of Pseudomonas aeruginosa that infects both plants and humans are two separate species. This study strongly disputes that notion until the modern molecular technology proves otherwise. This paper examines a spectrum of strains occurring in nature, their habitats, dissemination, their relationship to clinical strains, and the environmental conditions that favor their colonization of plants. The isolates were obtained from clinical specimens, plants, soil, and water. The identity of these strains was confirmed using pyocin typing and biochemical assays. The data reveal that agricultural soils, potted ornamental plants, hoses, fountains, and faucets frequently harbored P. aeruginosa. However, it was not commonly found in semi-arid areas, suggesting that moisture and high humidity is necessary for colonization and survival. Though found in soil, P. aeruginosa was seldom isolated on edible plant parts. The pathogenicity of various strains on plants was tested by inoculating vegetables, lettuce slices (Lactuca sativa L. "Great Lakes"), celery stalks (Apium graveolens L. var. Dulce], potato tuber slices (Solanum tuberosum L. "Whiterose"), tomato (Lycopersicon esculentum L. Mill), cucumber (Cucumis sativus L.), rutabaga (Brassica campestris L.), and carrot (Daucus carota L. var sativa). There was considerable variation in the strains' ability to cause rot, but no difference was observed between clinical isolates and others from agricultural fields, water, and soil. Two of the clinical isolates from burn patients, P. aeruginosa PA13 and PA14, exhibited the greatest virulence in causing rot in all the plants that were tested, especially on cucumber, lettuce, potato, and tomato. The study discusses how closely the epidemiology of P. aeruginosa relates to many plant pathogens, and the ability of human isolates to colonize plants and food material under favorable conditions. The biochemical and phenotypic similarity among strains from the clinical and agricultural material is strongly indicative that they are the same species and that plants and soil are natural reservoirs for P. aeruginosa.