Pseudomonas pseudomallei: II. Laboratory and experimental studies in animals.

The cultural, biochemical characteristics and antibiotic sensitivity of strains of Pseudomonas pseudomallei isolated from four cases of melioidosis admitted to Ramathibodi Hospital are described. The organisms were gram-negative bacilli often with bipolar staining. The colonies were wrinkled when incubated for long periods. The characteristic non-specific uptake of dye from media into the colonies and their musty or earthy odour rendered them easily distinguishable from other organisms. All strains were sensitive to chloramphenicol and all but one were sensitive to tetracycline. All strains were resistant to colimycin and gentamicin. The pathogenicity of the strain isolated from a fatal case of peritonitis was studied in guinea pigs. The findings showed that following a large inoculation intraperitoneally, the animal developed acute septicaemia and died shortly afterwards. Only a few micro-abscesses were found on the surface of the liver. Chronic infection of longer duration occurred when a small number of organisms were introduced through a cutaneous abrasion. The lesions included pneumonitis and multiple abscesses of various organs including subcutaneous tissue, liver, spleen and mediastinum.