An investigation of physiological characteristics and virulence of Pseudomonas aeruginosa cystic fibrosis strains

Selected physiological parameters of 33 classic and rough Pseudomonas aeruginosa strains from sputum of cystic fibrosis (CF) patients have been examined. An associaton of a patient's clinical condition (good or poor) with strain physiology has been made. Rough strains from patients in poor clinical condition (P strains) demonstrated severe alterations in motility parameters. Of the 10 rough P strains studied, 70% lacked flagella as determined be electron microscopy. Flagellated P strains demonstrated weak motility in soft agar and in the capillary assay as well as a 40-90% reduction in chemotactic response to three amino acid attractants. A majority of classic and rough strains from patients in good clinical condition (G strains) were highly motile and chemotactic. Characteristics such as auxotrophy and growth rate were not significantly altered in G and P strains; but the absence of protease activity was associated predominantly with P strains.

A series of varied morphological types of CF sputum strains was examined for virulence in an invasive burned mouse model. All 24 strains examined demonstrated reduced virulence when compared to M-2, a virulent burn strain (LD₅₀ = 1.5 x 10^{1 CFU). Ninety-two precent of the strains tested were avirulent at doses of 103 - 10 5 CFU. The LD₅₀ of nine representative flagellated CF strains was determined in the same animal model. Five of the strains tested had LD₅₀ > 106 CFU. Reduced virulence of each strain appeared to be associated with loss of one or more physiological characteristics. Strain 35c resembled M-2 being of classic colonial morphology, protease-positive, 0-antigen typable, flagellated and chemotactic. It was the most virulent of the strains (LD₅₀ = 8 x 102 CFU). A mucoid (G) strain, 412a, intermediate in virulence (LD₅₀ = 104 CFU), polyagglutinated in 0 antisera and showed reduced motility (60% of M-2). Results suggested that any virulence detected was associated with classic (G) strains prevalent in early, non-chronic infections. It appears that a selection transition occurs favoring P aeruginosa avirulence (i.e. alterations in factors such as protease production, cell envelope, motility and cheraotaxis) as chronic infection is established in the CF lung.}