Isolation and characterization of an attenuated strain of Pseudomonas aeruginosa AC869, a 3,5-dichlorobenzoate degrader.

Pseudomonas aeruginosa AC869, a 3,5-dichlorobenzoate degrader, is a mouse pathogen and has a reported 50% lethal dose (LD50) of 1.05 x 10(7) CFU when given intranasally to C3H/HeJ mice (S.E. George, M.J. Kohan, M.I. Gilmour, M.S. Taylor, H.G. Brooks, J.P. Creason, and L.D. Claxton, Appl. Environ, Microbiol. 59:3585-3591, 1993). AC869 was serotyped as O6 when grown in CD-1 mouse cecal and lung mucus but could not be assigned an O serotype when grown in Luria broth (LB). After growth in mouse cecal mucus, a less virulent mutant, AC869-11, was isolated from AC869 by using bacteriophage E79, which adsorbs to the O side chain of lipopolysaccharide (LPS). AC869-11 produced significantly less O antigen on its LPS than AC869 when grown in mouse lung and cecal mucus. The mutant also produced half the amount of exoenzyme S and 16-fold less extracellular protease than AC869 and was more sensitive than its parent to a number of antibiotics when grown either in LB or in mouse lung mucus. AC869-11 had ninefold higher LD50 than AC869 in CD-1 mice when administered intranasally. AC869-11 was found in the lungs, small intestine, cecum, and large intestine in numbers at least 100-fold below AC869, 3 h after intranasal exposure of mice to a sublethal dose of the two strains. Moreover, AC869-11 induced a decreased pulmonary inflammatory response relative to AC869. In contrast to AC869, AC869-11 did not translocate to the mesenteric lymph nodes, liver, and spleen following a sublethal dose. Despite attenuation, AC869-11 grew as well as AC869 with 3,5-dichlorobenzoate as the sole carbon and energy source. However, although AC869-11 survived in 3,5-dichlorobenzoate-contaminated soil as well as AC869 for 1 week, it failed to survive as well thereafter. These results suggest the possibility that mutations that lead to pulmonary attenuation of P. aeruginosa in mice also lead to weakness in the environment, despite such mutants maintaining the ability to degrade toxic substances under laboratory conditions.