No abstract

Summary. Aminoglycoside-resistant variants of Pseudornonas aeruginosa strain P A 0 1 were readily selected by culturing the organism in medium containing increasing concentrations of gentamicin, tobramycin or amikacin until the strains were growing in a concentration of drug 128-fold greater than the minimal inhibitory concentration for the sensitive parent strain. These resistant strains exhibited characteristics previously associated with the impermeability type of resistance mechanism, i.e., they grew more slowly than the parent strain, the resistance was unstable in the absence of the antibiotic, and adaptation to one of the antibiotics conferred crossresistance to other aminoglycosides. The adapted strains grew, with minimal morphological alterations, in concentrations of the various aminoglycosides that normally produced cell envelope damage, misshapen and filamentous cell formation, and cell lysis in the sensitive strain. Neither protein H1 nor phospholipid alterations appear to play a significant role in adaptive resistance to aminoglycoside antibiotics in this model system. The acquisition of adaptive resistance to the aminoglycoside antibiotics did not confer resistance to polymyxin B, another cationic antibiotic which is thought to share binding sites within the outer membrane with the aminoglycosides.

Outer membrane protein F (porin) was purified by extraction from polyacrylamide gels of cell envelope proteins of the Pseudomonas aeruginosa PA01 strain. Rats were immunized intramuscularly with 25 ,ug of protein F on days 1 and 14 and then challenged on day 28 via intratracheal inoculation of bacterium-containing agar beads. On day 35 the lungs were either fixed for histological examination or submitted for quantitation of the bacteria present. Protein F immunization afforded significant protection against challenge with six of six heterologous lipopolysaccharide immunotype strains of P. aeruginosa. By an enzyme-linked immunosorbent assay, the protein F-immunized rats had both immunoglobulin G and M antibody responses to cell envelopes of all six of the heterologous immunotype strains. Protein F immunization greatly enhanced the ability of the rats to clear the inoculated P. aeruginosa from the lungs and significantly reduced the incidence and severity of pulmonary lesions as compared with those in bovine serum albumin-immunized control rats. These data show the efficacy of outer membrane protein F as a protective vaccine in a rat model of chronic pulmonary infection.