Outer surface changes of Pseudomonas aeruginosa in relation to resistance to gentamicin and carbenicillin

The outer surface structure of clinical isolates of Pseudomonas aeruginosa resistant to carbenicillin or gentamicin or both was studied by thin-section electronmicroscopy and compared with that of sensitive isolates. The latter had a fairly smooth outer layer. Strains resistant to both antibiotics were characterised by extrusions that appeared to constitute extensions of the outer membrane. The outer membrane appeared wavy with distortion of its tripartite structure. The latter findings were also present in isolates resistant to only one of the two antibiotics. The disorganisation of the outer membrane might contribute to the expression of resistance.