The Journal of Medical Microbiology, Vol 17, Issue 2 159-169, Copyright © 1984 by Society for General Microbiology
The morphological response of Pseudomonas aeruginosa to azthreonam, cefoperazone, ceftazidime and N-formimidoyl thienamycin
T. S. Elliott and D. Greenwood
The morphological responses of Pseudomonas aeruginosa to N-formimidoyl
thienamycin, azthreonam, ceftazidime and cefoperazone were studied by
transmission electron microscopy. They were correlated with the results of
viable counts and continuous turbidimetric monitoring. N-formimidoyl
thienamycin initially caused the formation of abnormally shaped cells which
developed into spheroplasts. The other antibiotics caused filamentation of
the bacteria, which subsequently underwent lysis. The degree and mechanism
of lysis varied between the antibiotics. Exposure to azthreonam also
resulted in the deposition of electron-dense intracellular material. As
judged by conventional minimum-inhibitory-concentration tests, all the
agents exhibited similar activity against the strains of P. aeruginosa
tested, with ceftazidime displaying the highest activity. However,
N-formimidoyl thienamycin caused the most extensive morphological damage
and resulted in the most rapid fall in viable count.
