The response of Pseudomonas aeruginosa to azlocillin, ticarcillin and cefsulodin.

The morphological response of Pseudomonas aeruginosa to azlocillin, ticarcillin and cefsulodin was investigated by electron microscopy. Each antibiotic initially caused the formation of filaments. On further incubation in the presence of azlocillin, deposits of dense intracellular material were observed; these were absent from cells exposed to the other two antibiotics. On continued incubation, lysis of the filaments occurred, but the mode of lysis differed between the antibiotics: azlocillin caused breakage at a restricted number of sites in the cell wall, ticarcillin produced breakage at many points and cefsulodin caused extensive cell-wall damage. In addition, ticarcillin and cefsulodin appeared to cause more lysis and spheroplast formation than did azlocillin. The morphological changes correlated with turbidimetric measurements of bacterial response to the three antibiotics, which showed ticarcillin and cefsulodin to act more rapidly than azlocillin.