Effect of subminimum inhibitory concentration of ceftriaxone on adherence of Pseudomonas aeruginosa to inert surfaces in an experimental model.

The effect of subminimum inhibitory concentration (subMIC) of ceftriaxone on adherence of two isolates of Pseudomonas aeruginosa onto inert surfaces (catheter, plastic and glass) was studied. It was found that the phase of growth of Ps. aeruginosa and the nature of the inert surfaces affected the adherence. One-twenty fourth of the M.I.C. increased the adherence of the clinical isolate in the exponential phase of growth but decreased it during the stationary phase; the reverse was the case for the wild type isolate. When the inert surfaces were coated with serum, the adherence of the clinical isolate also increased during the exponential phase of growth, while that of the wild type increased in the stationary phase. Changes in the surface properties of the test organisms indicated that the subMIC of Ceftriaxone mediated increase in hydrophobicity at both phases of growth. These results suggest that sub-inhibitory levels of Ceftriaxone may decrease the virulence of P. aeruginosa since a good polymorphnuclear leucocytebacterium contact will result in the bacterium being strongly phagocytosed because adherence has also been implicated in the process of phagocytosis.