Abstract
The combined effect of amikacin and colistin on Pseudomonas aeruginosa was studied by the agar plate two-fold dilution method. The author further studied this effect by using the hole plate method.
Inhibition by amikacin at 3.13 μg/ml of gentamicin resistant P. aeru-ginosa was much more remarkable when amikacin was applied alone than in cases where it was used in combination with colistin. The concomitant use of colistin at concentractions of one-eighth to one-half the MIC of colistin increased the concentration required to inhibit the growth of the strains to twice the MIC of amikacin.
Bacteriostatic antagonism was thus detected between amikacin and colistin against gentamicin resistant P. aeruginosa. The author assumed that this phenomenon was mainly due to a lowered activity of amikacin rather than of colistin. The above mentioned phenomenon was then confirmed by the hole plate method. Such bacteriostatic antagonism was also detected between amikacin and colistin as well as between gentamicin and colistin when used against gentamicin sensitive P. aeruginosa.
The author suggests, based on his in vitro observations, that the combined use of these antibiotics should not be taken as clinical practice.
