In vitro susceptibility of pseudomonas to four beta-lactamantibiotics (ampicillin, cephalothin, carbenicillin, piperacillin), to four aminoglycosides (kanamycin, amikacin, gentamicin, tobramycin) and to colimycin.

Of 97 well-defined strains of Pseudomonas, isolated from sputum of patients with 
cystic fibrosis (CF), the minimum inhibitory concentration (MIC) of several antibiotics 
was determined with a broth dilution method. The majority of the 
strains were resistant to ampicillin and cephalothin, moderately susceptible to carbenicillin 
(70% to 100 microgram/ml) and highly susceptible to piperacillin (100% to 
25 microgram/ml, 88% to 6.25 microgram and 60% to 3.12 microgram/ml). 
If the pharmacological properties of piperacillin are comparable with those of 
carbenicillin, it can be expected that the sputum level of this 
drug will be adequate to treat Pseudomonas pulmonary infections. At the 
lowest concentration tested (0.78 microgram/ml) 3% of the strains were susceptible 
to kanamycin, 85,5% to amikacin, 95% to gentamicin, 98% of tobramycin, 
and 80% to colimycin. With regard to clinically attainable concentrations, 98.9% 
of the strains were susceptible to gentamicin and tobramycin 97.9% to 
amikacin, 96.9% to colimycin, 88.6% to piperacillin, 38% to carbenicillin, 25.7% 
to kanamycin, 12.3% to ampicillin, and 1% to cephalothin. 