The susceptibility of 102 clinical isolates of P. aeruginosa to ciprofloxacin(Ci), norfloxacin (Nf), seven antipseudomonal β-lactams and four aminoglycosides was determined in vitro by a standard agar dilution method. Aztreonam,
imipenem, Ci, Nf were the most active. Five point nine percent of the isolates were resistant to Ci (MIC, ≥4 g/ml).
Concurrent resistance to Ci and β-lactams (0.9-4%) or aminoglycosides (0.9-4%) was observed infrequently.
Nineteen isolates were selected for studies of Ci with for antipseudomonal β-lactams and amikacin(Ak) by a checkerboard agardilution technique, Synergism or additive combinations of Ci in clinically applicable concentrations were most
frequent with piperacillin(74%), followed by moxalactan(Mx) (68%), cefotaxime(38%), Ak(37%), cefoperazone(26%).
In studies of moxalactam in combination with Ak and gentamicin, synergistic or additive interactions were observed in 32% and 49%, respectively, Interestingly, in each combination, synergistic or additive interactions of
Mx-resistant
strains were higher than that of Mx-susceptible strains, representing rate of 70%, 100% and 26%, 32% respectively.
Antagonism was not observed in any combination.
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