The study includes 23 isolates of Pseudomonas aeruginosa isolated from wound
infections .The Minimum Inhibitory Concentration (MIC) to each of Levofloxacin
and Ceftazidime for these isolates were determined. The results showed 11(47.8%)
isolates sensitive to both antibiotics, 5(21.7%) isolates resistant to each one of the
antibiotics and 7(30.5%) isolates appeared resistance to one of them and sensitive to
the other. Mutant Prevention Concentration (MPC) to both Levofloxacin and
Ceftazidime alone and in combination were determined to the 5 sensitive and 5
resistant isolates to both antibiotics. Mutant Selection Window (MSW) was
calculated according to the data of MPC and MIC to both levofloxacin and
Ceftazidime alone and in combination to the same isolates which their MPC were
determined (10 isolates). The decrease in the value of MSW by 1-2 times were noted
when both antibiotics together (in combination) were used in comparison with its
value when Levofloxacin was used alone (before combination) to the sensitive
isolates (5 isolates), and this indicates a synergistic action whereas, no synergistic
action appeared in the resistant isolates (5 isolates) according to the MSW values,
this emphasizes that the combination between levofloxacin and ceftazidime against
resistant isolates is useless.