engleski

Effect of subinhibitory concentrations of antibiotics on the serum sensitivity of wild-type Pseudomonas aeruginosa strains

Aim was to determine the effect of subminimal inhibitory concentrations (subMICs) of ceftazidime, meropenem and gentamicin on the serum sensitivity of Pseudomonas aeruginosa strains isolated from a variety of isolation sites. Antibiotics are often present at the site of infection at subinhibitory concentrations, because in human treated with intermittent dosage schedules of antibiotics, suprainhibitory concentrations will always be followed by subinhibitory levels. The aim of this research was to determine which of the studied antibiotics has the best characteristic in order to be capable to affect the serum resistance of P. aeruginosa strains. Study design: Ex vivo study Setting: Two medical wards and an intensive care unit in a tertiary government university hospital Patients with symptoms and signs of underlying infection of the system involved. A total of 20 serum-resistant P. aeruginosa strains isolated from different specimens (urine, bronchial secretion, endotracheal and wound aspirates) were selected. The MICs of ceftazidime, meropenem and gentamicin were determined for each investigated strain. Bacteria were exposed to 1/2, 1/4, 1/8, 1/16, and 1/32 of MIC of each antibiotic tested. Sensitivity of P. aeruginosa strains to bactericidal action of normal human serum before and after bacterial exposure to subMICs was determined. Significant difference in serum sensitivity of the strains was observed after the bacteria were exposed to subMICs of ceftazidime and meropenem, while the exposure to subMICs of gentamicin did not affect the resistance of investigated strains to the bactericidal action of the serum. Comparing the number of serum-resistant strains before and after exposure to subMICs of antibiotics, statistically significant differences were determined (p<0.01) after exposure of the strains to 1/2, 1/4, 1/8 and 1/16 MIC of meropenem, and after exposure to 1/2, 1/4 and 1/8 MIC of ceftazidime. The alterations of bacterial morphology caused by subMICs of ceftazidime and meropenem could be connected with consecutive bacterial sensitivity to serum bactericidal activity.

Pseudomonas aeruginosa; serum sensitivity; antibiotics; subinhibitory concentrations

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