engleski

Effect of subinhibitory concentrations of antibiotics on the morphology and adherence ability of Pseudomonas aeruginosa wild-type strains

Objectives: 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 study was to determine the effect of subminimal inhibitory concentrations (subMICs) of ceftazidime and meropenem on the adherence ability of Pseudomonas aeruginosa strains isolated from a variety of isolation sites. Methods: A total of 35 P. aeruginosa strains isolated from different clinical specimens (urine, bronchial secretion, and ear, throat and wound swabs) were used. The ability of strains to adhere to three different cell lines (Buffalo green monkey kidney, HeLa, and human fetal fibroblasts) was detected by immunofluorescence staining. Bacterial adherence to the cell line was tested before and after treatment with antibiotics. Comparisons were made beetwen the morphology before and that after exposure of strains to 1/2, 1/4, 1/8, 1/16 and 1/32 MIC of antibiotics, as well as between the number of bacteria attached to the cells before and the number after their exposure to the same concentrations of antibiotics. Results: Most strains (89%) adhered well to the used cell lines, and there was no significant difference between adherence of the strains to the three cell lines used. Upon comparison of the number of attached bacteria before and after exposure to subMICs of antibiotics, statistically significant difference was determined (p<0.01) after exposure of the strains to 1/2, 1/4, 1/8 and 1/16 MIC of ceftazidime, and after exposure of the strains to all the concentrations of meropenem used. SubMICs of antibiotics alter not only bacterial adherence ability but also their morphology. Morphological changes were most prominent after bacterial exposure to 1/2, 1/4 and 1/8 MIC of ceftazidime and meropenem. Higher concentrations of those antibiotics caused formation of very long filaments with irregular swellings, which measured about 30 &#956; m at the concentration of 1/2 MIC. A very high correlation was observed between the changes in the length of bacteria and their loss of adherence ability. Conclusion: The alteration in bacterial morphology caused by subMICs of ceftazidime and meropenem was related to subsequent loss of bacterial adherence ability.

antibiotics; subinhibitory concentrations; Pseudomonas aeruginosa; adherence

nije evidentirano