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Assay determines activity of ceftazidime+tobramycin against
An assay was developed to determine the activity of ceftazidime in combination with tobramycin against Pseudomonas aeruginosa.
According to recent research from North Ireland, "It is standard clinical practice to use a combination of two or more antimicrobial agents to treat an infection caused by Pseudomonas aeruginosa.
"The antibiotic combinations are usually selected empirically, with methods to determine the antimicrobial effect of the combination such as the time-kill assay rarely used as they are time-consuming and too labor intensive to perform."
"Here, we report a modified time-kill assay, based on the reduction of the tetrazolium salt, 2,3-bis[2-methyloxy-4-nitro-5-sulfopheny1] -2H-tetrazolium-5-carboxanilide (XTT), that allows simple, inexpensive and more rapid determination of the in vitro activity of antibiotic combinations against P. aeruginosa," wrote F. Moriarty and colleagues at Queens University Belfast in Antrim.
"The assay was used to determine the in vitro activity of ceftazidime and tobramycin in combination against P. aeruginosa isolates from cystic fibrosis patients and the results obtained compared with those from conventional viable count time-kill assays.
"There was good agreement in interpretation of results obtained by the XTT and conventional viable count assays," said investigators, "with similar growth curves apparent and the most effective concentration combinations determined by both methods identical for all isolates tested."
"The XTT assay clearly indicated whether an antibiotic combination had a synergistic, indifferent or antagonistic effect and could, therefore, provide a useful method for rapidly determining the activity of a large number of antibiotic combinations against clinical isolates," the authors concluded.
Moriarty and colleagues published their study in the Journal of Microbiological Methods (Development of a rapid colorimetric time-kill assay for determining the in vitro activity of ceftazidime and tobramycin in combination against Pseudomonas aeruginosa.