Diffusion of teicoplanin and vancomycin in agar.
Teicoplanin, although more active than vancomycin [by minimum inhibitory concentration (MIC)], produces smaller inhibition zones in sensitivity testing with 30-microgram disks. Our data support the hypothesis that this is due to lower diffusion of teicoplanin in agar media. After 6 hr of incubation, approximately 70% of vancomycin, but only 20% of teicoplanin entered the agar from a paper disk charged with 30 micrograms of antibiotic. This is due to a difference between the diffusion coefficients: 0.47 mm2/hr for teicoplanin and 0.72 mm2/hr for vancomycin. With the methodology used in this work, it is possible to calculate the range of concentrations of the antibiotic occurring at times likely to include the critical time--the time when the inhibition zone is formed--of most strains at any given distance from the reservoir. One can thus estimate the breakpoint diameter for a given MIC breakpoint; for example, an MIC breakpoint of less than or equal to 4 micrograms/ml would correspond to a greater than or equal to 15-mm breakpoint diameter for vancomycin (30-microgram disk) and a greater than or equal to 13-mm breakpoint diameter for teicoplanin (30-microgram disk).
Cavenaghi
L A
LA
Marion Merrell Dow Research Institute--Lepetit Center, Gerenzano (VA), Italy.
Biganzoli
E
E
Danese
A
A
Parenti
F
F
D000362:Agar; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology; D003470:Culture Media; D004058:Diffusion; D006020:Glycopeptides / Q000737:chemistry / Q000494:pharmacology; D008826:Microbial Sensitivity Tests / Q000592:standards*; D013211:Staphylococcus aureus / Q000187:drug effects; D017334:Teicoplanin; D014640:Vancomycin / Q000737:chemistry* / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D003470:Culture Media; D006020:Glycopeptides; D017334:Teicoplanin; D014640:Vancomycin; D000362:Agar