Disk diffusion susceptibility testing

A short report demonstrated the absence of a reliable correlation between kiUing kinetics and normal laboratory tests for pristinamycin susceptibility testing of some pneumococci (42). Eight selected multiresistant clinical isolates and two reference pristinamycin-resistant Streptococcus pneumoniae strains were studied. Disk diffusion susceptibility and MICs were determined by the agar dilution method, and all clinical isolates appeared to be susceptible to pristinamycin, whereas the two reference strains were not. In contrast, time-kill experiments identified a limited bactericidal effect of pristinamycin in three clinical and both reference strains. These three strains had been classified as pristinamycin-resistant by the Vitek-II system, which uses a kinetic turbidimetric measurement of bacterial growth. Epidemiological information is hindered by the use of highly selected strains for the study. 

TESTING FOR MICROBIAL SENSITIVITY TO ANTIMICROBIAL AGENTS Bacterial strains, even from the same species, may vary widely in sensitivity to antibiotics. Information about the antibiotic sensitivity of the infecting microorganism is important for appropriate drug selection. Various methods are used to assess susceptibility, including disk-diffusion, dilution test, and automated broth dilution. The results are either reported on a semi-quantitative scale i.e., resistant, intermediate, or susceptible) or in terms of the minimal inhibitory concentration (MIC). 

Kirby-Bauer Disk-Diffusion Method and Modified Kirby-Bauer Susceptibility Test (a. 15)... 

UHLAND FC and HIGGINS R (2006), Evaluation of the susceptibility of Aeromonas salmonicida to oxytetracycline and tetracycline using antimicrobial disk diffusion and dilution susceptibility tests , Aquaculture, 257,111-117. 

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