The effects of soluble polysaccharides of agar on antibiotic susceptibility testing.

The effects of soluble polysaccharides of agar on antibiotic susceptibility testing was studied, using five lots of Agar (Bacto Difco) and 85 strains of organisms from the Enterobacteriaceae. Washing Agar at 60°c, according to the procedure of Duckworth and, Yaphe (1971), increased gel strength and concentration of 3,6-anhydrogalactose, and decreased the magnesium and calcium ion concentration in the, five lots of commercial agar. The washing procedure provided a purified agar with a low concentration of divalent ions and, sulphated polysaccharides. The relationship between MICs in Mueller-Hinton broth and zone sizes on Mueller-Hinton Agar Were compared using both washed and unwashed agars. The correlation between MICs and zone sizes in the gentamicin assay was significantly increased when zone diameters were measured on media prepared with washed agars. Similarly an increase in correlation of lone sizes was obtained on Mueller-Hinton media prepared with five different lots of washed Agar. These correlations, however, were not as great when using neomycin and tetracycline. Washing commercial Agar removes impurities which affect antibiotic susceptibility testing, and provides an Agar which allows more reproducible results.Les effets des polysaccarides solubles d'agar sur le test de susceptibilité antibiotique ont été étudiés à partir de cinq lots d'aqar (Bacto Difco) et da quatre-vingt-cinq lignées d'organismes d'Entérobactériacées. En lavant l'agar à 60°C, conformément su procédé de Duckworth et de Yaphe (1971), on a observé non seulement une augmentation du titre de colloide et de la concentration en anhydrogalactose- 3,6, mais aussi une diminution de la concentration en magnésium et ion calcium. […