Nutrient blood agar

Serial dilution in 5% blood agar figures in brackets are MIC Values in nutrient broth. These data are taken from the personal communication of Dr R. J. Stoodley, (The University of Newcastle upon Tyne), whom we thank for these in vitro data. 

Blood of normal subjects was obtained from an antecubital vein, diluted 1 5 with pH 4.5 buffer,2 and autoclaved 30 minutes to convert bound cobalamin into its microbiologically active form serum was treated like blood. This procedure allowed estimation of total vitamin Bi2. For the subsequent inoculation of specimens (a) E. coli as a loopful from nutrient agar suspended in 25 ml of medium, (b) L. leichmannii, an 18-hour culture diluted 1 10 in basal medium, (c) E. gracilis, strain Z, and (d) O. malhamensis are inoculated directly from a 5-day culture grown in liquid maintenance medium. One drop into a culture flask served as inoculum. The bacteria required 18-hours for full growth protozoa, 4-5 days. 

This medium was prepared by adding sterile defribrinated sheep blood (10%) to sterile molten nutrient agar (Oxoid) at 55 °C. 

Differential media contain chemicals or additives which allow similar microorganisms to be differentiated from each other. A typical example would be the addition of blood from various species to nutrient agar, to distinguish different types of streptococci. 

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