BLOOD AGAR BASE W/ LOW pH

Blood Agar Base is a highly nutritious medium generally used as a basal medium for preparing blood agar by supplementation with blood. It can also be used as general-purpose media without the addition of blood. If the culture medium is to be used without addition of blood, the pH should be adjusted to 7.2 to 7.4, since most bacteria can grow better in a slightly alkaline medium. The low pH of Blood Agar Base w/ low pH (pH 6.8) stabilizes the red blood corpuscles and favors the formation of clear zone of haemolysis. Also it is advantageous for cultivation of Streptococci and Pneumococci Blood Agar Base media can be used with added phenolphthalein phosphate for the detection of phosphate producing staphylococci, with added salt and agar for assessment of surface contamination on equipment and pig carcass and to determine salinity range of marine Flavobacteria. It can also be used for preparation of Salmonella Typhi antigens.
Addition of blood makes the medium more nutritious by providing additional growth factors required by fastidious organisms. It also helps in visualizing the haemolytic reactions. However, haemolytic reactions depend on the animal blood used. Sheep blood gives best results for Group A Streptococci. But sheep blood fails to support growth of Haemophilus haemolyticus since sheep blood is deficient in pyridine nucleotides. However when horse blood is used H.haemolyticus colonies produce haemolysis and mimic Streptococcus pyogenes.

for isolation and cultivation of fastidious organisms after addition of blood