The growth of Pasteurella haemolytica strain H44L was studied under aerobic conditions in a medium of acid-hydrolyzed casein, supplementary cysteine, inorganic salts, vitamins, and a carbon source. The concentration of casein hydrolysate necessary for optimal growth was 1.5 or 2.0%, depending upon the carbon source employed. Essential vitamins were calcium pantothenate, nicotinamide, and thiamine. Concentrations as low as 0.01 μg/ml of thiamine monophosphate or thiamine pyrophosphate supported maximal growth, but thiamine hydrochloride or thiamine nitrate were active only at the unusually high levels of 10 to 20 μg/ml. The best carbon sources were d-galactose or sucrose. Maximal growth resulted from an inoculum containing fewer than 10 cells per milliliter of medium. Cellular yields averaged 6 × 109 to 7 × 109 cells per milliliter for the test organism and five other strains of P. haemolytica isolated from cases of bovine respiratory diseases.
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