GROWTH OF LEUCONOSTOC CITROVORUM IN SKIMMILK AT 22-C AND 30-C

Strains of Leuconostoc citrovorum were compared for their growth characteristics in sterile skimmilk at 22 and 30 C. Numbers of organisms were determined periodically during incubation using f count procedure and Elliker's lactic agar. Microscopic observations were made on all strains at intervals during the 46-hr incubation period used in most of these experiments. Maximum growth of all L. citrovorum strains tested occured after an incubation of 14-30 hr at 22 and 30 C, depending on the strain; however, most strains examined attained maximum numbers after incubation for 18 hr at 30 C or 22 hr at 22 C. Four strains developed nearly equal maximum populations at both incubation temperatures, whereas four others tended toward higher numbers at 22 than 30 C. Although strain variation existed, generally chains formed by the cultures tended to be longest after 10 to 14 hr of incubation, regardless of temperature. Chains formed by most strains tended to be slightly longer (average values seldom more than five cells greater) at 30 C incubation than at 22 C. Populations of nearly all cultures remained essentially stationary for at least 46 hr when held at either 22 or 30 C. Tests on three strains indicated their maximum stationary phase extended beyond 100 hr at 22 C. At 30 C, numbers of two strains began to decline slightly after 62 and 78 hr of incubation. A third strain revealed an initial decrease in numbers between 26 and 46 hr of incubation, followed by a slow increase which continued for at least 106 hr. Overall, a somewhat more rapid rate of growth during the logarithmic phase was observed at 30 C (average generation time, 3.8 hr). In comparison, average generation times of strains attaining nearly equal number at 22 and 30 C were 3.4 hr at 30 C and 4.3 hr at 22 C incubation. Generation times for strains with highest populations at 22 C were 2.4 hr at 30 C and 3.1 hr at 22 C incubation. © 1969, American Dairy Science Association. All rights reserved.