Antibiotics and Lactic Acid Starter Cultures " 2

The problem of antibiotics in milk was brought to light in 1948 by Kastli (1948), who was the first to report specifically that milk from a quarter of an udder treated with penicillin would impair the manufacture of butter and cheese. He found that from 0.1 to 1.0 unit of penicillin per ml of milk was sufficient to inhibit the growth of the widely used starter cultures, Streptococcus cremoris and Streptococcus lactis. Katznelson and Hood (1949), and Krienke (1949), later found that complete inhibition of acid production occurred when 0.5 unit of penicillin per ml of milk was present and that as little as 0.1 unit produced strong inhibition. Hunter (1949) found that pasteurization within the temperature limits available to the cheesemaker does not alter the toxic activity of penicillin in milk. Petersen (1950) found that species of the genus Leuconostoc were very sensitive to penicillin, which impaired the development of flavor and aroma in cream used for butter manufacture. Wilkowske and Krienke (1951), also working with penicillin, found that the genus Lactobacillus was sensitive to penicillin levels of 0.3 to 0.6 unit per ml of milk. Hansen et al. (1950) reported that milk from a cow treated with 1 g of streptomycin showed no acid production by the starter organisms involved. They also found that as little as 1 per cent cream treated with streptomycin restricted the growth of starter organisms used in buttermaking. Hargrove et al. (1950) found that 5 mg of streptomycin inhibited the growth of both Streptococcus thermophilus and Propionibacterium shermanii, and that 1 mg of streptomycin per ml of milk stopped Lactobacillus bulgaricus from producing lactic acid. Bell et al. (1951) reported that aureomycin was present in the milk 48 hours after udder infusion and that its presence interfered with starter activity. Krienke (1950a) reported that cows treated with aureomycin showed inhibitory concentrations of the antibiotic on the production of lactic acid for as long as 12 milkings after treatment for bovine mastitis. Bradfield (1949) treated cows with 200 mg of aureomycin ointment and reported that their mixed milk failed to develop suffi-