Growth of Escherichia coli in whole and skim milk from endotoxin-induced mastitic quarters: in vitro effects of deferoxamine, zinc, and iron supplementation.

A marked growth inhibition of Escherichia coli 0101 K99 F41 was observed in whole and skim milk collected from inflamed quarters 18 and 36 h after intramammary administration of .1 mg E. coli lipopolysaccharide. Individual cow variation in the ability of milk from endotoxin-infused quarters to inhibit growth of E. coli was found. Growth inhibition of E. coli was observed in milk from endotoxin-infused quarters and was most pronounced in skim milk sampled at postinfusion h 18, and incubated at 38 degrees C. The mechanism by which bacterial growth was depressed was probably of noncellular origin. Addition of Fe (45.5 micrograms/ml) and Zn (2.7 micrograms/ml) to whole and skim milk sampled from inflamed quarters at 18 h after endotoxin infusion resulted in a growth-promoting effect. Addition of deferoxamine (6 mg/ml) depressed bacterial growth. Effects of Fe, Zn, and deferoxamine on bacterial growth did not differ in whole and skim milk. No clear relationship was observed between reduction in Zn concentrations in skim milk from inflamed quarters at 18 h after endotoxin infusion and growth inhibition of E. coli in the same samples.