The effect of dietary bacitracin on the incidence ofstreptococcus faecalissubspeciesliquefaciensand related streptococci in the intestines of young chicks

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Abstract
1. A study has been made of changes occurring in the numbers and types of faecal streptococci in the intestines of chicks from hatching to 23 d of age, when fed on a diet containing 50 mg bacitracin/kg. 2. It was found that Streptococcus faecalis sub‐species liquefaciens predominated in chicks prior to feeding and in control birds the organism remained as a significant part of the flora throughout the experiment. 3. Strep. faecalis s.s. liquefaciens was not found after the first week in birds given dietary bacitracin. 4. Although outnumbered initially in the caeca by Strep, faecalis s.s. liquefaciens, other streptococci were present at 106 to 107/g contents from 14 d onwards in both control and bacitracin‐treated birds; these included Strep. faecium biotypes and two other unidentified but related groups. 5. Tests made in vitro showed that Strep. faecalis s.s. liquefaciens was more sensitive to bacitracin than Strep. faecium. 6. The possible effects of Strep. faecalis s.s. liquefaciens on the developing bird are discussed.