THE NON-MEDICAL USE OF ANTIBIOTICS AND THE RISK OF CAUSING MICROBIAL DRUG-RESISTANCE.

One of the hazards involved in the use of antibiotics in animal feeds is that it may lead to the development of bacterial drug-resistance. An analysis of the phenomenon shows that this possibility largely depends on the size of the bacterial populations involved and on the possibility of selective multiplication of the resistant mutants that may be present. Additional factors involved in the development of resistance are the type of drug applied and the time during which the bacteria are in contact with it.Animal experiments and general practical experience show that resistance, especially in E. coli, Salm. typhimurium and Staph. aureus, may considerably increase as higher doses are added to the feed. Therefore, the lowest effective level for growth promotion (5-20 p.p.m. of penicillin or tetracycline) is to be preferred over higher levels.AS TO THE PRACTICE OF FOOD PRESERVATION BY MEANS OF ANTIBIOTICS, A DANGEROUS SITUATION MAY ARISE IF TWO FACTORS COMBINE: emergence of bacterial resistance in Salmonella and perhaps other pathogenic bacteria in the animal as a result of the addition of a certain antibiotic to feeds, and subsequent use of the same substance for preservation of the meat.