The effect of the use of antibacterial drugs, particularly as food additives, on the emergence of drug-resistant strains of bacteria in animals

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Abstract
Extract The importance of the development of drug-resistant strains of bacteria in human medicine was noted early in the antibiotic era because the diseases against which the first available antibiotic, penicillin, was initially employed included those caused by Staphylococcus aureus. This species contained a numerically inferior group of strains that were penicillin-resistant. The selection pressure provided by penicillin therapy resulted in these strains becoming dominant in hospital wards where they presented serious problems. This situation was repeated following the introduction of other drugs such as streptomycin and the tetracyclines, the end result frequently being the emergence of multiply-resistant strains. The position in regard to another comparable human pathogen, Streptococcus pyogenes, was quite different. Penicillin-resistant strains did not emerge and now, some twenty-five years after its introduction, penicillin remains as effective as ever against diseases caused by this bacterial species.