The Survival of R-Plasmids in the Absence of Antibiotic Selection Pressure
There is now no doubt that antibiotic use favours the emergence of resistant bacterial populations (1). This can be seen both on a worldwide scale, where the introduction of a novel antibiotic is frequently followed by the appearance of bacteria resistant to that agent, and also in individual human beings, where a therapeutic course of an antibiotic commonly results in the conversion of the bacterial population in the person’s alimentary tract to a resistant state. As examples, Fig. 1 shows the emergence of hospital strains of Staphylococcus aureus resistant to benzyl penicillin in the years immediately following the introduction of that antibiotic into clinical use in 1946 (ref. 2). On the other hand, Fig. 2 shows the effect of a therapeutic course of tetracycline on the resistance of the gut coliforms in the person under treatment (3, 4). In both cases, the use of the antibiotic encourages the resistant bacteria to outgrow the sensitive, with a resulting change in the properties of the population.
KeywordsUrinary Tract Infection Resistant Bacterium Antibiotic Resistant Bacterium Faecal Flora Chicken Carcass
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