Antibiotic (kanamycin and streptomycin) resistance traits in the environment

摘要

Antibiotics have been and are being widely used in human medicine and animal husbandry, and are key antibacterial factors determining much of the success of 20th century medicine. Unfortunately, an increasing incidence of antibiotic resistance amongst bacterial isolates has invariably been noted following the introduction of each new antibiotic. In particular, the enhanced occurrence of antibiotic resistant pathogenic bacteria has often hampered antibiotic treatments (Hinton et al. 1986; Saunders 1984). The massive use of antibiotics has undoubtedly been crucial in this resistance development, since it provided strong selective pressure under which underlying mechanisms of bacterial adaptation could emerge. For instance, it was shown that the rate of production and application of antibiotics in medicine and farming from the fifties to the late seventies parallelled the incidence of e.g. antibiotic-resistant Salmonella and Shigella isolates (Linton 1984; van Elsas 1992). In all likelihood, there are two mechanisms involved in the development of antibiotic resistant bacterial populations. After emergence of an antibiotic resistance trait, clonal selection due to selective pressure exerted by the antibiotic may ensue. Alternatively, spread of the resistance trait to other bacteria can be mediated by gene transfer via transformation, transduction or conjugation. The resistance determinants currently often found on plasmids have indeed been selected under conditions of antibiotic selective pressure associated with clinical use of antibiotics, since the core replicons of self-transmissible plasmids involved in antibiotic resistance gene transfer were devoid of resistance determinants in the (antibiotic sensitive) bacteria isolated in the pre-antibiotic era (Hughes and Datta 1983).