Conjugative plasmids in bacteria of the ‘pre-antibiotic’ era

Abstract

Antibiotic resistance is common in bacteria that cause disease in man and animals and is usually determined by plasmids. The prevalence of such plasmids, and the range of drugs to which they confer resistance, have increased greatly in the past 25 yr. It has become clear from work in many laboratories that plasmids have acquired resistance genes, of ultimately unknown origin, as insertions into their circular DNA. The intensive use of antibiotics since their introduction in the 1940s can explain the spread of plasmids that have acquired such genes but little is known of the incidence of plasmids in pathogenic bacteria before the widespread use of antibiotics in medicine. E.D.G. Murray collected strains of Enterobacteriaceae from 1917 to 1954; we now report that 24% of these encode information for the transfer of DNA from one bacterium to another. From at least 19% of the strains, conjugative plasmids carrying no antibiotic resistance were transferred to Escherichia coli K-12.

Gene cassettes encoding resistance to quaternary ammonium compounds: a role in the origin of clinical class 1 integrons?

“…Lateral gene transfer has played a critical role in the dissemination of these resistance determinants, but we still have little information about the sources of resistance genes and their mobile vectors. Examination of enterobacterial isolates collected during the 1920s found no antibiotic resistance genes Hughes and Datta, 1983); so clearly, over the last 90 years such genes have been repeatedly sampled from the vast reservoir of microbial diversity that resides in natural environments. Studying the pool of potential resistance genes and mobile vectors could help predict future threats posed by lateral gene transfer events (D'Costa et al, 2006).…”

Microbiological indicators of water quality in the Xochimilco canals, Mexico City

“…Antimicrobial resistance transferred by conjugation, suggests that resistance genes are encoded in a plasmid that could be transferred to other promiscuous pathogenic bacteria. 10,11 Evidence for plasmid-mediated antibiotic multiresistant environmental strains has been reported from Mexico City, indicating that such mechanisms may have a greater epidemiological impact than previously expected, 12 as dissemination of resistance antibiotic genes could be transferred to other bacteria in animals or human gut and will be selected by the use of antibiotics. antibiotic resistance patterns 13,14 will be useful in assessing sources of fecal contamination in Xochimilco waters.…”

Antibiotic-resistant soil bacteria in transgenic plant fields

“…Ampicillin was deployed in 1961, and resistance was first observed 15 years later (36). Antibiotic resistance genes detected on numerous plasmids today were apparently lacking from bacterial replicons isolated in the preantibiotic era (37,38). These dramatic changes confirm the fundamental role of horizontal gene transfer (HGT) in the dispersion of these genes between bacteria.…”