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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.
Insights
Before widespread antibiotic use, many pathogenic bacteria already possessed plasmids enabling DNA transfer. These findings shed light on the early prevalence of mobile genetic elements in bacteria.
Area of Science:
- Microbiology
- Genetics
- Evolutionary Biology
Background:
- Antibiotic resistance in pathogenic bacteria is primarily mediated by plasmids, which have significantly increased in prevalence and drug resistance range over the past 25 years.
- Plasmids acquire resistance genes through insertion, but the incidence of plasmids in pathogenic bacteria before the widespread use of antibiotics remains largely unknown.
Purpose of the Study:
- To investigate the prevalence and characteristics of plasmids in pathogenic bacteria prior to the extensive use of antibiotics in medicine.
- To understand the historical incidence of bacterial conjugation and mobile genetic elements in Enterobacteriaceae.
Main Methods:
- Analysis of bacterial strains collected by E.D.G. Murray between 1917 and 1954.
- Detection of plasmid-encoded DNA transfer capabilities within these historical Enterobacteriaceae strains.
- Conjugation experiments to transfer plasmids to a laboratory strain of Escherichia coli K-12.
Main Results:
- 24% of historical Enterobacteriaceae strains analyzed contained genetic information for bacterial DNA transfer.
- Conjugative plasmids, lacking antibiotic resistance genes, were successfully transferred from at least 19% of these strains to Escherichia coli K-12.
- Evidence suggests the presence and transferability of plasmids predates the widespread application of antibiotics.
Conclusions:
- Plasmids capable of DNA transfer were present in pathogenic bacteria well before the antibiotic era.
- The findings indicate that mobile genetic elements, such as conjugative plasmids, have a long evolutionary history in bacterial populations.
- This historical perspective is crucial for understanding the long-term dynamics of bacterial genetics and the evolution of antibiotic resistance.