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Chloramphenicol resistance mutation in Escherichia coli which maps in the major ribosomal protein gene cluster
Abstract:
Localized mutagenesis and selection for streptomycin resistance were utilized to isolate a chloramphenicol resistance mutation in Escherichia coli K-12 linked to the strA (rpsL) locus. Bacteriophage P1 transduction verified the map position of the new resistance mutation at 72 min, placing it within a dense cluster of ribosomal protein genes. The map position differs from that of known cmlA and cmlB mutations, which map at 18 and 21 min, respectively. Ribosomes prepared from chloramphenicol-resistant and -sensitive isogenic transductants were analyzed in vitro for activity in formation of N-formylmethionyl-puromycin, polyphenylalanine, and polylysine in the presence of inhibitory concentrations of chloramphenicol. Comparisons were also made of 14C-chloramphenicol binding to 70S ribosomes and of the two-dimensional polyacrylamide gel electrophoresis pattern of ribosomal proteins from each strain. There was no detectable difference between ribosomes from sensitive and resistant strains as measured by these assays. Enzymatic modification by chloramphenicol acetyltransferase is not responsible for the observed phenotype.
Insights
Researchers identified a new chloramphenicol resistance mutation in Escherichia coli K-12. This mutation, located near ribosomal protein genes, does not affect ribosome function or involve enzymatic modification.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Antibiotic resistance is a growing public health concern.
- Understanding the genetic basis of resistance is crucial for developing new strategies.
- Escherichia coli is a model organism for studying bacterial genetics and antibiotic resistance.
Purpose of the Study:
- To isolate and characterize a novel chloramphenicol resistance mutation in Escherichia coli K-12.
- To determine the genetic locus and potential mechanism of this resistance.
- To investigate the effect of the mutation on ribosomal function.
Main Methods:
- Localized mutagenesis and selection for streptomycin resistance.
- Bacteriophage P1 transduction for mapping the mutation.
- In vitro analysis of ribosome activity (N-formylmethionyl-puromycin, polyphenylalanine, polylysine synthesis).
- 14C-chloramphenicol binding assays.
- Two-dimensional polyacrylamide gel electrophoresis of ribosomal proteins.
Main Results:
- A new chloramphenicol resistance mutation was isolated and mapped to the 72-min region of the Escherichia coli K-12 chromosome, within a cluster of ribosomal protein genes.
- This mutation's map position is distinct from previously identified chloramphenicol resistance loci (cmlA and cmlB).
- No significant differences were detected in in vitro ribosome activity, 14C-chloramphenicol binding, or ribosomal protein profiles between resistant and sensitive strains.
- The observed chloramphenicol resistance phenotype is not due to enzymatic modification by chloramphenicol acetyltransferase.
Conclusions:
- The identified chloramphenicol resistance mutation in Escherichia coli K-12 is novel and maps to a unique chromosomal location.
- The resistance mechanism does not appear to involve alterations in ribosome function or enzymatic inactivation of the antibiotic.
- Further investigation is needed to elucidate the precise molecular mechanism underlying this resistance phenotype.