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Nucleotide sequence analysis of the cat gene of Proteus mirabilis: comparison with the type I (Tn9) cat gene
Abstract:
In Proteus mirabilis PM13 chloramphenicol resistance is mediated by the cat gene, a single copy of which is present in both resistant and sensitive isolates and which reverts at a high frequency. RNA measurements show an about 8.5-fold increase in cat-specific mRNA in cells expressing the resistance phenotype as compared with those which are sensitive to chloramphenicol. DNA sequence analysis has revealed a high degree of homology between the P. mirabilis cat gene and the type I cat variant (Tn9), 76% at the amino acid level and 73% when nucleotides in the coding sequence are compared. Sequence homology between the strain PM13 cat variant and Tn9 cat was not apparent however in the 5' and 3' flanking regions. Segments of near identity were seen when the upstream sequence of the cat of P. mirabilis was compared with the 5' regions of the Salmonella typhimurium flagellin genes H1 and H2, which are alternately expressed by a flip-flop control mechanism involving an invertible promoter and a trans-acting product.
Insights
Proteus mirabilis exhibits high-frequency chloramphenicol resistance due to increased cat gene expression. This resistance mechanism shares homology with Tn9 but has unique flanking regions, suggesting novel regulatory elements.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Chloramphenicol resistance in Proteus mirabilis is a significant clinical concern.
- The cat gene is implicated in mediating chloramphenicol resistance.
- Understanding the genetic basis of antibiotic resistance is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the mechanism of chloramphenicol resistance in Proteus mirabilis PM13.
- To analyze the genetic and molecular characteristics of the cat gene in resistant and sensitive isolates.
- To explore potential regulatory elements influencing cat gene expression.
Main Methods:
- RNA expression analysis to quantify cat-specific mRNA levels.
- DNA sequencing to determine the genetic structure of the cat gene and its flanking regions.
- Comparative sequence analysis to identify homologies with known genetic elements.
Main Results:
- Resistant Proteus mirabilis PM13 isolates showed an 8.5-fold increase in cat-specific mRNA compared to sensitive isolates.
- The P. mirabilis cat gene exhibits significant homology to the type I cat variant (Tn9) at the amino acid and coding nucleotide levels.
- Non-coding flanking regions of the P. mirabilis cat gene showed homology to Salmonella typhimurium flagellin gene regulatory sequences.
Conclusions:
- Increased expression of the cat gene is the primary driver of chloramphenicol resistance in Proteus mirabilis PM13.
- The P. mirabilis cat gene shares ancestry with Tn9 but possesses distinct regulatory regions.
- Novel regulatory mechanisms, potentially involving invertible promoter elements, may control cat gene expression in P. mirabilis.