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Published on: July 3, 2016
Catalytic and structural properties of IRT-21 beta-lactamase (TEM-77) from a co-amoxiclav-resistant Proteus mirabilis
Abstract:
Proteus mirabilis strain MAG1, a clinical isolate that is resistant to broad-spectrum penicillins and co-amoxiclav, produces inhibitor-resistant TEM (IRT)-21, a novel mutant of TEM beta-lactamase. This enzyme has a pI of 5.2 and is derived from the bla(TEM-1a) gene ancestor. It contains two major amino acid substitutions specific for co-amoxiclav resistance (Leu-69 for Met and Ser-244 for Arg) that have never been found together previously. The dramatic loss of sensitivity to clavulanic acid, the enhancement of K(m) for all beta-lactams and markedly for ticarcillin, and the decrease in the catalytic efficiency makes IRT-21 comparable to the other IRTs with substitutions at position 244 or double substitutions.
Insights
A novel beta-lactamase, inhibitor-resistant TEM (IRT)-21, was identified in Proteus mirabilis. This enzyme confers resistance to broad-spectrum penicillins and co-amoxiclav due to unique amino acid substitutions.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- Proteus mirabilis is a common cause of urinary tract infections.
- Beta-lactamase enzymes are a major mechanism of bacterial resistance to beta-lactam antibiotics.
- Inhibitor-resistant TEM (IRT) beta-lactamases are a significant challenge in treating bacterial infections.
Purpose of the Study:
- To characterize a novel TEM beta-lactamase mutant, IRT-21, identified in a clinical isolate of Proteus mirabilis.
- To investigate the genetic basis and biochemical properties conferring resistance to beta-lactamase inhibitors.
Main Methods:
- Genetic analysis of the bla(TEM-1a) gene ancestor.
- Biochemical characterization of the IRT-21 enzyme, including determination of pI, K(m) values for various beta-lactams, and catalytic efficiency.
- Amino acid sequencing to identify key substitutions.
Main Results:
- Proteus mirabilis strain MAG1 produces a novel TEM beta-lactamase mutant, IRT-21.
- IRT-21 possesses two unique amino acid substitutions (Leu-69 for Met and Ser-244 for Arg) not previously found together.
- The enzyme exhibits reduced sensitivity to clavulanic acid, increased K(m) for beta-lactams, and decreased catalytic efficiency, conferring resistance.
Conclusions:
- IRT-21 represents a new class of inhibitor-resistant TEM beta-lactamases.
- The identified amino acid substitutions are crucial for conferring resistance to co-amoxiclav.
- Understanding IRT-21 is important for developing strategies to combat antibiotic resistance.
