Two novel plasmid-mediated cefotaxime-hydrolyzing beta-lactamases (CTX-M-5 and CTX-M-6) from Salmonella typhimurium

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Antimicrobial resistance is a growing global health threat.
• Beta-lactamase enzymes are a major mechanism of resistance to beta-lactam antibiotics.
• Novel beta-lactamases contribute to the evolving resistance landscape.

Purpose of the Study:

• To characterize two novel plasmid-mediated beta-lactamases, CTX-M-5 and CTX-M-6.
• To determine the genetic basis and enzymatic properties of these new enzymes.
• To understand their relationship to existing beta-lactamase families.

Main Methods:

• Isolation and characterization of beta-lactamase enzymes from clinical Salmonella typhimurium strains.
• Determination of enzyme properties, including isoelectric point (pI) and substrate hydrolysis profile.
• Cloning and sequencing of the genes encoding the novel beta-lactamases (bla genes).
• Bioinformatic analysis of deduced amino acid sequences.

Main Results:

• Two novel plasmid-mediated beta-lactamases, CTX-M-5 and CTX-M-6, were identified.
• Both enzymes exhibited an isoelectric point (pI) of 8.4.
• CTX-M-5 and CTX-M-6 hydrolyzed oxyimino-beta-lactams and were inhibited by mechanism-based inhibitors.
• Sequence analysis revealed homology to plasmid class A CTX-M-type enzymes and relatedness to Klebsiella oxytoca chromosomal beta-lactamases.

Conclusions:

• CTX-M-5 and CTX-M-6 represent new additions to the CTX-M family of beta-lactamases.
• These enzymes possess characteristics associated with extended-spectrum beta-lactamase (ESBL) activity.
• The findings highlight the continuous evolution of beta-lactamase-mediated resistance in Salmonella.