Genetic Characterization of a Conjugative Plasmid That Encodes Azithromycin Resistance in Enterobacteriaceae

Area of Science:

• Microbiology
• Genetics
• Antimicrobial Resistance

Background:

• Azithromycin resistance mechanisms are not well understood.
• The emergence of antibiotic resistance poses a significant threat to public health.
• Klebsiella pneumoniae is an opportunistic pathogen that can cause severe infections.

Purpose of the Study:

• To identify and characterize azithromycin resistance mechanisms in Klebsiella pneumoniae.
• To investigate the dissemination potential of azithromycin resistance genes.
• To assess the implications of azithromycin resistance for treating bacterial infections, particularly Salmonella.

Main Methods:

• Isolation and characterization of a conjugative plasmid from a clinical Klebsiella pneumoniae isolate.
• Conjugation experiments to transfer the plasmid to recipient strains (Escherichia coli, Salmonella, etc.).
• Identification of macrolide resistance genes on the plasmid (erm(B), erm(42), mph(A)).
• Functional analysis of the novel erm(42) gene through gene cloning and MIC determination.

Main Results:

• A conjugative IncFIB/IncHI1B plasmid conferring azithromycin resistance was identified.
• The plasmid carries three macrolide resistance genes: erm(B), a novel erm(42), and mph(A).
• The plasmid was efficiently transferred to various Gram-negative bacteria, including Salmonella.
• The novel erm(42) gene was confirmed to confer azithromycin resistance.

Conclusions:

• A novel azithromycin resistance gene, erm(42), has been identified on a conjugative plasmid.
• The plasmid's efficient dissemination poses a significant risk for the spread of azithromycin resistance.
• Particular concern exists regarding the transfer to extensively drug-resistant Salmonella, limiting treatment options.
• Monitoring the dissemination of this plasmid in clinical Enterobacteriaceae is crucial.