First description of qnrS1-IncN plasmid in a ST11 Salmonella Enteritidis clinical isolate from Portugal

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Molecular Epidemiology

Background:

• Nontyphoidal Salmonella are significant foodborne pathogens.
• Decreased susceptibility to ciprofloxacin is a growing public health concern.
• The qnr and qepA genes are known to confer resistance to fluoroquinolones.

Purpose of the Study:

• To investigate the presence and characteristics of qnr and qepA genes in ciprofloxacin-resistant nontyphoidal Salmonella from Portugal.
• To determine the genetic context and potential for transfer of these resistance genes.

Main Methods:

• Phenotypic screening of 300 Salmonella isolates for decreased susceptibility to ciprofloxacin.
• Molecular detection of qnr and qepA genes using PCR.
• Plasmid analysis and sequencing to characterize the genetic environment of positive isolates.

Main Results:

• The qnrS1 gene was detected in one Salmonella Enteritidis isolate.
• This isolate belonged to Sequence Type 11 (ST11).
• The qnrS1 gene was located on a conjugative IncN plasmid, suggesting potential for horizontal gene transfer.

Conclusions:

• The study identified the qnrS1 gene in a Salmonella Enteritidis strain from a human source in Portugal.
• The presence of qnrS1 on a conjugative plasmid highlights a potential mechanism for the spread of fluoroquinolone resistance.
• Salmonella Enteritidis, particularly ST11, warrants continued surveillance for antimicrobial resistance markers.