Description and plasmid characterization of qnrD determinants in Proteus mirabilis and Morganella morganii

Area of Science:

• Microbiology
• Genetics
• Antimicrobial Resistance

Background:

• Enterobacteriaceae are a family of bacteria, some of which can cause infections.
• Fluoroquinolones and third-generation cephalosporins are important antibiotics used to treat bacterial infections.
• Antibiotic resistance is a growing global health concern, necessitating the surveillance of resistance genes.

Purpose of the Study:

• To investigate the prevalence of specific antibiotic resistance genes (qnrC and qnrD) in Enterobacteriaceae.
• To characterize the genetic elements carrying these resistance genes.
• To understand the potential dissemination of these resistance genes within bacterial populations.

Main Methods:

• Screening of 756 non-replicate Enterobacteriaceae isolates from Italy for the presence of qnrC and qnrD genes.
• Selection criteria for isolates included non-susceptibility to fluoroquinolones and/or resistance to third-generation cephalosporins.
• Plasmid DNA carrying the qnrD gene was isolated, fully sequenced, and analyzed for genetic content.

Main Results:

• The qnrD gene was detected in five isolates: four Proteus mirabilis and one Morganella morganii.
• These isolates represented 0.66% of the total Enterobacteriaceae studied.
• The qnrD gene was located on a 2687-base-pair plasmid that contained no other identifiable coding regions and was un-typable.
• The gene was found in unrelated P. mirabilis strains, indicating potential independent acquisition or frequent association.

Conclusions:

• The qnrD gene is present in Enterobacteriaceae in Italy, specifically within the Proteeae tribe.
• The findings suggest a potential frequent association between the qnrD gene and bacteria belonging to the Proteeae tribe.
• Further surveillance is warranted to monitor the spread of qnrD and its impact on fluoroquinolone resistance.