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Transferable fluoroquinolone resistance in Enterobacteriaceae and Pseudomonas aeruginosa isolated from hemocultures
Background:
The main mechanisms causing high-level resistance to fluoroquinolones (FQ) are encoded chromosomally; that includes mutations in genes coding DNA-gyrase, but overexpression of efflux pumps contributes to increased minimum inhibitory concentration (MIC) of FQ as well. However, genes responsible for FQ-resistance may be harboured in transferable/conjugative plasmids. For some time, there was an assumption that resistance to FQ cannot be transferable in conjugation due to their synthetic origin, until 1998, when plasmid-mediated resistance transmission in Klebsiella pneumoniae was proved. We aimed to detect the occurrence of transferable FQ-resistance among Gram- negative bacteria isolated from patients in Czech and Slovak hospitals.
Methods:
In this study, we tested 236 clinical isolates of Gram-negative bacteria for transferable resistance. Among relevant isolates we performed PCR detection of transferable fluoroquinolone genes (qnr).
Results:
We have observed transfer of determinants of cephalosporin-resistance, aminoglycoside resistance as well as FQ-resistance (in 10 cases; 4.24%) not only intra-species but inter-species too. The presence of qnr gene was detected in two isolates of forty tested (5%). We have also observed that determinants of cephalosporin-resistance and aminoglycoside-resistance were linked to those of FQ-resistance and were transferred en block in conjugation.
Conclusion:
We have proved that resistance to fluoroquinolones can be transferred horizontally via conjugation among Gram-negative bacteria of different species and is associated with resistance to other antibiotics.
Insights
Fluoroquinolone resistance in Gram-negative bacteria can be transferred between species via plasmids. This horizontal gene transfer also carries resistance to other antibiotics, posing a significant public health threat.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- High-level fluoroquinolone (FQ) resistance is mainly chromosomal, involving DNA-gyrase mutations or efflux pump overexpression.
- However, genes conferring FQ resistance can be located on transferable plasmids, enabling horizontal gene transfer.
- Initially, FQ resistance was thought non-transferable, but plasmid-mediated transfer was proven in 1998.
Purpose of the Study:
- To investigate the occurrence of transferable fluoroquinolone resistance in Gram-negative bacteria from Czech and Slovak hospitals.
- To determine if FQ resistance genes are present on conjugative plasmids in clinical isolates.
Main Methods:
- Tested 236 clinical Gram-negative bacterial isolates for transferable resistance.
- Performed PCR to detect transferable fluoroquinolone resistance genes (qnr) in relevant isolates.
Main Results:
- Observed inter- and intra-species transfer of cephalosporin, aminoglycoside, and FQ resistance determinants in 4.24% of isolates.
- Detected the qnr gene in 5% of tested isolates.
- Found that FQ resistance determinants were linked with cephalosporin and aminoglycoside resistance, transferring together.
Conclusions:
- Confirmed that fluoroquinolone resistance is transferable via conjugation among different Gram-negative bacterial species.
- Demonstrated that transferable FQ resistance is often associated with resistance to other antibiotic classes.