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Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
Genetic Characterization of a Linezolid- and Penicillin-Resistant Enterococcus hirae Isolate Co-Harboring poxtA and
Jinhu Huang1, Aijuan Li1, Mengli Wang1
1MOE Joint International Research Laboratory of Animal Health and Food Safety, Risk Assessment Center of Veterinary Drug Residue and Antimicrobial Resistance, Center for Veterinary Drug Research and Evaluation, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, China.
Abstract:
Linezolid and penicillin are critical for treating multidrug resistant (MDR) Gram-positive infections, but the emergence of resistance to both seriously threatens public health. Here, we first report the cocarrying poxtA (oxazolidinone resistance) and pbp5fm (β-lactam resistance) genes by the plasmid in a strain of Enterococcus hirae HDC14-2 derived from porcine. The isolate also exhibits MDR phenotypes to phenicols, oxazolidinones, tetracyclines, β-lactams, aminoglycosides, macrolides, and lincosamides. Whole-genome sequencing (WGS) revealed these resistance genes, along with tet(L), tet(M), catA, erm(B), aac(6)-aph(2"), aadE, spw, lsa(E), lnu(B), sat4, and aphA3, were clustered in a novel MDR region flanked by IS1216 elements on plasmid pHDC14-2.133K. This IS1216-bounded MDR region formed translocatable units (TUs), including an IS1216-poxtA TU that was also identified on a secondary plasmid, pHDC14-2.27K. Functional assays demonstrated the excisability and mobility of these TUs, indicating its potential ability integration into other plasmids or chromosomes. Critically, electrotransformation confirmed the transfer of pHDC14-2.27K (poxtA-carrying) to Enterococcus faecalis JH2-2, with retained TU activity and minimal fitness cost. This study provides the evidence of colocalized poxtA and pbp5fm on plasmids in enterococci, highlighting their role in disseminating pan-resistance among bacteria. Although E. hirae is not an important pathogenic bacterium to humans and animals, but its potential risk to horizontally spread of these resistance genes important in medicine still cannot be ignored.
Insights
This study reports the first co-occurrence of oxazolidinone and beta-lactam resistance genes on a plasmid in Enterococcus hirae. This finding highlights the potential for horizontal gene transfer and the spread of multidrug resistance in bacteria.
Area of Science:
- Microbiology
- Genetics
- Antimicrobial Resistance
Background:
- Multidrug-resistant (MDR) Gram-positive infections pose a significant public health threat due to limited treatment options.
- Emergence of resistance to critical antibiotics like linezolid and penicillin necessitates understanding resistance mechanisms and dissemination.
- Enterococcus species are known reservoirs and vectors for antibiotic resistance genes.
Purpose of the Study:
- To identify and characterize novel mechanisms of multidrug resistance in Enterococcus species.
- To investigate the genetic basis and mobility of co-occurring resistance genes, specifically oxazolidinone (poxtA) and beta-lactam (pbp5fm) resistance.
- To assess the potential for horizontal gene transfer of these resistance determinants.
Main Methods:
- Isolation and whole-genome sequencing (WGS) of a multidrug-resistant Enterococcus hirae strain (HDC14-2).
- Plasmid analysis, including identification of resistance genes and mobile genetic elements (IS1216).
- Functional assays for translocatable unit (TU) excisability and mobility, and electrotransformation experiments for gene transfer.
Main Results:
- Identification of a novel MDR region on plasmid pHDC14-2.133K in E. hirae, containing co-localized poxtA and pbp5fm resistance genes, alongside other resistance determinants.
- Demonstration of the mobility of IS1216-bounded MDR regions as translocatable units (TUs), including an IS1216-poxtA TU found on a second plasmid (pHDC14-2.27K).
- Successful transfer of the poxtA-carrying plasmid (pHDC14-2.27K) to Enterococcus faecalis JH2-2 via electrotransformation, with retained TU activity and minimal fitness cost.
Conclusions:
- This study provides the first evidence of colocalized oxazolidinone and beta-lactam resistance genes on plasmids in enterococci.
- The identified translocatable units facilitate the spread of MDR regions, contributing to pan-resistance development in bacteria.
- Although Enterococcus hirae is not a primary pathogen, its role in horizontally spreading clinically important resistance genes cannot be overlooked.
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