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The gene encoding the low-affinity penicillin-binding protein 3r in Enterococcus hirae S185R is borne on a plasmid
1Centre d'Ingénierie des Protéines, Institut de Chimie, Université de Liège, Sart Tilman, Belgium.
Abstract:
Two plasmid-derived NcoI DNA fragments of 14 and 4.5 kb, respectively, have been isolated from the multidrug-resistant strain Enterococcus hirae S185R and analyzed. The 14-kb fragment contains two inverted (L and R) IS1216 insertion modules of the ISS1 family. These modules define a Tn5466 transposon-like structure that contains one copy of the methylase-encoding ermAM conferring erythromycin resistance and one copy of the adenylyl-transferase-encoding aadE conferring streptomycin resistance. Immediately on the left side of IS1216L there occurs a copy of pbp3r encoding the low-affinity penicillin-binding protein (PBP) PBP3r, itself preceded by a psr-like gene (psr3r) that controls the synthesis of PBP3r. ermAM, aadE, and the transposase gene (tnp) of IS1216R have the same polarities, and these are opposite those of psr3r, pbp3r, and the tnp gene of IS1216L. The 4.5-kb fragment is a copy of the 4.5-kb sequence at the 5' end of the 14-kb fragment, although it is not a restriction product of the 14-kb fragment. It contains three genes with the same polarity: psr3r, pbp3r, and tnp in an IS1216 element. Because of the very high degree of identity (99%) with the chromosomal psrfm and pbp5fm genes of Enterococcus faecium D63R, it is proposed that both the psr3r and pbp3r genes were transferred from an E.faecium strain and inserted in a plasmid of E. hirae. E. hirae is the first known bacterial species in which a low-affinity PBP-encoding gene has been found to be plasmid borne.
Insights
Researchers identified a novel plasmid in Enterococcus hirae carrying genes for low-affinity penicillin-binding protein (PBP) and antibiotic resistance. This discovery marks the first instance of a plasmid-borne low-affinity PBP gene in this bacterial species.
Area of Science:
- Molecular Biology
- Genetics
- Antimicrobial Resistance
Background:
- Multidrug-resistant Enterococcus hirae S185R was analyzed for plasmid-derived DNA.
- Previous studies have identified various resistance mechanisms in Enterococcus species, but plasmid-borne low-affinity penicillin-binding proteins were not previously characterized in E. hirae.
Purpose of the Study:
- To isolate and characterize plasmid-derived DNA fragments from Enterococcus hirae S185R.
- To investigate the genetic basis of antibiotic resistance, specifically erythromycin and streptomycin resistance.
- To identify and analyze genes encoding penicillin-binding proteins (PBPs) and their regulatory elements.
Main Methods:
- Isolation and NcoI digestion of plasmid DNA from Enterococcus hirae S185R.
- Analysis of 14 kb and 4.5 kb DNA fragments using molecular biology techniques.
- Gene sequencing and comparison with known genetic elements, including IS1216 insertion modules and Enterococcus faecium genes.
Main Results:
- A 14-kb fragment contained a Tn5466-like transposon with ermAM (erythromycin resistance) and aadE (streptomycin resistance) genes, alongside IS1216 insertion modules.
- The fragment also included psr3r and pbp3r genes, encoding a PBP3r synthesis regulator and a low-affinity penicillin-binding protein (PBP), respectively.
- A 4.5-kb fragment contained psr3r, pbp3r, and a transposase gene, showing high identity to Enterococcus faecium chromosomal genes, suggesting horizontal gene transfer.
Conclusions:
- Enterococcus hirae S185R harbors a plasmid carrying genes for antibiotic resistance and a low-affinity penicillin-binding protein (PBP3r).
- The psr3r and pbp3r genes likely originated from an Enterococcus faecium strain and were transferred to the E. hirae plasmid.
- This study reports the first instance of a plasmid-borne low-affinity PBP-encoding gene in the bacterial species Enterococcus hirae.