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Characterization of a nosocomially significant, multiple drug-resistant strain of Serratia marcescens
Abstract:
A multiple drug-resistant strain of Serratia marcescens (bacteriocin type 18) was isolated from three clinical patients. The isolates were found to carry a conjugally nontransferable, nonmobilizeable resistance plasmid (R-plasmid) with resistance-(r)-determinants against ten antimicrobial drugs: ampicillin, carbenicillin, chloramphenicol, gentamicin, kanamycin, neomycin, streptomycin, tobramycin, triple sulfonamides, cotrimoxazole, and--possibly--nalidixic acid, as determined with exposure to 'curing' agents (ethidium bromide, acridine orange, and sodium dodecyl sulfate) and by the high rate of spontaneous loss of r-determinants. Dyebuoyant density centrifugation allowed recovery of R-plasmid DNA that measured roughly 24 mum in contour length; after 'curing' with concomitant loss of 9 r-determinants, the contour length of the R-plasmid DNA of one isolate (No. SE 154) had decreased to roughly 15 mum, and none was detected in the sole variant of the isolate that spontaneously had lost 11 r-determinants.
Insights
A multidrug-resistant Serratia marcescens strain was identified, carrying a resistance plasmid conferring resistance to ten antibiotics. This R-plasmid
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Multiple drug resistance (MDR) in bacteria poses a significant global health threat.
- Serratia marcescens is an opportunistic pathogen frequently associated with hospital-acquired infections.
- The emergence of MDR strains necessitates understanding the genetic basis of resistance.
Purpose of the Study:
- To characterize a multidrug-resistant strain of Serratia marcescens isolated from clinical patients.
- To identify and analyze the resistance plasmid (R-plasmid) responsible for conferring resistance to multiple antimicrobial drugs.
- To investigate the genetic stability and characteristics of the R-plasmid.
Main Methods:
- Isolation and identification of Serratia marcescens strains from clinical samples.
- Plasmid curing experiments using ethidium bromide, acridine orange, and sodium dodecyl sulfate.
- Determination of antimicrobial resistance profiles using standard antimicrobial susceptibility testing.
- Plasmid DNA extraction and characterization using dye-buoyant density centrifugation and contour length measurements.
Main Results:
- A multidrug-resistant strain of Serratia marcescens (bacteriocin type 18) was isolated from three clinical patients.
- The isolates harbored a conjugally nontransferable, nonmobilizable R-plasmid conferring resistance to ten antimicrobial drugs.
- Plasmid curing experiments and spontaneous loss indicated the presence of multiple resistance determinants on the R-plasmid, with DNA length correlating to the number of lost determinants.
Conclusions:
- The identified R-plasmid in Serratia marcescens is a stable genetic element carrying multiple antibiotic resistance genes.
- Understanding the characteristics of such R-plasmids is crucial for developing effective strategies to combat MDR infections.
- This study highlights the genetic mechanisms underlying multidrug resistance in clinically relevant bacterial pathogens.