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Characteristics of Serratia marcescens containing a plasmid coding for gentamicin resistance in nosocomial infections
Abstract:
Strains of gentamicin-resistant Serratia marcescens (GRSM) that originated in a crowded neurosurgical close observation unit (COU) became established during a 2.5-year interval at several affiliated hospitals in Charleston, South Carolina. Most patients with GRSM had colonization or infection of the urinary tract associated with indwelling bladder catheters. Infected patients in the COU more often had pyuria and less often received systemic steroids than COU patients not harboring GRSM. However, length of stay, use of urinary catheters, exposure to systemic antibiotics, and exposure to gentamicin were not significantly different between the two groups. Of the strains of GRSM, 92% contained a conjugative 41-megadalton plasmid tht encoded resistance to ampicillin, carbenicillin, tetracycline, kanamycin, gentamicin, and tobramycin and elaborated similar aminoglycoside 3-acetyltransferases. Seven 41-megadalton plasmids from outbreak strains and a 41-megadalton plasmid from a 1973 isolate of GRSM gave identical DNA fragments after restriction endonuclease digestion.
Insights
Gentamicin-resistant Serratia marcescens (GRSM) spread in hospitals, often causing urinary tract infections linked to catheters. A key plasmid mediated multi-drug resistance in most GRSM strains studied.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Hospital Epidemiology
Background:
- Gentamicin-resistant Serratia marcescens (GRSM) emerged in a neurosurgical close observation unit (COU).
- GRSM spread to affiliated hospitals over 2.5 years.
- Urinary tract colonization/infection was common, particularly with indwelling catheters.
Purpose of the Study:
- To investigate the epidemiology and genetic basis of GRSM spread.
- To identify risk factors associated with GRSM colonization/infection in the COU.
Main Methods:
- Surveillance of GRSM strains across multiple hospitals.
- Clinical data analysis comparing patients with and without GRSM.
- Plasmid analysis, including conjugation, restriction endonuclease digestion, and characterization of resistance genes.
Main Results:
- GRSM strains were established in multiple hospitals, originating from a COU.
- Patients with GRSM more frequently presented with pyuria and less often received steroids.
- A 41-megadalton conjugative plasmid encoding resistance to multiple antibiotics (including gentamicin, tobramycin, ampicillin, tetracycline) was present in 92% of GRSM strains.
- Identical DNA fragments were observed after restriction digestion of outbreak plasmids and a historical GRSM plasmid.
Conclusions:
- A specific 41-MDa plasmid likely facilitated the dissemination of multi-drug resistant GRSM.
- Understanding plasmid-mediated resistance is crucial for controlling hospital-acquired infections.
- Further research into GRSM transmission dynamics and resistance mechanisms is warranted.