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Epidemiological study of an outbreak due to multidrug-resistant Enterobacter aerogenes in a medical intensive care
1Laboratoire de Microbiologie, Université de Bordeaux II, France.
Abstract:
In 1993, 63 isolates of Enterobacter aerogenes were collected from 41 patients in a medical intensive care unit (ICU). During the same period, only 46 isolates from 32 patients were collected in the rest of the hospital. All isolates were analyzed by antibiotic resistance phenotype, and 77 representative isolates were differentiated by plasmid restriction analysis, ribotyping, and arbitrarily primed (AP)-PCR. The extended-spectrum beta-lactamases produced by 22 strains were characterized by determination of their isoelectric points and by hybridization of plasmid DNA with specific probes. The isolates were divided into 25 antibiotic resistance phenotypes, either susceptible (group I) or resistant (group II) to aminoglycosides, and exhibited three phenotypes of resistance to beta-lactams: chromosomally derepressed cephalosporinase alone or associated with either extended-spectrum beta-lactamases (mainly of the SHV-4 type) or imipenem resistance. The results of the tests divided the 77 representative isolates (group I, n = 21; group II, n = 56) into 15 plasmid profiles, 14 ribotypes, and 15 AP-PCR patterns. Although the resistant isolates (group II) exhibited different plasmid profiles, ribotyping and AP-PCR analysis demonstrated an identical chromosomal pattern, indicating an epidemiological relatedness. They were mainly found in the medical ICU and occasionally in other units. The susceptible strains (group I) had various and distinct markers and were mainly isolated in units other than the medical ICU. In conclusion, the presence of a nosocomial outbreak in an ICU and the spread of a multidrug-resistant epidemic strain throughout the hospital was confirmed. Ribotyping and AP-PCR represent discriminatory tools for the investigation of nosocomial outbreaks caused by E. aerogenes.
Insights
A 1993 study identified a multidrug-resistant Enterobacter aerogenes outbreak in a medical intensive care unit (ICU). Ribotyping and arbitrarily primed (AP)-PCR confirmed an epidemic strain spread throughout the hospital, highlighting their value in investigating nosocomial infections.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Epidemiology
Background:
- Enterobacter aerogenes is a significant nosocomial pathogen, particularly in intensive care units (ICUs).
- Antibiotic resistance in E. aerogenes poses a growing threat to patient safety and treatment efficacy.
- Understanding the molecular epidemiology of E. aerogenes outbreaks is crucial for effective control strategies.
Purpose of the Study:
- To investigate a suspected nosocomial outbreak of Enterobacter aerogenes in a medical ICU.
- To characterize the antibiotic resistance patterns and genetic relatedness of E. aerogenes isolates.
- To evaluate the discriminatory power of molecular typing methods for outbreak investigation.
Main Methods:
- Antibiotic resistance phenotyping of 63 ICU and 46 non-ICU E. aerogenes isolates.
- Molecular typing of 77 representative isolates using plasmid restriction analysis, ribotyping, and arbitrarily primed (AP)-PCR.
- Characterization of extended-spectrum beta-lactamases (ESBLs) using isoelectric focusing and DNA hybridization.
Main Results:
- Resistant E. aerogenes isolates (group II) from the ICU shared identical chromosomal patterns via ribotyping and AP-PCR, indicating epidemiological relatedness.
- Susceptible strains (group I) exhibited diverse genetic markers and were isolated outside the ICU.
- An epidemic strain of multidrug-resistant E. aerogenes was confirmed to have spread from the ICU throughout the hospital.
Conclusions:
- The study confirmed a nosocomial outbreak caused by a multidrug-resistant E. aerogenes strain in the ICU.
- Ribotyping and AP-PCR are highly discriminatory tools for investigating E. aerogenes nosocomial outbreaks.
- Effective infection control measures are essential to prevent the spread of resistant strains in healthcare settings.