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Apparent increased prevalence of high-level aminoglycoside-resistant Enterococcus durans resulting from false
A Tsakris1, N Woodford, S Pournaras
1Department of Microbiology, Medical School, Aristotelian University of Thessaloniki, Greece. atsakris@med.auth.gr
Abstract:
Identification of enterococci by using a semiautomated system (PASCO; Difco Laboratories, Detroit, Mich.) in the AHEPA University Hospital, Thessaloniki, Greece, revealed a high proportion of Enterococcus durans, particularly among isolates highly resistant to gentamicin and streptomycin. When 14 isolates were further tested by a conventional biochemical scheme and by PCR, all were reidentified as Enterococcus faecalis. Antibiotic resistance and pulsed-field gel electrophoresis patterns showed that unrelated strains were misidentified.
Insights
A semiautomated system misidentified Enterococcus durans as Enterococcus faecalis, particularly in gentamicin- and streptomycin-resistant strains. Further testing confirmed the correct species, highlighting potential diagnostic inaccuracies with automated systems for bacterial identification.
Area of Science:
- Clinical microbiology
- Bacterial identification
- Antimicrobial resistance
Background:
- Enterococci are significant nosocomial pathogens.
- Accurate identification of enterococci is crucial for effective treatment.
- Semiautomated systems are widely used for bacterial identification.
Purpose of the Study:
- To evaluate the accuracy of the semiautomated PASCO system for enterococcal identification.
- To investigate the species identification of gentamicin- and streptomycin-resistant enterococcal isolates.
- To compare the performance of the PASCO system with conventional methods and PCR.
Main Methods:
- Bacterial isolates were initially identified using the semiautomated PASCO system.
- Conventional biochemical testing was performed for further characterization.
- Polymerase chain reaction (PCR) was employed for species confirmation.
- Antibiotic resistance profiling and pulsed-field gel electrophoresis (PFGE) were conducted.
Main Results:
- The PASCO system initially identified a high proportion of isolates as Enterococcus durans.
- Subsequent conventional and PCR-based methods reidentified all 14 tested isolates as Enterococcus faecalis.
- Antibiotic resistance patterns and PFGE profiles indicated that the misidentified strains were unrelated.
Conclusions:
- The semiautomated PASCO system demonstrated limitations in accurately identifying certain enterococcal species, specifically E. durans.
- Misidentification occurred particularly in isolates exhibiting high-level resistance to gentamicin and streptomycin.
- Conventional and molecular methods are essential for confirming bacterial identification, especially in cases of antimicrobial resistance.