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Identification and susceptibility testing of Enterococcus casseliflavus and Enterococcus gallinarum by Phoenix 100 system (Becton Dickinson)

Abstract number: P855

Chatzigeorgiou K.-S., Tarpatzi A., Siafakas N., Pantelaki M., Charalampaki N., Zerva L.

Objectives: Although E. casseliflavus/flavescens and E. gallinarum are of low pathogenic potential, they may be implicated in invasive infections. The aim of the present study was to assess their correct recognition by Phoenix and to investigate their antimicrobial susceptibility profile using the same system.

Methods: A total of 82 consecutive non-E. faecalis and non-E. faecium enterococcal isolates were collected during two hospital surveillance studies for VRE faecal carriage; all were identified as E. casseliflavus/gallinarum by Phoenix (without species discrimination). Speciation was confirmed by a multiplex PCR assay (specific for ddl-E. faecium, ddl-E. faecalis, vanA, vanB, vanC1/2, vanD, vanE and vanG genes). Pigment production was also recorded. Susceptibilities towards 8 antimicrobials (penicillin, ampicillin, erythromycin, gentamicin, streptomycin, linezolid, teicoplanin and vancomycin) were determined by Phoenix and E-tests (AB, Biodisk) against linezolid and teicoplanin were performed for selected isolates.

Results: According to PCR all 82 isolates harboured the vanC ligase gene and by pigment production 66 were identified as E. gallinarum and 16 as E. casseliflavus/flavescens. All but one isolates tested susceptible to both penicillin and ampicillin. Eleven strains (13.4%) were found to be intermediately resistant and 5 (6.1%) resistant to erythromycin. Five isolates (6.1%) exhibited resistance against streptomycin. For 3 E. gallinarum isolates Phoenix produced a teicoplanin MIC >16 mg/ml, not confirmed by the E-test and PCR (3 major errors, 3.6%). Vancomycin MICs by Phoenix ranged from 4 to >16 mg/ml. Regarding linezolid, Phoenix characterised 6 strains as resistant (all susceptible by E-test; at least 6 major errors) and 21 strains as intermediately resistant (only 4 intermediately resistant by E-test; at least 17 minor errors). On repeat testing Phoenix classified again 8 susceptible isolates as intermediately resistant and 1 intermediately resistant strain as susceptible (at least 9 minor errors).

Conclusion:E. gallinarum and E. casseliflavus/flavescens are accurately identified as a group by Phoenix and are rather multi-susceptible species with the former being more frequently recovered from faecal samples of hospitalised patients. Rare major errors with teicoplanin and major and minor errors with linezolid, which may call into question correct speciation, stress the need for confirmation with supplementary testing.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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