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Direct identification and susceptibility testing of Gram-positive cocci from positive Bactec blood cultures with BD Phoenix Automated Microbiology System

Abstract number: p442

Huang  T.-D., Laurent  C., Gigi  J., Simon  A.

Aim of the study: 

Rapid identification and antibacterial susceptibility testing of micro-organisms isolated in blood cultures (BC) can be valuable for clinical management of sepsis. In the present study, we evaluated the performance of a scheme based on direct identification and susceptibility testing of gram-positive cocci by direct inoculation of specially treated fluid collected from positive Bactec 9240 culture bottles into BD Phoenix Automated Microbiology System (PHX system; BD). Results were compared to those obtained by usual standard procedures.

Materials and methods: 

100 positive monomicrobic blood cultures showing gram-positive cocci (Streptococcus spp. excluded) collected between March 2005 and August 2005 were assessed in the study. Shortly, a Serum Separator Tube (Vacutainer SST-II; BD) filled with fluid aspirated from a positive BC bottle was centrifuged in a swinging bucket rotor. After discarding the supernatant, the bacterial layer was resuspended and then inoculated dropwise into a PHX system ID broth in order to obtain a suspension matching a McFarland 0.5 standard. The remaining of the panels setup and loading was performed according to the manufacturer's instructions.

Results: 

By comparison with the identification obtained by standard procedure, direct method by Phoenix system correctly identified 27/36 (75%) Staphylococcusaureus, 12/20 (60%) Staphylococcus epidermidis, 18/30 (60%) coagulase-negative Staphylococcus other than S. epidermidis and 9/14 (65%) Enterococcus spp. Among the 1378 antibiotic-isolate combinations of antimicrobial susceptibility tested, 97.7% showed category agreement. The number of very major, major and minor error was 4 (0.3% of false susceptibility), 4 (0.3% of false resistance) and 21 (1.5% of all antibiotic-organism combinations) respectively.

Conclusion: 

For gram-positive cocci, the rapid direct method combining BD Phoenix System and Bactec cultures does not provide acceptable bacterial identification, but the susceptibility results obtained more rapidly are accurate for routine use and can be valuable in the clinical management of sepsis.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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