Evaluation of direct inoculation of the BD PHOENIX system from positive BACTEC blood cultures for both Gram-positive cocci and Gram-negative rods

Christina FM van der Donk,Catharina FM Linssen,Annelies Verbon,Judith Beuving,Petra FG Wolffs

doi:10.1186/1471-2180-11-156

Christina FM van der Donk, Catharina FM Linssen

Open Access

https://doi.org/10.1186/1471-2180-11-156

Copy DOI

Journal: BMC Microbiology	Publication Date: Jun 30, 2011
Citations: 52	License type: cc-by

Affiliation: Maastricht University, Erasmus MC

Abstract

BackgroundRapid identification (ID) and antibiotic susceptibility testing (AST) of the causative micro-organism of bloodstream infections result in earlier targeting of antibiotic therapy.In order to obtain results of ID and AST up to 24 hours earlier, we evaluated the accuracy of direct inoculation of the Phoenix system from positive blood cultures (BACTEC) by using Serum Separator Tubes to harvest bacteria from positive blood cultures. Results were compared to those of standard Phoenix procedure. Discrepancies between the two methods were resolved by using the API system, E-test or microbroth dilution.ResultsID with the direct method was correct for 95.2% of all tested Enterobacteriaceae (n = 42) and 71.4% of Pseudomonas aeruginosa strains (n = 7).AST with the direct method showed a categorical agreement for Gram-negative rods (GNR) of 99.0%, with 0.7% minor errors, 0.3% very major errors and no major errors. All antibiotics showed an agreement of >95%.The direct method for AST of Staphylococcus (n = 81) and Enterococcus (n = 3) species showed a categorical agreement of 95.4%, with a minor error rate of 1.1%, a major error rate of 3.1% and a very major error rate of 0.4%. All antibiotics showed an agreement of >90%, except for trimethoprim-sulfamethoxazole and erythromycin.ConclusionsInoculation of Phoenix panels directly from positive blood cultures can be used to report reliable results of AST of GNR a day earlier, as well as ID-results of Enterobacteriaceae. For Staphylococcus and Enterococcus species, results of AST can also be reported a day earlier for all antibiotics, except for erythromycin and trimethoprim-sulfamethoxazole.

Highlights

Rapid identification (ID) and antibiotic susceptibility testing (AST) of the causative micro-organism of bloodstream infections result in earlier targeting of antibiotic therapy
Mortality is high, ranging from 14 to 57% [5]. In this group of patients, rapid identification (ID) and antibiotic susceptibility testing (AST) of the causative microorganism are essential since they result in earlier targeting of antibiotic therapy [6,7,8,9]
The inoculum of Gram-positive cocci (GPC) in ID broth was on average 3.6 × CFU/ml, whereas that of Gram-negative rods (GNR) was 1.8 × CFU/ml, which was a significant difference

Summary

Introduction

Rapid identification (ID) and antibiotic susceptibility testing (AST) of the causative micro-organism of bloodstream infections result in earlier targeting of antibiotic therapy. Mortality is high, ranging from 14 to 57% [5] In this group of patients, rapid identification (ID) and antibiotic susceptibility testing (AST) of the causative microorganism are essential since they result in earlier targeting of antibiotic therapy [6,7,8,9]. The introduction of automated blood culture systems and automated systems for ID and AST have reduced the time to diagnosis in bloodstream infections For these systems, blood cultures have to be subcultured on agar before ID and AST can be performed, which can take up to 24 hours

Methods

Results

Discussion

Conclusion