Evaluation of a new rapid method for microbial growth analysis and antimicrobial susceptibility test in human biological fluids

Abstract number: 1734_116

Tessari A., Parisi S.G., Cavallaro A.

Objectives: The Uro-Quick system is an automated rapid method for bacteriuria screening which uses laser nephelometry to detect bacterial growth. We evaluated the Uro4 HB&L system for a rapid micro organisms detection and antimicrobial susceptibility test (AST) directly performed on human biological fluids.

Methods: 233 human biological samples counting respiratory (36%), articular, peritoneal and other drainages (64%), were analysed for culture with Uro-4 system. Gram stain microscopy and plate subculture analysis was performed on every sample analysed with Uro-4 after 6 hours incubation. Sixty-nine samples (57 mono and 12 polimicrobial) detected positive by Uro-4 were then processed for a direct AST (3 hours incubation). Four different antimicrobial panels were designed for Enterobatteriaceae, Streptococcus, Staphylococcus and non fermenting Gram negatives. Culture and AST performed on Uro-4 were compared with traditional culture methods on agar plates and with VITEK 2 system for AST.

Results: 136 samples were concordant positive. Microbial growth analysis performed on Uro-4 showed 94.4% sensitivity and 93.3% specificity compared with the traditional culture method. Uro-4 test coupled with Gram stain microscopy after incubation gave 100% sensitivity. Positive counted monomicrobial samples (76%), including 69% Gram positive bacteria, 24% Gram negative and 7% yeast, and polimicrobial samples (24%). Direct AST performed on 26 monomicrobial Gram positive cultures resulted in 95% agreement with the reference method (Streptococcus/Enterococcus panel 100%, Staphylococcus 92.4%) meanwhile AST conducted on 31 monomicrobial Gram negative samples revealed a 96% agreement (Enterobacteriaceae 94.9%, non fermenting 97.3%). No very major error (sensible vs. resistant) was detected. Polimicrobial samples gave discordant results by reason of the variable composition of the mixture and the small number of analysis.

Conclusion: Uro-4 is able to perform bacterial growth analysis and a subsequent AST within 7–9 hours, with a great saving of time respect to the traditional cultural and AST methods. The system revealed optimal performance on microbial agents detection when coupled with Gram stain analysis. The Uro-4 AST showed an high level agreement with the reference method when the test was conducted on mono microbial samples. Further investigations are pending for polimicrobial samples.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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