Comparison of direct antimicrobial susceptibility testing methods for rapid analysis of bronchial secretion samples in ventilator-associated pneumonia

4th Department of Internal Medicine, Infectious Diseases Laboratory, University of Athens Medical School, Athens, Greece.
International journal of antimicrobial agents (Impact Factor: 4.3). 08/2011; 38(2):130-4. DOI: 10.1016/j.ijantimicag.2011.04.011
Source: PubMed


Two hundred and fifty tracheal aspirates were subjected to direct antimicrobial susceptibility testing by disk diffusion, Etest and inoculation on antibiotic-enriched MacConkey agar plates. Results were compared with those obtained using an automated system on microorganisms recovered from standard quantitative culture. A total of 255 microorganisms were isolated from 194 positive samples by the standard quantitative procedure. A total of 85.1%, 82.5% and 72.5% agreement between direct disk diffusion, Etest and antibiotic-enriched MacConkey agar plates, respectively, and the standard procedure was observed in 64 microorganisms obtained from monomicrobial cultures that corresponded to 240 individual microorganism-antimicrobial agent combinations. Three (1.3%) and four (1.7%) very major errors for direct disk diffusion and Etest methods were observed, respectively. The antibiotic-enriched MacConkey agar plate method compared with the standard procedure demonstrated an unacceptable rate of very major (6.7%) and major errors (14.2%). Clinical evaluation of direct susceptibility tests based on the speculative impact on clinical practice by guiding patient's early treatment, if all positive cultures corresponded to infection, was correct in 79.9% for the direct disk diffusion test, 77.8% for the direct Etest method and 68.0% for antibiotic-enriched MacConkey agar plates. Direct diffusion tests (Etest or disk diffusion) applied on respiratory samples are rapid techniques that provide results comparable with standard antimicrobial susceptibility testing in <24 h.

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Available from: Irene Galani, Nov 25, 2015
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    • "However, the number of antibiotics that can be tested using E-tests is limited, and the method is more expensive than disc diffusion. In one study, in which the disc diffusion method was employed to perform DAST, only three clinically relevant antibiotics (piperacillin/tazobactam, meropenem and ciprofloxacin) were tested [11]. In our study, we combined the main advantage of disc diffusion (the fact that a large number of antimicrobial agents can be tested simultaneously; we tested 16 different antibiotics) with a standardized inoculum based on direct smear examination. "
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    ABSTRACT: In line with a rapid de-escalation of empirical antimicrobial therapy, this study assessed the validity of an E-test-based direct specimen testing method on bronchoalveolar lavage (BAL) samples from ventilator-associated pneumonia (VAP) patients. E-test strips were directly applied onto Mueller-Hinton agar plates seeded with BAL samples and read after 24 h of incubation. In parallel, the BAL samples were analyzed by the routine diagnostic laboratory. The microbroth dilution approach was used as a control method. In a cohort of 20 patients, 135 microorganism-antibiotic combinations were studied. Total agreement between the 2 methods was achieved for 88.9% combinations, with 1.5% very major errors (isolates susceptible by E-test and reported resistant by the diagnostic laboratory) and 9.6% major errors (isolates resistant by E-test and reported susceptible by the diagnostic laboratory). These results indicate that applying E-test directly on BAL samples is a promising method for obtaining susceptibility data after 24 h in critical patients with VAP.
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