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: 3.03). 08/2011; 38(2):130-4. DOI: 10.1016/j.ijantimicag.2011.04.011
Source: PubMed

ABSTRACT 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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    ABSTRACT: Objective: To evaluate the influence of a rapid diagnostic test (RDT) in antibiotic therapeutic decisions in non-paediatric patients with Gram-negative bacteraemia (GNB). Patients and methods: A RDT consisting of a direct antibiogram was used on blood isolates of GNB. GNB were also identified and sensitivity tests were performed according to standard criteria. Information on empirical treatment was registered (T1), as well as the antibiotic administered once the results of the RDT were available (T2). Finally, we noted the ideal antibiotic that the infectious diseases specialist (IDS) would have prescribed (T3). The decision regarding T2 was always taken by the patient's physician or the physician on duty. Results: A RDT was performed for 248 patients. The most frequently isolated bacterium was Escherichia coli (13% producing extended-spectrum beta-lactamase). T1 was considered appropriate in 74% and appropriate but optimizable in 43%. T2 was considered appropriate in 95%, appropriate but optimizable in 36%, and inappropriate in 5%. The cost of the optimizable treatment (T2) was € 2210, while the cost of the ideal treatment would have been € 416; the saving in antibiotic cost of 1 day of treatment would have been € 1694. Conclusions: Treatment prescribed by a non-IDS after a RDT was inappropriate in 5% and optimizable in 36%. It is our recommendation that information provided by a RDT should be interpreted by an IDS to make the information more beneficial both economically and 'ecologically'.
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