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Evaluation of the Etest and broth dilution methods for susceptibility testing of Brucella melitensis

Abstract number: R2412

Aliskan H., Can F., Demirbilek M., Colakoglu S., Yazici C., Arslan H.

Objectives: In vitro susceptibility tests are not standardised for Brucella species and they are not rountinely performed. The main objective of the present study was to evaluate the degree of agreement of two in vitro tests (E-test and the broth dilution method) with several antibiotics including tigecycline againist Brucella melitensis (B. melitensis).

Material and Methods: 16 B. melitensis isolates were collected between May 2003-October 2004 from blood cultures of adults patients with acute brucellosis at Baskent University Adana Practice and Research Center. Samples of blood were cultured using an automated culture system (BACTEC 9050, Becton Dickinson, Maryland, USA). The antimicrobial agents used in this study were: tigecycline (Wyeth Research, Pearl River, NY, USA), rifampin, trimethoprim-sulfametoxazole, and levofloxacin (Sigma-Aldrich, USA).

E-test method: Bacterial inoculum was prepared 0.5 McFarland turbidity standart by Mueller-Hinton broth (Oxoid). The bacterial suspension was spread on Mueller-Hinton agar (Oxoid) plates supplemented with %5 sheep's blood agar and E-test strips (AB Biodisk, Solna, Sweden) were applied.

Broth dilution method:The MIC values of antibiotics were determined by the broth dilution technique, according to Clinical Laboratory Standarts Institue with brucella broth (Merck, Germany), using an inoculum of 104 colony-forming units (CFU). Brucella broth medium was used within 12 hours after preperation. Tigecycline solutions prepared fresh on the day of testing. The plates incubated at 350C in ambient air, and the results were read after 48 h.

Results: In our study, the rate of agreement obtained with levofloxacin, rifampin, co-trimoxazole, and tigecycline between the E-test and broth dilution methods were 25%, 18.75% 0%, and 18.75%, respectively. Statistically significant difference was found between the methods for MIC values of levofloxacin, rifampin, co-trimoxazole, and tigecycline (p < 0.01, p < 0.001, p < 0.001, p < 0.05) (Table)

Table: Median and standard deviation values for MICs of antibiotics determined by E-test and broth dilution method

Conclusion: The MIC values determined with E-test method were lower than the values determined with the broth dilution method. This situation should be considered when evaluating the results of E-test method for B. melitensis.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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