Synergy Tests by E Test and Checkerboard Methods of Antimicrobial Combinations against Brucella melitensis

Abstract

Two different synergy testing methods, the checkerboard and the E test methods, were used to compare the in vitro efficacies of various antimicrobial combinations against 16 Brucella melitensis strains isolated from blood cultures. The rate of agreement of the E test and checkerboard methods was found to be 55%. The most concordant results were found for the streptomycin-doxycycline combination in 12 (75%) tests, in which four strains showed synergistic activity by E test and antagonistic activity by the checkerboard method and in which one strain showed antagonistic activity by both methods. Even though each of these methods uses different conditions and endpoints, the results of both methods frequently agreed.Brucellosis is still an important health problem in developing countries and leads to serious economic losses (15,19). The disease causes abortion and sterility in animals and septicemia that progresses to chronic localized infections in various organs of humans (4,16,19). Although brucellosis has been eradicated from animals in some developed countries, 500,000 new cases are reported yearly throughout the world, and it is still a widespread zoologic disease in Turkey (8,11).Because brucellae are localized intracellularly, infections with these bacteria should be treated with antibiotics that can penetrate the cell at high concentrations. The World Health Organization recommends the use of two antibiotics in combination and, in some cases, four antibiotics in combination for the treatment of brucellosis. Because of the lack of effectiveness of present therapies, relapses, and difficulties related to the antibiotics used, such as adverse effects, absorbance disturbances, and the limited ability of certain age groups to use certain antibiotics, researchers have been forced to discover new treatment regimens (2, 19).Antimicrobial susceptibility tests are not yet standardized for brucellae, and routine susceptibility tests cannot be performed in microbiology laboratories. However, the antimicrobial susceptibilities and even the in vitro synergistic effects of antibiotics in combination against these microorganisms, which have scant growth in culture, can easily be performed by E test. The aim of this study was to evaluate the rate of agreement of two in vitro tests for synergy, E test and the checkerboard method, with various combinations of antibiotics that penetrate the cell wall against Brucella melitensis isolates recovered from blood. MATERIALS AND METHODSSixteen strains of B. melitensis isolated from blood cultures at the Microbiology Laboratory of Gaziantep University from January through December 2003 were included in this study. Blood samples were collected from in-and outpatient clinics of the Medical Faculty Hospital, and they were cultured in vials of the BACTEC 9120 system (Becton Dickinson, Rutherford, N.J.) at 37°C for at least 7 days. The isolates were identified on the basis of colony morphology, staining, and slide agglutination with antiserum. Small, round, and convex colonies that grew on ...

Evaluation of the best method to assess antibiotic potentiation by phytochemicals against Staphylococcus aureus

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Enhanced bactericidal effect of enterocin A in combination with thyme essential oils against L. monocytogenes and E. coli O157:H7

“…Combinations of the concentrations below each MIC level that caused complete inhibition of microbial growth of L. monocytogenes were evaluated across serial dilutions of enterocin A and thyme EOs by checkerboard technique using a sterile 96-well microplates and BHI broth (Orhan et al 2005;NCCLS 2003). All aliquots were prepared using the same solvents (acetonitrile + BHI) as in the MIC assay and blank solutions containing the solvent at concentrations equivalent to those in the test solutions were also prepared.…”

Biguanides enhance antifungal activity against Candida glabrata

“…Fractional inhibitory concentration index (ƩFIC) for rapamycin and metformin combinations was determined as a measurement of drug interaction between the two compounds. The combination is considered synergistic when the ΣFIC is ≤ 0.5, non-synergistic when the ΣFIC is ≥ 0.5 and ≤ 4, and antagonistic when ΣFIC is ≥ 4 [28,29]. Rapamycin and metformin ΣFIC was 0.84 ± 0.09, suggesting non-synergistic interaction between the two compounds.…”

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