Fractional inhibitory concentration

The interaction between two antimicrobial agents can be expressed by the fractional inhibitory concentration (FIC) index ... 

Two methods are used to determine the expected effects of combination antibiotic therapy. For the most part, both methods are not used commonly in the clinical microbiology laboratory owing to the substantial labor involved with these tests and the lack of strong correlation with clinical outcome in the majority of infections. The first method is the microtiter fractional inhibitory concentration (FlC, or checkerboard method). The FlC is performed in a similar manner to the microtiter broth MIC except that two antibiotics are tested in the same microtiter plate. Twofold serial dilutions of one antibiotic are made in one direction on the plate (e.g., from right to left), whereas dilutions of the second antibiotic are made from the other direction on the same plate (e.g., from top to bottom). This method produces all possible combinations of twofold concentrations for the two drugs being tested. An inoculum of test bacteria is added to all wells, and the results are read in a similar manner as the MIC test. The FlC is expressed mathematically by calculation of the FlC index. The FlC index is calculated as... 

The optimal fractional inhibitory concentration indices (FlCl) for a number of combinations of individual EO compounds with regard to different microorganisms are shown in Table 40.7. EG and Lin combination displayed a synergistic activity (FlCl = 0.375) for S. aureus. Carv and EG, Carv and Lin, Carv and Pentfuran exhibited a useful addictive effect with a FlCl of 0.75 against E. coli, B. subtilis, and S. cerevisiae, respectively. However, no indifferent or antagonistic effects were observed for any of these combinations (Liang et al., 2012). 

The antimicrobial activity of cinnamon bark, lavender, marjoram, tea tree, peppermint EOs combined with ampicillin, piperacillin, cefazolin, cefuroxime, carbenicillin, ceftazidime, and merope-nem was investigated against p-lactamase-producing E. coll Fractional inhibitory concentration (FIC) values were the results of the trial. It was found that peppermint EO improved the activity of piperacillin against multidrug-resistant E. coli strains (FIC 0.31) compared with piperacillin alone. Also the used dose of meropenem can be reduced when combined with peppermint oil (FIC 0.26) (Xi Yap et ah, 2013). 

In order to identify novel lead compounds with antiviral effects, methanol and aqueous extracts of some medicinal plants in the Zingiberaceae family were screened for inhibition of proteases from human immunodeficiency virus type 1 (HIV-1), hepatitis C virus (HCV) and human cytomegalovirus (HCMV). By bioassay-guided fractionation, eight fiavones were isolated from the black rhizomes of Kaempferia parviflora Wall, ex Baker. The most effective inhibitors, 5-hydroxy-7-methoxyfiavone and 5,7-dimethoxyflavone, inhibited HIV-1 protease, with an inhibitory concentration 50 (IC50) values of 19 0,M. Moreover, 5-hydroxy-3,7-dimethoxyflavone inhibited HCV protease and HCMV protease, with IC50 values of 190 and 250 pM, respectively. 

Crude extracts prepared from different parts of Turkish T. baccata have also been evaluated for their antimycobacterial activity. A CHCI3 fraction of the heartwood and ethanol extract of the leaves exhibited a minimum inhibitory concentration value (MIC) against Mycobacterium tuberculosis H37Ra strain of 200 pg/mL [102]. 

A new method of bioactivity-directed fractionation, based on multidrug resistant pump (MDR) inhibition in Staphylococcus aureus, was reported for medicinal plants. This work resulted in the isolation, from berberine-containing Berberis species, two compounds that are themselves devoid of antibacterial activity, but that form potent synergistic couples with a sub-inhibitory concentration of berberine. The bacterial MDR pump inhibitors were identified as the flavonolignan 2 and the porphyrin 3 [98]. The isoflavones not only enhanced the antibacterial activity of the natural product, berberine. Fig. 4, but also the activity of synthetic... 

Erythrocytes do not contain mitochondria and any anion-sensitive ATPase activity in a particulate fraction must therefore be attributed to the plasma membrane. An Mg-ATPase, which could be stimulated by bicarbonate was found in rabbit erythrocyte membranes [31-33] and should thus be plasma-membrane bound. The properties of the enzyme in rabbit erythrocyte membranes are, however, completely different from those of the anion-sensitive ATPase from other tissues. Whereas sulfite is a good stimulant for the Mg-ATPase in mitochondrial and microsomal fractions of various tissues, it only slightly stimulates [32] or even inhibits [33] the erythrocyte enzyme. Other oxy-anions inhibit the ATPase of erythrocyte membranes [32]. The substrate dependence of the enzyme is greatly different from that of the enzyme from other tissues [32,33]. The half maximal inhibitory concentration of... 

Caramel color interacts with other food components. As an example, a concentration higher than 700 ppm caramel in cola increased the rate of hydrolysis of the aspartame, forming alpha-L-aspartyl-L-phenylalanine. Caramelization products inhibited enzymic browning by 85.8 and 72.2% when heated at pH 4 and 6, respectively, for 90 min. The highest inhibitory activity was found for the fraction with molecular weight of 1000 to 3000. Caramel is often used for adulteration of juices and other foods like honey or coffee. It can be determined by quantification of marker molecules such as 5-HMF, 4-Mel, and DFAs. ... 

For initiated oxidation, the inhibitory criterion could be defined as the ratio v0/v or (v0/ v — v/v0), where v0 and v are the rates of initiated oxidation in the absence and presence of the fixed concentration of an inhibitor, respectively. Another criterion could be defined as the ratio of the inhibition coefficient of the combined action of a few antioxidants / to the sum of the inhibition coefficients of individual antioxidants when the conditions of oxidation are fixed (fx = IfiXi where f, and x, are the inhibition coefficient and molar fraction of z th antioxidant terminating the chain). It should, however, be noted that synergism during initiated oxidation seldom takes place and is typical of autoxidation, where the main source of radicals is formed hydroperoxide. It is virtually impossible to measure the initial rate in the presence of inhibitors in such experiments. Hence, inhibitory effects of individual inhibitors and their mixtures are usually evaluated from the duration of retardation (induction period), which equals the span of time elapsed from the onset of experiment to the moment of consumption of a certain amount of oxygen or attainment of a certain, well-measurable rate of oxidation. Then three aforementioned cases of autoxidation response to inhibitors can be described by the following inequalities (r is the induction period of a mixture of antioxidants). 

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