Minimal inhibitory concentration test

FIGURE 66-3. Macrotube minimal inhibitory concentration (MIC) determination. The growth control (C), 0.5 mg/dL, and 1 mg/dL tubes are visibly turgid, indicating bacterial growth. The MIC is read as the first clear test tube (2 mg/dL). (Reprinted from Rybak MJ, Aeschlimann JR. Laboratory tests to direct antimicrobial pharmacotherapy. In In DiPiro JT, Talbert RL, Yee GC, et al, (eds.) Pharmacotherapy A Pathophysiologic Approach. 6th ed. New York McGraw-Hill 2005 1897.)... 

An effective approach of antimicrobial therapy of an infection is based on the isolation and identification of the infected organism and determining its sensitivity to antimicrobial drngs. In vitro tests, snch as diffnsion in agar and determining the minimally inhibitory concentration in a liqnid medinm are the most widely used tests. 

The 7-azabenzisoselenazol-3(27/)-ones (169) (Fig. 12), substituted at the 2-position with phenyl or alkyl groups, and the methiodides (170) were found in the antiviral assay to be strong inhibitors of cytopathic activity of herpes simplex type 1 virus (HSV-1) and encephalomyocarditis virus (EMCV), more potent than ebselen. The minimal inhibitory concentration (MIC) values were in the range 0.4-6.0 pg mL 1, substantially lower than those when toxicity was observed. The vesicular stomatis virus (VSV) remained resistant toward tested compounds, except moderately active methiodide (171) [51, 271],... 

While this approach has limitations related to the peptidic nature of the linker such as stability to harsh reaction conditions and requirement of specific functional groups to be coupled with the linker arms, its application to particular libraries and chemistries may be useful. Its biological utility was assessed in a bead-based antimicrobial assay on bacterial cells [54], which produced good correlations between the MIC (minimal inhibitory concentration) values for the compounds released in situ in the culture medium from the beads or tested as standard solutions. 

The concentration of choice for mode of action studies is the lowest drug concentration which inhibits growth entirely. This can either be estimated by extrapolation of the probit-transformed log dosage response correlation or by determination of the MIC, ie. minimal inhibitory concentration, by the method of serial twofold dilution of drug-containing medium in test tubes, inoculation of these media and visual observation of growth after incubation overnight. 

In a common type of susceptibility testing, serial dilutions of the antibacterial drug are inoculated with the bacteria to determine a minimal inhibitory concentration (MIC), which is the lowest concentration of the drug that... 

FIGURE 103-3. Macrotube minimal inhibitory concentration (MIC) determination. The growth control (C), 0.5 mg/dL, and 1 mg/dL tubes are visibly turbid, indicating bacterial growth. The MIC is read as the first clear test tube (2 mg/dL). 

FIGURE 103-6. Photograph of E-strip susceptibility test The minimal inhibitory concentration (MiC) is determined from the point where the zone of inhibition intersects with the numerical scale. (Photograph courtesy of the Anti-Infective Research Laboratory, Wayne State University, Detroit, Michigan.)... 

FIGURE 103-7. Killing curve depicting the effect of concentration on antibiotic bactericidal activity. CPU = colony-forming units MIC = minimal Inhibitory concentration. 0.25-64 times the MIC the organism tested was P. aeruginosa ATCC 27853. (From ref 51.)... 

Minimal inhibitory concentration (MIC) test. In this test, various concentrations of test product in a growth medium are inoculated with the test strain. After incubation, the lowest concentration that does not exhibit bacterial growth gives the MIC level. 

A sensitive and simple chemiluminescent (CL) method for measuring antioxidant activity was developed. The determination of TEAC (Trolox equivalent antioxidant capacity) is based on the inhibition of CL intensity of luminol by an antioxidant. Antimicrobial activity was tested as a minimal inhibitory concentration (MIC) by broth microdilution method on gram-positive Enterococcus faecalis. Staphylococcus aureus) and gram-negative Pseudomonas aeruginosa, Escherichia coli) bacterial strains. 

Minimal inhibitory concentrations (MICs) of heavy metals values registered in solid culture are represented in Table 1. The tests obtained in liquid medium were essentially the same. The results obtained indicate that these strains are potent resistant to heavy metals. Indeed, each strain shows a resistance to different compounds tested with a great MICs compared to those reported by several authors (Devincent, 1990 Blaghen et al., 1993 Spangler, 1983 Filali, 2000). 

TESTING FOR MICROBIAL SENSITIVITY TO ANTIMICROBIAL AGENTS Bacterial strains, even from the same species, may vary widely in sensitivity to antibiotics. Information about the antibiotic sensitivity of the infecting microorganism is important for appropriate drug selection. Various methods are used to assess susceptibility, including disk-diffusion, dilution test, and automated broth dilution. The results are either reported on a semi-quantitative scale i.e., resistant, intermediate, or susceptible) or in terms of the minimal inhibitory concentration (MIC). 

Minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) tests are used often to determine the activity of the drug on certain species of bacteria. MIC is defined as the lowest concentration of antimicrobial or drug that will inhibit the visible growth of bacteria after overnight incubation (Levison, 2004), while MBC is the lowest concentration of antibacterial agent required to kill a particular bacterium (Wiegand et al., 2008). 

The test to identify the minimal inhibitory concentration of E. coli was conducted using the strain E. coli IFA-No. 00-058,00. 

Table 1. Minimal inhibitory concentration MIC of S. typhimurium in different test substances...

Minimal inhibitory concentrations (MIC, mg/ml) were determined by a broth microdilution method adapted from the tentative reference method (document MJ7-T) recommended hy the Committee on Antifungal Susceptibility Testing (36). Antibiotic medium 3 was used rather than RPMI 1640 medium. The MIC is defined as the lowest concentration of compound chat completely snhihited growth when tested with LY303366, cilofungin, or amphotericin B. 

Table 3 Minimal Inhibitory Concentrations of LY303366 and Amphotericin B that Inhibited 50% (MIC ) and 90% (MlC g) of 107 Clinical Isolates of C. albic

The possible antioxidative effect should be mentioned. Laciar et al. [136] tested the EO of Artemisia echegarayi for it antioxidant activity. It inhibited, with one exception, the growth of Gram-positive and -negative bacteria. It had the lowest minimal inhibitory concentration against Listeria monocytogenes and Bacillus cereus. Thujone and camphor are believed to be responsible for the antibacterial activity. 

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