Agar dilution method

The antibiotic concentration of the first plate showing 99% inhibition is taken as 

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A short report demonstrated the absence of a reliable correlation between kiUing kinetics and normal laboratory tests for pristinamycin susceptibility testing of some pneumococci (42). Eight selected multiresistant clinical isolates and two reference pristinamycin-resistant Streptococcus pneumoniae strains were studied. Disk diffusion susceptibility and MICs were determined by the agar dilution method, and all clinical isolates appeared to be susceptible to pristinamycin, whereas the two reference strains were not. In contrast, time-kill experiments identified a limited bactericidal effect of pristinamycin in three clinical and both reference strains. These three strains had been classified as pristinamycin-resistant by the Vitek-II system, which uses a kinetic turbidimetric measurement of bacterial growth. Epidemiological information is hindered by the use of highly selected strains for the study. 

A1 Dabbas et al. [163] reported the antibacterial activity of the ethyl acetate extract of the whole aerial part of Varthemia iphinoides L. The bioassay-guided fractionation led to the isolation and identification of an antibacterial eudesmane sesquiterpene, selina-4,ll(13)-dien-3-on-12 oic acid. Fig. (10). This compound exhibited potent antimicrobial activity against 6 bacterial species Staphylococcus aureus, Bacillus subtilis. Micrococcus luteus, Escherichia coli. Bacillus cereus and Salmonella enter Hides ). The MIC values of this sesquiterpene, which was determined by the agar dilution method, ranged between 250 and 500 ig/ml. 

Table II. Minimum Inhibitory Concentrations of Pentachlorophenyl Acrylate, (1), and its Homopolymer Toward Micro-ogranlsms Using an Agar Dilution Method. (- means no growth + means growth).

The question of whether or not a polymer-anchored biocide can be active against microorganism growth was first tested by comparing the minimum inhibitory concentrations (MIC) of pentachlorophenol, its acrylate, 8, and the homopolymer of pentachlorophenyl acrylate 8. An agar dilution method was used. To a sterilized agar, a solution of the compound to be tested was added in the appropriate amount to make final concentrations of 1000, 500, 250, 100, 50, and 10 ppm. Following inoculation, the... 

Toward Microorganisms Using An Agar Dilution Method... 

Wexler HM, Molitoris E, Murray PR, et al. Comparison of spiral gradient endpoint and agar dilution methods for suscephbihty testing of anaerobic bacteria A multilaboratory collaborahve evaluation. J Chn Microbiol 1996 34 170-174. 

EM s chemical structure consists of a 14-membered macrocyclic lactone ring (erythronolide) connected to a deoxyamino sugar (desosamine) and a deoxy sugar (cladinose) as shown in Fig. 5. We synthesized about 250 EM derivatives and examined their GMS and antibacterial activities [19, 20]. GMS activity was tested by intravenous injection of the test compounds to fasted conscious dogs with permanently implanted force transducers in the stomach, and antibacterial activity was estimated as minimum inhibitory concentration (MIC) by agar dilution method. The EM derivatives shown in Fig. 5 exhibited higher GMS activities with less antibacterial activities compared with those of EM (Table I). 

Table 4. Antimicrobial spectrum of bromomonilicin (118), by agar dilution method on glucose nutrient agar.

The strain of Actinamadura spiralis isolated from a soil sample produced new antibiotics, pyralomicins (169-175). Pyralomicins inhibited the growth of Micrococcus luteus and Escherichia coli at the concentration of 0.2-25 (xg/ml by agar dilution method. Pyralomicin la (169) and pyralomicin 2a (173) did not show any acute toxicity in mice at 100 mg/kg ip [205]. 

MICs were determined by the agar dilution method with PPLO agar supplemented with 0.2% DMCD. 

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