Inhibition zone

As mentioned earlier, a-D-carba-galactopyranose (1) has been found in a fermentation broth of Streptomyces sp. MA-4145, as an antibiotic. The potency of the antibiotic was rather low. A concentration of—125 fig/mh is required in order to produce a standard inhibition zone of 25-mm diameter against Klebsiella pneumoniae MB-1264, using 13-mm assay discs in a disc-plate assay. A sample of the synthetic a-DL-carba-galactopyranose (17) was... 

Fungicidal activity was determined by the disc method and zones of inhibition were recorded by measuring the diameter (mm) of the inhibition zone. Yeast cultures (S. cerevisiae) showed growth inhibition (clear area surrounding disc) by sediment extracts from all stations when compared to control discs. HPLC analysis of sediment extracts showed more than 20 components in the migration profile of each station. Of these components, a fraction demonstrated to possess cytolytic activity in the crude extract (Ve = 24 ml) was present in all stations when compared to the migration profile of the active fraction (Figure 2). 

Another growth inhibition test of P. cereus is used to determine the toxicity of chemicals and sediments [41]. This test is based on the measurement of an inhibition zone. 

An agar plate method is presented by Liu et al [47]. On an agar plate covered by a bacterial suspension, an inhibition zone is formed and measured around the spot where the toxic sample has been placed. The duration of the test depends on the growth of the bacterial species (from 3 to 24 hours). This assay is not available in a commercial kit but it is simple to perform as... 

Inhibition zone Inhibition zone MIC Inhibition zone... 

An antibiotic inhibition zone often appears around Trichoderma spp. interacting with other fungi. The genus contains many species which produce secondary metabolites. Claydon et al. (23) have identified an antibiotic from T. harzianum as a volatile, 6-n-pentyl-2H-pyran-2-one this was recently shown to be an active antibiotic from T. koningii (24). The volatile appeared to be the factor responsible for the coconut smell of some biocontrol-effective strains of T. harzianum (25). However, in a Petri-plate assay, it can be difficult to be certain that antibiosis is involved. As well as competitive growth, lytic enzymes could also contribute to the action and Trichoderma has been shown to produce / -l,3-glucanase and chitinase (26-29). 

Diameter of inhibition zone (8 mm paper disk was used), +=less than 11 mm, ++=between 11 and 18 mm, +++=more than 18 mm. Diameter of inhibition zone for kanamicin (10 ng/disk) is 22 mm. 

Difference in diameter of inhibition zone between Bacillus sublilis M45 (rec -) and HI 7 (rec +), diameter of inhibition zone on M45 minus that on H17 —diameters are same, =less than 2 mm, +=between 2 and 5 mm, ++=more than 5 mm. A positive control is mitomycin C (0.75 (ig/disk) the difference of inhibition zone is 6 mm. Inhibition zones of a negative control (kanamicin) were same for the both strains cCCfo of doxorubicin was 2 ng/mL. 

Additional analyses will normally be required in order to identify and quantify individual residues within a group of antimicrobials to determine whether a positive result exceeds the MRL level. For suspect penicillin residues, identification can be made by repeating the microbiological assay in the presence of -lactamase. If the inhibition zone disappears by this addition, penicillin residues are present in the sample. If not, no conclusion can be drawn because several new-generation -lactams are less sensitive to inactivation by -lactamase. 

Residues of TCs were quantified via the MCAC-HPLC method (26) in pork and chicken muscle tissue that had been previously screened with both a microbiological inhibition test using B. subtilis and an ELISA method. The correlation between the mean area of the inhibition zones and the DXC levels found in 28 samples by HPLC was 0.82 the correlation between the ELISA results and the DXC levels in the same samples was 0.73. The results indicated that an inhibition test was well suited to screen the mentioned samples for TCs residues. The authors found the more expensive ELISA screening test unnecessary, because only a minority of analyzed samples did not contain TCs. Confirmation with HPLC method was necessary because of the presence of some false-positive results. Moreover, the positive results from LC-fluorescence assay were confirmed using LC-MS-MS assay with electrospray ionization working in positive-ion mode (31). 

A new analytical method was based on the treatment of SAs with p-aminobenzoic acid, forming derivatives suitable for UV detection. The SAs were extracted from the kidney and liver samples, with recoveries ranging from 55% to 100%. The reaction yield was tested by microbial inhibition tests sensitive to low concentrations of SAs. After the incubation with / -aminobenzoic acid, none of eight SAs produced an inhibition zone on the assay medium, which showed 100% conversion to the appropriate derivatives (162). 

Besides physicochemical methods, the use of microbiological growth-inhibition assays to test meat and milk for the presence of antibiotics residues is popular over a long period of time. These tests use antibiotic-sensitive bacterial reporter strains, such as Bacillus subtilis and Bacillus stearothermophilus var. calidolactis. These bacteria are inoculated under optimal conditions with and without sample. After culturing, results are read from visible inhibition zones or from the color change of the bacterial suspension in agar gels [6]. 

To study the function of the chimeric cefE enzymes generated by recombination in S. lividans, the cell-free ring expansion abilities of several recombinants were determined. Three white strains, W21 (6.3-kb plasmid), W25 (8-kb) and W76 (8-kb) as well as the controls Bll and B18 (melanin-positive pJA680) showed activity, producing inhibition zones in the agar diffusion bioassay. Although S. 

To ascertain that the inhibition zones were due to formation of DAOG, the samples were analyzed by HPLC. After 2 hr of incubation, a peak corresponding to DAOG was clearly present on the chromatograms. 

The controlled release of biocides is the oldest approach for keeping surfaces free of biofllms. The released biocides usually form an outer inhibition zone and an inner kill zone that destroys microbes in the proximity of the surface. Because dead microbial cells cannot actively adhere, they usually do not cover the releasing material at high densities. Nevertheless, all of these systems eventually exhaust and become ineffective. Furthermore, in all cases a considerable reservoir in the form of a matrix must be involved. 

Newly synthesized compounds 22, 23, 25c-e, 26d and 29e were screened in vitro for their antimicrobial activities against Gram positive bacteria Staphylococcus aureus (NCTC-7447), Bacillus cereus (ATCC-14579) and Gram negative bacteria Serratia marcesens (IMRU-70) and Proteus merabitis (NTCC-289) using the paper disk diffusion method for the antibiotic sensitivity technique [60]. The tested compounds were dissolved in N,N-dimclhylformamidc (DMF) to obtain a 1 mg/mL solution. The inhibition zones of microbial growth produced by different compounds were measured in millimeters at the end of an incubation period of 48 h at 28 °C. DMF alone showed no inhibition zone. 

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