Determination of anti-Aspergillus activity of antifungal agents based on the dynamic growth rate of a single hypha

In vitro phytochemical analysis and antibacterial and antifungal efficacy assessment of ethanolic and aqueous extracts of Rumex nervosus leaves against selected bacteria and fungi

Background and Aim

Scientists are interested in identifying natural antibiotic substitutes that are effective against drug-resistant pathogenic microbes and spoilage fungi to counter pathogens and reduce the major public health problem of antibiotic residues in animal products. This study aimed to evaluate the antimicrobial activity of Rumex nervosus leaves (RNLs) as a medicinal herb against four bacterial and two fungal strains using absolute ethanol, 50% ethanol, and aqueous extracts.

Materials and Methods

The antimicrobial activities of various RNL extracts against selected microbes were evaluated using the disk diffusion antibiotic susceptibility test, minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), minimum fungicidal concentrations, and the poisoned food technique.

Results

The absolute ethanol RNL extract showed the best bacteriostatic/bactericidal activity against Salmonella Typhimurium, Escherichia coli, and Staphylococcus aureus (MIC/MBC: 0.20/0.40, 0.20/0.40, and 0.32/0.65 mg/mL, respectively). The diameter of the zone of inhibition was larger (p < 0.05) for the 100% ethanol RNL extract (8.17 mm) against Salmonella Typhimurium, the 50% ethanol-RNL extract (11.5 mm) against E. coli, and the aqueous RNL extract (14.0 mm) against S. aureus than for any other bacterial isolate. The aqueous RNL extract strongly (p < 0.0001) inhibited the mycelial growth of Aspergillus fumigatus (100%) and Aspergillus niger (81.4%) compared with the control.

Conclusion

The results of this study suggest that RNL is a promising new natural antimicrobial agent for food preservation. To date, most research on the antimicrobial properties of natural herbs has been conducted in vitro, with few exceptions in vivo and intervention-based research.

Evaluation of the inhibitory effect of amphotericin B on the apical growth ofF. solaniusing the BioCell-Tracer®System

The BioCell-Tracer (BCT) system is an automatic microscopic method used for measuring the growth rate of a single fungal hyphae, which has not yet been applied to study Fusarium spp. Considering the large resistance of Fusarium species to the available chemotherapy and that hyphae is the morphological fungal form most often seen in vivo, in this work, Amphotericin B MIC and MFC values for a Fusarium solani strain were obtained by the conventional assay method testing conidia and also by the BCT monitoring system. Both MIC and MFC values of AMB against F. solani determined by broth dilution method resulted in 4.0 microg ml(-1). By the BCT system, their values were 1.0 microg ml(-1), with an inhibition rate of 99.5% (Exp-GR) and 100.0% (Post-GR), showing that when testing hyphae directly, MIC and MFC were determined at two lower dilutions than the MIC and MFC values obtained with conidia. Using the BCT system, 4.0, 2.0 and 1.0 microg ml(-1) of AMB concentrations inhibited hyphae growth in 50 min whereas 0.5 microg ml(-1) of AMB needed 100 min to start hyphae growth inhibition. These findings lead us to conclude that antifungal susceptibility varies between conidia and hyphae. For this strain of Fusarium solani, hyphae were more susceptible to AMB than conidia.

Amino acid production processes

With the exploitation of new uses and the growing markets of amino acids, amino acid production technology has made large progress during the latter half of the 20th century. Fermentation technology has played crucial roles in this progress, and currently the fermented amino acids represent chief products of biotechnology in both volume and value. This area is highly competitive in the world market and process economics are of primary importance. For cost-effective production, many technologies have been developed to establish high-productive fermentation and recovery processes. The producer organisms used in large-scale, well-established processes have been developed to a high level of production efficiency. The tools of genetic engineering of amino acid-producing organisms have been well developed and are now being applied for enlargement of biosynthetic and transport capacity, which is beginning to have a great impact on the amino acid industry. Furthermore, the rapid strides in genome analysis are bound to revolutionize the strain improvement methodology.

Biotechnological manufacture of lysine

L-Lysine has been manufactured using Corynebacterium glutamicum for more than 40 years. Nowadays production exceeds 600,000 tons per year. Based on conventionally bred strains, further improvement of lysine productivity has been achieved by genetic engineering. Pyruvate carboxylase, aspartate kinase, dihydrodipicolinate synthase, homoserine dehydrogenase and the specific lysine exporter were shown to be key enzymes for lysine production and were characterized in detail. Their combined engineering led to a striking increase in lysine formation. Pathway modeling with data emerging from 13C-isotope experiments revealed a coordinated flux through pentose phosphate cycle and tricarboxylic acid cycle and intensive futile cycling between C3 compounds of glycolysis and C4 compounds of tricarboxylic acid cycle. Process economics have been optimized by developing repeated fed-batch techniques and technical continuous fermentations. In addition, on-line metabolic pathway analysis or flow cytometry may help to improve the fermentation performance. Finally, the availability of the Corynebacterium glutamicum genome sequence has a major impact on the improvement of the biotechnological manufacture of lysine. In this context, all genes of the carbon flow from sugar uptake to lysine secretion have been identified and are accessible to manipulation. The whole sequence information gives access to post genome technologies such as transcriptome analysis, investigation of the proteome and the active metabolic network. These multi-parallel working technologies will accelerate the generation of knowledge. For the first time there is a chance of understanding the overall picture of the physiological state of lysine overproduction in a technical environment.

Flow sensing in mycelial fungi

Hyphae of a variety of mycelial fungi were shown to reorient their direction of growth to grow upstream in a continuous flowing current of liquid medium. Among those tested fungi, Aspergillus niger hyphae was most polarized towards the upstream. Hyphae of A. niger which had been attached to poly-L-lysine coated plates on the base of a continuous-culture flow cell were exposed to a current of medium of flow rates in the range of 0-6400 microns s-1 for 1-4 h. Hyphal tips quickly reoriented towards the upstream of the flowing medium and became aligned parallel to the flow axis as they grew larger. At flow rates above 1600 microns s-1, however, the percentage of polarization of hyphae reached a constant level. With other fungi, germ tube emergence was not polarized but hyphae and branches grew towards the upstream. There was no detectable difference in the pH and oxygen concentration of the flowing medium between inlet and outlet of the flow cell. This result suggests that hyphae of mycelial fungi sense transient flow of liquid medium over their surface and reorient their direction to grow upstream.

Antifungal activity and kinetics of inhibition by essential oil isolated from leaves of Aegle marmelos

The antifungal activity of essential oil isolated from the leaves of bael (Aegle marmelos (L.) Correa ex Roxb., Rutaceae) has been evaluated using spore germination assay. The oil exhibited variable efficacy against different fungal isolates and 100% inhibition of spore germination of all the fungi tested was observed at 500 ppm. However, the most resistant fungus, Fusarium udum was inhibited 80% at 400 ppm. Kinetic studies showed concentration as well as time dependent complex inhibition of spore germination by the essential oil.

Transmission of the effect of an antifungal agent within a single hypha

A micro-compartment culture method was devised in which a single hypha of Rhizopus stolonifer growing on an agar section traversed an antifungal non-diffusible barrier to another agar section; thus the local environment of the distal or proximal part of the hypha could be controlled independently. The responses in terms of hyphal extension of the test fungus to local application of amphotericin B in this culture system were estimated by using an automatic analysing system. After hyphae had traversed the barrier, distal application of amphotericin B caused no appreciable effect on the proximal hyphae. In contrast, proximal application of amphotericin B caused inhibition of the extension of distal hyphae. The reversal of polarized cytoplasmic streaming also occurred during the inhibition of distal hyphal extension. The extents of inhibition of the distal hyphal extension and the cytoplasmic streaming were dependent upon the hyphal distance between the amphotericin B application site and the hyphal tip. These results show that the effect of an antifungal agent on a hypha depends on the region of the hypha exposed. Cytoplasmic streaming may play key role in the transmission of antifungal effects within a single hypha.