Potato dextrose agar antifungal susceptibility testing for yeasts and molds: evaluation of phosphate effect on antifungal activity of CMT-3

Assessment of microbial flora and pesticidal effect of vermicast generated from Azadirachta indica (neem) for developing a biofertilizer-cum-pesticide as a single package

The soil comprising organic matter, nutrients, serve as substrate for plant growth and various organisms. In areas where there are large plantations, there is a huge leaf litter fall. The leaf litter upon decomposition releases nutrients and helps in nutrient recycling, for which the soil engineers such as earthworms, ants and termites are important key players. In this context, the present study was conducted to assess the characteristics of the vermicast obtained by vermicomposting neem leaf litter in terms of microbial flora, plant growth promoting properties and antagonistic activities of the vermicast against phytopathogens. Vermicomposting of neem leaf litter was done using two epigeic earthworm species Eisenia fetida and Eudrilus eugeniae. The vermicast exhibited antagonistic potential against plant pathogens. Out of the four vermiwash infusions studied, the 75 % formulation reduced the disease incidence against mealybug by 82 % in the tree Neolamarkia cadamba. The result of the study suggests that vermicast made from neem leaf litter may be a potent combination of a biofertilizer and a pesticide.

Rice crop residue management by the microbial consortium for rapid decomposition of straw

Globally, more than 5 billion tons of crop residue (mainly rice straw) are produced yearly, and their management results in pollution, which kills microbes and limits soil nutrient recycling. Therefore, on-farm management that boosts degradation speed will improve the practicability of crop residue retention practices. The present study evaluated the 21 microbial isolates (Pseudomonas, Bacillus, Aspergillus, Trichoderma, Fusarium, and Rhizopus) from the soil of different agroclimatic zones obtained from rice fields for in situ straw degradation. The microbial diversity of these isolates was analyzed using 16 s rRNA and 18 s rRNA primers from various soil samples. The rice straw was used for degradation from isolated pathogens individually and in combination, and the results were analyzed using FTIR (Fourier transform infrared spectroscopy). The result suggested that the straw's degradation was the maximum with Trichoderma and Aspergillus, followed by the mixture of the isolates (Pseudomonas, Bacillus, Aspergillus, Trichoderma, Fusarium, and Rhizopus). Furthermore, SEM (scanning electron microscope) observed the degradation rate on different days of inoculation (7, 14, 28, 56, 70, and 100 DAI). The results showed that 90 DAI caused the highest degradation of rice straw. Therefore, Trichoderma containing microbial consortia could be used for vermicompost production from rice straw in field conditions, and it could increase crop productivity. Overall, our study added knowledge in rice straw management through a microbial consortium for better utilization in predominantly rice-growing countries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03982-z.

The activity of antimicrobial peptoids against multidrug-resistant ocular pathogens

BACKGROUND

Ocular infections caused by antibiotic-resistant pathogens can result in partial or complete vision loss. The development of pan-resistant microbial strains poses a significant challenge for clinicians as there are limited antimicrobial options available. Synthetic peptoids, which are sequence-specific oligo-N-substituted glycines, offer potential as alternative antimicrobial agents to target multidrug-resistant bacteria.

METHODS

The antimicrobial activity of synthesised peptoids against multidrug-resistant (MDR) ocular pathogens was evaluated using the microbroth dilution method. Hemolytic propensity was assessed using mammalian erythrocytes. Peptoids were also incubated with proteolytic enzymes, after which their minimum inhibitory activity against bacteria was re-evaluated.

RESULTS

Several alkylated and brominated peptoids showed good inhibitory activity against multidrug-resistant Pseudomonas aeruginosa strains at concentrations of ≤15 μg mL-1 (≤12 µM). Similarly, most brominated compounds inhibited the growth of methicillin-resistant Staphylococcus aureus at 1.9 to 15 μg mL-1 (12 µM). The N-terminally alkylated peptoids caused less toxicity to erythrocytes. The peptoid denoted as TM5 had a high therapeutic index, being non-toxic to either erythrocytes or corneal epithelial cells, even at 15 to 22 times its MIC. Additionally, the peptoids were resistant to protease activity.

CONCLUSIONS

Peptoids studied here demonstrated potent activity against various multidrug-resistant ocular pathogens. Their properties make them promising candidates for controlling vision-related morbidity associated with eye infections by antibiotic-resistant strains.

Antifungal activity of thiosemicarbazones, bis(thiosemicarbazones), and their metal complexes

Fungi are ubiquitous in nature, and typically cause little or no environmental or pathogenic damage to their plant, animal, and human hosts. However, a small but growing number of pathogenic fungi are spreading world-wide at an alarming rate threatening global ecosystem health and proliferation. Many of these emerging pathogens have developed multi-drug resistance to front line therapeutics increasing the urgency for the development of new antifungal agents. This review examines the development of thiosemicarbazones, bis(thiosemicarbazones), and their metal complexes as potential antifungal agents against more than 65 different fungal strains. The fungistatic activity of the compounds are quantified based on the zone of inhibition, minimum inhibitory concentration, or growth inhibition percentage. In this review, reported activities were standardized based on molar concentrations to simplify comparisons between different compounds. Of all the fungal strains reported in the review, A. niger in particular was very resistant towards a majority of tested compounds. Our analysis of the data shows that metal complexes are typically more active than non-coordinated ligands with copper(II) and zinc(II) complexes generally displaying the highest activity.

Extraction and optimization of Penicillium sclerotiorum strain AK-1 pigment for fabric dyeing

Recently, the demand for fungal pigments has increased due to their several benefits over synthetic dyes. Many species of fungi are known to produce pigments and a large number of fungal strains for pigment production are yet to be extensively investigated. The natural pigment from sustainable natural sources has good economic and industrial value. Many synthetic colorants used in textile and various industries have many harmful effects on the human population and environment. Pigments and coloring agents may be extracted from a wide range of fungal species. These compounds are among the natural compounds having the most significant promise for medicinal, culinary, cosmetics, and textile applications. This study attempts to isolate and optimize the fermentation conditions of Penicillium sclerotiorum strain AK-1 for pigment production. A dark yellow-colored pigment was isolated from the strain with significant extractive value and antioxidant capacity. This study also identifies that the pigment does not have any cytotoxic effect and is multicomponent. The pigment production was optimized for the parameters such as pH, temperature, carbon and nitrogen source. Fabric dyeing experiments showed significant dyeing capacity of the pigment on cotton fabrics. Accordingly, the natural dye isolated from P. sclerotiorum strain AK-1 has a high potential for industrial-scale dyeing of cotton materials.

High level of conservation and diversity among the endophytic seed bacteriome in eight alpine grassland species growing at the Qinghai Tibetan Plateau

Seed borne microorganisms play an important role in plant biology. Concerns have recently been raised about loss of seed microbial diversity by seed treatments, crop domestication and plant breeding. Information on the seed microbiomes of native plants growing in natural ecosystems is beneficial as they provide the best settings to detect indigenous plant microbe interactions. Here, we characterized the seed bacterial community of 8 native alpine grassland plants. First, seed bacterial diversity was examined using Illumina DNA sequencing, then 28 cultivable bacteria were isolated and potential functions were explored. Across 8 plant species, 343 different bacterial genera were identified as seed endophytes, 31 of those were found in all plant species, indicating a high level of conservation. Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes and Chloroflexi were the top five dominant phyla. Plant species identity was a key determinant shaping the seed endophytic bacteriome. ACC deaminase activity, siderophores production and secretion of lytic enzymes were common functions shown by isolated bacteria. Our results demonstrate that highly diverse and beneficial bacterial populations are hosted by seeds of alpine grassland species to ensure the establishment of best bacterial symbionts for the next generation. This information is useful for crop improvement by reinstating beneficial seed microbial diversities for high-quality forage and crop seeds.

Seasonal Variation in Antimicrobial Activity of Crude Extracts of Psammaplysilla sp. 1 from Phillips Reef, South Africa

Marine invertebrates constitute a diverse group of marine organisms beneficial to humanity due to their therapeutic significance. The marine sponge species Psammaplysilla sp. 1 was collected from Philips Reef, South Africa, over a four-season period and assayed for antimicrobial potential. The physicochemical parameters of the collection site were also recorded. The sponge crude extracts' antimicrobial activity was evaluated using an agar well diffusion assay against 5 pathogens. Phytochemical screening was conducted to identify the presence of 7 critical phytochemical groups. During the four seasons, the mean water temperature was 17.35°C ± 2.06, with autumn recording the highest (20°C) temperature. Antifungal activity was observed by Psammaplysilla sp. 1 (30 mm) against C. albicans, and this was higher than that showed by standard drugs ICZ-10 µg (15 ± 0.1 mm), FLU-15 µg (21 ± 0.2 mm), and VCZ-5 µg (17 ± 0.1 mm), respectively. Similar bioactivities were observed seasonally with Psammaplysilla sp. 1 (22 mm and 24 mm) during autumn and spring, respectively, against C. difficile while only crude extracts collected in spring showed bioactivity against C. albicans. Psammaplysilla sp. crude extracts showed broad-spectrum bioactivity against all test pathogens. DCM : ME crude extracts tested positive for the presence of 2/7 of the phytochemicals (terpenoids and flavonoids). GC-MS revealed several previously reported biologically active compounds such bicyclo[4.2.0]octa-1,3,5-trien-7-ol and phenol, 2,6-dibromo, some of which have been found in plants. This study revealed that sponge bioactivity is dependent on the season and further validated the antimicrobial potential of South African marine sponges.

Antimicrobial Potential and Phytochemical Screening of Clathria sp. 1 and Tedania (Tedania) stylonychaeta Sponge Crude Extracts Obtained from the South East Coast of South Africa

Scientists have continuously searched for novel bioactive compounds to overcome the inherent problems associated with drug resistance, the evolution of unknown diseases, and the toxicity of currently used compounds. The ocean has been considered a rich source of compounds that possess unique chemical structures and novel biological capabilities. Biologically active molecules isolated from marine flora and fauna have shown significant advancement over the past century in the pharmaceutical industry. Marine natural products (MNPs) have been used as nanomedicine, cosmetics, wound healing, antimicrobial agents, anticancer agents, and anti-inflammatory agents. The physicochemical parameters of the collection site were also recorded. This study's marine sponge species were collected from Phillip's Reef, South Africa, at 12 m during the spring season. Ethyl acetate (EA) and dichloromethane : methanol (DCM : ME, 1 : 1) were used as extraction solvents. Crude extracts of the marine sponges were tested against MRSA, P. aeruginosa, C. difficile, A. fumigatus, and C. albicans. Phytochemical screening was conducted to identify seven critical phytochemical groups. A pH reading of 8.01 and a temperature of 15.45°C were recorded at the sampling site. Clathria sp. 1 and Tedania (Tedania) stylonychaeta EA crude extracts showed bioactivity against all five test pathogens. The DCM : ME crude extract of Clathria sp. 1 was the only bioactive crude extract from DCM : ME extracts. This crude extract was only bioactive against C. albicans as no activity was observed against the other four pathogens. EA crude extracts of Clathria sp. 1 yielded more significant inhibition zones against both fungal pathogens. These EA crude extracts performed better than fluconazole as inhibition zones of 35 ± 0 mm at 24 mg/ml, 31 ± 0 mm at 19 mg/ml, 31 ± 0 mm at 14.4 mg/ml, 30 ± 0 mm at 9.6 mg/ml, and 25 ± 0 mm at 7.2 mg/ml were recorded. Clathria sp. 1 crude extracts exhibited higher inhibition zones compared to Tedania (Tedania) stylonychaeta. The antibiotic imipenem (26 ± 0.7 mm at 10 μg) and ciprofloxacin (30 ± 0.3 mm at 5 μg) exhibited higher zones of inhibition than EA crude extracts of Tedania (Tedania) stylonychaeta at all test concentrations. In this study, Clathria sp. 1 was observed to have broad-spectrum bioactivity as EA crude extracts were bioactive against MRSA, P. aeruginosa, C. difficile, A. fumigatus, and C. albicans. In addition to this, the EA crude extract of Clathria sp. 1 was bacteriostatic (9.6 mg/ml). Clathria sp. 1 DCM : ME crude extract only tested positive for the presence of terpenoids. In contrast, EA crude extracts did not test positive for the existence of any of the seven phytochemicals. Our study has revealed that Tedania (Tedania) stylonychaeta and Clathria sp. 1 sponge species collected from Phillip's Reef in South Africa can produce bioactive compounds useful against bacterial and fungal species.

Two new 23S,26R-hydroxylated spirostanoid saponins from the fruits of Solanum indicum var. recurvatum

Solanum indicum var. recurvatum, distributed mainly in Hekou, Simao and Menghai areas of Yunnan province, China, is characterized by stellate pubescent leaves with irregular lengths and oblong, short, and downwardly curved anthers. The original species, S. indicum, has been used as an anti-inflammatory, wound-healing agent, an analgesic, and for the treatment of rhinitis, cough, and breast cancer in Chinese folk medicine. The variety was chemically studied for the first time, leading to the isolation of two new rare 23S,26R-hydroxylated spirostanoid saponins, together with five known steroidal components, two of which the rare natural ketosteroids 6-hydroxyandrosta-1,4-diene-3,17-dione and rostadienedione have been isolated from the genus Solanum for the first time. Elucidation of the structures was accomplished by extensive 1D and 2D NMR, UV, and HRESIMS spectroscopic methods.

Garlic, from Remedy to Stimulant: Evaluation of Antifungal Potential Reveals Diversity in Phytoalexin Allicin Content among Garlic Cultivars; Allicin Containing Aqueous Garlic Extracts Trigger Antioxidants in Cucumber

Garlic has the charisma of a potent remedy and holds its repute of a therapeutic panacea since the dawn of civilization. An integrated approach was adopted to evaluate the genetic diversity among Chinese garlic cultivars for their antifungal potency as well as allicin content distribution and, furthermore; a bioassay was performed to study the bio-stimulation mechanism of aqueous garlic extracts (AGE) in the growth and physiology of cucumber (Cucumis sativus). Initially, 28 garlic cultivars were evaluated against four kinds of phytopathogenic fungi; Fusarium oxysporum, Botrytis cinerea, Verticillium dahliae and Phytophthora capsici, respectively. A capricious antifungal potential among the selected garlic cultivars was observed. HPLC fingerprinting and quantification confirmed diversity in allicin abundance among the selected cultivars. Cultivar G025, G064, and G074 had the highest allicin content of 3.98, 3.7, and 3.66 mg g(-1), respectively, whereas G110 was found to have lowest allicin content of 0.66 mg g(-1). Cluster analysis revealed three groups on the basis of antifungal activity and allicin content among the garlic cultivars. Cultivar G025, G2011-4, and G110 were further evaluated to authenticate the findings through different solvents and shelf life duration and G025 had the strongest antifungal activity in all conditions. minimum inhibitory concentration and minimum fungicidal concentration of Allicin aqueous standard (AAS) and AGE showed significant role of allicin as primary antifungal substance of AGE. Leaf disk bioassay against P. capsici and V. dahliae to comparatively study direct action of AGE and AAS during infection process employing eggplant and pepper leaves showed a significant reduction in infection percentage. To study the bioactivity of AGE, a bioassay was performed using cucumber seedlings and results revealed that AGE is biologically active inside cucumber seedlings and alters the defense mechanism of the plant probably activating reactive oxygen species at mild concentrations. However, at higher concentrations, it might cause lipid peroxidation and membrane damage which temper the growth of cucumber seedlings. At the outcome of the study, an argument is advanced that current research findings provide bases for cultivar selection in antifungal effectivity as well as genetic variability of the cultivars. Allicin containing AGE can be used in specialized horticultural situations such as plastic tunnel and organic farming as a bio-stimulant to enhance cucumber growth and attenuate fungal degradation of agricultural produce.

Characterization and evaluation of antimicrobial and cytotoxic effects of Streptomyces sp. HUST012 isolated from medicinal plant Dracaena cochinchinensis Lour

A highly potent secondary metabolite producing endophytic strain, Streptomyces sp. HUST012 was isolated from the stems of the medicinal plant Dracaena cochinchinensis Lour. Strain HUST012 showed antimicrobial and antitumor activities which were significantly much higher than those of dragon's blood extracted from D. cochinchinensis Lour. On further analysis, the strain was found to produce two metabolites, SPE-B11.8 (elucidated to be a novel metabolite (Z)-tridec-7-ene-1,2,13-tricarboxylic acid) and SPE-B5.4 (elucidated as Actinomycin-D). The Minimum Inhibitory Concentration values of SPE-B11.8 against a set of test bacterial organisms (Methicillin-resistant Staphylococcus epidermis ATCC 35984, Methicillin-resistant Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Klebsiella pneumoniae ATCC 13883) ranged between 15.63 and 62.5 μg/ml while that for SPE-B5.4 ranged between 0.04 and 2.24 μg/ml. The compound SPE-B11.8 showed cytotoxic effect at 41.63 and 29.54 μg/ml IC 50-values against Hep G2 and MCF-7, respectively, while the compound SPE-B5.4 exhibited stronger activities against them at 0.23 and 0.18 μg/ml IC 50-values.

Characterization of a Chitin-Binding Protein from Bacillus thuringiensis HD-1

Strains of Bacillus thuringiensis produce insecticidal proteins. These strains have been isolated from diverse ecological niches, such as soil, phylloplane, insect cadavers and grain dust. To effectively propagate, these strains produce a range of molecules that facilitate its multiplication in a competing environment. In this report, we have examined synthesis of a chitin-binding protein and evaluated its effect on fungi encountered in environment and its interaction with insecticidal proteins synthesized by B. thuringiensis. The gene encoding chitin-binding protein has been cloned and expressed. The purified protein has been demonstrated to interact with Cry insecticidal protein, Cry1Ac by Circular Dichrosim spectroscopy (CD) and in vitro pull down assays. The chitin-binding protein potentiates insecticidal activity of bacillar insecticidal protein, Cry1Ac. Further, chitin-binding protein was fungistatic against several soil fungi. The chitin binding protein is expressed in spore mother cell and deposited along with insecticidal protein, Cry1Ac. It interacts with Cry1Ac to potentiate its insecticidal activity and facilitate propagation of Bacillus strain in environment by inhibiting growth of certain fungi.

Isolation of an unusual metabolite 2-allyloxyphenol from a marine actinobacterium, its biological activities and applications

A marine actinobacterium isolated from the Bay of Bengal, India and previously found to be producing an antimicrobial and cytotoxic terpenoid was further investigated for antimicrobial metabolites. The bacterium was preliminarily identified as a new species of the genus Streptomyces (strain MS1/7). The cell-free culture broth was extracted with n-butanol and purified using silica gel column chromatography and high-performance liquid chromatography. Molecular characterization was done using ESI mass, IR and 1H and 13C NMR spectrometry. 2-Allyloxyphenol (MW 150; C9H10O2), a synthetic drug and chemical intermediate, was obtained as a natural product for the first time. Serendipitous natural occurrence provided new insights into the synthetic molecule. 2-Allyloxyphenol was found to be inhibitory to 21 bacteria and three fungi in the minimum range 0.2-1.75 mg mL(-1) determined by agar dilution method. 2-Allyoxyphenol possesses strong antioxidant property (IC(50) 22 microg mL(-1), measured by 1, 1-diphenyl-2-picryl hydrazyl scavenging activity). Hydroxyl and allyloxy groups in 2-allyloxyphenol were responsible for antimicrobial and antioxidant activities. 2-Allyloxyphenol has marked resemblance to smoky aroma and is two to three times more active as an antimicrobial than some commercial smoke-flavour compounds. Absence of hemolytic toxicity, potential carcinogenicity, cytotoxicity and reports of toxic reactions in literature suggest possible application of 2-allyloxyphenol as a food preservative and an oral disinfectant.

Human laminin-332 degradation by Candida proteinases

BACKGROUND

Human laminin-332 (Lm-332) degradation by 12 Candida strains and effects of synthetic proteinase inhibitors [Ilomastat (ILM), EDTA, chemically modified tetracycline-3(CMT-3), CMT-308, synthetic peptide CTT-2, and Pefabloc] were studied.

MATERIALS AND METHODS

Laminin-332 was incubated with sonicated cell fractions and 10 times concentrated cell-free fractions of reference and clinical strains of C. albicans, C. dubliniensis, C. guilliermondii, C. glabrata, C. krusei, and C. tropicalis. Proteolysis, pH effects, and inhibitors were analyzed by fluorography and zymography.

RESULTS

Cell fractions of all species except C. guilliermondii and cell-free fractions of C. albicans, and C. dubliniensis showed 20-70 kDa gelatinases at pH 5.0 and 6.0. At pH 7.6, C. glabrata, C. krusei, and C. tropicalis cell fractions and C. tropicalis cell-free fractions showed 55-70 kDa gelatinases. CMT-3, CMT-308, and CTT-2 inhibited Candida gelatinases slightly better than Pefabloc, ILM, and EDTA. No Candida fractions degraded Lm-332 at pH 7.6, but at pH 5.0, 100 kDa bands were generated by cell fractions of C. dubliniensis and C. tropicalis; C. albicans and C. glabrata clinical strains; and C. guilliermondii reference strain. C. krusei reference strain yielded three 100-130 kDa bands. C. albicans, C. dubliniensis, and C. tropicalis reference and clinical strain's cell-free fractions generated 100 kDa band.

CONCLUSIONS

Laminin-332 degradation is pH-dependent and differences exist between studied Candida strains. Lm-332 degradation can exert functional disturbances on basement membrane integrity, possibly aiding Candida cell invasion into tissues. Certain synthetic matrix metalloproteinase inhibitors (CMTs, CTT) can inhibit Candida proteinases and may be therapeutically useful in future.

Production and purification of a bioactive substance inhibiting multiple drug resistant bacteria and human leukemia cells from a salt-tolerant marine Actinobacterium sp. isolated from the Bay of Bengal

Four marine actinobacteria tolerant to 200 g NaCl l(-1) were screened for antibacterial activity against eight patient-derived multiple drug resistant (MDR) bacteria. The active compound (MW 300.2, predicted molecular formula C(20)H(28)O(2)) from an actinobacterium, was inhibitory to three Gram-positive and three Gram-negative MDR bacteria, seven non-clinical Gram-positive, four Gram-negative bacteria and five fungi (MIC: 3.5-4.0 microg ml(-1)). Also, 54% of human leukemia (HL-60) cells were killed by the compound at 0.05 microg ml(-1). Bioreactor production demonstrated unusual primary metabolite kinetics. Molecular phylogenetic analysis showed this typical intertidal inhabitant to be a member of the Streptomyces genus and distinct from other salt-tolerant actinobacteria. As no compound was found to match the properties in several electronic databases, our screening strategy should increase the possibility of discovering bioactive molecules from rare actinobacteria.

Laboratory evaluation of new antifungal agents against rare and refractory mycoses

PURPOSE OF REVIEW

An increase in refractory invasive fungal infections in the setting of marrow/solid organ transplantation and other immune-compromising clinical entities has provided the impetus for the development of new, more efficacious/less toxic antifungal agents. This review (1) examines currently available laboratory methods for the in-vitro evaluation of these new agents against both yeasts and filamentous fungi; (2) provides a summary of the most attractive investigational agents currently undergoing clinical trials/development; and (3) outlines the major refractory mycoses in contemporary medicine.

RECENT FINDINGS

Fluconazole-resistant Candida spp., Trichosporon spp., zygomycetous genera, the endemic mycoses, Scedosporium, Aspergillus, and Fusarium spp., and an ever-expanding list of lesser-known hyaline and phaeoid genera inciting invasive fungal infections comprise the bulk of refractory mycoses in the immune-compromised host. In-vitro data generated from reference-based antifungal susceptibility testing methods indicate an increased armamentarium of potentially efficacious agents against most of these mycoses.

SUMMARY

The newly approved antifungal agents caspofungin and voriconazole, used either as monotherapy or in combination regimens, have a significantly improved spectrum of activity over previously available therapeutic options. Correlation of clinical outcomes with investigational agents demonstrating in-vivo/in-vitro activity will provide critical information needed for the development of clinically significant minimum inhibitory concentration interpretative breakpoints.

A chemically modified tetracycline (CMT-3) is a new antifungal agent

Several chemically modified tetracycline analogs (CMTs), which were chemically modified to eliminate their antibacterial efficacy, were unexpectedly found to have antifungal properties. Of 10 CMTs screened in vitro, all exhibited antifungal activities, although their efficacies varied. Among these compounds, CMT-315, -3, and -308 were found to be the most potent as antifungal agents. The MICs of CMT-3 against 47 strains of fungi in vitro were determined by using amphotericin B (AMB) and doxycycline as positive and negative controls, respectively. The MICs of CMT-3 were generally found to be between 0.25 and 8.00 microg/ml, a range that approximates the blood levels of this drug when administrated orally to humans. Of all the yeast species tested to date, Candida albicans showed the greatest sensitivity to CMT-3. The filamentous species most susceptible to CMT-3 were found to be Epidermophyton floccosum, Microsporum gypseum, Pseudallescheria boydii, a Penicillium sp., Scedosporium apiospermum, a Tricothecium sp., and Trichophyton rubrum. Growth inhibition of C. albicans by CMT-3, determined by a turbidity assay, indicated a 50% inhibitory concentration of 1 microg/ml. Thirty-nine strains, including 20 yeasts and 19 molds, were used to measure viability (the ability to grow after treatment with a drug) inhibition by CMT-3 and AMB. CMT-3 exhibited fungicidal activity against most of these fungi, especially the filamentous fungi. Eighty-four percent (16 of 19) of the filamentous fungi tested showed more than 90% inhibition of viability by CMT-3. In contrast, AMB showed fungicidal activity against all yeasts tested. However, most of the filamentous fungi (16 of 19) showed less than 50% inhibition of viability by AMB, indicating that AMB is fungistatic against most of these filamentous fungi. To begin to identify the sites in fungal cells affected by CMT-3, C. albicans and a Penicillium sp. were incubated with the compound at 35 degrees C, and then the fluorescence of CMT-3 was observed by confocal laser scanning electron microscopy. CMT-3 appeared to have widespread intracellular distribution throughout C. albicans and the Penicillium sp. The mechanisms of the antifungal activity of CMT-3 are now being explored.