A fraction from Escherichia coli with anti-Aspergillus properties

Intestinal bacteria-a powerful weapon for fungal infections treatment

The morbidity and mortality of invasive fungal infections are rising gradually. In recent years, fungi have quietly evolved stronger defense capabilities and increased resistance to antibiotics, posing huge challenges to maintaining physical health. Therefore, developing new drugs and strategies to combat these invasive fungi is crucial. There are a large number of microorganisms in the intestinal tract of mammals, collectively referred to as intestinal microbiota. At the same time, these native microorganisms co-evolve with their hosts in symbiotic relationship. Recent researches have shown that some probiotics and intestinal symbiotic bacteria can inhibit the invasion and colonization of fungi. In this paper, we review the mechanism of some intestinal bacteria affecting the growth and invasion of fungi by targeting the virulence factors, quorum sensing system, secreting active metabolites or regulating the host anti-fungal immune response, so as to provide new strategies for resisting invasive fungal infection.

Lacticaseibacillus rhamnosus C1 effectively inhibits Penicillium roqueforti: Effects of antimycotic culture supernatant on toxin synthesis and corresponding gene expression

Recently, consumers are increasingly concerned about the contamination of food by molds and the addition of chemical preservatives. As natural and beneficial bacteria, probiotics are a prospective alternative in food conservation because of their antimycotic activities, although the mechanism has not been explained fully at the level of metabolites. This study aimed at investigating the antifungal activities and their mechanisms of five potential probiotic strains (Lacticaseibacillus rhamnosus C1, Lacticaseibacillus casei M8, Lactobacillus amylolyticus L6, Schleiferilactobacillus harbinensis M1, and Limosilactobacillus fermentum M4) against Penicillium roqueforti, the common type of mold growth on the bread. Results showed that C1 emerged the strongest effectiveness at blocking mycelium growth, damaging the morphology of hyphae and microconidia, decreasing DNA content and interfering in the synthesis of the fungal toxins patulin, roquefortine C and PR-toxin, as well as downregulating the expression of key genes associated with the toxin biosynthesis pathways. Further metabonomic investigation revealed that protocatechuic acid with the minimum inhibitory concentration of 0.40 mg/mL, may be most likely responsible for positively correlated with the antimycotic effects of C1. Thus, C1 is expected to be both a potentially greatly efficient and environmental antimycotic for controlling P. roqueforti contamination in foods.

Interactions between invasive fungi and symbiotic bacteria

Infection rates and mortality associated with the invasive fungi Candida, Aspergillus, and Cryptococcus are increasing rapidly in prevalence. Meanwhile, screening pressure brought about by traditional antifungal drugs has induced an increase in drug resistance of invasive fungi, which creates a great challenge for the preservation of physical health. Development of new drugs and novel strategies are therefore important to meet these growing challenges. Recent studies have confirmed that the dynamic balance of microorganisms in the body is correlated with the occurrence of infectious diseases. This discovery of interactions between bacteria and fungi provides innovative insight for the treatment of invasive fungal infections. However, different invasive fungi and symbiotic bacteria interact with each other through various ways and targets, leading to different effects on their growth, morphology, and virulence. And the mechanism and implication of these interactions remains largely unknown. The present review aims to summarize the research progress into the interaction between invasive fungi and symbiotic bacteria with a focus on the anti-fungal mechanisms of symbiotic bacteria, providing a new strategy against drug-resistant fungal infections.

Growth kinetics of Escherichia coli O157:H7 on the epicarp of fresh vegetables and fruits

Despite the increasing reports on the incidence of fresh vegetables and fruits as a possible vehicle for human pathogens, there is currently limited knowledge on the growth potential of Escherichia coli O157:H7 on different plant substrates. This study analyzed the selective adhesion and growth of E. coli O157:H7 on chili habanero (Capsicum chinense L.), cucumber (Cucumis sativus), radish (Raphanus sativus), tomato (Lycopersicon esculentum), beet (Beta vulgaris subsp. vulgaris), and onion (Allium cepa L.) under laboratory conditions. The Gompertz parameters were used to determine the growth kinetics. Scanning electron microscopy was used to visualize the adhesion of E. coli O157:H7 on the epicarp of the samples. Predictive models were constructed to compare the growth of E. coli O157:H7 on the samples with different intrinsic factors and to demonstrate the low selectivity of the pathogen. No significant difference was observed in the lag-phase duration (LPD), generation time (GT), and exponential growth rate (EGR) of the pathogen adhered to the samples. The interaction between the microorganism and the substrate was less supportive to the growth of E. coli O157:H7 for onion, whereas for tomato and cucumber, the time for the microorganism to attain the maximum growth rate (M) was significantly longer than that recorded for other samples.

Chemoenzymatic Synthesis, Nanotization, and Anti-Aspergillus Activity of Optically Enriched Fluconazole Analogues

Despite recent advances in diagnostic and therapeutic methods in antifungal research, aspergillosis still remains a leading cause of morbidity and mortality. One strategy to address this problem is to enhance the activity spectrum of known antifungals, and we now report the first successful application of Candida antarctica lipase (CAL) for the preparation of optically enriched fluconazole analogues. Anti-Aspergillus activity was observed for an optically enriched derivative, (-)-S-2-(2',4'-difluorophenyl)-1-hexyl-amino-3-(1‴,2‴,4‴)triazol-1‴-yl-propan-2-ol, which exhibits MIC values of 15.6 μg/ml and 7.8 μg/disc in broth microdilution and disc diffusion assays, respectively. This compound is tolerated by mammalian erythrocytes and cell lines (A549 and U87) at concentrations of up to 1,000 μg/ml. When incorporated into dextran nanoparticles, the novel, optically enriched fluconazole analogue exhibited improved antifungal activity against Aspergillus fumigatus (MIC, 1.63 μg/ml). These results not only demonstrate the ability of biocatalytic approaches to yield novel, optically enriched fluconazole derivatives but also suggest that enantiomerically pure fluconazole derivatives, and their nanotized counterparts, exhibiting anti-Aspergillus activity may have reduced toxicity.

Synthesis and Antifungal Activity of Novel (1-Arylmethyl-3-Aryl-1H-Pyrazol-5-yl)(4-Arylpiperazin-1-yl)Methanone Derivatives

A series of novel (1-arylmethyl-3-aryl-1 H-pyrazol-5-yl)(4-arylpiperazin-1-yl)methanone derivatives were synthesised. Preliminary study of the structure–activity relationship revealed that 4-chlorophenyl, 4- tert-butylphenyl, 4-fluorophe-nyl and 3-methoxyphenyl had a promising effect on the antifungal activity.

Biochemical characterization of an anti-Candida factor produced by Enterococcus faecalis

Background

Because Candida albicans is resistant to several antifungal antibiotics, there is a need to identify other less toxic natural products, particularly antimicrobial proteins, peptides or bacteriocin like inhibitory substances. An attempt has been made to purify and characterise an anti-Candida compound produced by Enterococcus faecalis.

Results

An anti-Candida protein (ACP) produced by E. faecalis active against 8 C. albicans strains was characterised and partially purified. The ACP showed a broad-spectrum activity against multidrug resistant C. albicans MTCC 183, MTCC 7315, MTCC 3958, NCIM 3557, NCIM 3471 and DI. It was completely inactivated by treatment with proteinase K and partially by pronase E.

The ACP retained biological stability after heat-treatment at 90°C for 20 min, maintained activity over a pH range 6–10, and remained active after treatment with α-amylase, lipase, organic solvents, and detergents. The antimicrobial activity of the E. faecalis strain was found exclusively in the extracellular filtrate produced in the late logarithmic growth phase. The highest activity (1600 AU mL^-1) against C. albicans MTCC 183 was recorded at 48 h of incubation, and activity decreased thereafter. The peptide showed very low haemagglutination and haemolytic activities against human red blood cells. The antimicrobial substance was purified by salt-fractionation and chromatography.

Partially purified ACP had a molecular weight of approximately 43 KDa in Tricine-PAGE analysis. The 12 amino acid N terminal sequence was obtained by Edman degradation. The peptide was de novo sequenced by ESI-MS, and the deduced combined sequence when compared to other bacteriocins and antimicrobial peptide had no significant sequence similarity.

Conclusions

The inhibitory activity of the test strain is due to the synthesis of an antimicrobial protein. To our knowledge, this is the first report on the isolation of a promising non-haemolytic anti-Candida protein from E. faecalis that might be used to treat candidiasis especially in immunocompromised patients.

Characterization of theEscherichia coliAntifungal Protein PPEBL21

An antifungal protein isolated from Escherichia coli BL21 (PPEBL21) and predicted to be alcohol dehydrogenase (ADH) was subjected to biological characterization. The PPEBL21, indeed, demonstrated propionaldehyde-specific ADH activity. The Km and Vmax of PPEBL21 were found to be 644.8 μM and 1.2 U/mg, respectively. In-gel activity assay also showed that PPEBL21 was a propionaldehyde-specific ADH. The pI of PPEBL21 was observed to be 7.8. PPEBL21 was found to be stable up to a temperature of 40°C with optimum activity at pH 7.5. The decrease in pH decreased the activity of PPEBL21. These results suggested that PPEBL21 having alcohol dehydrogenase activity and stability at significantly high temperature might be an important lead antifungal molecule. Experiments were performed to identify the possible target of PPEBL21 in the pathogen A. fumigatus. Results revealed that PPEBL21 inhibited completely the expression of a 16 kDa protein in A. fumigatus. The 16 kDa protein of A. fumigatus targeted by PPEBL21 was identified as a hypothetical protein by peptide mass fingerprinting. It is thus hypothesized that a 16 kDa factor is essentially required by A. fumigatus for survival and its impaired synthesis due to treatment with PPEBL21 may lead to the death of pathogen.

An antifungal protein from Escherichia coli

A cytosolic protein was purified fromEscherichia coliBL21 that demonstrated potent antifungal activity against pathogenic strains ofAspergillus fumigatus,Aspergillus flavus,Aspergillus nigerandCandida albicans. The MIC of purified protein fromE. coliBL21 (PPEBL21) againstAspergillusspecies andC. albicanswas 1.95–3.98 and 15.62 μg ml−1, respectively.In vitrotoxicity tests demonstrated no cytotoxicity of PPEBL21 to human erythrocytes up to the tested concentrations of 1250 μg ml−1. Amphotericin B was lethal to 100 % of human erythrocytes at a concentration of 37.5 μg ml−1. The N-terminal amino acid sequence of PPEBL21 was found to be DLAEVASR, which showed 75 % sequence similarity with alcohol dehydrogenase of yeast. Mass fingerprinting by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry also substantiated these observations. The results suggested thatE. coliBL21 might be an important bioresource of lead molecules for developing new peptide-based therapies for treating fungal infections.

Synthesis, characterization and in vitro biological studies of novel cyano derivatives of N-alkyl and N-aryl piperazine

Cyano derivatives of N-alkyl and N-aryl piperazine have been synthesized and screened for antibacterial and antifungal activities. All the synthesized compounds showed the antibacterial activity against pathogenic strains of Staphylococcus aureus (MTCCB 737), Pseudomonas aeruginosa (MTCCB 741), Streptomyces epidermidis (MTCCB 1824) and Escherichia coli (MTCCB 1652) and antifungal activity against pathogenic strains of Aspergillus fumigatus (ITCC 4517), Aspergillus flavus (ITCC 5192) and Aspergillus niger (ITCC 5405). All compounds showed mild to moderate antimicrobial activity. However, compounds 3c, 4a and 6 showed potent antibacterial activity against pathogenic strains used in the study. Compounds 3a, 3b, 4b, and 4d showed mild to moderate antifungal activity against Aspergillus pathogenic strains. The compounds reported in this study were assessed for there cytotoxicity using MTT colorimetric assay on Hela cells. All the compounds showed cell viability more than the control drug gentamicin, with compound 2 having highest i.e. 95% cell viability.

Synthesis and antifungal activity of substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles

Series of substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles derivatives have been synthesized and examined for their activity against pathogenic strains of Aspergillus fumigatus (ITCC 4517), Aspergillus flavus (ITCC 5192) Aspergillus niger (ITCC 5405) and Candida albicans (ITCC No 4718). All synthesized compounds showed mild to moderate activity, except for 2-substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles 6a-d. The most active 1-(4-chlorophenyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole 4c exhibited a MIC value of 5.85 microg/disc against A. fumigatus and 11.71 microg/disc against A. flavus and A. niger in disc diffusion assay. Anti-Aspergillus activity of active compound 4c by microbroth dilution assay was found to be 15.62 microg/ml in case of A. fumigatus and 31.25 microg/ml with A. flavus and A. niger. The MIC90 value of the most active compound by percent germination inhibition assay was found to be 15.62 microg/ml against A. fumigatus. The MIC90 values of substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles against C. albicans ranged from 15.62 to 250 microg/ml. The in vitro toxicity of the most active 1-(4-chlorophenyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole 4c was evaluated using haemolytic assay, in which the compound was found to be non-toxic to human erythrocytes up to a concentration of 312.50 microg/ml. The standard drug amphotericin B exhibited 100% lysis at a concentration of 37.5 microg/ml.

Synthesis and antimicrobial activity of N-alkyl and N-aryl piperazine derivatives

A series of substituted piperazine derivatives have been synthesized and tested for antimicrobial activity. The antibacterial activity was tested against Staphylococcus aureus (MTCCB 737), Pseudomonas aeruginosa (MTCCB 741), Streptomyces epidermidis (MTCCB 1824) and Escherichia coli (MTCCB 1652), and antifungal activity against Aspergillus fumigatus, Aspergillus flavus and Aspergillus niger. All synthesized compounds showed significant activity against bacterial strains but were found to be less active against tested fungi. In vitro toxicity tests demonstrated that compounds 4d and 6a showed very less toxicity against human erythrocytes.

Synthesis and antibacterial activity of substituted 1,2,3,4-tetrahydropyrazino [1,2-a] indoles

A series of substituted 1,2,3,4-tetrahydropyrazino [1,2-a] indole derivatives have been synthesized and tested against the Gram positive and Gram negative strains of bacteria namely Staphylococcus aureus (MTCCB 737), Salmonella typhi (MTCCB 733), Pseudomonas aeruginosa (MTCCB 741), Streptomyces thermonitrificans (MTCCB 1824) and Escherichia coli (MTCCB 1652). All synthesized compounds showed mild to moderate activity. However, compounds 4d-f were found to have potent activity against pathogenic bacteria used in the study. Their MIC ranged from 3.75 to 60 microg/disc. In vitro toxicity tests demonstrated that toxicity of 4d-f was not significantly different than that of gentamycin. However, at higher concentration (1000-4000 microg/ml) difference was highly significant.