Investigations on anti-Aspergillus properties of bacterial products

Phytochemical analysis, antioxidant, antimicrobial, and anti-enzymatic properties of Alpinia coriandriodora (sweet ginger) rhizome

Alpinia coriandriodora, also known as sweet ginger, is a medicinal and edible plant. A. coriandriodora rhizome is popularly utilized in traditional Chinese medicine and as flavouring spices, but there are few reports on its constituents and bioactivities. This study analyzed the phytochemical components of A. coriandriodora rhizome by GC-MS and UHPLC-Q-Orbitrap-MS and evaluated its antioxidant, antimicrobial, and anti-enzymatic properties. According to the GC-FID/MS data, its rhizome essential oil (EO) consisted mainly of (E)-2-decenal (53.8%), (E)-2-decenyl acetate (24.4%), (Z)-3-dodecenyl acetate (3.5%), and (E)-2-octenal (3.5%). Its water extract (WE) and 70% ethanol extract (EE) showed high total phenolic content (TPC, 52.99-60.49 mg GAEs/g extract) and total flavonoid content (TFC, 260.69-286.42 mg REs/g extract). In addition, the phytochemicals of WE and EE were further characterized using UHPLC-Q-Orbitrap-MS, and a total of sixty-three compounds were identified, including fourteen phenolic components and twenty-three flavonoid compounds. In the antioxidant assay, WE and EE revealed a potent scavenging effect on DPPH (IC50: 6.59 ± 0.88 mg/mL and 17.70 ± 1.15 mg/mL, respectively), surpassing the BHT (IC50: 21.83 ± 0.89 mg/mL). For the antimicrobial activities, EO displayed excellent antibacterial capabilities against Proteus vulgaris, Enterococcus faecalis, Bacillus subtilis, Escherichia coli, and Staphylococcus aureus with DIZ (12.60-22.17 mm), MIC (0.78-1.56 mg/mL), and MBC (3.13 mg/mL) and significantly inhibited Aspergillus flavus growth (MIC = 0.313 mg/mL, MFC = 0.625 mg/mL, respectively). In addition to weak tyrosinase and cholinesterase inhibition, EE and WE had a prominent inhibitory effect against α-glucosidase (IC50: 0.013 ± 0.001 mg/mL and 0.017 ± 0.002 mg/mL), which was significantly higher than acarbose (IC50: 0.22 ± 0.01 mg/mL). Hence, the rhizome of A. coriandriodora has excellent potential for utilization in the pharmaceutical and food fields as a source of bioactive substances.

Secondary Metabolites Produced during Aspergillus fumigatus and Pseudomonas aeruginosa Biofilm Formation

In cystic fibrosis (CF), mucus plaques are formed in the patient's lungs, creating a hypoxic condition and a propitious environment for colonization and persistence of many microorganisms. There is clinical evidence showing that Aspergillus fumigatus can cocolonize CF patients with Pseudomonas aeruginosa, which has been associated with lung function decline. P. aeruginosa produces several compounds with inhibitory and antibiofilm effects against A. fumigatus in vitro; however, little is known about the fungal compounds produced in counterattack. Here, we annotated fungal and bacterial secondary metabolites (SM) produced in mixed biofilms under normoxia and hypoxia conditions. We detected nine SM produced by P. aeruginosa. Phenazines and different analogs of pyoverdin were the main compounds produced by P. aeruginosa, and their secretion levels were increased by the fungal presence. The roles of the two operons responsible for phenazine production (phzA1 and phzA2) were also investigated, and mutants lacking one of those operons were able to produce partial sets of phenazines. We detected a total of 20 SM secreted by A. fumigatus either in monoculture or in coculture with P. aeruginosa. All these compounds were secreted during biofilm formation in either normoxia or hypoxia. However, only eight compounds (demethoxyfumitremorgin C, fumitremorgin, ferrichrome, ferricrocin, triacetylfusigen, gliotoxin, gliotoxin E, and pyripyropene A) were detected during biofilm formation by the coculture of A. fumigatus and P. aeruginosa under normoxia and hypoxia conditions. Overall, we showed how diverse SM secretion is during A. fumigatus and P. aeruginosa mixed culture and how this can affect biofilm formation in normoxia and hypoxia. IMPORTANCE The interaction between Pseudomonas aeruginosa and Aspergillus fumigatus has been well characterized in vitro. In this scenario, the bacterium exerts a strong inhibitory effect against the fungus. However, little is known about the metabolites produced by the fungus to counterattack the bacteria. Our work aimed to annotate secondary metabolites (SM) secreted during coculture between P. aeruginosa and A. fumigatus during biofilm formation in both normoxia and hypoxia. The bacterium produces several different types of phenazines and pyoverdins in response to presence of the fungus. In contrast, we were able to annotate 29 metabolites produced during A. fumigatus biofilm formation, but only 8 compounds were detected during biofilm formation by the coculture of A. fumigatus and P. aeruginosa upon either normoxia or hypoxia. In conclusion, we detected many SM secreted during A. fumigatus and P. aeruginosa biofilm formation. This analysis provides several opportunities to understand the interactions between these two species.

Genetic variation is associated with differences in facilitative and competitive interactions in the Rhizobium leguminosarum species complex

Competitive and facilitative interactions influence bacterial community composition, diversity and functioning. However, the role of genetic diversity for determining interactions between coexisting strains of the same, or closely related, species remains poorly understood. Here, we investigated the type (facilitative/inhibitory) and potential underlying mechanisms of pairwise interactions between 24 genetically diverse bacterial strains belonging to three genospecies (gsA,C,E) of the Rhizobium leguminosarum species complex. Interactions were determined indirectly, based on secreted compounds in cell-free supernatants, and directly, as growth inhibition in cocultures. We found supernatants mediated both facilitative and inhibitory interactions that varied greatly between strains and genospecies. Overall, gsE strains indirectly suppressed growth of gsA strains, while their own growth was facilitated by other genospecies' supernatants. Similar genospecies-level patterns were observed in direct competition, where gsA showed the highest susceptibility and gsE the highest inhibition capacity. At the genetic level, increased gsA susceptibility was associated with a non-random distribution of quorum sensing and secondary metabolite genes across genospecies. Together, our results suggest that genetic variation is associated with facilitative and competitive interactions, which could be important ecological mechanisms explaining R. leguminosarum diversity.

Interaction of Aspergillus flavus and A. parasiticus with Salmonella spp. isolated from peanuts

Although Aspergillus flavus and Aspergillus parasiticus are the main microorganisms of concern in peanuts, due to aflatoxin contamination, several Salmonella outbreaks from this product have been reported over the last ten decades. Thus, it is important to understand the relationship between microorganisms to predict, manage and estimate the diversity in the peanut supply chain. The purpose of this study was to evaluate aflatoxin production during the co-cultivation of Aspergillus section Flavi and Salmonella both isolated from peanuts. Three strains of A. section Flavi: A. flavus producing aflatoxin B, A. flavus non-producing aflatoxin and A. parasiticus producing aflatoxin B and G were co-cultivated with seven serotypes of Salmonella of which six were isolated from the peanut supply chain (S. Muenster, S. Miami, S. Glostrup, S. Javiana, S. Oranienburg and S. Yoruba) and one was S. Typhimurium ATCC 14028. First of all, each Salmonella strain was inoculated by pour plate (ca. 5 log cfu/mL) in PDA (potato dextrose agar). Then, each pre-cultured fungus was inoculated in the center of the petri dish. The plates were incubated at 30 °C and the fungal colony diameter was measured once a day for 7 days. As a control each Aspergillus strain was cultivated in the absence of Salmonella culture. All three strains of Aspergillus with absence of Salmonella (control) reached the maximum colony diameter and their growth rate was influenced when co-cultivated (p < 0.05) with all Salmonella serotypes tested. The maximum inhibition in the colony diameter was 20% for A. flavus aflatoxin B producer and A. parasiticus, and 18% for A. flavus non- aflatoxin producer when cultivated with Salmonella. However, no significant difference (p < 0.05) in reduction of colony diameter was observed among the Salmonella serotypes. Aflatoxin production was determined previously, by using the agar plug technique on thin layer chromatography (TLC). The production of aflatoxin G by A. parasiticus in co-cultivation with Salmonella was not observed. On the other hand, A. flavus preserved their characteristics of aflatoxin B production. The quantification of aflatoxin reduction by Salmonella interaction was evaluated using HPLC method. There was a maximum reduction of aflatoxin production of 88.7% and 72.9% in A. flavus and A. parasiticus, respectively, when cultivated with Salmonella. These results indicate that some serotypes of Salmonella may interfere with aflatoxin production and fungal growth of A. flavus and A. parasiticus in the peanut supply chain.

Interactions of Aspergillus fumigatus and Stenotrophomonas maltophilia in an in vitro Mixed Biofilm Model: Does the Strain Matter?

Introduction:Aspergillus fumigatus (Af) and Stenotrophomonas maltophilia (Sm) are pathogenic microorganisms, which coexist in the respiratory tract of cystic fibrosis (CF) patients. We recently developed an in vitro model of mixed biofilm associating Af ATCC 13073-GFP (Af13073) and Sm ATCC 13637 (Sm13637) and described an antibiosis effect. The present study aim was to assess the antibiosis of Sm on Af using different strains and to analyze the potential synergistic virulence of these strains in an in vivo Galleria mellonella model.

Methods: The effect of Sm13637 was evaluated on eight Af strains and the effect of nine Sm strains was evaluated on Af13073. The strains originated from clinical cases (human and animal) and from environment. Fungal and bacterial inocula were simultaneously inoculated to initiate mixed biofilm formation. Fungal growth inhibition was analyzed by qPCR and CLSM and the fungal cell wall modifications by TEM analysis. The virulence of different Sm strains was assessed in association with Af in G. mellonella larvae.

Results: All strains of Af and Sm were able to produce single and mixed biofilms. The antibiosis effect of Sm13637 was similar whatever the Af strain tested. On the other hand, the antibiosis effect of Sm strains was bacterial-fitness and strain dependent. One strain (1/9) originated from animal clinical case was never able to induce an antibiosis, even with high bacterial concentration. In the G. mellonella model, co-inoculation with Sm13637 and Af13073 showed synergism since the mortality was 50%, i.e., more than the summed virulence of both.

Conclusion: Human clinical strains of Sm yielded in higher antibiosis effect on Af and in a thinner mixed biofilm, probably due to an adaptive effect of these strains. Further research covering Af increased wall thickness in the presence of Sm strains, and its correlation with modified antifungal susceptibility is encouraged in patients with chronic respiratory infections by these 2 microorganisms.

Synthesis and Antimicrobial Studies of Pyrimidine Pyrazole Heterocycles

Prompted from the diversity of the wider use and being an integral part of genetic material, an effort was made to synthesize pyrimidine pyrazole derivatives of pharmaceutical interest by oxidative cyclization of chalcones with satisfactory yield and purity. A novel series of 1,3-dimethyl-6-hydroxy-2,4-dioxo-5-(1′-phenyl-3′-aryl-1H-pyrazol-5′-yl)-1,2,3,4-tetrahydropyrimidines (5a–d) and 1,3-diaryl-6-hydroxy-4-oxo-2-thioxo-5-(1′-phenyl-3′-aryl-1H-pyrazol-5′-yl)-1,2,3,4-tetrahydropyrimidines (5e–l) has been synthesized. The structures of these compounds were established on the basis of FT-IR, 1H NMR, 13C NMR, and mass spectral analysis. All the synthesized compounds were screened for their antimicrobial activity against bacteria and fungi. Among all the compounds, 5g was found to be the most active as its MIC was 31.25 µg/mL against S. aureus and B. cereus. The compounds 5h, 5c, and 5e also possess antibacterial activity with MIC values as 62.50, 125.00, and 500.00 µg/mL, respectively. The compounds 5c and 5j were found to have antifungal activity against Aspergillus spp. As antifungal drugs lag behind the antibacterial drugs, therefore we tried in vitro combination of these two compounds with standard antifungal drugs (polyene and azole) against Aspergillus spp. The combination of ketoconazole with 5c and 5j showed synergy at 1 : 8 (6.25 : 50.00 µg/mL) and 1 : 4 (25 : 100 µg/mL) against A. fumigatus (ITCC 4517) and A. fumigatus (VPCI 190/96), respectively.

Antifungal constituents isolated from the seeds of Aegle marmelos

Antifungal constituents, 2-isopropenyl-4-methyl-1-oxa-cyclopenta[b]anthracene-5,10-dione and (+)-4-(2'-hydroxy-3'-methylbut-3'-enyloxy)-8H-[1,3]dioxolo[4,5-h]chromen-8-one in addition to known compounds imperatorin, beta-sitosterol, plumbagin, 1-methyl-2-(3'-methyl-but-2'-enyloxy)-anthraquinone, beta-sitosterol glucoside, stigmasterol, vanillin and salicin were isolated during phytochemical investigation on seeds of Aegle marmelos Correa.