Marcela Carina Audisio

Antibacterial activity of naringin derivatives against pathogenic strains

Aims:  To study the antimicrobial activity of naringin (NAR), a flavonoid extracted from citrus industry waste, and NAR derivatives [naringenin (NGE), prunin and alkyl prunin esters] against pathogenic bacteria such as L. monocytogenes, E. coli O157:H7 and S. aureus. The relationship between the structure of the chemical compounds and their antagonistic effect was also analysed.

Evaluation of antibacterial and cytotoxic effects of nano-sized bioactive glass/collagen composites releasing tetracycline hydrochloride.

To evaluate the antibacterial efficacy of silicate bioactive glass nanoparticles/collagen composites functionalized with tetracycline hydrochloride (TCH).

Antagonistic effects of Bacillus subtilis subsp. subtilis and B. amyloliquefaciens against Macrophomina phaseolina: SEM study of fungal changes and UV-MALDI-TOF MS analysis of their bioactive compounds.

The antifungal effect of Bacillus subtilis subsp. subtilis PGPMori7 and Bacillus amyloliquefaciens PGPBacCA1 was evaluated against Macrophomina phaseolina (Tassi) Goid. Cell suspension (CS), cell-free supernatant (CFS) and the lipopeptide fraction (LF) of PGPMori7 and PGPBacCA1 were screened against three different M. phaseolina strains. CS exhibited the highest inhibitory effect (around 50%) when compared to those of CFS and LF, regardless of the fungal strain studied. The synthesis of lipopeptides was studied by UV-MALDI TOF. Chemical analysis of Bacillus metabolite synthesis revealed that surfactin and iturin were mainly produced in liquid medium. Potential fengycin was also co-produced when both Bacillus were cultivated in solid medium. In co-culture assays, the bacterial colony-fungal mycelium interface at the inhibition zone was evaluated by both scanning electron microscopy (SEM) and UV-MALDI TOF, the former to determine the structural changes on M. phaseolina cells and the latter to identify the main bioactive molecules involved in the inhibitory effect. PGPBacCA1 produced surfactin, iturin and fengycin in the inhibition zone while PGPMori7 only produced these metabolites within its colony and not in the narrow inhibition zone. Interestingly, SEM revealed that PGPBacCA1 induced damage in M. phaseolina sclerotia, generating a fungicidal effect as no growth was observed when normal growth conditions were reestablished. In turn, PGPMori7 inhibited the growth of the Macrophomina mycelium without fungal injury, resulting only in a fungistatic activity. From these results, it was determined that the two bacilli significantly inhibited the growth of an important phytopathogenic fungus by at least two different mechanisms: lipopeptide synthesis and competition among microorganisms.

Antimicrobial properties of prunin, a citric flavanone glucoside, and its prunin 6″-O-lauroyl ester

Aims:  To determine the antimicrobial potential of prunin (P), a flavanone glucoside resulting from the hydrolysis of naringin present in grapefruit, and of its prunin 6″‐O‐lauroyl ester (PL), synthesized by enzymatic catalysis.

Bacillus subtilis subsp. subtilis CBMDC3f with antimicrobial activity against Gram-positive foodborne pathogenic bacteria: UV-MALDI-TOF MS analysis of its bioactive compounds.

In this work a new Bacillus sp. strain, isolated from honey, was characterized phylogenetically. Its antibacterial activity against three relevant foodborne pathogenic bacteria was studied; the main bioactive metabolites were analyzed using ultraviolet matrix assisted laser desorption-ionization mass spectrometry (UV–MALDI MS). Bacillus CBMDC3f was phylogenetically characterized as Bacillus subtilis subsp. subtilis after rRNA analysis of the 16S subunit and the gyrA gene (access codes Genbank JX120508 and JX120516, respectively). Its antibacterial potential was evaluated against Listeria monocytogenes (9 strains), B. cereus (3 strains) and Staphylococcus aureus ATCC29213. Its cell suspension and cell-free supernatant (CFS) exerted significant anti-Listeria and anti-S. aureus activities, while the lipopeptides fraction (LF) also showed anti-B. cereus effect. The UV-MALDI-MS analysis revealed surfactin, iturin and fengycin in the CFS, whereas surfactin predominated in the LF. The CFS from CBMDC3f contained surfactin, iturin and fengycin with four, two and four homologues per family, respectively, whereas four surfactin, one iturin and one fengycin homologues were identified in the LF. For some surfactin homologues, their UV-MALDI-TOF/TOF (MS/MS; Laser Induced Decomposition method, LID) spectra were also obtained. Mass spectrometry analysis contributed with relevant information about the type of lipopeptides that Bacillus strains can synthesize. From our results, surfactin would be the main metabolite responsible for the antibacterial effect.

Withanolides with Antibacterial Activity from Nicandra john-tyleriana

Eleven new withanolides (1-11) were isolated and characterized from the aerial parts of Nicandra john-tyleriana. Five of these withanolides have an unmodified skeleton (1-5), two are acnistins (6, 7), and four are withajardins (8-11). These new isolates were fully characterized using a combination of spectroscopic techniques (including multidimensional NMR) and mass spectrometry. All compounds were evaluated for their antibacterial activity against Bacillus, Enterococcus, Escherichia, Listeria, Pseudomonas, and Staphylococcus strains.

Laboratory evaluation of Lactobacillus johnsonii CRL1647 metabolites for biological control of Musca domestica

The house fly, Musca domestica L. (Diptera: Muscidae), is a key problem in animal producing and rearing areas. Currently, the use and abuse of chemical pest‐control compounds has generated resistance in M. domestica and, hence, new approaches are required. In this work, the potential entomopathogenic activity of Lactobacillus johnsonii Fujisawa et al. CRL1647 was evaluated against M. domestica, under laboratory conditions. Bioassays were done for three consecutive years using bacterial cell suspensions (CS) and cell‐free supernatants (CFS) under controlled conditions (27 ± 1 °C, 57 ± 2% r.h., and L12:D12 photoperiod). Both the CS and CFS displayed high levels of larvicidal (96%) and pupicidal (97%) activities. Chemical characterization of the CFS revealed that the bioactive metabolites are acidic compounds, not affected by thermal treatment or by trypsin. Organic acids were identified and quantified by high‐performance liquid chromatography (HPLC); only lactic acid (129.7 ± 1.0 mM), acetic acid (37.3 ± 0.8 mM), and phenyllactic acid (0.3 ± 0.1 mM) were detected. A significant decrease in fecundity of the house flies was observed in females from larvae fed on CFS; male fertility was not affected. Interestingly, only the mixture of organic acids exerted the biological effects. These results suggest that the metabolites synthesized by L. johnsonii CRL1647 can be used in a novel biocontrol strategy against house flies.