Synergistic antifungal activity and potential mechanism of action of a glycolipid-like compound produced by Streptomyces blastmyceticus S108 against Candida clinical isolates

Evaluation of antimicrobial efficacy against spoilage microorganisms and impact on beverage color and turbidity of commercial preservatives derived from edible mushrooms

The antimicrobial efficacy and the impact on sensory quality of preservatives from different natural sources can vary dramatically. This makes it challenging for manufacturers to incorporate natural preservatives in shelf-stable beverage formulation. This study compares new-to-market natural glycolipids (NG) derived from Dacryopinax spathularia and white button mushroom extract (WBME) containing chitosan from Agaricus bisporus. The antimicrobial efficacy was evaluated in a microbial spoilage challenge study wherein three-species suspensions of yeasts (Saccharomyces cerevisiae YG25, Zygosaccharomyces bailii DSM 70492 and Candida parapsilosis TD-0020), bacteria (Lactiplantibacillus plantarum DSM 12028, Lactococcus lactis DSM 20481 and Gluconobacter oxydans AC39) and fungal spores (Aspergillus brasiliensis DSM 1988, Byssochlamys nivea DSM 1824 and Penicillium roqueforti DSM 1079) were inoculated (100 CFU/mL per species) in acidified iced tea and juice drink. The preservatives were tested at concentrations within the range proposed by their respective manufacturers. They were also benchmarked against sodium benzoate (SB) and potassium sorbate (PS). Beverage samples were maintained at ambient temperature for 12 weeks and analyzed for microbial counts, pH, total soluble solids (TSS) at week 0, 1, 2, 4, 8 and 12. The impact on color and turbidity was assessed in a separate trial without spoilage microorganisms. Overall, NG was more effective and consistent than WBME and PS + SB in preventing spoilage by selected bacteria, yeasts, and molds in this study without significant impact on pH and TSS. WBME counterproductively supported the growth G. oxydans AC39 in acidified iced tea. WBME at high concentration appeared to reduce growth of S. cerevisiae YG25 and Z. bailii DSM 70492, but not C. parapsilosis TD-0020 whereas PS + SB could not inhibit any yeast species. WBME reduced mold spoilage for 4 weeks, after which the antifungal effects wore off. Finally, WBME and NG at high concentrations may cause separation, which increases beverage turbidity upon remixing and lightens the beverage color, especially if the beverage contains a significant amount of pectin.

Antibacterial and biofilm disruptive nonribosomal lipopeptides from Streptomyces parvulus against multidrug-resistant bacterial infections

BACKGROUND

In recent years, new drugs for the treatment of various diseases, thereby the emergence of antimicrobial resistance tremendously increased because of the increased consumption rate of various drugs. However, the irrational use of antibiotics increases the microbial resistance along with that the frequency of mortality associated with infections is higher. Broad-spectrum antibiotics were effectively against various bacteria and the unrestricted application of antibiotics lead to the emergence of drug resistance. The present study was aimed to detect the antibacterial properties of lipopeptide novel drug producing Streptomyces parvulus.

METHODS

A lipopeptide-producing S. parvulus was isolated from the soil sample. The inhibitory effect of lipopeptide was detected against Gram-positive and Gram-negative bacteria. Bactericidal activity and minimum inhibitory concentration (MIC) were assayed. The IC50 value was analysed against ovarian and human melanoma cell lines. The experimental mouse model was infected withKlebsiella pneumoniae and treated with lipopeptide and bactericidal activity was determined.

RESULTS

The results indicated that the antibacterial activity of lipopeptide ranges from 13 ± 1 mm to 32 ± 2 mm against Gram-positive and Gram-negative strains. The lowest MIC value was noted as 1.5 ± 0.1 µg/mL against K. pneumoniae and the highest against E. aerogenes (7.5 ± 0.2 µg/mL). The IC50 value was considerably high for the ovarian cell lines and human melanoma cell lines (426 µg/mL and 503 µg/mL). At 25 µg/mL concentration of lipopeptide, only 16.4% inhibition was observed in the ovarian cell line whereas 20.2% inhibition was achieved at this concentration in the human melanoma cell line. Lipopeptide inhibited bacterial growth and was completely inhibited at a concentration of 20 µg/mL. Lipopeptide reduced bacterial load in experimental mice compared to control (p < 0.05).

CONCLUSION

Lipopeptide activity and its non-toxic nature reveal that it may serve as a lead molecule in the development of a novel drug.