The antimicrobial peptide aureocin A53 as an alternative agent for biopreservation of dairy products.

AIMS: The aim of this study was to investigate the potential of aureocin A53, a staphylococcal antimicrobial peptide, for improving food safety. METHODS AND RESULTS: The antimicrobial activity of aureocin A53 against strains of Listeria monocytogenes isolated from food was tested and the bacteriocin proved to be bactericidal and bacteriolytic against the listerial strains. Aureocin A53 was neither toxic to eukaryotic cell lines nor haemolytic against sheep erythrocytes. It also exhibited a remarkable stability during storage at different temperatures and sensitivity to both simulated gastric juice and bile salts. When the antibacterial activity of aureocin A53 (256 AU ml(-1) ) was tested in skimmed milk artificially inoculated with a L. monocytogenes strain (1·0 × 10(4)  CFU ml(-1) ) isolated from food, during storage at 4°C, the bacteriocin reduced the viable counts by 7·7-log10 units up to 7 days of incubation, when compared with the controls not treated with the bacteriocin. CONCLUSIONS: Aureocin A53 exhibited several features considered important for biopreservation and remained fully active in a food matrix. SIGNIFICANCE AND IMPACT OF THE STUDY: Taken together, the results confirmed that aureocin A53 has potential to be used as a food preservative, representing an alternative to the use of nisin in biopreservation of dairy products.

Investigation of biotechnological potential of sponge-associated bacteria collected in Brazilian coast.

Marine bacteria are a rich source of structurally unique natural compounds, several of which have shown a wide variety of biological activities. In this study, the metabolites present in the culture supernatants of the eight sponge-associated bacteria were extracted using ethyl acetate, and all extracts showed activity against Staphylococcus aureus. Subsequently, the extracts of the Pseudomonas fluorescens H40 and H41, and Pseudomonas aeruginosa H51 were subjected to solvent partitioning, and the active fractions were submitted to chromatographic separation. Three different active fractions were obtained, one of which was identified as diketopiperazine cyclo-(L-Leu-L-Pro). This substance was bactericidal for Staph. aureus and Ps. aeruginosa and showed cytotoxic activity against HEp-2 tumour cells. Putative gene fragments coding for the type I polyketide synthase (PKS-I) and nonribosomal peptide synthetase (NRPS) domains were PCR-amplified from five and three strains, respectively. The results suggest that sponge-associated bacteria analysed in this study may represent a potential source for production of antimicrobial substances against bacterial pathogens of medical importance.

Marine sponges: potential sources of new antimicrobial drugs.

Sponges (phylum Porifera) are sessile marine filter feeders that have developed efficient defense mechanisms against foreign attackers such as viruses, bacteria, or eukaryotic organisms. Marine sponges are among the richest sources of pharmacologically-active chemicals from marine organisms. It is suggested that (at least) some of the bioactive secondary metabolites isolated from sponges are produced by functional enzyme clusters, which originated from the sponges and their associated microorganisms. More than 5,300 different products are known from sponges and their associated microorganisms, and more than 200 new metabolites from sponges are reported each year. As infectious microorganisms evolve and develop resistance to existing pharmaceuticals, the marine sponge provides novel leads against bacterial, viral, fungal and parasitic diseases. Many marine natural products have successfully advanced to the late stages of clinical trials, as for example ara-A (vidarabine), an anti-viral drug used against the herpes simplex encephalitis virus. This substance is in clinical use for many years. Moreover, a growing number of candidates have been selected as promising leads for extended preclinical assessment, including manzamine A (activity against malaria, tuberculosis, HIV, and others), lasonolides (antifungal activity) and psammaplin A (antibacterial activity). In this review we have surveyed the discoveries of products derived from marine sponges and associated bacteria that have shown in vivo efficacy or potent in vitro activity against infectious and parasitic diseases, including bacterial, viral, fungal and protozoan infections. Our objective was to highlight the substances that have the greatest potential to lead to clinically useful treatments.