Aims: The aim of this research was to investigate the production of bacteriocins by Bacillus spp. isolated from native soils of south of Brazil. Methods and Results: A bacteriocin produced by the bacterium Bacillus cereus 8 A was identified. The antimicrobial activity was produced starting at the exponential growth phase, although maximum activity was at stationary growth phase. A crude bacteriocin obtained from culture supernatant fluid was inhibitory to a broad range of indicator strains, including Listeria monocytogenes, Clostridium perfringens, and several species of Bacillus. Clinically relevant bacteria such as Streptococcus bovis and Micrococcus luteus were also inhibited. Bacteriocin was stable at 80°C, but the activity was lost when the temperature reached 87°C. It was resistant to the proteolytic action of trypsin and papain, but sensitive to proteinase K and pronase E. Bacteriocin activity was observed in the pH range of 6AE0-9AE0. Conclusions: A bacteriocin produced by Bacillus cereus 8 A was characterized, presenting a broad spectrum of activity and potential for use as biopreservative in food. Significance and impact of study: The identification of a bacteriocin with large activity spectrum, including pathogens and spoilage microorganisms, addresses an important aspect of food safety.

The antibacterial activity of a series of 1,4-naphthoquinones was demonstrated. Disk diffusion tests were carried out against several Gram-positive and Gram-negative bacteria. The compound 5-amino-8-hydroxy-1,4-naphthoquinone was the most effective, presenting inhibition zones measuring 20 mm against staphylococci, streptococci and bacilli at 50 µg/ml. Methicillin-resistant Staphylococcus aureus and several clinical isolates of this bacterium were also inhibited. Naphthazarin, 5-acetamido-8-hydroxy-1,4-naphthoquinone, and 2,3-diamino-1,4-naphthoquinone were the next most active compounds. The minimal inhibitory concentration of the active compounds was determined against S. aureus, ranging from 30 to 125 µg/ml. All compounds presented a minimal bactericidal concentration higher than 500 µg/ml, indicating that their effect was bacteriostatic. The EC 50 , defined as the drug concentration that produces 50% of maximal effect, was 8 µg/ml for 5-amino-8-hydroxy-1,4-naphthoquinone against S. aureus, S. intermedius, and S. epidermidis. These results indicate an effective in vitro activity of 5-amino-8-hydroxy-1,4-naphthoquinone and encourage further studies for its application in antibiotic therapy.

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Aims: To purify and to characterize the antimicrobial compound cerein 8A. Methods and Results: Cerein 8A was isolated by ammonium sulfate precipitation, 1-butanol extraction and ionexchange chromatography. Direct activity on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was observed. The purified substance corresponded to a 26 kDa peptide band. The native protein eluted at the void volume of Sephadex G-100, but within the included volume when a 1AE5 mol l )1 NaCl buffer was used,indicating that cerein 8A aggregates extracellularly. The antimicrobial activity was lost by treatment with proteases and heat. The ultraviolet spectrum was typical of a polypeptide and the infrared spectrum indicates that the peptide contains acyl group(s) in its structure. Intact Bacillus cereus spores were sensitive to cerein 8A at 1600 AU ml )1 .Conclusions: Cerein 8A show distinct properties from other antimicrobial peptides of B. cereus, and has a significant inhibitory effect on spores.Significance and Impact of the Study: The characterization of a substance active against important pathogens addresses an important aspect of food safety.

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