Aureocin A53

Resistance to nonribosomally synthesized peptide antibiotics affecting the cell envelope is well studied and mostly associated with the action of peptide-sensing and detoxification (PSD) modules, which consist of a two-component system (TCS) and an ATP-binding cassette (ABC) transporter. In contrast, the mechanisms of resistance to ribosomally synthesized bacterial toxic peptides (bacteriocins), which also affect the cell envelope, are studied to a lesser extent, and the possible cross-resistance between them and antibiotics is still poorly understood. In the present study, we investigated the development of resistance of Lactococcus lactis to aureocin A53- and enterocin L50-like bacteriocins and cross-resistance with antibiotics. First, 19 spontaneous mutants resistant to their representatives were selected and also displayed changes in sensitivity to peptide antibiotics acting on the cell envelope (bacitracin, daptomycin, and gramicidin). Sequencing of their genomes revealed mutations in genes encoding the ABC transporter YsaCB and the TCS KinG-LlrG, the emergence of which induced the upregulation of the dltABCD and ysaDCB operons. The ysaB mutations were either nonsense or frameshift mutations and led to the generation of truncated YsaB but with the conserved N-terminal FtsX domain intact. Deletions of ysaCB or llrG had a minor effect on the resistance of the obtained mutants to the tested bacteriocins, daptomycin, and gramicidin, indicating that the development of resistance is dependent on the modification of the protein rather than its absence. In further corroboration of the above-mentioned conclusion, we show that the FtsX domain, which functions effectively when YsaB is lacking its central and C-terminal parts, is critical for resistance to these antimicrobials.

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.

Aureocin A53 is an N-formylated antimicrobial peptide (AMP) produced by Staphylococcus aureus. Aureocin A53 has a broad spectrum of antimicrobial activity against human and animal pathogens. In the present study, its antagonistic activity was investigated towards 30 strains of S. aureus and 30 strains of Streptococcus spp. isolated from bovine mastitis cases in Brazil. Bovine mastitis is a disease that causes a major economic impact worldwide. Aureocin A53 inhibited the growth of all 60 strains tested, including multidrug-resistant streptococcal isolates and strains of S. aureus belonging to different pulsotypes. This AMP proved to be bactericidal against the six target strains randomly selected among staphylococci and streptococci, also exhibiting a lytic mode of action against the staphylococcal cells. Furthermore, it was determined that 2,048 AU/mL of the AMP were required to inhibit 99.99% of the cell growth of the strain less sensitive to aureocin A53. Aureocin A53 was not toxic to bovine mammary gland epithelial cells after a 24-h exposure and maintained its antimicrobial activity when tested in the excised-teat model against strains of S. aureus and Streptococcus agalactiae, the species responsible for most intramammary infections, not only in Brazil but in other countries as well. Therefore, the use of aureocin A53 in the development of new pharmacological products for the prophylaxis and/or treatment of bovine mastitis was considered promising.