Genetic and biochemical characterization of hyicin 3682, the first bacteriocin reported for Staphylococcus hyicus

Effects of Sub-Minimum Inhibitory Concentrations of Bacteriocin BM173 on Listeria Monocytogenes Biofilm Formation

Listeria monocytogenes is a significant foodborne pathogen that can form biofilms on various food processing surfaces, thereby enhancing resistance to disinfectants and exacerbating harm to human health. Previous studies have indicated that bacteriocin BM173 exhibits antibacterial and antibiofilm activities. In the current study, our aim was to assess the inhibitory mode of action of sub-inhibitory concentrations (SICs, 1/32 × MIC and 1/16 × MIC) of BM173 on the biofilm formation L. monocytogenes. Crystal violet staining assay revealed that SICs of BM173 significantly inhibit L. monocytogenes biofilm formation. Furthermore, the results of swimming motility assay, plate count, ruthenium red staining, and scanning electron microscopy (SEM) revealed that SICs of BM173 could effectively reduce the movement, cell adhesion, and exopolysaccharide (EPS) production of L. monocytogenes, thereby inhibiting biofilm formation. Real-time quantitative PCR analyses further demonstrated that SICs of BM173 down-regulated the expression of biofilm-associated genes, including those encoding adhesion, virulence factors, and quorum sensing. Additionally, SICs of BM173 effectively reduced the biofilm formation of L. monocytogenes on the surfaces of three food-grade materials (glass, stainless steel, and silicone) at 4 and 25 °C. These outcomes suggest that BM173 holds great potential for development as a promising food preservative for application in the food industry.

A Review on Enterocin DD14, the Leaderless Two-Peptide Bacteriocin with Multiple Biological Functions and Unusual Transport Pathway

Enterocin DD14 (EntDD14) is a two-peptide leaderless bacteriocin (LLB) produced by Enterococcus faecalis 14, a human strain isolated from meconium. Studies performed on EntDD14 enabled it to show its activity against Gram-positive bacteria such as Listeria monocytogenes, Clostridium perfringens, Enterococcus faecalis, and Staphylococcus aureus. EntDD14 was also shown to potentiate the activity of different antibiotics such as erythromycin, kanamycin, and methicillin when assessed against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and in vivo in the NMRI-F holoxenic mouse model. Additionally, EntDD14 has an antiviral activity and decreased the secretion of pro-inflammatory IL-6 and IL-8 in inflamed human intestinal Caco-2 cells. The genome of E. faecalis 14 was sequenced and annotated. Molecular tools such as Bagel4 software enabled us to locate a 6.7kb-EntDD14 cluster. Transport of EntDD14 outside of the cytoplasm was shown to be performed synergistically by a channel composed of two pleckstrin-homology-domain-containing proteins, namely DdE/DdF and the ABC transporter DdGHIJ. This latter could also protect the bacteriocinogenic strain against extracellular EntDD14. Here, we focus on academic data and potential therapeutic issues of EntDD14, as a model of two-peptide LLB.

Comprehensive Approaches for the Search and Characterization of Staphylococcins

Novel and sustainable approaches are required to curb the increasing threat of antimicrobial resistance (AMR). Within the last decades, antimicrobial peptides, especially bacteriocins, have received increased attention and are being explored as suitable alternatives to antibiotics. Bacteriocins are ribosomally synthesized antimicrobial peptides produced by bacteria as a self-preservation method against competitors. Bacteriocins produced by Staphylococcus, also referred to as staphylococcins, have steadily shown great antimicrobial potential and are currently being considered promising candidates to mitigate the AMR menace. Moreover, several bacteriocin-producing Staphylococcus isolates of different species, especially coagulase-negative staphylococci (CoNS), have been described and are being targeted as a good alternative. This revision aims to help researchers in the search and characterization of staphylococcins, so we provide an up-to-date list of bacteriocin produced by Staphylococcus. Moreover, a universal nucleotide and amino acid-based phylogeny system of the well-characterized staphylococcins is proposed that could be of interest in the classification and search for these promising antimicrobials. Finally, we discuss the state of art of the staphylococcin applications and an overview of the emerging concerns.

Butelase 1-Mediated Enzymatic Cyclization of Antimicrobial Peptides: Improvements on Stability and Bioactivity

Antimicrobial peptides (AMPs) have broad-spectrum antibacterial properties and safety as food preservatives, whereas the stability and antibacterial activity require improvement. Here, the "head-to-tail" cyclization of linear AMP GKE was catalyzed by butelase 1, which resulted in an improved pronouncedly antibacterial effect. Cell morphology and propidium iodide uptake revealed that the increased membrane permeability was one of the bacteriostatic mechanisms of GKE and could be enhanced after cyclization. As cyclic GKE (cGKE) exhibited more stability than the linear counterpart under the microorganism culture environment, the increase in effective bacteriostatic concentration should be a reason for the superior antibacterial effect. Moreover, cGKE exhibited the ordered secondary structure, while GKE possessed a similar structure only in sodium dodecyl sulfate micelles. The structure was also beneficial to improve the antibacterial activity caused by the increased affinity of cGKE to the membranes. Overall, butelase 1-mediated cyclization is a promising strategy for enhancing the antibacterial activity of linear AMPs.

Bacteriocin-Like Inhibitory Substances in Staphylococci of Different Origins and Species With Activity Against Relevant Pathogens

Bacteriocins are antimicrobial peptides with relevance in the modulation of human and animal microbiota that have gained interest in biomedical and biotechnological applications. In this study, the production of bacteriocin-like inhibitory substances (BLIS) was tested among a collection of 890 staphylococci of different origins (humans, animals, food, and the environment) and species, both coagulase-positive (CoPS, 238 isolates of 3 species) and coagulase-negative staphylococci (CoNS, 652 isolates of 26 species). Of the 890 staphylococci, 60 (6.7%) showed antimicrobial activity by the spot-on-lawn method against at least one of the 25 indicator bacteria tested. BLIS-producer (BLIS⁺) isolates were detected in 8.8% of CoPS and 6.0% of CoNS. The staphylococcal species with the highest percentages of BLIS⁺ isolates were S. chromogenes (38.5%), S. pseudintermedius (26.7%), and S. warneri (23.1%). The production of BLIS was more frequently detected among isolates of pets, wild animals, and food. Moreover, 13 BLIS⁺ isolates showed wide antimicrobial activiy spectrum, and 7 of these isolates (of species S. aureus, S. pseudintermedius, S. sciuri, and S. hominis) demonstrated antimicrobial activity against more than 70% of the indicator bacteria tested. The genetic characterization (by PCR and sequencing) of the 60 BLIS⁺ isolates revealed the detection of (a) 11 CoNS and CoPS isolates carrying putative lantibiotic-like genes; (b) 3 S. pseudintermedius isolates harboring the genes of BacSp222 bacteriocin; and (c) 2 S. chromogenes isolates that presented the gene of a putative cyclic bacteriocin (uberolysin-like), being the first report in this CoNS species. Antimicrobial susceptibility testing was performed in BLIS⁺ isolates and one-third of the CoNS isolates showed susceptibility to all antibiotics tested, which also lacked the virulence genes studied. These BLIS⁺ CoNS are good candidates for further characterization studies.

Staphylococcins: an update on antimicrobial peptides produced by staphylococci and their diverse potential applications

Staphylococcins are antimicrobial peptides or proteins produced by staphylococci. They can be separated into different classes, depending on their amino acid composition, structural complexity, and steps involved in their production. In this review, an overview of the current knowledge on staphylococcins will be presented with emphasis on the information collected in the last decade, including a brief description of new peptides. Most staphylococcins characterized to date are either lantibiotics or linear class II bacteriocins. Recently, gene clusters coding for production of circular bacteriocins, sactipeptides, and thiopeptides have been mined from the genome of staphylococcal isolates. In contrast to class II bacteriocins, lantibiotics, sactipeptides, and thiopeptides undergo post-translational modifications that can be quite extensive, depending on the peptide. Few staphylococcins inhibit only some staphylococcal species, but most of them have proven to target pathogens belonging to different genera and involved in a variety of infectious diseases of clinical or agronomic importance. Therefore, these peptides exhibit potential application as anti-infective drugs in different areas. This review will also cover this diverse and remarkable potential. To be commercialized, however, staphylococcin production should be cost-effective and result in high bacteriocin yields, which are not generally achieved from the culture supernatant of their native producers. Such low yields make their production quite costly and not suitable at large industrial scale. Efforts already made to overcome this limitation, minimizing costs and time of production of some staphylococcins and employing either chemical synthesis or in vivo biosynthesis, will be addressed in this review as well. KEY POINTS: • Staphylococci produce a variety of antimicrobial peptides known as staphylococcins. • Most staphylococcins are post-translationally modified peptides. • Staphylococcins exhibit potential biotechnological applications. Graphical abstract.

Staphylococcal-Produced Bacteriocins and Antimicrobial Peptides: Their Potential as Alternative Treatments for Staphylococcus aureus Infections

Staphylococcus aureus is an important pathogen of both humans and animals, implicated in a wide range of infections. The emergence of antibiotic resistance has resulted in S. aureus strains that are resistant to almost all available antibiotics, making treatment a clinical challenge. Development of novel antimicrobial approaches is now a priority worldwide. Bacteria produce a range of antimicrobial peptides; the most diverse of these being bacteriocins. Bacteriocins are ribosomally synthesised peptides, displaying potent antimicrobial activity usually against bacteria phylogenetically related to the producer strain. Several bacteriocins have been isolated from commensal coagulase-negative staphylococci, many of which display inhibitory activity against S. aureus in vitro and in vivo. The ability of these bacteriocins to target biofilm formation and their novel mechanisms of action with efficacy against antibiotic-resistant bacteria make them strong candidates as novel therapeutic antimicrobials. The use of genome-mining tools will help to advance identification and classification of bacteriocins. This review discusses the staphylococcal-derived antimicrobial peptides displaying promise as novel treatments for S. aureus infections.

Study of the effectiveness of staphylococcins in biopreservation of Minas fresh (Frescal) cheese with a reduced sodium content

Reducing salt content in foods such as cheeses, while limiting the growth of spoilage microorganisms and foodborne pathogens, is a difficult challenge. One method that may prove useful is use of staphylococcins, which are bacteriocins produced by staphylococci. Therefore, staphylococcin antimicrobial activity against six strains of S. aureus isolated from cheese was tested aiming at their industrial application in biopreservation of Minas fresh (Frescal) cheese with reduced sodium content. Three staphylococcins were selected for these tests: Pep 5, aureocin A53 and lysostaphin. All three staphylococcins proved to be bacteriolytic against all six strains of S. aureus. The antimicrobial activity of the partially purified staphylococcins was subsequently investigated against strains S. aureus Q1 and QJ3 in cheese matrices (6.0 log CFU/g) with different NaCl contents (control, a 25% reduction, and a 50% reduction), kept under refrigeration at 4 °C, for 21 days. Both strains were shown to be of concern for food industry as they carry the SEA, SEB and SEH enterotoxin genes, and are resistant to β-lactam drugs and moderate biofilm formers when grown in TSB. When used singly, Pep5, aureocin A53 and lysostaphin reduced approximately 95%, 99% and 99.99% of the viable cell counts, respectively, irrespective of the sodium content of the cheese matrix. The combined action of aureocin A53 and Pep5 resulted in an additional and significant reduction (p < 0.05) of ~1.0 log CFU/g when compared with the reduction caused by the use of either one singly. The combined action of lysostaphin and aureocin A53 or lysostaphin and Pep5 resulted in a reduction similar to or slightly smaller (p > 0.05) than that observed when lysostaphin was employed singly. Lysostaphin also proved to reduce the number of the staphylococcal viable cells to a level (~ 2.0 log CFU/g) at which enterotoxin production should not reach a sufficient quantity to cause food poisoning. Therefore, lysostaphin may have a practical application in the food industry to control staphylococcal contamination of Minas fresh cheese with a sodium content reduced up to 50%, providing consumers with more safe options to reduce their intake of sodium.

Hyicin 4244, the first sactibiotic described in staphylococci, exhibits an anti-staphylococcal biofilm activity

Hyicin 4244 is a small antimicrobial peptide with a broad spectrum of activity that was found in the culture supernatant of Staphylococcus hyicus 4244, the genome of which was then sequenced. The bacteriocin gene cluster (hyiSABCDEFG) was mined from its single chromosome and exhibited a genetic organization similar to that of subtilosin A. All genes involved in hyicin 4244 biosynthesis proved to be transcribed and encode proteins that share at least 42% similarity to proteins encoded by the subtilosin A gene cluster. Due to its resemblance to subtilosin A and the presence of three thioether bonds in its structure, hyicin 4244 is assumed to be a 35-amino acid circular sactibiotic, the first to be described in staphylococci. Hyicin 4244 inhibited 14 staphylococcal isolates from either human infections or bovine mastitis, all biofilm formers. Hyicin 4244 significantly reduced the number of colony-forming units (CFU) and the biofilm formation by two strong biofilm-forming strains randomly chosen as representatives of the strains involved in human infections and bovine mastitis. It also reduced the proliferation and viability of sessile cells in established biofilms. Therefore, hyicin 4244 proved not only to prevent biofilm formation by planktonic cells, but also to penetrate the biofilm matrix in vitro, exerting bactericidal activity against staphylococcal sessile cells. This bacteriocin has the potential to become an alternative antimicrobial for either prevention or treatment of biofilm-related infections caused by different staphylococcal species.