Influence of Nisin-Biogel at Subinhibitory Concentrations on Virulence Expression in Staphylococcus aureus Isolates from Diabetic Foot Infections

Abstract

A new approach to diabetic foot infections (DFIs) has been investigated, using a nisin-biogel combining the antimicrobial peptide (AMP) nisin with the natural polysaccharide guar-gum. Since in in vivo conditions bacteria may be exposed to decreased antimicrobial concentrations, known as subinhibitory concentrations (sub-MICs), effects of nisin-biogel sub-MIC values corresponding to 1/2, 1/4 and 1/8 of nisin’s minimum inhibitory concentration (MIC) on virulence expression by six Staphylococcus aureus DFI isolates was evaluated by determining bacteria growth rate; expression of genes encoding for staphylococcal protein A (spA), coagulase (coa), clumping factor A (clfA), autolysin (atl), intracellular adhesin A (icaA), intracellular adhesin D (icaD), and the accessory gene regulator I (agrI); biofilm formation; Coa production; and SpA release. Nisin-biogel sub-MICs decreased bacterial growth in a strain- and dose-dependent manner, decreased agrI, atl and clfA expression, and increased spA, coa, icaA and icaD expression. Biofilm formation increased in the presence of nisin-biogel at 1/4 and 1/8 MIC, whereas 1/2 MIC had no effect. Finally, nisin-biogel at sub-MICs did not affect coagulase production, but decreased SpA production in a dose-dependent manner. Results highlight the importance of optimizing nisin-biogel doses before proceeding to in vivo trials, to reduce the risk of virulence factor’s up-regulation due to the presence of inappropriate antimicrobial concentrations.

Bacteriostasis of nisin against planktonic and biofilm bacteria: Its mechanism and application

“…PIA plays a crucial role in the cell–cell adhesion and leads to the formation of the multi‐layer structures in biofilms and also associates with the immune response of bacteria to escape their hosts (Cramton et al., 1999). Many adhesion proteins, such as type IV pilus protein (PILY1), biofilm‐associated protein 1 (Bap1), fibronectin‐binding protein A (FnBPA), fibrinogen‐binding protein (Fbe), and adhesion factor A (ClfA), contribute to bacterial adhesion in biofilm (Jesus et al., 2021; Jiang et al., 2021; Xu et al., 2017). In addition to the above adhesion‐related components, EPS released by microbial cells is another essential component for adhesion, making cells irreversibly adhere to the surface of objects (Roy et al., 2018).…”

“…In the presence of 1/8 MIC nisin–biogel, the formation of S. aureus biofilm significantly increased by about 1.3‐fold. When detected by RT‐qPCR, the expression levels of some virulence‐related genes, such as agr I , atl (encoding autolysase), and clf A , significantly decreased, while the expression levels of some biofilm‐related genes, such as coa (encoding coagulase), ica A , and ica D , increased to some extent (Jesus et al., 2021). Overall, under nisin treatment at sub‐inhibitory concentrations, the expression of biofilm‐related genes increased, while the expression of virulence genes reduced.…”

Efficiency of Antimicrobial Peptides Against Multidrug-Resistant Staphylococcal Pathogens

“…Nisin encapsulated in nanofibers made of polyvinyl alcohol, wheat gluten, and zirconia exhibited well-controlled release and high inhibition activity against S. aureus (H. Wang et al, 2015 ). Nisin-biogel, a delivery system for nisin based on guar gum gel, has been developed and displayed antimicrobial activity against S. aureus ( Jesus et al, 2021 ). At subinhibitory levels, it suppressed some virulence factors, such as the factors related to biofilm formation, coagulase, and protein A; however, the expression of some other virulence genes, such as spA (staphylococcal protein A), coa (coagulase), icaA (intracellular adhesin A), and icaD (intracellular adhesin D), was elevated, requiring a thorough consideration of the optimal dosage when applying nisin in clinical practice ( Jesus et al, 2021 ).…”