Influence of a nisin-biogel on virulence factors expression by Staphylococcus aureus isolates from Diabetic Foot Infections

• Autor(a) principal: Jesus, Carolina de Oliveira
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/113713
• topic: Diabetic Foot Infections; Staphylococcus aureus; Nisin-biogel; Subinhibitory concentrations; Virulence-related factors; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Diabetic Foot Ulcers (DFUs) constitute a favorable environment for colonization by opportunistic pathogens, and Staphylococcus aureus is the most frequent species isolated from DFUs. Due to the increasing dissemination of antibiotic-resistant strains, including S. aureus, antimicrobial peptides (AMPs) have been recognized as promising candidates for treating resistant bacterial infections. In this study, the AMP nisin had been combined with the natural polysaccharide guar gum to create nisin-biogel, to be evaluated as a new therapeutic approach to Diabetic Foot Infections (DFIs). In in vivo infections, bacteria may be exposed to a decreased effective concentration of antimicrobial agents, referred to as subinhibitory concentrations (sub-MICs). Sub-MICs of antimicrobial agents may lead to changes in bacteria metabolism, namely in biofilm formation ability and virulence genes expression. We analyzed nisin-biogel sub-MICs effects on six different S. aureus clinical isolates, including: (1) multiplication rate by determining optical density at 600 nm; (2) virulence gene expression, including 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), by relative quantitative RT-PCR; (3) biofilm formation by a microtiter technique; (4) Coa production using rabbit plasma; and (5) SpA release using a specific ELISA. Nisin-biogel sub-MICs contributed to a decrease in bacteria multiplication in a strain-dependent and dose-dependent manner, not influencing the typical sigmoidal pattern. A decrease on AgrI, Atl and ClfA mRNA expression, and a trend to increase SpA, Coa, IcaA and IcaD mRNA expression were observed in the presence of nisin-biogel at sub-MICs. The biofilm-forming ability of S. aureus clinical isolates exhibited a trend to increase in the presence of nisin-biogel at 1/4 and 1/8 MIC, whereas a concentration corresponding to 1/2 MIC had no effect on biofilm formation. Nisin-biogel at sub-MICs did not influence significantly coagulase production. Regarding SpA production, nisin-biogel at sub-MICs exhibited a trend to decrease the amount of SpA produced in a dose-dependent manner. These results highlight the importance of optimizing antimicrobial biogel doses before proceeding to in vivo trials, not only to obtain a maximal antibacterial effect but also to reduce the risk for upregulation of virulence factors and, consequently, undesirable effects on the treatment of DFIs.