Avaliação da atividade antibiofilme da nisina sobre cepas de Staphylococcus aureus isoladas de mastite bovina

Abstract

Mastitis, an inflammation of the mammary gland, is the most common disease in dairy cattle, frequently caused by Staphylococcus aureus, a pathogen with a high capacity for biofilm formation, which complicates treatment due to its resistance to conventional antimicrobials. Increasing antimicrobial resistance demands new approaches, with nisin, a bacteriocin produced by Lactococcus lactis, emerging as a promising peptide for its activity against Gram-positive bacteria, including S. aureus. This study aimed to evaluate the in vitro antimicrobial efficacy of nisin against S. aureus strains isolated from bovine mastitis cases, specifically in inhibiting biofilm formation and eradicating established biofilms. A standard nisin solution was prepared at 1000 UI, dissolved in HCl and applied to S. aureus samples distributed in 96-well microtiter plates. The experimental method was divided into two main stages: first, the capacity of nisin to inhibit biofilm formation was tested on pre-standardized strains, followed by an assessment of the capacity of nisin to eradicated biofilms established after 24 hours of incubation. To measure biofilm formation and reduction, procedures included washing, methanol fixation, and crystal violet staining, with subsequent optical density (OD) readings taken in a microplate reader at 600 nm. The results showed that nisin significantly reduced the initial bacterial adhesion, indicating its effectiveness in preventing biofilm formation (z = 2.366, p<0.0001, r = 0.63). However, when applied to biofilms formed after 24 hours, it demonstrated low removal capacity, revealing the limited efficacy of this antimicrobial peptide in disrupting established biofilms (z = -0.330, p = 0.0395, r = 0.1). These findings underscore the need for new strategies, including the combined use of nisin with other antimicrobials or controlled-release technologies, to enhance its action against mature biofilms. This study contributes to the field by identifying the limitations of nisin as a standalone agent and highlights the importance of exploring alternatives that could enhance its use against bovine mastitis associated with resistant S. aureus strains. This research contribute for further investigations around antibiofilm treatments and other innovative approaches, relevant in the context of increasing antimicrobial resistance in veterinary pathogens.