Resumo:
Leptospirosis is a zoonotic infectious disease caused by bacteria of the genus
Leptospira. Dogs are highly susceptible, often presenting renal impairment with clinical and
epidemiological significance. Leptospira can form biofilms in the environment, in chronic hosts
and in vitro, however, this feature has not been investigated in acute infections. Biofilm
formation represents a One Health threat, as it is associated with therapeutic failures and the
persistence of pathogenic bacteria in the human-animal-environment interface. This study
aimed to investigate biofilms in the renal parenchyma of dogs naturally infected with acute
leptospirosis. Anti-lipL32 immunohistochemistry and Alcian Bleu and periodic acid-Schiff
staining were applied to identify Leptospira and detect components of the exopolysaccharide
matrix. Additionally, four strains (C20, C29, C51 and C82), isolated from these dogs, were
subjected to antimicrobial susceptibility assays in both planktonic and biofilm (7 and 21 days)
forms, using doxycycline, ciprofloxacin and p-coumaric acid (p-CA) at concentrations ranging
from 0,02μg/mL to 1,600μg/mL. After antimicrobial exposure, the disruption of biofilm
architecture was evaluated by scanning electron microscopy. No histological staining of the
extracellular matrix was detected; however, incipient biofilms, in the form of L. interrogans
aggregates, were observed. Biofilm maturity negatively affected antimicrobial efficacy, with
lower susceptibility observed in biofilms as early as 7 days compared to planktonic forms. In
both growth conditions, p-CA exhibited lower MICs than the tested antibiotics. Despite
variations in biofilm architecture after disruption, intact bacterial cells were present in all
treatments. These findings highlight the need to investigate the role of bacterial aggregates in
in vivo biofilm progression, the specific mechanisms of p-CA action in L. interrogans biofilms,
and more effective therapeutic combinations than conventional treatments.
