RESUMO
The Enterobacteriaceae family is recognized as a primary group of Gram-negative pathogens responsible for foodborne illnesses and is frequently associated with antibiotic resistance. The present study explores the natural-based compound trans-cinnamaldehyde (TC) against drug-resistant Enterobacteriaceae and its synergism with gentamicin (GEN) to address this issue. The research employs three strains of Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae, previously isolated from shrimp. The antibacterial activity was evaluated by the disk diffusion method, microdilution test, kinetics of growth, and time-kill curve. In addition, the synergistic effect between TC/GEN was investigated by checkerboard assay. All strains showed sensitivity to TC with an inhibition zone diameter > 35 mm. The TC showed inhibitory and bactericidal action in the most tested bacteria around 625 µg/mL. Sub-inhibitory amounts (1/2 and 1/4 MIC) of TC interfered with the growth kinetics by lag phase extension and decreased the log phase. Time-kill curves show a reduction of viable cells after the first hour of TC treatment at bactericidal concentrations. The synergistic effect between TC/GEN was observed for E. coli and E. cloacae strains with FICi ranging from 0.15 to 0.50. These findings, therefore, suggest TC as a promising alternative in the fight against drug-resistant Enterobacteriaceae that can cause foodborne illnesses.
RESUMO
The aim of this work was to evaluate the anti-Escherichia coli effect of cell-free supernatant (CFS) of Lactobacillus spp. against planktonic and biofilm forms of foodborne isolates. Escherichiacoli strains (P12, P25, P35 and P36), previously isolated from fresh filets of fish, were subjected to antimicrobial susceptibility determination by the disc-diffusion agar method. Subsequently, the antagonistic effect between probiotic and pathogenic strains was determined by spot overlay assay. Finally, the CFS activity against pre-established (12 h) biofilms was demonstrated through biomass quantification by crystal violet staining and scanning electron microscopy (SEM). All isolates presented some pattern of resistance, primarily to ampicillin and tetracycline. Probiotic strains presented high antagonistic effects against all E. coli strains, presenting inhibition zones (R) ranging from 15.60 to 20.67 mm. Additionally, the residual biomass of pre-established (12 h) biofilm was drastically reduced about 50% after CFS treatment (P < 0.01). What can be noted by SEM images, which show less surface-attached cells of CFS-treated biofilms of E. coli (P12). Thus, cell-free preparations produced from Lactobacillus spp. may represent a tool in the battle against planktonic cells and biofilm forms of antibiotic-resistant E. coli.
