Abstract: The inhibitory activity of lactic acid against the biofilm formation of Enterobacter cloacae CY4 was evaluated by a crystal violet staining assay, and its potential molecular mechanism was explored by studying cell swimming and swarming motilities, exopolysaccharide production, biofilm microstructure and gene expression levels. The results showed that lactic acid at subinhibitory concentrations could significantly inhibit biofilm formation and decrease cell swimming and swarming motilities of E. cloacae CY4 (P < 0.05), as well as decrease biofilm polysaccharide production. Laser confocal microscopy and scanning electron microscopy showed that lactic acid at subinhibitory concentrations could greatly reduce the thickness of the biofilm and increase its surface roughness and porosity, as well as loosen the biofilm structure with greater cell length and wider gaps between cells. Lactic acid decreased the expression of genes involved in the synthesis of pili and polysaccharides as evaluated by real-time polymerase chain reaction (PCR). This study demonstrates that lactic acid has a significant inhibitory effect on biofilm formation of E. cloacae CY4, which may be related to its influence on cell adhesion and aggregation, and the production of extracellular polysaccharides.

Key words: Enterobacter cloacae, biofilm, lactic acid, extracellular polysaccharides, cell motility