Cholate-Stimulated Biofilm Formation by Lactococcus lactis Cells

Abstract

Bile acid resistance by Lactococcus lactis depends on the ABC-type multidrug transporter LmrCD. Upon deletion of the lmrCD genes, cells can reacquire bile acid resistance upon prolonged exposure to cholate, yielding the ⌬lmrCD r strain. The resistance mechanism in this strain is non-transporter based. Instead, cells show a high tendency to flocculate, suggesting cell surface alterations. Contact angle measurements demonstrate that the ⌬lmrCD r cells are equipped with an increased cell surface hydrophilicity compared to those of the parental and wild-type strains, while the surface hydrophilicity is reduced in the presence of cholate. ⌬lmrCD r cells are poor in biofilm formation on a hydrophobic polystyrene surface, but in the presence of subinhibitory concentrations of cholate, biofilm formation is strongly stimulated. Biofilm cells show an enhanced extracellular polymeric substance production and are highly resistant to bile acids. These data suggest that non-transporter-based cholate resistance in L. lactis is due to alterations in the cell surface that stimulate cells to form resistant biofilms.Lactococcus lactis, like other lactic acid bacteria, survives, albeit weakly, in the human gastrointestinal tract (23). Importantly, bacteria that colonize the gastrointestinal tract need to be resistant to bile salts. When they successfully colonize such a niche, they must transit from a planktonic phase to a biofilm phase. A biofilm community is classically characterized by a sessile mode of existence, in which cells are encased in a secreted extracellular matrix while attached or exposed to a surface (21). However, the condition of surface attachment is flexible, since free-floating flocs with minimal surface attachment are also regarded as biofilms (24). Bacteria growing in biofilms exhibit a specific phenotype and are often but not always more resistant (38) to antimicrobial agents than their planktonic counterparts. Such enhanced resistance appears to be caused by numerous mechanisms (14). Several studies have implicated efflux pumps in the antimicrobial resistance of biofilms (14, 25). Although in Gram-positive bacteria ABC-type drug transporters are known to contribute to drug resistance of planktonic cells (25), so far none have been implicated in biofilm-specific antimicrobial resistance. A recent report suggests the involvement of a putative ABC transporter in biofilmspecific resistance in Gram-negative bacteria (42).The ABC-type multidrug resistance (MDR) transporter LmrCD is a major determinant of drug resistance in L. lactis, but it is also involved in bile acid resistance (41). Consequently, L. lactis cells that lack the lmrCD genes are sensitive to bile acids, such as cholate. When these cells are exposed to stepwiseincreasing sublethal concentrations of cholate, they develop an improved resistance to cholate and several other bile acids (41). The resultant strain was termed the L. lactis ⌬lmrCD r strain. Transcriptome and functional analysis suggests that the resistance by this strain is no longer tran...

Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces

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Biofilm Formation and Detachment in Gram-Negative Pathogens Is Modulated by Select Bile Acids

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