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Co-ordinated regulation of multidrug efflux and biofilm formation in 1 Salmonella . 2
S. Baugh, Amelia J. Lawler, V. Ricci, A. Ekanayaka, L. Piddock, M. Webber
13 Objectives. We have recently shown that inactivation of any of the multidrug efflux 14 systems of Salmonella results in loss of ability to form a competent biofilm, the aim of 15 this study was to determine the mechanism linking multidrug efflux …
13 Objectives. We have recently shown that inactivation of any of the multidrug efflux 14 systems of Salmonella results in loss of ability to form a competent biofilm, the aim of 15 this study was to determine the mechanism linking multidrug efflux and biofilm 16 formation. 17 Methods. Mutants lacking components of the major AcrAB-TolC system were 18 investigated for their ability to form a biofilm, aggregate and produce biofilm matrix 19 components. The potential for export of a biofilm relevant substrate via efflux pumps 20 was investigated as well as expression of genes that regulate multidrug efflux and 21 production of biofilm matrix components. 22 Results. Mutants of Salmonella enterica serovar Typhimurium which lack TolC or 23 AcrB but surprisingly not AcrA were compromised in their ability to form biofilms. 24 This defect was not related to changes in cellular hydrophobicity, aggregative ability 25 or export of any biofilm specific factor. The biofilm defect associated with inactivation 26 of acrB or tolC resulted from transcriptional repression of curli biosynthesis genes 27 and consequent inhibition of the production of curli by mutants lacking AcrB or TolC. 28 This repression was associated with up-regulation of the global regulator, ramA and 29 artificial over-expression of ramA, marA and soxS each decreased biosynthesis of 30 curli, and inhibited biofilm formation. However, inactivation of these regulators did not 31 rescue the ability of efflux mutants to form a biofilm. 32 Conclusions. This work shows biofilm formation and multidrug efflux are co33 ordinately regulated, and that transcriptional repression of curli biosynthesis causes 34 a lack of biofilm formation which occurs in response to lack of efflux activity or as a 35 result of over-expression of global regulators ramA, marA and soxS. 36
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