Infiltration of Matrix-Non-producers Weakens the Salmonella Biofilm and Impairs Its Antimicrobial Tolerance and Pathogenicity.

Chakravarthy S Srinandan,Monalisha Elango,Dipshikha Chakravortty,Divya P Gnanadhas

doi:10.3389/fmicb.2015.01468

Abstract

Bacterial biofilms display a collective lifestyle, wherein the cells secrete extracellular polymeric substances (EPS) that helps in adhesion, aggregation, stability, and to protect the bacteria from antimicrobials. We asked whether the EPS could act as a public good for the biofilm and observed that infiltration of cells that do not produce matrix components weakened the biofilm of Salmonella enterica serovar Typhimurium. EPS production was costly for the producing cells, as indicated by a significant reduction in the fitness of wild type (WT) cells during competitive planktonic growth relative to the non-producers. Infiltration frequency of non-producers in the biofilm showed a concomitant decrease in overall productivity. It was apparent in the confocal images that the non-producing cells benefit from the EPS produced by the Wild Type (WT) to stay in the biofilm. The biofilm containing non-producing cells were more significantly susceptible to sodium hypochlorite and ciprofloxacin treatment than the WT biofilm. Biofilm infiltrated with non-producers delayed the pathogenesis, as tested in a murine model. The cell types were spatially assorted, with non-producers being edged out in the biofilm. However, cellulose was found to act as a barrier to keep the non-producers away from the WT microcolony. Our results show that the infiltration of non-cooperating cell types can substantially weaken the biofilm making it vulnerable to antibacterials and delay their pathogenesis. Cellulose, a component of EPS, was shown to play a pivotal role of acting as the main public good, and to edge-out the non-producers away from the cooperating microcolony.

Highlights

Salmonellosis is the leading cause of food borne diseases worldwide (Kothari et al, 2008; Westrell et al, 2009; CDC, 2011)
We reasoned that the Wild Type bacteria (WT), which form biofilm would incur a metabolic cost to produce extracellular polymeric substances (EPS)
The cultures were grown in monocultures and a co-culture of wild type (WT) and csgD cells were grown in 1:1 ratio, and the colony forming units was measured at log and stationary phases

Summary

Introduction

Salmonellosis is the leading cause of food borne diseases worldwide (Kothari et al, 2008; Westrell et al, 2009; CDC, 2011). Salmonella biofilms are known to occur on different surfaces including water distribution systems, food processing equipment, plant, and epithelial surfaces, Influence of Matrix-Non-producers on Biofilm while they form persistent biofilms on gall stones in the host (Steenackers et al, 2012). Cells in a biofilm are notorious for their tolerance toward high doses of antimicrobials relative to their planktonic counterparts. Salmonella biofilm cells are resilient to high doses of chlorine and other sanitizers, especially due to the EPS matrix, and they pose potential risks in water distribution systems and food processing units (Joseph et al, 2001; Solano et al, 2002; Scher et al, 2005; Corcoran et al, 2014)

Methods

Results

Conclusion