Nutrient Composition Promotes Switching between Pellicle and Bottom Biofilm in Salmonella.

Sonia Paytubi,Cristina Madrid,Cintia Cansado,Carlos Balsalobre

doi:10.3389/fmicb.2017.02160

Abstract

Salmonella is one of the most frequently reported causes of foodborne illness worldwide. Non-typhoidal serovars cause gastroenteritis in humans. Salmonella can grow on surfaces forming biofilms, contributing to its persistence since biofilms are difficult to eradicate due to the high resistance to antimicrobials and disinfectants. It has been described that there are two crucial biofilm promoting factors in Salmonella: curli and cellulose. The expression of both factors is coordinately regulated by the transcriptional regulator CsgD. Most biofilm studies of Salmonella have been performed by growing bacteria in low osmolarity rich medium and low temperature (25°C). In such conditions, the biofilm is formed at the air–liquid interface (pellicle biofilm). Remarkably, when Salmonella grow in minimal medium, biofilm formation switches from the air–liquid interface to the solid–liquid interface (bottom biofilm). In this report, the switching between pellicle and bottom biofilm has been characterized. Our data indicate that curli, but not cellulose, is crucial for the formation of both kinds of biofilms. In minimal medium, conditions promoting formation of bottom biofilm, a high transcriptional expression of csgD and consequently of the genes involved in the synthesis of curli and cellulose was detected. The nutritional status of the cells seems to be pivotal for the spatial distribution of the biofilms formed. When bacteria is growing in minimal medium the addition of amino acids downregulates the expression of csgB and causes the switch between bottom and pellicle biofilm. The crosstalk between general metabolism and biofilm formation is also highlighted by the fact that the metabolic sensor cAMP modulates the type of biofilm generated by Salmonella. Moreover, cAMP regulates transcriptional expression of csgD and stimulates pellicle biofilm formation, suggesting that the physiological conditions define the type of biofilm formed by Salmonella. The consequences of the switching between pellicle and bottom biofilm during either infection or survival in natural environments remain undercover.

Highlights

Microbial communities attached to surfaces and embedded in a self-produced extracellular polymeric matrix are defined as biofilms
Salmonella forms a biofilm at the air–liquid interface
We described that S. enterica serovar Enteritidis strain 3934 forms a pellicle biofilm when grown in colonization factor antigen (CFA) but forms a solid–liquid interface biofilm when MM (E minimal medium) is used

Summary

Introduction

Microbial communities attached to surfaces and embedded in a self-produced extracellular polymeric matrix are defined as biofilms. Those complex structures are the principal mode of microbial growth in nature (Steenackers et al, 2012). Development of a biofilm starts when a motile bacterial cell approaches and adheres reversibly to a surface. The subsequent synthesis of an extracellular matrix will support the formation of a mature three-dimensional biofilm. As bacterial biofilms may provide a reservoir of pathogenic bacteria, they represent a threatening concern by increasing the risk of microbial contamination. When bacteria are part of a biofilm are extremely difficult to eradicate (O’Toole et al, 2000; Bridier et al, 2011)

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Results

Conclusion