Active Suppression of Early Immune Response in Tobacco by the Human Pathogen Salmonella Typhimurium

Abstract

The persistence of enteric pathogens on plants has been studied extensively, mainly due to the potential hazard of human pathogens such as Salmonella enterica being able to invade and survive in/on plants. Factors involved in the interactions between enteric bacteria and plants have been identified and consequently it was hypothesized that plants may be vectors or alternative hosts for enteric pathogens. To survive, endophytic bacteria have to escape the plant immune systems, which function at different levels through the plant-bacteria interactions. To understand how S. enterica survives endophyticaly we conducted a detailed analysis on its ability to elicit or evade the plant immune response. The models of this study were Nicotiana tabacum plants and cells suspension exposed to S. enterica serovar Typhimurium. The plant immune response was analyzed by looking at tissue damage and by testing oxidative burst and pH changes. It was found that S. Typhimurium did not promote disease symptoms in the contaminated plants. Live S. Typhimurium did not trigger the production of an oxidative burst and pH changes by the plant cells, while heat killed or chloramphenicol treated S. Typhimurium and purified LPS of Salmonella were significant elicitors, indicating that S. Typhimurium actively suppress the plant response. By looking at the plant response to mutants defective in virulence factors we showed that the suppression depends on secreted factors. Deletion of invA reduced the ability of S. Typhimurium to suppress oxidative burst and pH changes, indicating that a functional SPI1 TTSS is required for the suppression. This study demonstrates that plant colonization by S. Typhimurium is indeed an active process. S. Typhimurium utilizes adaptive strategies of altering innate plant perception systems to improve its fitness in the plant habitat. All together these results suggest a complex mechanism for perception of S. Typhimurium by plants.

Impact ofSalmonella entericaType III Secretion System Effectors on the Eukaryotic Host Cell

“…In fact, transcriptomic analysis indicated that 649 host genes are induced specifically by the T3SS1 mutant, and many of these genes encode proteins related to responses against pathogens [170]. Consistent with this idea, wild-type bacteria, but not a T3SS1 mutant, were able to suppress the oxidative burst and the increase in extracellular pH after inoculation of a tobacco cell culture [171]. Clearly, the role of Salmonella T3SSs and the outcome of the interactions are different depending on plant species and cultivars and on Salmonella serovars [166,172].…”

Influence of the Plant Defense Response to Escherichia coli O157:H7 Cell Surface Structures on Survival of That Enteric Pathogen on Plant Surfaces

“…A recent study showed that live Salmonella enterica serovar Typhimurium can actively suppress the defense responses in tobacco plants. Infection with live Salmonella did not induce plant defense responses, although heat-killed Salmonella and purified LPS did so (32).…”

“…EPS and LPS are involved in bacterial adherence, colonization, and biofilm structure (2,13). In addition, those bacterial surface structures were demonstrated to activate host defenses, inducing host immune responses (25,32).…”

Diversity and Antimicrobial Resistance of Salmonella enterica Isolates from Surface Water in Southeastern United States

“…Furthermore, natural waters can serve as a vehicle for dissemination of Salmonella in the environment and as a route of transmission among hosts (16). Although Salmonella traditionally has been regarded as a host-associated food-borne pathogen, irrigation water has increasingly been recognized as a route of transmission of Salmonella (19), with subsequent introduction of Salmonella enterica to leafy vegetables (20,21). Fruits and vegetables have been increasingly recognized as an important source of Salmonella enterica in food-borne outbreaks (22,23).…”