Salmonella Biofilm Formation, Chronic Infection, and Immunity Within the Intestine and Hepatobiliary Tract

Abstract

Within the species of Salmonella enterica, there is significant diversity represented among the numerous subspecies and serovars. Collectively, these account for microbes with variable host ranges, from common plant and animal colonizers to extremely pathogenic and human-specific serovars. Despite these differences, many Salmonella species find commonality in the ability to form biofilms and the ability to cause acute, latent, or chronic disease. The exact outcome of infection depends on many factors such as the growth state of Salmonella, the environmental conditions encountered at the time of infection, as well as the infected host and immune response elicited. Here, we review the numerous biofilm lifestyles of Salmonella (on biotic and abiotic surfaces) and how the production of extracellular polymeric substances not only enhances long-term persistence outside the host but also is an essential function in chronic human infections. Furthermore, careful consideration is made for the events during initial infection that allow for gut transcytosis which, in conjunction with host immune functions, often determine the progression of disease. Both typhoidal and non-typhoidal salmonellae can cause chronic and/or secondary infections, thus the adaptive immune responses to both types of bacteria are discussed with particular attention to the differences between Salmonella Typhi, Salmonella Typhimurium, and invasive non-typhoidal Salmonella that can result in differential immune responses. Finally, while strides have been made in our understanding of immunity to Salmonella in the lymphoid organs, fewer definitive studies exist for intestinal and hepatobiliary immunity. By examining our current knowledge and what remains to be determined, we provide insight into new directions in the field of Salmonella immunity, particularly as it relates to chronic infection.

Salmonella Enteritidis Fatal Septicemia with Meningoencephalitis in a Tiger (Panthera tigris) Cub

“…When septicemia ensues, characteristic systemic signs occur (e.g., fever, vascular damage, and multi-organ dysfunction) due to the effects of circulating endotoxin. However, the complex mechanisms involving and promoting transmission between the primary site of infection and the other sites (brain, heart, liver, lungs, and spleen) still remain unclear [ 28 ]. Thus, the acute and severe clinical and histopathological findings herein described are quite unusual.…”

Bacterial Biofilms and Their Implications in Pathogenesis and Food Safety

“…Salmonella also form biofilms on food, the environment, and human and animal intestine [ 160 ]. Several factors are responsible for the formation of biofilm including curli, flagella, Bap, cellulose, and e-DNA [ 161 , 162 , 163 ] ( Table 2 ). Biofilm formation by Salmonella has been proposed to exert anti-virulence properties [ 159 , 164 ].…”

Gre Factors Are Required for Biofilm Formation in Salmonella enterica Serovar Typhimurium by Targeting Transcription of the csgD Gene

“…A transcriptional pause in the 3′-UTR of the hilD gene was the target for the Gre factors [ 7 ]. S. Typhimurium has the ability to form biofilm on diverse biotic and abiotic surfaces, such as interacting with epithelial cells during the infection process [ 8 ] and adhering to abiotic surfaces such as plastic, glass and steel, leading to transmission and outbreaks of S. Typhimurium during food processing [ 9 ]. Most studies on S. Typhimurium biofilm have been performed upon growth on/in rich media, low osmolarity and low temperature (25–28 °C).…”