Lecture 15 - Salmonella enterica

What are the main characteristics of Enterobacteriaceae

Facultative anaerobes, g-r, catalase pos, oxidase neg

What are the three serotypes of Salmonella?

LPS O antigen, flagellar H antigen, and capular Vi (K)

Characteristics of Salmonella?

facultative anaerobes, g-r, and motile with peritrichous flagella

What sugars are unique to Gram negative LPS O Side chains?

Dideoxy sugars such as colitose, abequose, tyvelose, and paratose

Which Salmonella serovar only grows in humans?

S. Typhi

Which serovar causes typhoid fever in humans?

S. Typhi and S. Paratyphi

Which serovar causes disease in mice and humans?

S. Typhimurium causes gastroenteritis in humans and typhoid-like disease in mice

What are the two main groupings of Salmonella based on disease?

NTS (non-typhoidal Salmonella) and Typhoidal strains

NTS Strains

S. Typhimurium common cause of self-limiting gastroenteritis such as vomiting, fever, pain, diarrhea

Typhoidal Strains

S. Typhi is able to spread thru the bod to cause typhoid fever

What are the main ways S. Typhi and NTS invade?

M cell invasion and Enterocyte invasion via ruffles

What is the third route of entry for NTS?

Dendritic cells

How does NTS invade through dendritic cells?

They use adhesins to attach to intestinal epithelium or can be directly taken up by dendritic cells

How can Salmonella be transmitted?

Contaminated water and food such as raw eggs, reptile pets

What are some virulence plasmids and what do they do?

pSLT (S. Typhimurium) and pSLV (S. Enteritidis) that encode for fimbriae for attachment to enterocyte microvilli

What do Salmonella Pathogenicity Islands encode for?

Encodes for T3SS apparatus

S. Typhi Pathogenicity Island

Has more islands than any other serovar and carries viaB locus for Vi polysaccharide capsule synthesis, and genes for type IV pilli

Type III Secretion Systems in Salmonella

Structurally homologous to flagellar export apparatus

SPI-1 and SPI-2 of S. Typhimurium

SPI-1 encodes for T3SS for invasion of enterocytes while SPI-2 encodes for second T3SS essential for escape, replication, and spread of bacteria

How is SPI-1 regulated?

Expressed during invasion then down regulated during intracellular phase

SPI-2 Regulation?

Specifically induced during intracellular phase

Vi antigen of Salmonella Typhi

Capsular polysaccharide not present in all serovars so it is unclear but when present it make bacteria resistant to complement and phagocytosis

S. Typhi antibiotic treatment

Essential for survival and currently use third gen cephalosporins and fluoroquinolones

S. Typhimurium antibiotics

Only systematic infectious require antibiotics