LECTURE - Salmonella Flashcards
Characteristics of Salmonella
- facultatively anaerobic
- gram neg rods; catalase pos and oxidase neg
- subdivided into serovars based on LPS O antigen, flagellar H (2 types), capsular Vi (Kaufmann-White system)
- formerly, each serotype was given a distinctive ‘species’ name
- NOW, each serotype is termed a variant of one species (ex: Salmonella enterica serovar Typhimurium or simply S. Typhimurium)
T or F. Salmonella is motile
T! peritrichous flagella
characteristic core sugars of LPS
heptose and KDO (2-keto-3-deoxy-D-manno-octanoate)
Depending on this, Salmonella can infect multiple vertebrate hosts
serovar
- some serovars cause different diseases in different hosts (S. Typhimurium causes gastroenteritis in humans and a typhoid-like disease in mice)
The exception in Salmonella; this serovar grows exclusively in humans
S. Typhi
These cause disseminated disease in humans
S. Typhi and S. Paratyphi
sopE gene in Salmonella
- affects the severity of disease symptoms
- carried on a bacteriophage that is not present in all strains
- NOT ALL Salmonella strains contain the sample complement of T3SS effectors or plasmids
Two main groupings of Salmonella based on disease
- NTS (Non-typhoidal Salmonella): S. Typhimurium = common cause of self-limiting gastroenteritis; in immunocompromised, ma cause bacteremia; severity depends on strain, complement of virulence factors and HEALTH of individual
- Typhoidal strains: able to spread throughout the body to cause typhoid fever regardless of health of an individual; early treatment with antibiotics is effective and saves lives
Genetic sources of Salmonella virulence factors
- virulence plasmids = occurs in all Slamonela whether typhoidal or not; ex: pSLT Typhimurium, pSLV in Enteritidis; encode fimbriae (attachment to enterocyte microvilli); spv = including SpvB (ADP-ribosylating toxin)
- SPIs (Salmonella Pathogenecity Islands) in bacterial chromosome; T3SS apparatus and effector proteins
T or F. Shigella is much less common than Salmonella or Campylobacter
T!
Comparison between the two Salmonella serovars helped to define the molecular basis for …
systemic disease vs. gastroenteritis and to begin to identify host specificity determinants
S. Typhi PIs
- more PIs than other serovars
- SPI-7 carries the viaB locus for Vi exopolysaccharide (capsule) synthesis which is missing from most other Salmonella species. This island also contains genes for type IV pili.
Salmonella Typhimurium Pathogenicity Islands
S. Typhimurium: SPI-1 encodes a T3SS that mediates invasion of enterocytes..
S. Typhimurium: SPI-2 encodes a second T3SS essential for intracellular replication, escape from phagosomes (e.g., in Mϕ) and for systemic spread of bacteria.
SPI-1
SPI-1 mutants are attenuated for virulence because they cannot invade host cells.
Invasion is an active process, not simply receptor-mediated endocytosis
Attachment induces cytoskeletal rearrangements, seen as membrane ruffling in host epithelial cells.
Entry results in formation of the Salmonella-containing vacuole (SCV). Surrounded by a membrane that is derived from the host cell membrane.
SPI-2
- Maintenance of the SCV and formation of Salmonella-induced filaments (SIFs) are phenotypes that correlate with virulence (although the function of SIFs is still a mystery!)
- SCV and SIFs are dependent upon the translocated effector SifA.
- SPI-2 effectors such as SopD2 and SpiC mediate the altered trafficking of the SCV.
- SPI-2 effectors are essential for bacterial replication inside the SCV.
