Salmonella

Salmonella

Two main types of pathogens: S. typhi and S. typhimurium

S. typhi causes typhoid fever and is the species name

S. typhimurium is the subspecies and is what’s on eggs causes typhoid fever in mice

Causes three major diseases: Enteritis, Septicemia, Typhoid fever

Enteritis

Does food poisoning

Caused by S. typhimurium

Vomiting and diarrhea (no dysentery) symptoms last about 10 days but start later

Sepsis can occur but usually just an in-between step unlike typhoid

Usually from eggs or poultry because it is found in chickens

Cells invade intestines (always occurs) and can be internalized (sepsis)

Uses macrophage as uber so they want to get into macrophage but not die

Want to get to liver and spleen

M-Cells of Peyer’s patches (immune cells) use cells antigen collection mechanism in GALT (Gut Associated Lymphoid Tissue) tissue and can lead to septicemia

M-Cells and Peyer’s Patches

Function to distinguish food from something that need immune response

Salmonella binds to these and then get picked up by macrophage

Septicemia

Infection in intestines spreads to endothelium

Usually only a problem from immunocompromised host

Typhoid Fever

Caused by S. typhi in humans

Febrile Disease

Bacteria invade macrophage and are carried to liver and spleen where they form new infection

Most pathology is caused by inflammation due to lipid A

Presence of bacteria in organ (LPS plays a role in intoxication)

Virulence Factors

Lipid A from LPS causes inflammation

Plasmids (typhimurium)

inv genes encode invasion and intracellular reproduction

hil hyperinvasive locus

pathogenicity islands with large clusters involved in virulence

Acid tolerance response which allow bacteria to survive in the stomach

Survival in macrophages

Catalase and Superoxide dismutase degrades H2O2 and reactive oxygen radicals so killing is prevented

Regulates intracellular genes by using PhoP/PhoQ system

Two Component Regulatory Systems

Two molecules involved

Sensor: Acts as a membrane bound receptor for a specific condition, typically autophosphorylates a histidine on inside of membrane

Affecter: Activated by phosphorylation of sensor and acts as transcriptional regulator

Alters gene expression biased on environmental conditions

More important in bacteria that experience range of conditions