Topic 1-13 (Lecture 13) Flashcards
What is Mycobuacterium tuberculosis’ “nickname”?
TB
What disease does M. turberculosis cause?
Tuberculosis
What is tuberculosis?
Infection of the lungs, which causes an inflammatory reaction from the engulfment of bacteria by phagocytic cells
How is tuberculosis spread?
Spread from person to person directly
What problems to tuberculosis present to the immune system?
They persist and multiply inside macrophages; the cell-mediated immunity works but is NOT completely effective - bacteria can remain dormant, potentially leading to rapid reactivation in the future (that may or may not result in death)
What type of people is TB most prevalent in?
Poor people and AIDS patients living in large cities
What is the treatment of M. tuberculosis?
Long term (9-12 months) antibacterial therapy often with multiple antibiotics
How resistant is M. tuberculosis to antibiotics?
Has widespread resistance; resistance to the main antibiotic, isoniazid has been observed. Some strains are resistant to all 8 “front-line” antibiotics in use”
Is there a vaccine for M. tuberculosis, and if so, how does it work?
The TB vaccine uses a live strain of Mycobacterium bovis (BCG), which is immunologically similar (shares same antigens) with TB
What is salmonella?
A range of very closely related bacteria that causes disease in humans and animals
What are the general characteristics of salmonella?
Gram-negative
flagellated
facultatively anaerobic bacteria
What are the 3 major antigens of salmonella?
H (flagellar) antigen
O (somatic) antigen
K (capsular) antigen
How is salmonella transmitted?
From the feces of infected people or animals to others via contaminated food or drink
What are the 2 disease associated with salmonella infections
Salmonellosis and typhoid fever
How are salmonella divided into species?
Based of serology/serovars (using surface antigens)
What are some virulence factors that salmonella havew?
Adhesins, LPS, capsules, two type III secretion systems, ability to invade and replicate inside host cells
Where are genes encoding virulence factors found in Salmonella?
Pathogenicity islands (PAIs)
How are pathogenicity islands acquired?
May have been acquired during evolution via horizontal gene transfer (ex. bacteriophage, prophages)
What is SPI1?
Salmonella pathogenicity island 1. Contains genes associated with virulence genes and their regulation. (ex. inv genes, involved with invasion of host cells; type III secretion system used to inject proteins to mediate invasion and inflamation in eukaryotic cells)
What individuals are at risk for Salmonella infections?
Those with little/no stomach acidity are at increased risk
What diesease is caused by Salmonella enterica serovar Typhi? (AKA S. typhi)
Typhoid fever
What are some characteristics of typhoid fever?
Pathogenic only to humans
transmitted by eating contaminated food or water
Often fatal disease
What are symptoms related to typohid fever?
Nausea Persistently high fever and chlils Flushed appearance Anorexia (vomiting) Convlusions delirium
Where do S. typhiinfect the body?
Multiply in spleen and liver
Can move to gall bladder (thus are shed in bile)
What is the incubation period of typhoid fever?
Week to a month (however, people may become asymptomatic carriers, or recover but become chronic carriers due to persistent bacteria in gall bladder)
What disease does Salmonella enterica serovar Typhimurium (S. typhimurium) cause?
Thyphoid-like disease in mice
Self-limiting gastroenteritis (salmonellosis) in humans
What is the incubation period of self-limiting gastroenteritis?
6-24 hours after ingestion; disease lasts up to 7 days
What are symptoms of gastroenteritits?
diarrhea, abdominal cramps, vomiting, nausea
Sometimes can enter bloodstream in immunocompromised or elderly people and cause systemic shock (often fatal)
How is S. typhimurium transmitted?
By ingestion of contaminated food (most commonly chicken and eggs). Farm animals may become colonized yet are asymptomatic, thus potentially contaminating animal carcasses during slaughter
Who was Typhoid Mary? (in a short abridged form)
Woman who worked as a hired maid/cook; healthy asymtomatic carrier that caused multiple outbreaks due to her carrying S. typhi.
>Didn’t believe she was at fault
>Wouldn’t stop working as a cook, even though told not to (by changing her name)
>Got arrested twice, second time quarantined until she died
>Shows that healthy carriers are dangerous, as there is no way to visually identify healthy carriers
What is the difference between food poisoning and food infection?
Food infection - symptoms arise after pathogen has time to replicate in intsetine - can develop several days AFTER ingestion
Food poisoning - results from ingestion of food contaminated with toxins - do NOT have to replicate in host/be alive
How do Salmonella invade and infect mice?
Enter through “M cells” - cells that sample antigens from lumen of intestine
Bacteria picked up by macrophages associated with Peyer’s patches (lymph tissue of intestine)
Bacteria replicate inside unactivated macrophages
How does S. typhimurium cause diarrhea?
By injecting proteins into the intestinal cell via type III secretion system (needle-like secretion apparatus)
Virulence proteins disrupt normal cell function & promote internalization of bacteria
Cell responds with chemokines, induces inflammatory response
Neturophils arriving produce PROSTAGLANDIN that increase cAMP levels, which inhibits sodium ion uptake
This results in Chloride secretion into intestinal lumen
Charge imbalance results in osmosis of water into lumen, resulting in diarrhea
What causes the abdominal pain associated with S. typhimurium infection?
Likely due to inflamatory response resulting from LPS recognition and cytokine release
How is salmonella diagnosed?
Isolation of bacteria, which is then grown on selective and differential media and identified by biochemical tests
Serotype identified by using polyvalent and specific antisera to identify O (cell wall) and H (flagella) antigens
How do salmonella invade cells?
Use adhesins to adhere (ex. type I fimbriae, plasmid-encoded fibriae)
Uses SPI1 system to cause actin filament rearrangements in host cell to cause “ruffles” to form in membrane, resulting in internalization of bacteria in endocytic vesicle
How do salmnoella replicate within host cells?
Use SPI2 type III injector to inject endosome to prevent fusion with lysosome
Endosome used as a “home” for salmonella to grow and multiply
How does salmonella evade host responses?
By invading the cell:
-Evade innate and adaptive immune responses
By altering endosome:
-Prevent intracellular killing
How is salmonella treated?
S. typhimurium or S. enteritidis infection usually resolve within a week and DO NOT REQUIRE TREATMENT (antibiotics used to control infection that spread beyond intestines)
Re-hydration therapy may be needed for those with severe diarrhea
S. typhi typically are treated with chloramphenicol and ceftriaxone (antibiotics)
How is infections by S. typhimurium and S. enteritidis prevented?
Prevented by proper sanitation & handling and cooking of foods
Focus is on detection of bacteria and food and public education
Vaccines for chickens are being to developed
How are S. typhi infection prevented?
Vaccines; 3 vaccines exist, which 2 injected and one orally administered
