Tuberculosis and E. coli Flashcards
What are the 3 causative agents of tuberculosis?
- Mycobacterium tuberculosis (major cause)
- Mycobacterium bovis (minor cause)
- Mycobacterium avium (minor cause)
During what time period was TB a common cause of death?
from the middle ages through the 1800s
When did rates of TB sharply decline?
1940s- coincides with beginning of antibiotic use
Why have rates of TB begun to increase again?
HIV pandemic, general public health failures around the world, drug resistance
What were some causes of TB decline before the 1940s?
improved sanitation, increased general health, increased SES
What percent of the world is infected with TB? Of those infections, how many are active?
1/3 of the world’s population is infected, 10% of infections are active
What is the second leading cause of death due to a single infectious agent?
Tuberculosis
How many people die each year due to TB?
Greater than 1 million
What percentage of TB cases are in low/middle income countries?
95% (think of it as a disease of the poor)
What are the two modes of transmission for TB?
inhalation and ingestion
What is the infectious dose for TB that is inhaled?
1 bacterium
How is TB typically ingested? How can this be prevented?
highly contaminated milk; pasteurization
Does ingestion of TB require a large infectious dose?
Yes- much higher than inhalation; probably due to pH of GI tract
Describe the process of TB infection.
- TB enters alveoli and is taken up by alveolar macrophage (phagocytosis), phagasome has TB bacteria in it which blocks it from binding with lysosome
- TB replicates in phagasome until macrophage bursts
- TB from burst cell is able to infect surrounding macrophages
What is a granuloma?
Healthy macrophages, lymphocytes, and other immune cells surround infected macrophages and wall it off from the rest of the body
What is caseation? (TB)
Center of granuloma breaks down leaving cell parts and TB bacteria, resembles cheese like structure
What is calcification? (TB)
- happens to most caseous lesions in latent infections; calcium deposits inside of the granuloma
- the longer it takes to calcify the more likely it is to liquify
What is activation of lesions? (TB)
- liquefaction of caseous lesions; allows for rapid replication of bacteria; liquid may drain into airways
- this is how TB can spread to other people or cause more lesions
What is cavitation? (TB)
‘airfield granuloma,’ because TB likes oxygen it is able to replicate rapidly and spread to other areas of lungs/other people
What is the standard treatment for uncomplicated TB?
4 drugs for 2 months, followed by 2 drugs for 4 months (total of 6 months)
What are the factors of drug resistance in TB?
poor compliance, inappropriate treatment, poor quality drugs
What populations are at risk for developing drug resistant TB?
people w/ poor compliance, people that relapse after treatment, people visiting areas w/ high drug resistance
What does DOT stand for? What is it?
Directly observed therapy; treatment of people with TB is observed by professional either at home or in clinic
What is the purpose of DOT?
ensures compliance, can check for side-effects; combat development of drug resistance
What does MDR-TB stand for?
multi-drug resistant tuberculosis
What drugs is MDR-TB resistant to?
rifampin and isoniazid (first line drugs)
Where do the majority of cases of MDR-TB occur?
China, India, and Russia
How many cases of MDR-TB occurred in 2012? How much did this increase from 2011?
450,000 cases in 2012, almost twice what was seen in 2011
What is the mortality rate of MDR-TB?
About 40 percent (38)
What does XDR-TB stand for?
Extremely drug resistant tuberculosis
What drugs is XDR-TB resistant to?
rifampin & isoniazid plus a quinolone and a injectable second line drug
How many countries has XDR-TB been reported in?
92
What percent of MDR-TB are XDR?
about ten percent
What type of bacteria is E. coli O157:H7 classified as?
Enterohemorrhagic E. coli (EHEC)
What are three of the traits that EHEC gets from the 1,600 genes it has that commensal E. coli does not?
shiga toxin, enterohemolysin and proteases
When, where, and how did E. coli O157:H7 emerge?
Jack-in-the-Box fast food restaurants in the western US; due to undercooked hamburger meat
1982
What is the route of infection for E. coli?
Ingestion; 95% of bacteria thought to survive the stomach
Does E. coli survive refrigeration?
yes
What are ways in which E. coli can be spread?
meat, vegetables (spinach, lettuce, things eaten raw), contaminated water (either swimming or drinking), unpasteurized juice, daycare centers
What is the primary reservoir for E. coli?
cattle (no clinical signs of infection)
In what ways does E. coli persist in the environment?
- persists on grass for months
- stress response lets in survive in aquatic environments
- some strains form biofilms that are resistant to ameboids
- can survive within environmental protozoas
What are the symptoms of disease caused by O157?
- diarrhea (often bloody= probably from shiga toxin)
- Hemorrhagic colitis
- vomiting
- nausea
- cramps
- neurological symptoms (seizures, blindness)
Describe hemolytic uremic syndrome (HUS)?
- occurs in rare cases
- early symptoms similar to hem. colitis
- later symptoms= hemolytic anemia, thrombocytopenia, decreased urine output , can lead to kidney failure
- more common in young and elderly
- child mortality= ~5%
How is O157 treated?
Mainly electrolyte balance, antibiotic treatment can actually be detrimental due to release of shiga toxin
(HUS may require dialysis)
List preventative measures for O157.
cook food thoroughly, wash hands/food/surfaces/countertops, use a separate cutting board for meat/veggies, pasteurize milk and juice, avoid drinking pool water/contaminated water, trying to decrease prevalence in cattle
What factors led to the emergence of O157?
mutation, recognition of a new disease
