1. For Mycobacterium tuberculosis and Helicobacter pylori, know what (i) disease(s) they cause, (ii) how they are transmitted and the steps in causing the disease, (iii) treatment, (iv) any virulence factors we discussed in class and what they do, (v) general microbiological features of the organisms.

• Mycobacterium tuberculosis- (i) Causes tuberculosis.  (ii) Transmitted via water droplets and live in the lung where they are phagocytosed by macrophages; they grow and divide in the macrophage and then burst out creating an immune response from T-cells and other immune cells which wall off Mtb into a "tubercle."  Tubercle is the latent infection.  Later the tubercle can liquify usually in response to a compromised immune system, the antigen load becomes too much and cavities form in the lung, and bacteria get spilled into the airway and can then be spread to others.  (iii) Tuberculosis can be treated in either the latent infection or the active infection.  In the latent infection, a 9 month treatment is required, the patient can take isoniazid which is specific for Mtb and interferes with mycolic acid synthesis; the patient can also take rifampin which is an antibiotic.  In an active infection the patient has to do a 6 month treatment utilizing 4 different antibiotics.  (iv) Virulence factors for Mtb are the cell wall structure which has a high lipid content that is resistant to dessication and helps the bacterium to live externally for more than a week; it also has some antibiotic resistance.  Mycolic acid is the most common lipid and it gives the bacterium a waxy characteristic.  Next Mtb has a slow generation time, it doubles every 15-20 hours, so a colony forms over 3 weeks, this makes the disease difficult to detect.  Lastly, Mtb is an intracellular pathogen and it lives in the macrophages away from the immune system.  (v) General Characteristics of Mtb: Gram +, Acid Fast (resistant to taking up dye), Non-motile, Rod shaped, aerobe, intracellular pathogen, very slow growing.
• Helicobacter Pylori- (i) This is the microbe that causes ulcers.  (ii) H. pylori is spread either through oral/oral or fecal/oral interactions.  The bacterium is introduced to the stomach and begins making NH3 to buffer against host produced urea.  The bacterium is motile which helps it to live in the gastric mucosa where it erodes stomach tissue and causes ulcers.  (iii) The treatment against this disease is 2 antibiotics.  (iv) Virulence factors for H. pylori are: urease enzyme which breaks down host produced urea, motility/chemotaxis which helps the bacterium locate the gastric mucosa, and the cag pathogenicity island which encodes proteins that inject effectors into the host causing cancer.  (v) General microbiological features of H. pylori are: spiral/helical shape, flagellated, microaerophile.

2. After a person inhales Mtb, there are a couple of possible outcomes--what are these and how do they differ?  Why does one happen versus the others?

1. Mtb enters the lung and is taken up by a macrophage where it grows and multiplies and eventually bursts out.  Some Mtb is phagocytosed and antigens are made.  T-cells respond to the site of Mtb infection along with other immune cells; these cells form a wall around the Mtb colony resulting in a "tubercle."  Mtb can exist in the tubercle for decades, this is called latent infection.
2. The alternative is the active infection in which the tubercle liquifies which is good for Mtb growth, this is usually associated with a compromised immune system.  Once the tubercles liquifies the antigen load becomes too much and the surrounding lung tissue begins to necrose and rupture forming cavities in the lungs.  After the cavities form in the lung bacteria spill into the airway where the infetion can spread to other people.

3. Would it be a bad idea to antibiotic-treat everyone with a positive PPD/tuberculin test?  Be sure to answer what the tuberculin test tells you.

The tuberculin test is a test in which some Mtb protein is injected subcutaneously.  There is an immune response if the person taking the test is positive for Mtb.  It would not be wise to treat everyone who tested positive for this test with antibiotics because some people who test positive for Mtb may have the latent infection which is not being spread.  Treating everyone who tested positive for the tuberculin skin test with antibiotics could result in a higher rate of antibiotic resistance in the population of Mtb.  isoniazid would probably be a better treatment since it specifically targets Mtb.

4. What is different about the cell wall of Mycobacteria as compared to other bacteria?  What properties would this difference confer on the Mycobacteria?

The cell wall of Mtb contains a large amount of lipid including the lipid mycolic acid.  High lipid content allows the bacterium to live externally for more than a week and helps it to resist some antibiotics.  Mycolic acid makes the cell wall of Mtb waxy.

5. How does H. pylori fulfill or not fulfill Koch's postulates?

H. pylori does fulfill Koch's postulates in that:

• Same Pathogen must be present in all desiease cases: H. pylori is isolated from most gastric biopsies when it is a biopsy of an ulcer.
• Pathogen must be isolated from host and grown in culture: H. pylori is isolated from ulcers.
• Pure pathogen isolated from culture must cause disease in healthy animal: B. Marshall drinks H. pylori and gets gastritis, H. pylori was present in his biopsy.
• Pathogen isolated from diseased animal must be original pathogen: H. pylori was cultured from B. Marshall's biopsy.

6. Why don't we just treat everyone with an ulcer with antibiotics?

We should treat everyone with an ulcer with antibiotics if H. pylori is culture from their biopsy.  The only problem is that there is an old belief that stress causes ulcers and not H. pylori, so some old doctors keep treating patients the old way.

7. Would mutants that lack any of the M. tuberculosis or H. pylori virulence factors be able to infect animals?  In otherwords, what would happen if they lost those virulence factors?

Most likely if these pathogens lost their virulence factors they would most likely be dealt with in the same way that any other common pathogen would be dealt with.  That is to say that they would be phagocytosed and they would not cause any disease.