Microbiology

Question 1

Clostridium Difficile releases 2 toxins, Toxin A and Toxin B. What are the specific actions of the 2 toxins?

Answer 1

The cumulative effect is that the toxins disrupt the actin cytoskeletal structure and intracellular signaling of intestinal cells. Toxin A tends to cause intestinal inflammation and fluid effects. Toxin B is more cytotoxic.

Question 2

A virus is isolated and exposed to ether. After the exposure, it no longer infects. Why?

Answer 2

The virus must have an envelope. The ether (and other organic compounds) dissolves the lipid bilayer, making the virus unable to infect.

Question 3

What type of virus is capable of reassortment? (i.e. mixing virus material)

Answer 3

Rotavirus and orthomyxovirus (viruses with segmented genomes). This is a lot more than just a point mutation. They literally mix.

Question 4

A patient has a TB infection. What are the 4 drugs that can treat TB, and which one disrupts acid synthesis? Which one messes up RNA?

Answer 4

RIPE.
R=Rifampin. Messes up RNA. Rapid resistance. Rampus up CP-450.
I=Isoniazid. Disrupts acid synthesis.
P=Pyrazinamide. Uncertain mechanism.
E=Ethambutol. DEcreased carb polymerizaton of cell wall. Optic neuropathy.

Question 5

This isn’t really micro…BUT. What are the 8 core histone proteins in a nucleosome, and where is H1 located?

Answer 5

2 each of H2A, H2B, H3, and H4.

H1 is located outside of the core and helps to compact the core.

Question 6

Which type of hepatitis has a high mortality rate among pregnant women?

Answer 6

Hepatitis E. It’s an RNA hepevirus. Think Enteric, Expectant mothers, Epidemic.

Question 7

Painful blisters on penis, positive Tzanck smear. Diagnosis? Treatment?

Answer 7

Herpes Simplex Virus (probably HSV-2).
Treatment: Continuous daily valacyclovir (week course would only decrease shedding. Need daily to prevent reactivation of latent infection).

Question 8

A patient had flu-like symptoms 6 months ago, facial palsy 3 months ago, and now presents with a swollen right knee. Diagnosis and Treatment?

Answer 8

Diagnosis=Lyme Disease

Treatment=Doxycycline or Ceftriaxone (penicillin-like)

Question 9

A virus infects by being broken down to small fragments and then attaching to MHC1. What is responsible for breaking down the virus?

Answer 9

Ubiquitin Ligase and the proteosome. The ubiquitin ligase puts a ubiquitin tag on the virus which signals to the proteasome that the virus needs to be chopped up. The proteasome does the chopping, ubiquitin ligase does the tagging.

Question 10

What is the classic triad of congenital rubella? What is the preconception treatment for congenital rubella?

Answer 10

1) White pupils
2) Sensory-neural deafness
3) Patent ductus arteriosus
* Treatment=live attenuated vaccine.

Question 11

A patient has pneumonia. Their blood clots when the blood is cold, and then is normal when warm. What is the most likely cause?

Answer 11

Mycoplasma pneumonia.
Body produces cold antibodies to the bug.
Cold antibodies also found with EBV infection and hematologic malignancy.

Question 12

Both enterobacter and E. coli are gram negative rods that are lactose fermenters. How do you differentiate between the two?

Answer 12

E. coli=Indole positive
Enterobacter=Indole negative.
Indole=ability to convert tryptophan to indole.

Question 13

What type of tissue does HPV-6 and HPV-11 typically attack, and where are common locations?

Answer 13

Stratified squamous epithelium. Anal canal, Vagina, Anus, and true Vocal cords.

Question 14

A sexually active young woman comes in with a UTI. What is the most likely bug, and what makes it unique from other similar bugs?

Answer 14

Staph saprophyticus. It causes almost half of all UTIs in young women.
It is novobiocin resistant which distinguishes it from Staph aureus.

Question 15

A patient undergoes a dental procedure, then proceeds to get a firm mass that drains yellow pus through the overlying skin. Most likely bug? Treatment?

Answer 15

Bug: Actinomyces israelii. Known for cervico-facial issues in patients following dental procedures or facial trauma.
Treatment: Long-term penicillin and surgical debridement.

Question 16

Dengue typically is worse with a 2nd infection than it is the first.
What type of virus is it, how many different serotypes are there, and why is the 2nd time worse?

Answer 16

It’s a single stranded RNA virus with 4 different serotypes. The second time is worse because it is caused by a different viral serotype.

Question 17

“Medusa head colonies”, gram positive rod, someone who works with goats/wool, widened mediastinum.
Diagnosis? What makes this bacteria unique?

Answer 17

Diagnosis=Bacillus anthracis (Pulmonary anthrax).
It’s unique because it’s only bacteria with a polypeptide capsule–>Contains D-glutamate.
NOT a polysaccharide capsule.

Question 18

What are clinical signs of serotonin syndrome?

What antibiotic can cause this syndrome?

Answer 18

Triad: Autonomic instability, Altered mental status, neuromuscular irritability
Antibiotic: Linezolid (50S subinit inhibitor, block protein synthesis)

Question 19

What are common sources of Hep A?

Answer 19

It’s fecal oral transmission.

Common sources are contaminated water or food, and raw or steamed shellfish.

Question 20

What are the major virulence factors for Staph Aureus, Staph Epidermidis, Group A streptococci?
What virulence factor do H. flu, S. pneumo, and Neisseria share?

Answer 20

Staph Aureus: Protein A. Inhibits opsonization/phagocytosis.
Staph Epidermidis: Biofilm (synthesis of an extracellular polysaccharide matrix)
Group A Strep: Protein M
H. flu, S. pneumo, Neisseria: IgA protease

Question 21

Hypopigmentation, hair loss, loss of localized sensation, and responsible organism resides in the Schwann cells. Diagnosis?

Answer 21

Mycobacterium leprae.
This is the milder kind (tuberculoid leprosy). Th1 mediated.
The intense kind (Lepromatous leprosy) occurs in people w/ weak CMI Th2 mediated response. Skin thickening, lion faces, paresis, regional anesthesia, more intense hypopigmentation, testicular destruction, blindness.

Question 22

Name of the cell that has tennis racket looking things inside?

Answer 22

Langerhans cells found in dendritic cells

The tennis racket looking things are Birbeck granules, and they are master antigen presenting cells.

Question 23

What is penicillin similar in structure to?
How do the mechanisms of penicillins and vancomycin differ?
Where do cephalosporins fit in?

Answer 23

Penicillin similar to d-alanine d-alanine.
Penicillins bind to transpeptidases and block the cross-linking of peptidoglycan in the cell wall.
Vancomycin inhibits peptidoglycan formation completely by binding the D-ala D-ala portion of cell wall precursors. That’s why it’s not susceptible to beta-lactamases.
Cephalosporins do the same as penicillin (they bind to transpeptidases and inhibit cell wall synthesis). They’re less susceptible to beta-lactamases

Question 24

What is the virulence factor for Staph Aureus, and what does it do?

Answer 24

Protein A. Binds to the Fc portion of IgG and blocks complement activation, opsonization, and phagocytosis.

Question 25

How do penicillins and cephalosporins differ in terms of resistance?

Answer 25

Penicillins-beta lactamases are the major cause of resistance.
Cephalosporins-structural changes in penicillin-binding proteins (transpeptidases) are the major cause of resistance.

Question 26

What is the major immune response that prevents reinfection with the influenza A virus?

Answer 26

Antibodies against hemagglutinin (anti-hemagglutinin antibodies.
*Anti-neuraminidase antibodies are somewhat helpful but not the main source of protection.

Question 27

GNR, pink colonies on MacConkey agar, causing pneumonia in an alcoholic.
Currant jelly sputum

Answer 27

Klebsiella Pneumoniae.

Probable in immune deficiency people (ie alcoholics)

Question 28

Several bacteria produce IgA proteases. What is the purpose, and what is the net effect?
What bugs produce IgA proteases?

Answer 28

It cleaves IgA at the hinge region, impairing IgAs immune function, and enabling the bacteria to colonize the mucosa/respiratory mucosa.
Think SHiN
S. Pneumoniae
H. flu type B
Neisseria

Question 29

For what stain type is carbol fuchsin (Ziehl-Neelsen) used, and what bugs would stain with this?

Answer 29

It’s acid fast staining.

Mycobacteria and Nocardia, along with cryptosporidium oocysts

Question 30

Your patient has a histoplasmosis infection. You treat them with amphotericin B, but they start having palpitations. Why?

Answer 30

Renal toxicity. This messes up with your electrocyte balance, and you end up with hypokalemia.

Question 31

A patient’s biopsy shows segmental, transmural inflammation with fibrinoid necrosis of mid sized arteries.
Diagnosis?
Association?

Answer 31

Dx: Polyarteritis Nodosa
Association: Idiopathic, associated w/ Hepatitis B in 30%

Question 32

Which drugs can cause disulfiram-like reactions when combined with alcohol?
What does disulfiram do?

Answer 32

Metronidazole (used to treat trichomonas vaginitis and bacterial vaginosis).
Disulfiram is used to treat alcoholism, and it causes acetaldehyde accumulation by inhibiting acetaldehyde dehydrogenase. It then results in flushing/headache/abdominal cramps/N/V

Question 33

What are the beta-lactamase inhibitors (3 of them), and what is their purpose?

Answer 33

1) Clavulanic Acid
2) Sulbactam
3) Tazobactam
Can give them with antibiotics that don’t have beta lactam inhibiting activity to expand their spectrum of action so that they can kill those resistant bugs as well