Micro- General Principles

Question 1

Morphology of Enterococcus?

• Enterococci are part of the normal intestinal flora of humans and animals. Enterococcus faecalis and E Faecium are the most prevalent species cultured from humans and can cause:
  
  • UTI
  • Wound infection
  • Intraabdominal and pelvic infection
  • bacteremia/endocarditis

Answer 1

• Gram(+) cocci in chains
• Catalase negative (like all of the streptococci)
• Gamma hemolysis (no hemolysis)
• PYR(+) {like strep pyogenes)

Question 2

What organism uses Protein A? What is it’s function?

Answer 2

Staph Aureus (Gram+ cocci in clusters, catalase+, coagulase+)

Protein A binds with the Fc portion of IgG antibodies at the complement-binding site, thereby preventing complement activation. This results in decreased production of C3b, leading to impaired oponization and phagocytosis

Question 3

Which organisms produce IgA protease? What is the function of this virulence factor?

Answer 3

Strep pneumoniae & Neisseria gonorrhoeae

IgA protease cleaves IgA antibodies, preventing them from interfering with bacterial adhesion to mucous membranes

Question 4

Patient with diabetic ketoacidosis presents with:

• Facial pain
• headache
• black necrotic eschar in the nasal cavity

What is the causal organism, characteristics, and procedure to diagnose it?

Answer 4

Mucormycosis

Fungi show broad nonseptate hyphae with right-angle branching

Mucosal biopsy (histologic examination of the affected tissue) necessary to confirm diagnosis

Question 5

When is diagnosis of Malaria confirmed?

Answer 5

When trophozoites (intraerythrocytic, ringed inclusions) are seen on peripheral blood smear using Giemsa stain.

Note: manifestations of malaria arise due to erythrocyte rupture and include fever, flu-like symptoms, anemia, and indirect bilirubinemia.

Question 6

Malaria may remain dormant in what organ?

Answer 6

Liver

-dormant hepatic phase (hypnozoite phase)

Question 7

Gram(-) rod that causes neonatal meningitis? What is the most important virulence factor for development of this condition?

Answer 7

E. Coli

K1 capsule, allows the bacteria to survive in the bloodstream and establish meningeal infection.

Question 8

Alcohol based disinfectants are good at killing what type of organisms and why?

Answer 8

They kill enveloped viruses (e.g., influenza) by dissolving their outer lipid bilayer envelope

{non-enveloped viruses are less susceptible because they have no lipid envelope to target)

Question 9

Histology of patients with Histoplasma capsulatum

• Endemic to Ohio & Mississippi River Valleys
• Soil contaminated by bird or bat droppings

Pathophysiology: Inhaled—> phagocytosis by alveolar macrophages—> escapes lysosome destruction—> spreads to hilar/mediastinal lymph nodes

Answer 9

Macrophages filled with Intracellular ovoid/round yeast

Question 10

Transformation vs. Conjugation vs. Transduction

Answer 10

• Transformation
  
  • Allows bacterium to take up exogenous DNA fragments from environment, integrate the DNA into its genome, and express the encoded protein.
• Conjugation
  
  • Process begins with the donating bacterium producing a sex pious, which ten forms a direct connection with the receiving bacterium.
• Transduction
  
  • Bacteriophage, replicating in a host, may accidentally incorporate host bacterial DNA into the phage particle. Once it leaves the host, it can then transfer the DNA from the previous host to a newly infected bacterium. This mechanism allows bacteria to acquire genes for virulence and antibiotic resistance.

Question 11

• Define Antigenic Drift

- Define Antigenic Shift (aka. Genetic reassortment)

Answer 11

• Antigenic Drift—>Accumulation of a series of minor genetic mutations
• Antigenic Shift—> Involves “mixing” of genes (GENETIC REASSORTMENT) from influenza viruses from different species

Question 12

Most important virulence factor for E. Coli in causeing urinary tract infection?

Answer 12

P fimbriae—> allows adhesion to uroepithelium so it can infect the bladder, ureters, and kidneys (without it, the bacteria would simply be washed away during urination)

Question 13

• Most important virulence factor of E. Coli causing Gastroenteritis (watery)?
• Most important virulence factor of E. Coli causing Gastroenteritis (bloody)?

Answer 13

• Heat-stable/heat-labile enterotoxins
  - Promotes fluid & electrolyte secretion from intestinal epithelium
• Verotoxin (shiga-like toxin)
  - Inactivates the 60s ribosomal component, halting protein synthesis & causing cell death

Question 14

Most important virulence factor of E. Coli in causing bacteremia & septic shock?

Answer 14

• Lipopolysaccharide

- MOA: Macrophage activation causes widespread release of IL-1, IL-6, & TNF-alpha (pro-inflammatory cytokines)

Question 15

Non-lactose fermenting, Gram(-) rod, no H2S production?

What is the important pathogenic mechanism of this organism?

Answer 15

Shigella

Mucosal invasion

Question 16

Common site of viral replication for HHV-6, which causes Roseola infantum?
Presents as high fever followed by a diffuse maculopapular rash in children <2 years old

Answer 16

Mature lymphocytes

Question 17

• Virus that causes Erythema infectiosum (fifth disease)?
• Symptoms?
• Where does the virus replicate?

Answer 17

• Parvovirus B19 (ssDNA)
• Nonspecific prodrome (eg, malaise, fever, congestion) followed by a classic “slapped-cheek” facial rash and a lacy, reticular body rash
• Replicates in erythrocyte precursors in the bone marrow

Question 18

Gram(+) cocci that commonly causes UTI in sexually active young women

Answer 18

Staph. Saprophyticus

* Catalase(+)
* Coagulase(-)
* Novobiocin Resistant

Question 19

Most likely adherence site for Viridens Strep?

This bacteria is commonly associated with dentists

Answer 19

Adhere to Fibrin platelet aggregates, facilitated by dextrans produced by the bacteria