Microbiology

Question 0

Swollen, cherry-red epiglottis – most common cause?

Answer 0

Epitglottitis - fever, sore throat, dysphagia, drooling, airway obstruction with stridor

most commonly caused by H. flu
Hib vaccine now part of routine vaccination schedule in first few months

Question 1

What is Strep pneumo’s major virulence factor?

Answer 1

outer polysaccharide capsule

prevent phagocytosis and removal/neutralization with antibodies takes away pathogenicity

Question 2

Gram +, catalase -, beta hemolytic, bacitracin resistant? How to prevent?

Answer 2

Group B Strep
causes neonatal sepsis, pneumonia, meningitis

universal prenatal screening for group B by maternal vaginal and rectal culture at 35-37 weeks
culture-positive women take ampicillin prophylaxis

penicillin used to treat

Question 3

Which bacteria are found in soil and form spores? Other spore-forming bacteria?

Answer 3

Spore-forming in soil:
Bacillus anthracis, Clostridium perfringens, Clostridium tetani

Spore-forming:
Bacillus cereus, Clostridium botulinum and difficile, Coxiella burnetii

Question 4

Mucicarmine stain?

Answer 4

Cryptococcus neoformans

capsule stains red

Question 5

Cold hemagluttinins?

Answer 5

Mycoplasma pneumoniae

cross-reacting antibodies between M. pneumo and RBCs – can cause mild anemia that resolves with resolution of infection

Question 6

What stains red in an acid-fast stain?

Answer 6

mycolic acids in the cell walls of Mycobacteria and Nocardia

Question 7

NADPH oxidase deficiency leads to vulnerability to which organisms?

Answer 7

catalase-positive organisms:

• Staph. aureus
• Pseudomonas
• Serratia marcescens
• Nocardia
• Aspergillus

Question 8

Barking cough, dyspnea, and recent history of URI? Most common cause?

Answer 8

viral laryngotracheitis (croup)
most common cause is parainfluenza virus

croup:

• obstruction of inspiration (inspiratory stridor)
• obstruction of expiration (barking cough)

Question 9

High fever, watery diarrhea, headache – sputum gram stain with many neutrophils and no bacteria?

Answer 9

Legionella pneumophila – Legionnaire’s disease!

hyponatremia
need to silver stain (gram negative but doesn’t often not detected on gram stain)

Question 10

Grows with hematin (X factor) and NAD+ (V factor) and can cause fever, malaise, swollen right knee after history of otitis media? Major virulence factor is?

Answer 10

H. flu
septic arthritis

major virulence factor is antiphagocytic capsule
needed for pathogenicity

Question 11

Strep. pneumo – bile solubility? Hemolysis pattern?

Answer 11

Alpha-hemolytic
bile soluble (cannot grow in the presence of bile)

Question 12

Fungus that forms small ovoid bodies within macrophages and causes cough, low-grade fever, and hepatosplenomegaly? Associated with what type of transmission?

Answer 12

Histoplasmosis
(Histo “hides” in macrophages)

Bird or bat droppings contain spores that are inhaled

Question 13

What infectious agent is associated with progression to brochiectasis?

Answer 13

Allergic bronchopulmonary aspergillosis (ABPA)
due to Aspergillus fumigatus

causes transient recurrent pulmonary infiltrates and eventual proximal bronchiectasis

Question 14

What CD4 count is normal? What CD4 count puts you at risk for Pneumocystic jiroveci? What is the most common cause of pneumonia above that?

Answer 14

CD4 > 500 considered normal

CD4 < 200 puts you at risk for opportunistic P. jiroveci infection
most common cause of community-acquired pneumonia in immunocompetent host is Strep. pneumo

Question 15

Pneumonia in which X-ray that looks much worse that the patient appears clinically?

Answer 15

Mycoplasma pneumoniae

Question 16

Most common site of colonization by S. aureus and MRSA in healthcare workers?

Answer 16

anterior nares

Question 17

Pt off cruise-ship with high fever, abdominal pain, watery diarrhea, cough? Most common laboratory abnormality?

Answer 17

Legionella pneumophila

hyponatremia – most common lab abnormality

gram stain often shows many neutrophils but no organisms

Question 18

Spherules packed with endospores? Regions endemic?

Answer 18

Coccidioides immitis

endemic to southwestern US and California

Question 19

What features must an RNA virus have to be able to induce both viral protein synthesis and viral genome replication from its naked RNA genome?

Answer 19

must be SINGLE-STRANDED and POSITIVE-SENSE RNA
acts directly as mRNA using host intracellular machinery for translation

single-stranded negative-sense and double-stranded RNA are NOT infectious

Question 20

Why does asplenia predispose to encapsulated organisms? What are they?

Answer 20

• macrophages line trabecular meshwork in spleen and ingest trapped bacteria (both opsonized and NON-opsonized)
• macrophages present capture antigens to B and T cells in white pulp to generate immune response
• splenic B-lymphocytes make almost half of body’s total Igs – splenic opsonizing antibody especially important in encapsulated species clearance (since capsule allows them to evade innate phagocytosis!)

Encapsulated bacteria:

• S. pneumo
• H. flu
• N. meningitidis

Question 21

Bacteria that needs culture on charcoal-yeast extract and supplementation with L-cysteine to grow? Toxin and mechanism?

Answer 21

Pseudomonas

endotoxin (fever, shock)
exotoxin A (inactivates EF-2, similar to diphtheria toxin)

Question 22

Elderly patients with influenza infection prone to developing secondary bacterial pneumonia with which organisms?

Answer 22

Staph. aureus
H. flu
Strep. pneumo