Internal Medicine_Infectious Diseases_7

Question 1

What is the causative agent of whooping cough?

Answer 1

Bordetella pertussis, a gram-negative coccobacillus.

Question 2

What bacterial structure allows B. pertussis to adhere to the respiratory epithelium?

Answer 2

Filamentous hemagglutinin (FHA), a surface protein.

Question 3

What toxin produced by B. pertussis disrupts chemokine receptor signaling on lymphocytes?

Answer 3

Pertussis toxin disrupts chemokine receptors, leading to lymphocytosis.

Question 4

What is the mechanism of the pertussis toxin?

Answer 4

ADP-ribosylation of Gi proteins, increasing cAMP in host cells.

Pertussis toxin is an AB toxin (also called two-component toxin) with B enabling Binding and triggering uptake (endocytosis) of the Active A component. The A component is an ADP ribosyltransferase that activates adenylate cyclase (increasing cAMP) by inactivating the inhibitory subunit (Gi).

Question 5

What is the hallmark laboratory finding in pertussis?

Answer 5

Lymphocytosis (elevated lymphocytes in the bloodstream).

Question 6

Why do they call it Whooping cough?

Answer 6

Whooping cough
child coughs on expiration and “whoops” on inspiration
can cause “100-day cough” in adults
associated with posttussive emesis

Question 7

What are the three clinical stages of whooping cough?

Answer 7

Catarrhal : 1 to 2 weeks of flu like prodrome (cough/rhinitis)

Paroxysmal (whooping stage) : severe cough with an inspiratory whoop and post-tussive emesis that usually lasts for 2 to 6 weeks.

Convalescent : eventual resolution of symptoms.

Usually referenced the 100-day cough.

Question 8

What is the recommended treatment for pertussis infection?

Answer 8

Macrolides are the first-line treatment.

Recommended to start ASAP prior to the development of cough to mitigate severity of disease.

Question 9

How is whooping cough transmitted?

Answer 9

Respiratory droplets.

Question 10

What is the function of the adenylate cyclase toxin in B. pertussis?

Answer 10

It elevates cAMP, disrupting ion and water transport in epithelial cells.

The tracheal cytotoxin of Bordetella pertussis specifically targets and damages ciliated respiratory epithelial cells.

Question 11

What vaccines protect against pertussis?

Answer 11

DTaP and Tdap vaccines provide protection.

DTaP for child vaccination series (5 doses).
Tdap for older children and adults.

Question 12

what severe, yet abnormal clinical sign is associated with whooping cough?

Answer 12

rib fracture or even pneumothorax.

Question 13

How can the pertussis infection be diagnosed?

Answer 13

Culture, PCR or serology.

Question 14

What is the treatment for pertussis infection?

Answer 14

Macrolides and ensure patient has an updated Tdap.

Question 15

What is the treatment for pertussis if the patient is allergic to macrolides?

Answer 15

if allergic use TMP-SMX.

Question 16

What is the post-exposure prophylaxis for contacts of a patient who had a pertussis infection?

Answer 16

Macrolide.

Question 17

What type of bacterium is Corynebacterium diphtheriae?

Answer 17

Corynebacterium diphtheriae is a gram-positive, non-spore-forming bacillus.

Question 18

What is the causative organism of diphtheria?

Answer 18

Corynebacterium diphtheriae —
Gram-positive
Non-motile
Rod-shaped bacterium that produces an exotoxin.

Question 19

What is the unique characteristic of Corynebacterium diphtheriae seen on the microscope?

Answer 19

Palisading

Gram ⊕ rods

Occur in angular arrangements

Question 20

How does Corynebacterium diphtheriae typically appear under the microscope?

Answer 20

It forms V- or Y-shaped chains due to unique snapping division during replication.

Question 21

What staining characteristic helps identify Corynebacterium diphtheriae?

Answer 21

It contains metachromatic granules that stain red with aniline dyes, while the rest of the bacillus stains blue.

Question 22

What special media is used to culture Corynebacterium diphtheriae?

Answer 22

Tellurite agar (produces black/grey colonies) and Loeffler’s medium.

Question 23

What test differentiates toxigenic strains of Corynebacterium diphtheriae?

Answer 23

The Elek test.

Elek’s test is used for differentiating between toxigenic and nontoxigenic strains of Corynebacterium diphtheriae. This test involves streaking the isolated bacterium on a special agar plate covered with filter paper containing diphtheria antitoxin. If the bacterium produces diphtheria toxin, it diffuses into the filter paper and forms a line of precipitation known as a ‘toxigenic line.’

Question 24

What is the pathogenesis of diphtheria?

Answer 24

Causes diphtheria via exotoxin encoded by β-prophage.

The diphtheria toxin inhibits elongation factor-2 (EF-2), halting protein synthesis, leading to cell death and formation of a pseudomembrane in the pharynx, cardiac, and CNS tissue.

The A-B exotoxin inactivates elongation factor-2 (EF-2) via ADP-ribosylation, leading to inhibition of protein synthesis and cell death.

Question 25

What is the mechanism of the diphtheria toxin?

Answer 25

The toxin uses ADP ribosylation to inhibit elongation factor-2 (EF-2), causing ribosomal dysfunction, halting protein synthesis and causing cell death.

Question 26

What is a hallmark clinical manifestation of diphtheria in the throat?

Answer 26

Formation of a dense, grey pseudomembrane over the tonsils and pharyngeal area.

Question 27

How is diphtheria transmitted?

Answer 27

Respiratory droplets or contact with infected lesions on the skin or fomites.

Question 28

What systemic effects can the diphtheria toxin have?

Answer 28

• nerve damage (demyelination) and paralysis that generally beings at the posterior pharyngeal wall and soft palate.
• cardiac toxicity (heart blocks, myocarditis, arrhythmias).
• renal injury

Question 29

What are the hallmark clinical features of respiratory diphtheria?

Answer 29

Pseudomembrane
(gray-white membrane)
on the tonsils, pharynx, or larynx.

Bull neck due to severe cervical lymphadenopathy.

Sore throat and dysphagia.

Low-grade fever and malaise.

Question 30

What is the significance of bull neck in diphtheria?

Answer 30

Bull neck is marked swelling of the neck due to cervical lymphadenopathy and soft tissue edema caused by local toxin effects.

It refers to cervical edema and lymphadenopathy, causing a swollen appearance.

The most specific symptom of diphtheria is pseudomembranous pharyngitis (grayish-white membrane A ) with lymphadenopathy (“bull’s neck” appearance).

Question 31

What are the potential complications of diphtheria?

Answer 31

Airway obstruction from pseudomembrane.

Myocarditis (toxin-induced, potentially fatal).

Demyelination and paralysis of cranial and peripheral nerves.

Renal failure (due to toxin-induced necrosis).

Question 32

What is the vaccine for diphtheria composed of?

Answer 32

An inactivated exotoxin vaccine (inactivated diphtheria toxin), often combined with tetanus and pertussis vaccines (e.g., DTaP, Tdap).

Question 33

What is the diagnostic method for diphtheria?

Answer 33

Clinical diagnosis: presence of pseudomembrane in the pharynx.

Gram stain showing gram ⊕ rods with metachromatic (blue and red) granules and culture of throat swab on Loeffler medium or tellurite agar.

Elek test for toxin production.

Question 34

What is the role of the Elek test in diphtheria diagnosis?

Answer 34

The Elek test confirms toxin production by Corynebacterium diphtheriae. It is used to differentiate toxigenic from non-toxigenic strains.

Question 35

How do you differentiate diphtheria from streptococcal pharyngitis?

Answer 35

Diphtheria:
Presence of pseudomembrane, bull neck, and history of no vaccination.

Streptococcal pharyngitis: Exudative pharyngitis, fever, no pseudomembrane, positive rapid strep test.

Question 36

How is diphtheria acutely managed?

Answer 36

Diphtheria antitoxin (neutralizes unbound toxin).

Antibiotics: Penicillin or Erythromycin to eradicate bacteria.

Airway support if pseudomembrane causes obstruction.

Question 37

What is the treatment protocol if a patient is exposed to diphtheria but is asymptomatic?

Answer 37

Post-exposure prophylaxis with Erythromycin or Penicillin for close contacts.

Check vaccination status and administer a booster dose of DTap or Tdap if needed.

Question 38

How is diphtheria prevented?

Answer 38

DTaP vaccine for children (diphtheria, tetanus, acellular pertussis).

Tdap vaccine booster in adolescents and adults.

Question 39

What is the difference between respiratory diphtheria and cutaneous diphtheria?

Answer 39

Respiratory diphtheria:
Pseudomembrane in the oropharynx, sore throat, airway obstruction.

Cutaneous diphtheria:
Chronic, non-healing ulcers with a grayish membrane.

Question 40

Which populations are at the highest risk of diphtheria infection?

Answer 40

Unvaccinated individuals
(the “woke” community).

Residents of areas with low vaccination coverage (the “broke” community).

Individuals with travel history to endemic areas. (the “float” community).

Question 41

What type of bacteria is Legionella pneumophila?

Answer 41

gram-negative bacillus.

water-loving bacteria.

oxidase-positive.

Question 42

What special stain is required for Legionella pneumophila?

Answer 42

Silver stain.

Question 43

What type of agar does Legionella pneumophila thrive on?

Answer 43

Buffered charcoal yeast extract (BCYE) agar enriched with iron and cysteine.

Question 44

What are the two clinical diseases caused by Legionella pneumophila?

Answer 44

Legionnaires’ disease and Pontiac fever.

Question 45

Which population is more susceptible to Legionnaires’ disease?

Answer 45

Smokers.

Question 46

Legionnaires’ disease causes what extrapulmonary symptoms?

Answer 46

GI symptoms (diarrhea)

Nausea and vomiting

Fever (usually very high surpassing 102.2)

Myalgias

Headaches

Confusion

Question 47

What distinguishes Legionnaires’ disease on a chest X-ray?

Answer 47

Patchy consolidation, predominantly in the mid-to-lower lung zones.

Atypical pneumonia

Question 48

What electrolyte abnormality is commonly associated with Legionnaires’ disease?

Answer 48

Low sodium.

Hyponatremia.

Also hypokalemia and hypophosphatemia but resources seem to be more stuck on sodium.

Question 49

What is the characteristic fever presentation in Legionnaires’ disease?

Answer 49

High fever, often surpassing 39°C (102.2°F).

Question 50

Pontiac fever typically presents with … ?

Answer 50

Brief, self-resolving respiratory illness with symptoms resembling a mild flu.

Patients might also have a headache, fever, muscle aches due to inhalation of Legionella endotoxin.

This disease is self-limited and doesn’t require workup.

Question 51

How is Legionnaires’ disease typically diagnosed?

Answer 51

Rapid urine antigen test.

Question 52

What are the preferred antibiotics for treating Legionnaires’ disease?

Answer 52

Macrolides (e.g., azithromycin)

or

fluoroquinolones (e.g., levofloxacin or moxifloxacin) are less commonly used.

Question 53

What is unique about the structure of Mycoplasma pneumoniae?

Answer 53

Mycoplasma pneumoniae lacks a cell wall and cannot be visualized using Gram stain.

Mycoplasma pneumoniae is a gram-indeterminate pleomorphic bacterium.

Question 54

What adaptation allows Mycoplasma pneumoniae to maintain membrane integrity?

Answer 54

Incorporation of cholesterol molecules into its cell membrane.

Question 55

What clinical condition does Mycoplasma pneumoniae cause, and what is its colloquial name?

Answer 55

It causes atypical pneumonia, also known as “walking pneumonia” due to its mild symptoms that allow patients to remain active.

Other symptoms include: pharyngitis, headache, and malaise.

Question 56

What population is most commonly affected by Mycoplasma pneumoniae?

Answer 56

Young adults (younger than 30 and often children), particularly those in close-contact settings like military recruits or dormitories.

Question 57

What does the chest X-ray typically show in Mycoplasma pneumoniae infections?

Answer 57

A reticulonodular or patchy infiltrate, often appearing more severe than the clinical presentation.

Question 58

What laboratory test is used to detect Mycoplasma pneumoniae?

Answer 58

The cold agglutinin test, which detects IgM antibodies that agglutinate red blood cells at low temperatures.

IgM cold agglutinins may cause red blood cell agglutination and subsequent hemolysis.

Question 59

What medium is used to culture Mycoplasma pneumoniae?

Answer 59

Eaton’s agar is the specialized medium for cultivation.

Question 60

What is the treatment for Mycoplasma pneumoniae infections?

Answer 60

Macrolides (e.g., azithromycin, erythromycin) or respiratory fluoroquinolones.

Question 61

Why is Mycoplasma pneumoniae resistant to beta-lactam antibiotics?

Answer 61

It lacks a peptidoglycan cell wall, which is the target of beta-lactam antibiotics.