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

What are the three clinical stages of whooping cough?

Answer 6

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 7

Why do they call it Whooping cough?

Answer 7

Whooping cough:

The coughs occur on expiration and “whoops” occur on inspiration

This is also called the “100-day cough”

Question 8

What are some complications associated with the whooping cough?

Answer 8

associated with:

• post-tussive emesis
• syncope
• retinal hemorrhage
• fractured ribs

Question 9

what abnormal, yet severe, complication is associated with whooping cough?

Answer 9

pneumothorax.

Question 10

What is the recommended treatment for pertussis infection?

Answer 10

Macrolides are the first-line treatment.

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

Question 11

How is whooping cough transmitted?

Answer 11

Respiratory droplets.

Question 12

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

Answer 12

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 13

What vaccines protect against pertussis?

Answer 13

DTaP and Tdap vaccines provide protection.

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

Question 14

How can the pertussis infection be diagnosed?

Answer 14

Culture, PCR or serology.

Question 15

What is the treatment for pertussis infection?

Answer 15

Macrolides and ensure patient has an updated Tdap.

Question 16

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

Answer 16

if allergic use TMP-SMX.

Question 17

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

Answer 17

Macrolide.

Question 18

What type of bacterium is Corynebacterium diphtheriae?

Answer 18

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

Question 19

What is the causative organism of diphtheria?

Answer 19

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

Question 20

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

Answer 20

Palisading

Gram ⊕ rods

Occur in angular arrangements

Question 21

How does Corynebacterium diphtheriae typically appear under the microscope?

Answer 21

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

Question 22

What staining characteristic helps identify Corynebacterium diphtheriae?

Answer 22

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

Question 23

What special media is used to culture Corynebacterium diphtheriae?

Answer 23

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

Question 24

What test differentiates toxigenic strains of Corynebacterium diphtheriae?

Answer 24

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 25

What is the pathogenesis of diphtheria?

Answer 25

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 26

What is the mechanism of the diphtheria toxin?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

How is diphtheria transmitted?

Answer 28

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

Question 29

What systemic effects can the diphtheria toxin have?

Answer 29

• 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 30

What are the hallmark clinical features of respiratory diphtheria?

Answer 30

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 31

What is the significance of bull neck in diphtheria?

Answer 31

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 32

What are the potential complications of diphtheria?

Answer 32

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 33

What is the vaccine for diphtheria composed of?

Answer 33

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

Question 34

What is the diagnostic method for diphtheria?

Answer 34

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 35

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

Answer 35

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

Question 36

How do you differentiate diphtheria from streptococcal pharyngitis?

Answer 36

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

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

Question 37

How is diphtheria acutely managed?

Answer 37

Diphtheria antitoxin (neutralizes unbound toxin).

Antibiotics: Penicillin or Erythromycin to eradicate bacteria.

Airway support if pseudomembrane causes obstruction.

Question 38

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

Answer 38

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 39

How is diphtheria prevented?

Answer 39

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

Tdap vaccine booster in adolescents and adults.

Question 40

What is the difference between respiratory diphtheria and cutaneous diphtheria?

Answer 40

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

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

Question 41

Which populations are at the highest risk of diphtheria infection?

Answer 41

Unvaccinated individuals

Communities that may have an opposition to government or the healthcare industry.

Residents of areas with low vaccination coverage due to barriers to healthcare.

Individuals with travel history to endemic areas.

Question 42

What type of bacteria is Legionella pneumophila?

Answer 42

gram-negative bacillus.

water-loving bacteria.

oxidase-positive.

Question 43

What special stain is required for Legionella pneumophila?

Answer 43

Silver stain.

Question 44

What type of agar does Legionella pneumophila thrive on?

Answer 44

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

Question 45

What are the two clinical diseases caused by Legionella pneumophila?

Answer 45

Legionnaires’ disease and Pontiac fever.

Question 46

Which population is more susceptible to Legionnaires’ disease?

Answer 46

Smokers.

Question 47

Legionnaires’ disease causes what extrapulmonary symptoms?

Answer 47

GI symptoms (diarrhea)

Nausea and vomiting

Fever (usually very high surpassing 102.2)

Myalgias

Headaches

Confusion

Question 48

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

Answer 48

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

Atypical pneumonia

Question 49

What electrolyte abnormality is commonly associated with Legionnaires’ disease?

Answer 49

Low sodium.

Hyponatremia.

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

Question 50

What is the characteristic fever presentation in Legionnaires’ disease?

Answer 50

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

Question 51

Pontiac fever typically presents with … ?

Answer 51

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 52

How is Legionnaires’ disease typically diagnosed?

Answer 52

Rapid urine antigen test.

Question 53

What are the preferred antibiotics for treating Legionnaires’ disease?

Answer 53

Macrolides (e.g., azithromycin)

or

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

Question 54

What is unique about the structure of Mycoplasma pneumoniae?

Answer 54

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

Mycoplasma pneumoniae is a gram-indeterminate pleomorphic bacterium.

Question 55

What adaptation allows Mycoplasma pneumoniae to maintain membrane integrity?

Answer 55

Incorporation of cholesterol molecules into its cell membrane.

Question 56

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

Answer 56

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 57

What population is most commonly affected by Mycoplasma pneumoniae?

Answer 57

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

Question 58

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

Answer 58

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

Question 59

What laboratory test is used to detect Mycoplasma pneumoniae?

Answer 59

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 60

What medium is used to culture Mycoplasma pneumoniae?

Answer 60

Eaton’s agar is the specialized medium for cultivation.

Question 61

What is the treatment for Mycoplasma pneumoniae infections?

Answer 61

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

Question 62

Why is Mycoplasma pneumoniae resistant to beta-lactam antibiotics?

Answer 62

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