Bacterial Pharyngitis Strep Pyogenes And Diphtheria

Question 1

What is pharyngitis?

Answer 1

Pharyngitis (or sore throat) is one of the most common upper respiratory tract infections (URTI).

Question 2

What accounts for the majority of pharyngitis cases?

Answer 2

Viral pharyngitis accounts for the vast majority of cases and is usually self-limited.

Question 3

What are the common etiological agents of bacterial pharyngitis?

Answer 3

• Streptococcus pyogenes (most common)
• Corynebacterium diphtheriae
• Other ß-hemolytic streptococci (group C and G)
• Arcanobacterium hemolyticum
• Fusobacterium necrophorum
• Mycoplasma pneumoniae
• Neisseria gonorrhoeae

Question 4

What is the primary causative agent of streptococcal pharyngitis?

Answer 4

Streptococcus pyogenes (or group A Streptococcus).

Question 5

What are the clinical manifestations of streptococcal sore throat?

Answer 5

Localized (tonsillitis) or diffuse (pharyngitis) with symptoms such as erythema, swelling of pharyngeal mucosa, and purulent exudate formation.

Question 6

What are possible complications of streptococcal pharyngitis?

Answer 6

• Suppurative complications: peritonsillar abscess, retropharyngeal abscess, bacteremia
• Non-suppurative complications: acute rheumatic fever (ARF), poststreptococcal glomerulonephritis (PSGN)

Question 7

How can streptococcal pharyngitis be differentiated from diphtheria?

Answer 7

Diphtheria is characterized by the presence of a membrane over the tonsil.

Question 8

What is the laboratory diagnosis for streptococcal pharyngitis?

Answer 8

• Culture on blood agar
• Gram staining
• Antimicrobial susceptibility testing (AST)
• Rapid antigen detection test (RADT)
• ASO titer
• Molecular test (PCR assay)

Question 9

What is the recommended treatment for streptococcal pharyngitis?

Answer 9

Benzathine penicillin G, 1M single dose or oral penicillin V for 10 days.

Question 10

What is diphtheria?

Answer 10

Diphtheria is a highly infectious childhood disease caused by Corynebacterium diphtheriae, leading to exudative pharyngitis and membranous tonsillitis.

Question 11

What are the characteristic features of Corynebacterium diphtheriae?

Answer 11

• Gram-positive, non-capsulated, non-sporing, non-motile bacillus
• Chinese letter or cuneiform arrangement
• Metachromatic granules

Question 12

What is the primary virulence factor of diphtheria?

Answer 12

Diphtheria toxin (DT) is the primary virulence factor responsible for diphtheria.

Question 13

What is the mechanism of action of diphtheria toxin?

Answer 13

Fragment A of the toxin ADP ribosylates elongation factor 2 (EF-2), inhibiting protein synthesis.

Question 14

What are the symptoms of respiratory diphtheria?

Answer 14

• Formation of a tough leathery greyish white pseudomembrane
• Bull-neck appearance
• Foul breath, thick speech, stridor

Question 15

What laboratory tests are used for diagnosing diphtheria?

Answer 15

• Direct smear microscopy (Gram stain and Albert’s stain)
• Culture on enriched media
• Toxigenicity test

Question 16

What are the recommended specimens for diphtheria diagnosis?

Answer 16

• Throat swab containing fibrinous exudates
• Portion of pseudomembrane
• Nose or skin specimens

Question 17

What are the culture media for isolating Corynebacterium diphtheriae?

Answer 17

• Blood agar
• Chocolate agar
• Loeffler’s serum slope

Question 18

What is the typical incubation period for diphtheria?

Answer 18

The incubation period is about 3-4 days.

Question 19

What is the clinical significance of the pseudomembrane in diphtheria?

Answer 19

It is adherent to the mucosal base and bleeds on removal, indicating respiratory diphtheria.

Question 20

What is the appearance of C. diphtheriae under the microscope?

Answer 20

Green bacilli with bluish black metachromatic granules at the poles

Details of Albert’s staining procedure is given in Chapter 3.5.

Question 21

What type of medium does C. diphtheriae require for optimal growth?

Answer 21

Enriched medium such as blood agar, chocolate agar, and Loeffler’s serum slope

C. diphtheriae is fastidious, aerobe, and facultative anaerobe.

Question 22

What are the characteristics of colonies on blood agar for C. diphtheriae?

Answer 22

Small circular, white, and sometimes hemolytic (mitis biotype)

Plates are incubated at 37°C aerobically.

Question 23

What do colonies of C. diphtheriae look like on Loeffler’s serum slope?

Answer 23

Small, circular, glistening, and white with a yellow tinge in 6-8 hours

Growth can be detected as early as 6-8 hours.

Question 24

What is a disadvantage of using enriched medium for C. diphtheriae?

Answer 24

If incubated beyond 6-8 hours, it supports growth of other throat commensals

Enriched media can lead to contamination.

Question 25

What is the purpose of selective media in the isolation of C. diphtheriae?

Answer 25

Inhibits normal flora for better isolation from cases and carriers ## Footnote Throat commensals are inhibited.

Question 26

What color do colonies of C. diphtheriae turn on potassium tellurite agar?

Answer 26

Black ## Footnote C. diphtheriae reduces tellurite to metallic tellurium.

Question 27

What biochemical tests are used for the identification of C. diphtheriae?

Answer 27

Sugar fermentation test, Pyrazinamidase test, Urease test ## Footnote The last two tests are negative for C. diphtheriae.

Question 28

What is the significance of toxin demonstration in diagnosing diphtheria?

Answer 28

It determines the pathogenicity due to diphtheria toxin ## Footnote Mere isolation of bacilli does not complete the diagnosis.

Question 29

What is the Elek's gel precipitation test used for?

Answer 29

To demonstrate toxin and assess strain relatedness during outbreaks ## Footnote It produces an arrow-shaped precipitation band if the strain is toxigenic.

Question 30

What are the patterns observed in the Elek's test that indicate strain relatedness?

Answer 30

Cross-over indicates unrelated strain, Spur formation indicates partially related strain, Fused indicates identical strain ## Footnote This helps in epidemiological studies.

Question 31

What is the treatment of choice for diphtheria?

Answer 31

Antidiphtheritic serum or ADS (antitoxin) ## Footnote It neutralizes the toxin.

Question 32

Which antibiotics are considered the drug of choice for diphtheria?

Answer 32

Penicillin or erythromycin ## Footnote Antibiotics are useful if given early in infection.

Question 33

What is the recommended post-exposure prophylaxis for close contacts of diphtheria patients?

Answer 33

Booster dose of diphtheria vaccine + penicillin G or erythromycin ## Footnote This is to prevent the disease from developing.

Question 34

What is the primary component of the diphtheria vaccine?

Answer 34

Diphtheria toxoid ## Footnote It induces antitoxin production in the body.

Question 35

What does a protective titer of more than 0.01 Unit/mL of antitoxin prevent?

Answer 35

All forms of diphtheria ## Footnote Vaccine is not effective for prevention of cutaneous diphtheria.

Question 36

What are the different types of combined vaccines that include diphtheria toxoid?

Answer 36

DPT, DaPT, Td, Pentavalent vaccine ## Footnote DPT also contains pertussis and tetanus toxoids.

Question 37

What is the immunization schedule for children under the National Immunization Schedule of India 2020 for diphtheria?

Answer 37

Total seven doses: three doses of pentavalent vaccine followed by two booster doses of DPT and two booster doses of Td ## Footnote Booster doses are given at 16-24 months, 5 years, 10 years, and 16 years.

Question 38

What are diphtheroids?

Answer 38

Nondiphtherial corynebacteria that exist as normal commensals in various areas ## Footnote They can cause invasive disease in immunocompromised patients.

Question 39

How do diphtheroids differ from C. diphtheriae in terms of staining?

Answer 39

Diphtheroids stain more uniformly than C. diphtheriae ## Footnote They also exhibit a palisade arrangement.

Question 40

What is the palisade arrangement in diphtheroids?

Answer 40

Arranged in parallel rows rather than cuneiform pattern ## Footnote This helps in differentiating them from C. diphtheriae.