INFECTIOUS DISEASE

Question 1

Bacili with acid-fast cell walls

Answer 1

Mycobacterium:

Mycobacterium tuberculosis: Causes tuberculosis (TB).
Mycobacterium leprae: Causes leprosy (Hansen’s disease).
Mycobacterium avium complex (MAC): Causes opportunistic infections in immunocompromised individuals, especially those with AIDS.
Mycobacterium bovis: Associated with TB in cattle and can infect humans through unpasteurized milk.
Nocardia (partially acid-fast):

Nocardia asteroides: Causes nocardiosis, which can manifest as a pulmonary or disseminated infection.

Question 2

Budding yeasts forming germ tubes

Answer 2

Candida albicans

Question 3

Gram positive cocci growing in clusters

Answer 3

Staphylococcus aureus:

Coagulase-positive (distinguishes it from other Staphylococcus species).
Can cause a variety of infections, ranging from skin infections (boils, cellulitis) to severe systemic infections (bacteremia, endocarditis, toxic shock syndrome).
Produces several virulence factors, such as protein A, hemolysins, and toxins.
Staphylococcus epidermidis:

Coagulase-negative.
Part of the normal skin flora but can cause opportunistic infections, particularly in immunocompromised patients and those with implanted medical devices (e.g., catheters, prosthetic valves).
Staphylococcus saprophyticus:

Coagulase-negative.
A common cause of urinary tract infections in young sexually active women.

Question 4

Silver stain-positive motile spirochetes

Answer 4

Treponema pallidum

Borrelia species:
Borrelia burgdorferi: Causes Lyme disease, transmitted by ticks.
Borrelia recurrentis: Causes relapsing fever, transmitted by lice or ticks.

Leptospira species

Question 4

Lactose-fermenting gram-negative bacili

Answer 4

Escherichia coli:

Klebsiella species (e.g., Klebsiella pneumoniae):

Enterobacter species (e.g., Enterobacter cloacae):

Citrobacter species:

Question 5

What means acid-fast

Answer 5

Resistant to decolorization by acid after staining with carbolfuchsing

Question 6

Which are the BK virulence factors ?

Answer 6

“Cord Factor” - Evade immune response, cause granuloma formation and trigger cytokines release

Sulfatides - inihibts fusion of phagosome/ lysosomes

Catalase-peroxidase - Resist host cells oxidation

Question 7

What happens into the first week after primary infection by BK?

Answer 7

• Intra-macrophage proliferation

Question 8

What happens in two-five weeks after BK primary infection?

Answer 8

• Cell-mediate immune response
  Th1
  Activation of CD4+
  INF-gama
  Macrophages and cytotoxic T lymphocites

Question 9

What is the action mechanism of the Izoniazid?

Answer 9

Blocks synthesis of mycolic acids

Question 10

What is the mechanism of the neurotoxic effect of the Izoniazid?

Answer 10

Compete with vitamin B6 as co-factor neurotransmitter synthesis

Question 11

What is the action mechanism of the Rifampicin?

Answer 11

Inhibits bacterial DNA - dependent RNA polymerase blocking RNA synthesis

Question 12

Which BK drug causes Gout?

Answer 12

Pyrazinamide

Question 13

Which BK drug causes color blindness ?

Answer 13

Ethambutol

Question 14

What is the action mechanism of Ethambutol?

Answer 14

Inhibit arabinosyl transferase

Question 15

What is the sction mechanism of the Streptomycin?

Answer 15

It is an aminoglycoside that inhibit bacterial 30S ribosome subunit

Question 16

Tzancks smear with Giant cells

Answer 16

Simplix Herpes

Question 17

In which nerve the HSV-1 commonly hide?

Answer 17

Trigeminal ganglia

Question 18

Where HSV-2 commonly hide in the latent phase?

Answer 18

Lumbar-sacral ganglia

Question 19

What is the central nervous system infection caused by HSV-1 and HSV-2?

Answer 19

HSV-1: Temporal lobe encephalitis

HSV-2: Meningitis

Question 20

What are the infections caused by HSV-1?

Answer 20

Gingivostomatitis - Severe sore throat with painful vesicles

Labial herpes - “cold sores” vesicles with vermilion borders at the lip edge

Herpetic whitlow - painful lesions on the fingertip

Keratoconjunctivitis -

Encephalitis -

Question 21

Patient with recurrent HSV infections is treated with which drug? Why?

Answer 21

Daily valacyclovir continued indefinitely

It is an effective once-daly dose drug with minimal adverse effects

Question 22

Genital ulcer disease/ causative agent/ Lesion description

Answer 22

Syphilis / Treponema Pllidum / Single painless ulcer with heaped-up borders and clear base

Genital herpes / Herpes simplex virus (HSV-2) / Multiple, painful, superficial vesicles or ulcers with erythematous base

Chancroid/ Haemophilus Ducreyi / Deep, purulent, painful ulcers with matted/suppurative lymphadenitis

Donovanosis (Granuloma inguinale) / Klebsiella Granulomatis / Painless, progressive, red, serpinginous ulcerative lesions without lymphadenopathy