Bacterial Infections Part 1

Question 1

Staphylococcal Infections (Pyogenic)

Answer 1

• S. aureus: skin infections, osteomyelitis, pneumonia, endocarditis
• S. epidermidis: Opportunistic infections in IV drug abusers and in patients with catheters or prosthetic heart valves.
• S. saprophyticus: UTIs

Question 2

Staphylococcal Virulence Factors

Answer 2

• Toxins that damage host cell membranes (hemolysins), induce skin sloughing (exfoliative toxins), vomiting (enterotoxins), or shock (super antigens)

Question 3

Streptococcal Infections

Answer 3

• Classified by pattern of hemolysis on blood agur:
• -Beta is complete or clear hemolysis
• -Alpha is partial or green hemolysis
• -gamma has no hemolysis

Question 4

Beta-hemolytic streptococci

Answer 4

• Group A (S. pyogenes) causes pharyngitis, scarlet fever, impetigo, rheumatic fever, necrotizing fasciitis, and glomerulonephritis.
• Group B (S. agalactiae) colonizes female genital tract and causes chorioamnionitis in pregnancy.

Question 5

Alpha Hemolytic Streptococci

Answer 5

• Includes Strep Pneumoniae, a common cause of adult community acquired pneumonia and meningitis.

Question 6

Major cause of dental caries

Answer 6

Strep. Mutans.

Question 7

Streptococcal Virulence Factors

Answer 7

• Capsules (Pyogenes and Pneumoniae)
• M-proteins that inhibit complement (progenies)
• Exotoxins that cause fever and rash (progenies) in scarlet fever
• Pneumolysiin destroys host-cell membranes and damages tissues (pneumoniae)

Question 8

Streptococcal INfection Findings

Answer 8

• Diffuse interstitial neutrophilic infiltrates with minimal host tissue destruction except for some progenies that has been dubbed “flesh-eating bacteria”.

Question 9

Diptheria

Answer 9

• Corynebacterium Diptheriae: Slender Gram-positive rod with clubbed ends, passed as aerosol or through skin exudates.

Question 10

Diptheria Findings

Answer 10

• Oropharyngeal fibrinosupporative exudate, makes an exotoxin that injures heart, nerves, and other organs.
• Toxin is phage-encoded in two parts (A and B) that blocks protein synthesis.
• -B BINDs to cell surface and gets A in.
• -A blocks protein synthesis by ADP ribosylation and inactivation of elongation factor-2.

Question 11

Listeriosis

Answer 11

• L. Monocytogenes is Gram-positive, intracellular that causes food poisoning.
• Causes sepsis and meningitis in elderly and immosuppressed

Question 12

Listeriosis Mechanism

Answer 12

• Expresses leucine-rich proteins that called internal ins that bind epithelial E-cadherin and promote internalization.
• Bacillus then uses listeriolysin O and two phospholipases to degrade the phagolysosome membrane.

Question 13

Listeriosis Findings

Answer 13

• Resting Macrophages internalize but do not kill Listeria, the phages have to be activated by interferon gamma.
• Evokes exudative inflammation with neutrophils.

Question 14

Anthrax

Answer 14

• Spore forming Gram positive bacillus that humans contract through contaminated animal products or powdered spores.

Question 15

Anthrax Findings

Answer 15

• Necrotized lesions filled with neutrophils nd macrophages.
• Cutaneous: Painless, pruritic papules that become edematous vesicles followed by black eschar.
• Inhalation leads to sepsis, shock, and death.
• GI: contracted by eating contaminated meat, causes severe, bloody diarrhea.

Question 16

Antrax Toxin

Answer 16

• Composed of B subunit involved in toxin endocytosis and A subunits of two different types:
• -Edema Factor converts ATP to cyclic adenosine monophosphate (cAMP) that causes cellular water efflux.
• -Lethal Factor: protease that causes cell death by destroying mitogen-activated protein kinase kinases.

Question 17

Nocardia

Answer 17

• Aeroboic Gram-positive bacterium growing in branched chains that stain with acid-fast protocols.
• Found in soil and cause opportunistic infections in immunocompromised hosts.

Question 18

Nocardia Findings

Answer 18

• N. asteroides causes indolent resp infections, often with CNS spread. N. brasiliensis infects skin.
• Elicits suppurative responses with granulation tissue and fibrosis.

Question 19

Neisserial Infections

Answer 19

• Aerobic, Gram-negative diplococci that have growth requirements (sheep blood-enriched (chocolate) agar.

Question 20

N. Meningitidis

Answer 20

• Bacterial meningitis in children younger than 2.

Question 21

N. Gonorrhoeae

Answer 21

• Second most common STI.
• In men causes urethritis, in women is asymptomatic and can lead to PID, infertility, and ectopic pregnancy.
• Neonatal Infection can cause blindness.

Question 22

Neisserial Virulence Factors

Answer 22

• Capsule that inhibits opsonization and antigenic variation.
• • Adhesive pili undergo genetic recombination.

Question 23

Whooping Cough

Answer 23

• Bordetella pertussis, Gram-negative coccobacillus.
• Paroxysms of violent coughing.
• Causes laryngotracheobronchitis with mucosal erosion and mucopurulent exudates.

Question 24

Whooping Cough Virulence

Answer 24

• Expression regulated by Bordetella virulence gene (bvg)
• -Hemagglutinin binds to resp epithelium carbs and macrophage Mac-1 integrins.
• • Pertussis toxin ADP ribosylates and inactivates guanine nucleotide-binding proteins so G proteins cannot transduce signals, and bronchial epithelium are paralyzed.