micro5

Question 1

Corynebacterium diphtheriae

Answer 1

Gram ⊕ rod; transmitted via respiratory droplets. Causes diphtheria via exotoxin encoded by β-prophage. Potent exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2.
Symptoms include pseudomembranous pharyngitis (grayish-white membrane A ) with lymphadenopathy, myocarditis, and arrhythmias.

Lab diagnosis based on gram ⊕ rods with metachromatic (blue and red) granules and ⊕ Elek test for toxin. Toxoid vaccine prevents diphtheria.

Question 2

Listeria monocytogenes

Answer 2

Listeria monocytogenes

A

Gram ⊕ , facultative intracellular rod; acquired by ingestion of unpasteurized dairy products and cold deli meats, via transplacental transmission, or by vaginal transmission during birth. Grows well at refrigeration temperatures (4°–10°C; “cold enrichment”).

Forms “rocket tails” (red in A ) via actin polymerization that allow intracellular movement and cellto-cell spread across cell membranes, thereby avoiding antibody. Characteristic tumbling motility in broth.

Can cause amnionitis, septicemia, and spontaneous abortion in pregnant women; granulomatosis infantiseptica; neonatal meningitis; meningitis in immunocompromised patients; mild, selflimited gastroenteritis in healthy individuals.

Treatment: ampicillin.

Question 3

Nocardia

Answer 3

Aerobe,Acid fast (weak) ,Found in soil

Causes 🦋pulmonary infections in immunocompromised (can mimic TB but with ⊝ PPD); 🦋cutaneous infections after trauma in immunocompetent; can spread to CNS
Treat with sulfonamides (TMP-SMX)
Treatment is a SNAP: Sulfonamides—Nocardia; Actinomyces—Penicillin

Question 4

Actinomyces

Answer 4

Anaerobe

A

Not acid fast

B

Normal oral, reproductive, and GI flora

Causes oral/facial abscesses that drain through

sinus tracts; often associated with dental caries/ extraction and other maxillofacial trauma; forms yellow “sulfur granules”; can also cause PID with IUDs
Treat with penicillin

Question 5

Mycobacteria types

Answer 5

Mycobacteria

Mycobacterium tuberculosis (TB, often resistant to multiple drugs).

M avium–intracellulare (causes disseminated, non-TB disease in AIDS; often resistant to multiple drugs). Prophylaxis with azithromycin when CD4+ count < 50 cells/ mm.3

M scrofulaceum (cervical lymphadenitis in children).

M marinum (hand infection in aquarium handlers).

All mycobacteria are acid-fast organisms (pink rods; arrows in A ).

Question 6

TB sx

Answer 6

TB symptoms include fever, night sweats, weight loss, cough (nonproductive or productive), hemoptysis.

Cord factor creates a “serpentine cord” appearance in virulent M tuberculosis strains; activates macrophages (promoting granuloma formation) and induces release of TNF-α. Sulfatides (surface glycolipids) inhibit phagolysosomal fusion.

Question 7

Leprosy (Hansen disease)

Answer 7

Caused by Mycobacterium leprae, an acid-fast bacillus that likes cool temperatures (infects skin and superficial nerves—“glove and stocking” loss of sensation A ) and cannot be grown in vitro. Diagnosed via skin biopsy or tissue PCR. Reservoir in United States: armadillos.

Question 8

Hansen disease has 2 forms (many cases fall temporarily between two extremes):

Answer 8

ƒ 🦋Lepromatous—presents diffusely over the skin, with leonine (lion-like) facies B , and is

communicable (high bacterial load); characterized by low cell-mediated immunity with a

humoral Th2 response. Lepromatous form can be lethal.

ƒ 🦋Tuberculoid—limited to a few hypoesthetic, hairless skin plaques; characterized by high cell-

mediated immunity with a largely Th1-type immune response and low bacterial load. Treatment: dapsone and rifampin for tuberculoid form; clofazimine is added for lepromatous form.

Question 9

Neisseria

Answer 9

Gram ⊝ diplococci. Metabolize glucose and produce IgA proteases. Contain lipooligosaccharides (LOS) with strong endotoxin activity. N gonorrhoeae is often intracellular (within neutrophils) A .

MeninGococci ferment Maltose and Glucose. Gonococci ferment Glucose.

Question 10

Gonococci

Answer 10

No polysaccharide capsule

Maltose not fermented

No vaccine due to antigenic variation of pilus proteins

Sexually or perinatally transmitted

Causes gonorrhea, septic arthritis, neonatal

conjunctivitis (2–5 days after birth), pelvic inflammatory disease (PID), and Fitz-HughCurtis syndrome

Condoms  sexual transmission, erythromycin eye ointment prevents neonatal blindness

Treatment: ceftriaxone (+ azithromycin

or doxycycline, for possible chlamydial coinfection)

Question 11

Meningococci

Answer 11

Polysaccharide capsule

Maltose fermentation

Vaccine (type B vaccine not widely available)

Transmitted via respiratory and oral secretions

Causes meningococcemia with petechial

hemorrhages and gangrene of toes B , meningitis, Waterhouse-Friderichsen syndrome (adrenal insufficiency, fever, DIC, shock)

Rifampin, ciprofloxacin, or ceftriaxone prophylaxis in close contacts

Treatment: ceftriaxone or penicillin G

Question 12

Haemophilus influenzae

Answer 12

🦋Small gram ⊝ (coccobacillary) rod. Aerosol transmission.
🦋Nontypeable (unencapsulated) strains are the most common cause of mucosal infections (otitis media, conjunctivitis, bronchitis) as well as invasive infections since the vaccine for capsular type b was introduced. Produces IgA protease.

🦋HaEMOPhilus causes Epiglottitis (endoscopic appearance in A , can be “cherry red” in children; “thumb sign” on lateral neck x-ray B ), Meningitis, Otitis media, and Pneumonia.

🦋Treatment: amoxicillin +/− clavulanate for mucosal infections; ceftriaxone for meningitis; rifampin prophylaxis for close contacts.

Question 13

Haemophilus influenzae vaccines

Answer 13

Vaccine contains type b capsular polysaccharide (polyribosylribitol phosphate) conjugated to diphtheria toxoid or other protein. Given between 2 and 18 months of age.
in the hexa and penta
Does not cause the flu (influenza virus does).

Question 14

Bordetella pertussis

Answer 14

🦋Gram ⊝ , aerobic coccobacillus. Virulence factors include pertussis toxin (disables G), i adenylate cyclase toxin ( cAMP), and tracheal cytotoxin. Three clinical stages:

ƒ🦋Catarrhal—low-grade fevers, Coryza.

ƒ Paroxysmal—paroxysms of intense cough followed by inspiratory “whooP” (“whooping cough”), posttussive vomiting.

ƒ Convalescent—gradual recovery of chronic cough.

🦋Prevented by Tdap, DTaP vaccines. May be mistaken as viral infection due to lymphocytic infiltrate resulting from immune response.