Infectious Disease Flashcards

Flashcards covering key aspects of Mycoplasma, Rickettsia, and Chlamydia infections, including pathogenesis, clinical features, diagnosis, and treatment.

Mycoplasma pneumoniae

Smallest free-living bacterium; lacks cell wall; incorporates sterols into its plasma membrane; pleomorphic with 'fried egg' colony appearance; passes through 0.45 µm filter.

Mycoplasma pneumoniae pathogenesis

Attaches to respiratory epithelium via P1 adhesion protein binding to sialated glycoproteins, causing ciliostasis, epithelial cell destruction, and impaired mucociliary clearance; acts as a superantigen.

Clinical features and complications of Mycoplasma pneumoniae

Starts with mild fever, malaise, headache, progressing to nonproductive cough and bronchopneumonia; complications include otitis media, erythema multiforme, myocarditis, pericarditis, and CNS involvement.

Diagnosis and treatment of Mycoplasma pneumoniae

Diagnosis: PCR, serology (complement fixation or enzyme agglutination); Culture slow and microscopy ineffective. Treatment: erythromycin, tetracycline, fluoroquinolones (adults only).

Pathogenesis of Rocky Mountain Spotted Fever (Rickettsia rickettsii)

Transmitted via wood tick bite; infects endothelial cells lining small blood vessels; replicates in cytoplasm, causing cell lysis, vascular leakage, thrombosis, and vasculitis, leading to characteristic rash.

Clinical signs of Rocky Mountain Spotted Fever

Symptoms appear 2-14 days post tick bite; include high fever, headache, followed by petechial rash starting at extremities and involving palms/soles; complications: encephalitis, renal/respiratory failure.

Preferred diagnostic method and treatment for RMSF

Diagnosis: Microimmunofluorescence (MIF) for outer membrane proteins, PCR. Treatment: doxycycline; fluoroquinolones as alternative.

Rickettsia prowazekii

Causes epidemic typhus; transmitted by human body louse; thrives in crowded and unsanitary conditions.

Symptoms and mortality of epidemic typhus

Fever, severe headache, chills, myalgias, and arthralgias; 40% develop petechial rash; complications include myocarditis and CNS disorders; mortality can reach 66% without treatment.

Developmental cycle of Chlamydia trachomatis

Has two forms: Elementary body (EB) - infectious, metabolically inactive; and Reticulate body (RB) - noninfectious, metabolically active. EB enters cells, transforms to RB, replicates, and reverts to EB to exit.

Biovars and serovars of Chlamydia trachomatis

Trachoma: A, B, Ba, C; Urogenital: D-K; LGV: L1, L2, L2a, L3.

Trachoma

Chronic keratoconjunctivitis from serovars A-C; repeated infections cause conjunctival scarring, leading to inward eyelash growth (trichiasis) and corneal abrasion -> blindness.

Urogenital symptoms of Chlamydia

Males: urethritis with purulent discharge, epididymitis. Females: cervicitis, PID, salpingitis, often asymptomatic (up to 80%).

Lymphogranuloma Venereum (LGV)

Sexually transmitted infection by serovars L1-L3. Stage 1: painless ulcer; Stage 2: painful lymphadenitis with buboes; may rupture. Proctitis common in women and MSM.

Diagnosis and treatment of Chlamydia trachomatis

Diagnosis: DFA, PCR, culture on cell lines. Treatment: azithromycin, doxycycline; LGV requires 21-day tetracycline course; neonates treated with erythromycin.

Pathogens lacking a peptidoglycan cell wall and resistant to beta-lactams

Mycoplasma pneumoniae (no wall) and Chlamydia trachomatis (no peptidoglycan).

Distinguishing Rickettsial rash from measles or syphilis

Rickettsial rash involves palms and soles and begins at extremities; spreads to trunk unlike measles which starts at face/trunk.

Diagnostic technique shared across Rickettsia and Chlamydia

Microimmunofluorescence (MIF) is used to detect outer membrane proteins and confirm species in both genera.

Which pathogen causes walking pneumonia (atypical pneumonia)?

Mycoplasma pneumoniae

Which pathogen causes Rocky Mountain Spotted Fever?

Rickettsia rickettsii

Which pathogen causes epidemic typhus?

Rickettsia prowazekii

Which pathogen causes trachoma, the leading cause of infectious blindness?

Chlamydia trachomatis (serovars A-C)

Which pathogen causes lymphogranuloma venereum (LGV)?

Chlamydia trachomatis (serovars L1-L3)

Which pathogen causes neonatal conjunctivitis?

Chlamydia trachomatis

Which pathogen causes urogenital infections, the most common bacterial STD in the U.S.?

Chlamydia trachomatis (serovars D-K)

A patient has a bullseye rash and migratory joint pain. Which pathogen is likely involved?

Borrelia burgdorferi (Lyme disease)

A patient presents with a painless genital ulcer followed by painful lymphadenopathy. Which pathogen?

Chlamydia trachomatis (LGV)

A child presents with cough, headache, and fever that progresses to patchy bronchopneumonia. Which pathogen?

Mycoplasma pneumoniae

A patient presents with petechial rash on palms and soles, fever, and history of tick exposure. Which pathogen?

Rickettsia rickettsii

A soldier in a refugee camp presents with fever, rash, and myocarditis. Which pathogen?

Rickettsia prowazekii (epidemic typhus)

A newborn has swollen eyelids and purulent discharge a few days after birth. Which pathogen?

Chlamydia trachomatis

A young adult with a new sexual partner has urethritis with purulent discharge but no gonorrhea. Which pathogen?

Chlamydia trachomatis

Which pathogen causes conjunctival scarring that leads to trichiasis and blindness?

Chlamydia trachomatis (trachoma)

Which intracellular pathogen grows only in cytoplasm of eukaryotic endothelial cells and is vector-borne?

Rickettsia species

Which pathogen is resistant to penicillin due to absence of a cell wall?

Mycoplasma pneumoniae

Mycoplasma pneumoniae - Shape and Wall

Pleomorphic, lacks a cell wall, incorporates sterols into membrane.

Mycoplasma pneumoniae - Colony Appearance

Fried egg appearance on cell-free media.

Mycoplasma pneumoniae - Transmission

Inhaled droplets, requires close contact.

Mycoplasma pneumoniae - Adhesion Mechanism

Uses P1 protein to bind sialated glycoprotein receptors.

Mycoplasma pneumoniae - Clinical Name

Atypical pneumonia (walking pneumonia).

Mycoplasma pneumoniae - Key Complication

Stevens-Johnson syndrome (erythema multiforme).

Mycoplasma pneumoniae - Treatment

Erythromycin, tetracycline, fluoroquinolones (adults only).

Rickettsia rickettsii - Disease

Rocky Mountain Spotted Fever.

Rickettsia rickettsii - Transmission Vector

Wood tick.

Rickettsia rickettsii - Rash Pattern

Starts on extremities, spreads to trunk, includes palms and soles.

Rickettsia rickettsii - Treatment

Doxycycline.

Rickettsia prowazekii - Disease

Epidemic typhus.

Rickettsia prowazekii - Vector

Human body/head louse.

Rickettsia prowazekii - Complication

Myocarditis and CNS disorders.

Chlamydia trachomatis - Forms

Elementary Body (infectious), Reticulate Body (replicative).

Chlamydia trachomatis - Biovars

Trachoma (A-C), Urogenital (D-K), LGV (L1-L3).

Trachoma - Symptoms

Scarring of conjunctiva leads to inward eyelashes and blindness.

Inclusion Conjunctivitis - Transmission

Sexual or birth canal.

Chlamydia - Urogenital Infection

Often asymptomatic in women, purulent discharge in men.

LGV - Symptoms

Painless ulcer -> painful lymphadenitis and buboes.

Chlamydia Diagnosis - Tools

DFA, PCR, culture on cell lines.

Chlamydia - Treatment

Azithromycin, tetracycline, erythromycin (neonates).

Superantigen - M. pneumoniae

Triggers excessive immune response; damages host cells.

Ciliostasis - M. pneumoniae

Inhibits and destroys cilia of respiratory epithelium.

PCR Use - Mycoplasma

High sensitivity but may detect non-pathogenic strains.

MIF - Rickettsia Diagnosis

Microimmunofluorescence for species-level detection