(incomplete) Legionella; Mycoplasma; Diphtheria Flashcards
Describe characteristics of Legionella pneumophila: disease caused, Gm+/-, shape, growth pattern and location.
Pathogen of lung that causes pneumonia
Gm- pleomorphic rod
Intracellular growth
Resides within a free-living amoeba or free-living in biofilms
Frequently found in the water of cooling towers
List symptoms of Legionella pneumophila.
ATYPICAL pneumonia (acute disease)
- -Fever, chills, cough, loss of appetite, tiredness, headache, muscle aches
- -Atypical because of diffuse localization in lung (vs lobar with S. pneumoniae)
Can disseminate from lung -> systemic disease (LPS)
Pontiac fever = mild form of disease
Who is most vulnerable to Legionella pneumophila?
Renal transplant patients
Immunocompromised patients
Immunosuppressed patients
Pathogenicity of Legionella pneumophila: route of infection, reservoirs, incubation period, effects on cells
Airborne transmission from environmental contamination
- -Water in cooling towers, AC units
- -NOT transmitted person to person
Incubation period of 2-10 days
Uses a T4SS!
-> Apoptosis of MOs and alveolar epithelial cells
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Epidemiology of Legionella pneumophila: subclinical vs clinical infections, timing of outbreaks
Mostly subclinical, appears as a cold
Outbreaks in summer and early fall (increased use of AC units), but can be year-round
First recorded outbreak:
- -Large population affected
- -Geographically circumscribed
- -Significant mortality (15%)
- -Large at-risk population: elderly, immune-compromised individuals
**How is Legionella pneumophila diagnosed?
FASTIDIOUS: grown on charcoal yeast extract with iron and cysteine
Direct fluorescent Ab test for Ag in sputum (if sputum produced)
Ag can also be detected in urine
Can compare Ab levels in blood samples from 3-6
How is Legionella pneumophila prevented?
Proper water handling
- -Keep at proper temperature
- -Use chlorine
- -Cleaning
List characteristics of Mycoplasma pneumoniae.
Smallest replicating bacteria
No cell wall
–Resistant to anti-cell wall Abx [penicillins, cephalosporins]
–Cannot be identified by Gm stain
–Extremely pleomorphic
–Maintains membrane with lipoproteins: increase immune evasion, provide rigidity
Growth on cell-free media only if sterols, other nutrients provided by yeast extract & animal serum
–Will NOT grow on standard lab medium
–Needs cholesterol for growth, membrane rigidity
Colonies grow slowly (1-2 weeks)
Epidemiology of Mycoplasma pneumoniae: % of pneumonia caused, timing of epidemics and outbreaks, most affected groups, factors associated with vulnerability, number of serotypes, length of immunity
Only a human pathogen
Causes 15-50% of pneumonia
Associated with summer and fall pneumonias
Epidemics at 4-8 year intervals
Affects school-aged kids and teenagers; people living in close contact
More severe with age; associated with exacerbations of asthma, chronic lung disease, immunodeficiency
One serotype known
Immunity lasts 5-10 years
List symptoms of Mycoplasma pneumoniae.
Atypical pneumonia
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Pathogenesis of Mycoplasma pneumoniae:
- Transmitted by aerosols
- Attaches to epithelium via P1 adhesin
- Produces H2O2 -> oxidative damage, inflammation
- Induces cilliotosis -> necrosis
- Inflammation contributes to disease; prior exposure enhances inflammation
Diagnosis of Mycoplasma pneumoniae:
Culture NOT useful - too slow
History, clinical picture most useful
Sputum Gm stain is negative for bacteria, but prominent for Mos and PMNs
PCR detection
Cold agglutination test - cold agglutinins present in half of patients
Treatment of Mycoplasma pneumoniae:
***NO cell wall synthesis inhibitors, instead use protein synthesis inhibitors
Erythromycin -> good pulmonary localization
Tetracycline used, but not in children
M. hominis
a
M. artritidis
a
In general, how should we diagnose pathogens?
ALWAYS culture - this is the best way to detect
Do tests with what samples you have (if no sputum, can’t use sputum)
Only use direct immunofluorescence if someone is in real trouble
Use serial titrations (weeks apart) if patient is not getting better
Characteristics of Corynebacterium diphtheriae
Pleomorphic Gm+ rods, often club-shaped Arrange like Chinese characters Aerobes Do not form spores Two groups: Corynebacterium diphtheriae and all other corynebacteria (normal inhabitants of skin and throat)
Epidemiology of Corynebacterium diphtheriae:
Once a major cause of death, but not now (vaccine)
Epidemics seen in poorly immunized populations with inadequate medical care
Major problem in developing countries with inadequate pediatric immunization
–Should re-vaccinate travelers before departure
Clinical syndrome of Corynebacterium diphtheriae
a
Pathogenesis of Corynebacterium diphtheriae.
Creates gray pseudomembrane on back of throat (fibrin, necrotic epithelium, white cells)
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Describe toxins produced by Corynebacterium diphtheriae.
Diphtheria toxin: secreted as an exotoxin
–Inhibits protein synthesis via EF2 inhibition
–Lethal to eukaryotic cells
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Diagnosis of Corynebacterium diphtheriae
Severe cases easy to spot with hx Grow on Tellurite agar, Tinsdale's medium, and Leoffler medium --Visualize metachromatic granules KEY: demonstrate toxin production --PCR detection of toxin gene --Immune assay of serum --Elek test for direct presence of toxin
How is an Elek test performed? (not critical to know)
Grow bacteria on a single streaked line at right angle to strip of antitoxin-soaked paper
Toxin and antitoxin diffuse
Line of precipitate forms
Treatment of Corynebacterium diphtheriae
Antitoxin - produced in horses
- -Neutralizes the free diphtheria toxin
- -May induce hypersensitivity
- -Only available from CDC
Abx - penicillin reasonable
Reimmunization, prophylaxis of pts coming in contact with Corynebacterium diphtheriae
Immunization against Corynebacterium diphtheriae
Depends on presence of Ab against toxin
Toxoid given as part of DTaP
