(incomplete) Legionella; Mycoplasma; Diphtheria

Question 1

Describe characteristics of Legionella pneumophila: disease caused, Gm+/-, shape, growth pattern and location.

Answer 1

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

Question 2

List symptoms of Legionella pneumophila.

Answer 2

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

Question 3

Who is most vulnerable to Legionella pneumophila?

Answer 3

Renal transplant patients
Immunocompromised patients
Immunosuppressed patients

Question 4

Pathogenicity of Legionella pneumophila: route of infection, reservoirs, incubation period, effects on cells

Answer 4

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
FINISH

Question 5

Epidemiology of Legionella pneumophila: subclinical vs clinical infections, timing of outbreaks

Answer 5

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

Question 6

**How is Legionella pneumophila diagnosed?

Answer 6

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

Question 7

How is Legionella pneumophila prevented?

Answer 7

Proper water handling

• -Keep at proper temperature
• -Use chlorine
• -Cleaning

Question 8

List characteristics of Mycoplasma pneumoniae.

Answer 8

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)

Question 9

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

Answer 9

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

Question 10

List symptoms of Mycoplasma pneumoniae.

Answer 10

Atypical pneumonia

FINISH

Question 11

Pathogenesis of Mycoplasma pneumoniae:

Answer 11

1. Transmitted by aerosols
2. Attaches to epithelium via P1 adhesin
3. Produces H2O2 -> oxidative damage, inflammation
4. Induces cilliotosis -> necrosis
5. Inflammation contributes to disease; prior exposure enhances inflammation

Question 12

Diagnosis of Mycoplasma pneumoniae:

Answer 12

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

Question 13

Treatment of Mycoplasma pneumoniae:

Answer 13

***NO cell wall synthesis inhibitors, instead use protein synthesis inhibitors
Erythromycin -> good pulmonary localization
Tetracycline used, but not in children

Question 14

M. hominis

Answer 14

a

Question 15

M. artritidis

Answer 15

a

Question 16

In general, how should we diagnose pathogens?

Answer 16

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

Question 17

Characteristics of Corynebacterium diphtheriae

Answer 17

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)

Question 18

Epidemiology of Corynebacterium diphtheriae:

Answer 18

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

Question 19

Clinical syndrome of Corynebacterium diphtheriae

Answer 19

a

Question 20

Pathogenesis of Corynebacterium diphtheriae.

Answer 20

Creates gray pseudomembrane on back of throat (fibrin, necrotic epithelium, white cells)
FINISH

Question 21

Describe toxins produced by Corynebacterium diphtheriae.

Answer 21

Diphtheria toxin: secreted as an exotoxin
–Inhibits protein synthesis via EF2 inhibition
–Lethal to eukaryotic cells
FINISH

Question 22

Diagnosis of Corynebacterium diphtheriae

Answer 22

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

Question 23

How is an Elek test performed? (not critical to know)

Answer 23

Grow bacteria on a single streaked line at right angle to strip of antitoxin-soaked paper
Toxin and antitoxin diffuse
Line of precipitate forms

Question 24

Treatment of Corynebacterium diphtheriae

Answer 24

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

Question 25

Immunization against Corynebacterium diphtheriae

Answer 25

Depends on presence of Ab against toxin

Toxoid given as part of DTaP