Gram- Rods (Fastidious)

Question 1

General define fastidious bacteria.

Answer 1

A fastidious organism is any organism that has complex or particular nutritional requirements. In other words, a fastidious organism will only grow when specific nutrients are included in its medium.

Question 2

List 2 Gram- fastidious bacteria.

Answer 2

Legionella
Bordetella

Question 3

What are the currying requirements of fastidious bacteria

Answer 3

• Complex nutrient requirements
  
  • Enrichment (blood)
  • Specific components
• Environmental requirement
  
  • Lower O2
  • Higher CO2
• Slow growing
• Relatively infrequent causes of disease

Question 4

Outline Legionnaires disease and its unique manifestation.

Answer 4

• 1976 American Legion Conference outbreak (Fraser et al. 1977)
  
  • Symptoms of severe pneumonia but unable to identify any pneumonia based pathogen at the time.
  • High mortality rate 34 (14.5%) of 234 patients died
  • Unknown infection
  • 6 months to identify the causative agent, this is due to legionella is a slow-growing bacteria and back then tests would last for 48 hours and thus if no bacteria grew test was negative.

Legionella’s presentation is unique as it’s different from other types of pneumonia that would originate from bacteria in throat or from flu. Legionella would develop from the inhalation of water droplets from infected man made water systems.

Question 5

How would early diagnosis for legionella occur?

Answer 5

The process begins by determined the exact origin of the patients pneumonia—AKA if it bacterial/flu or legionella. If bacterial use penicillin if not further investigation is needed.

Legionella diagnostics used to be very slow by testing antibodies in blood and/or invasive by which a culture from the chest would be needed required a tube in the lungs and needle through the chest. However this was soon an obsolete practice after the development of the urine antigen test in 1990.

Question 6

List other symptoms of legionella infection.

Answer 6

Nonspecific sysjmptoms include;
Fever, cough, chills, etc.

Legionellosis;
- Legionnaire’s disease
- Pneumonic form of the disease
- 2-10 days incubation
- Potentially fatal
- Pontiac fever
- Milder influenza-like
- No pneumonic form
- 12-48 hours incubation
- No mortality

Question 7

Discuss the epidemiology of legionella infection.

Answer 7

Legionalle is present worldwide with a spcoeofc prevelance in more developed countries due to the pathogen affinity for man made water systems(which are kept at warmer temps.) rather than naruakl enviormental systems. Infection rates also peak in the summers due to temperature.

Question 8

Explain the infection route(s) of legionella.

Answer 8

Legionella exhibits the ability to persist within amoebae, indicating its capacity for internalization and replication. This capability extends to surviving within alveolar macrophages, where Legionella utilizes the Dot/Icm secretion system, akin to the T3/4SS, to deliver effectors. By partially engulfing itself within host cells, Legionella can evade aspects of the immune response.

Notably, the Dot/Icm system, if inhibited or if the effector SdhA (critical for Legionella internalization) is removed, results in the cessation of replication within alveolar macrophages. Intriguingly, this loss of functionality also leads to a loss of pathogenicity, underscoring the importance of these mechanisms in Legionella’s ability to establish infection.

Question 9

Outline the diagnosis and treatments of legionella.

Answer 9

Lab Diagnosis

• Culture is the ‘gold standard’
  
  • Charcoal Yeast Extract Agar (others available)
  • Difficult and demanding
  • High humidity + CO2
  • Up to 10 days
• Urinary antigen is fastest
  
  • Limited to serotype Lp1

Treatment

• Urine antigen test for all recommend for patients admitted with community-acquired pneumonia (CAP)
  
  • Testing specimens of respiratory secretions or sputum
  • Culture of legionella is very important
  • PCR identification
• Legionella are intracellular
  
  • Antibiotics need to accumulate and be active
• Effective antibiotics
  
  • Macrolides
  • Tetracyclines
  • Quinolones

Question 10

Briefly outline/define bordetella and the disease it causes.

Answer 10

Bordetella pertussis causes whooping cough in humans. Ts transmitted through aerosols and adheres to tracheal epithelial cells. It’s primarily a toxin-mediated disease. The general mechanism of action is attachment to cilia -> toxin production which paralyzes the URT -> inflammation and invasion via intracellular replication in macrophages.

Question 11

Explain Bordetella virulence factors AND PATHO

Answer 11

1. Attachment and Colonization:
   
   • Adhesins: Bordetella bacteria possess adhesins, such as filamentous hemagglutinin (FHA) and fimbriae, which enable them to adhere to ciliated respiratory epithelial cells.
   • Pili: Pili play a crucial role in the initial attachment and colonization of the respiratory mucosa.
2. Evasion of Host Immune Defenses:
   
   • Inhibition of Phagocytosis: Bordetella species, including B. pertussis, have mechanisms to inhibit phagocytosis by immune cells. This helps the bacteria resist clearance by the host’s innate immune system.
   • Toxin-Mediated Immune Evasion: Pertussis toxin (PT) produced by B. pertussis interferes with host cell signaling, impairing the function of immune cells and preventing effective clearance.
3. Toxin Production:
   
   • Pertussis Toxin (PT): PT is a major virulence factor that disrupts signaling pathways in host cells. It contributes to the characteristic symptoms of whooping cough, including severe coughing fits.
   • Adenylate Cyclase Toxin (ACT): ACT suppresses the immune response by inhibiting phagocytosis and impairing the function of immune cells.
4. Tissue Damage and Inflammation:
   
   • Tracheal Cytotoxin (TCT): Released by Bordetella during the log phase of growth, TCT causes ciliostasis, leading to the shedding of ciliated cells in the respiratory epithelium and contributing to tissue damage.
   • Inflammatory Response: Bordetella infection triggers an inflammatory response, leading to the recruitment of immune cells to the site of infection. This contributes to the characteristic symptoms of pertussis.
5. Transmission to New Hosts:
   
   • Airborne Transmission: Bordetella is primarily transmitted through respiratory droplets generated during coughing or sneezing by infected individuals.
   • Highly Contagious: Bordetella species are highly contagious, and the airborne transmission allows the bacteria to spread efficiently from person to person.
6. Adaptation to the Host Respiratory Tract:
   
   • Phase Variation: Bordetella undergoes phase variation, allowing the bacteria to adapt to the host respiratory tract environment. This variation contributes to immune evasion and persistence.

Others include: LPS which porctes against humoral defenses and tracgela toxin which destroys ciliated cells and prveents elimination of bacteria.

Question 12

Explain bordetellla disease progression.

Answer 12

1. Incubation Period:
   
   • Duration: About 7-10 days, but it can range from 6 to 20 days.
   • Symptoms: No apparent symptoms during this phase.
2. Catarrhal Stage:
   
   • Duration: 1-2 weeks.
   • Symptoms:
     
     • Resembles a common cold with mild coughing, sneezing, runny nose, and low-grade fever.
     • The infected person is highly contagious during this stage.
     • Symptoms may be mistaken for a viral respiratory infection.
3. Paroxysmal Stage:
   
   • Duration: 1-6 weeks or longer.
   • Symptoms:
     
     • Intense and persistent coughing fits (paroxysms) characterized by rapid, repetitive coughs.
     • Coughing fits often end with a “whooping” sound as the individual inhales forcefully.
     • Vomiting may occur after coughing fits.
     • Fatigue and exhaustion are common after coughing bouts.
     • Coughing may be more frequent at night.
4. Convalescent Stage:
   
   • Duration: Several weeks to months.
   • Symptoms:
     
     • Coughing becomes less severe and frequent but can persist for an extended period.
     • Individuals gradually recover, although fatigue may persist.

Question 13

Discuss the diagnostics and treatments of bordetella.

Answer 13

Diagnostics

• Listening for symptoms
• Culture
  
  • Cheapest
  • Antibiotic susceptibility
• PCR
  
  • More sensitive
  • Quicker
  • Technically demanding
  • Not specific for B. pertussis
• Blood test for bacterial antibodies
  
  • Anti-PT antibodies (B. pertussis specific)

Prevention & Treatment

• Vaccination (infants)
  
  • Whole-cell, inactivated Antigen-based
  • DPT combined
    
    • Diphtheria, Petussis, Tetanus
  • ~90% effective (2, 3 & 4 months)
  • Limited longterm protection
    
    • <10 years
    • Booster
• Antibiotics (children & adults)
  
  • Azithromycin, clarithromycin or erythromycin
    
    • Within 21 days of infection
    • Help prevent transmission
  • None past this date
    
    • Self-limiting