Gram-Negative Rods (II) Flashcards
Under what conditions can Haemophilus influenzae grow? What is the clinical significance of this?
Under essential factors X (heme) and V (NAD). This is a differential factor for identifying H. Flu that can only grow on chocolate agar.
Name at least 4 disease manifestations of Haemophilus influenzae.
- Otitis media - common in children
- Severe URT infection (epiglottitis) - distinctive
- Pneumonia
- Meningitis
What is H. Flu susceptible to?
- His conjugate vaccine given to children at 2 months of age.
- Susceptible to 3rd generation cephalosporins
What Gram-negative bacterium is known to cause the characteristic Whooping cough? What is the significance of this?
Bordetella pertussis - very infectious paroxysms of coughing. Takes 4-6 weeks to convalesce
What are the 3 virulence factors of Bordetalla pertussis that slows its clearance?
- Tracheal cytotoxic - stimulates IL-1 mediated killing of ciliated epithelial cells
- Adenylate cyclase toxin - inhibits phagocytosis
- Pertussis toxin - lymphocytosis, sensitization to histamine and inc insulin secretion
What vaccine is used to prevent B pertussis?
DTwP (= Diptheria, Tetanus and Whole cell pertussis) or DTaP (acellular component)
What can agar environment can Legionella pneumonophila grow on?
BCYE agar that contains buffer, charcoal, yeast extract, iron, cysteine and antibiotics. Will not even grow on just chocolate agar.
What diagnostic measure should a MD take when suspecting a patient infected with Legionella pneumophila?
Doc should prepare a culture and Urine Ag test to cover bases of the many disease-causing serotypes of Legionella pneumophila.
How is Legionella pneumophila able to grow inside warm-water environments (when there’s no nutrients there)?
These grow inside amoebae host that are usually exposed to aerosol from water supply. They are commonly found in A/C, water taps and shower heads.
Describe the transmission and MOA of Francisella tularensis.
Small Gram-negative zoonotic coccobacillus that is transmitted from wild animals. Evades phagosome in macrophages and causes them to undergo apoptosis.
What is the cause of and vector or Black Death (bubonic plague)? What is needed for diagnosis?
Yersinia pestis is transmitted from rodents (i.e. rats/ prairie dogs) via flea vectors to humans. Travel history is needed for diagnosis.
Describe the MOA for Yersinia pestis.
- Flea feeds on infected rodent
- Bacteria in flea gut cause blood to clot
- Flea regurgitates this on human during bite
- Bacteria enter human host via bit wound.
What is the clinical and histological presentation of Yersinia pestis infection?
Presents as buboes or enlarged,infected lymph nodes. They have a bipolar, “safety pin” appearance with Watson stain. From lymph node, the bacteria spreads to blood, lungs and meninges.
In what rare instance can a zoonotic disease lead to human to human transmission?
Yersinia pestis when in the lung causes pneumonic plague with a higher tendency to be transmitted between humans.
What microbe is an opportunistic gram (-) bacteria that forms biofilms?
Pseudomonas aeruginosa forms biofilms in environment and in CF patients. They are multi-drug resistant and common in hospitals.
Describe the MOA by which Pseudomonas aeruginosa can infect cells.
P aeruginosa can secrete exotoxins A virulence factor into macrophages to directly kill them. They act as molecular syringes.
Describe how P. aeruignosa can present in culture in patients with Cystic Fibrosis.
They have a mucous morphology to which they adapt in living in CF lung.
What bacterial infection is a feared complication of burn injury patients?
Pseudomonas aeroginosa
What is the significance Pseudomonas virulence factor?
Represents Exotoxins A which is also seen in pertussis
What Gram-negative, nosocomial pathogen is highly encapsulated, the causes necrotizing pneumonia and presents bloody sputum in infected patients? Name 2 important clinical features.
Klebsiella - ferment lactose and resist antibiotics via ESBL and carbapenemases
Describe some features and the growth requirements for Haemophilus influenza. List at least 2 diseases associated with this.
These are Gram-negative coccobacillary bacteria that grow on chocolate agar with Factor 5 (NAD) and 10 (Hemin). Epiglottitis, otitis media and meningitis (encapsulated Type B strain)
Name the 2 treatments that can be used to treat Haemophilus influenzae.
- Hib-vaccine at 2-18 months of age to stimulate an IgG response
- 3rd generation cephalosporins (Ceftriaxone)
Describe some clinical features of Legionella pneumophila (morphology, clinical features, tests, treatments)
- Slender, Gram-negative rods that are oxidase-positive
- Legionnaires Disease - hyponatremia, lung infiltrate pneumonia, diarrhea and headache
- Rapid Urine Ag test
- Macrolide and Fluoroquinolones
Describe some clinical features of Pseudomonas aeroginosa (morphology, clinical features, tests, treatments).
- Gram-negative opportunistic rod that’s catalase and oxidase-positive.
- Respiratory failure in CF patients, nosocomial pneumonia and otitis externa
- Mucoid morphology of cultured bacteria in CF patient
- Piperacillin, aminoglycosides and fluoroquinolones
