Gram-Negative Rods (II)

Question 1

Under what conditions can Haemophilus influenzae grow? What is the clinical significance of this?

Answer 1

Under essential factors X (heme) and V (NAD). This is a differential factor for identifying H. Flu that can only grow on chocolate agar.

Question 2

Name at least 4 disease manifestations of Haemophilus influenzae.

Answer 2

1. Otitis media - common in children
2. Severe URT infection (epiglottitis) - distinctive
3. Pneumonia
4. Meningitis

Question 3

What is H. Flu susceptible to?

Answer 3

1. His conjugate vaccine given to children at 2 months of age.
2. Susceptible to 3rd generation cephalosporins

Question 4

What Gram-negative bacterium is known to cause the characteristic Whooping cough? What is the significance of this?

Answer 4

Bordetella pertussis - very infectious paroxysms of coughing. Takes 4-6 weeks to convalesce

Question 5

What are the 3 virulence factors of Bordetalla pertussis that slows its clearance?

Answer 5

1. Tracheal cytotoxic - stimulates IL-1 mediated killing of ciliated epithelial cells
2. Adenylate cyclase toxin - inhibits phagocytosis
3. Pertussis toxin - lymphocytosis, sensitization to histamine and inc insulin secretion

Question 6

What vaccine is used to prevent B pertussis?

Answer 6

DTwP (= Diptheria, Tetanus and Whole cell pertussis) or DTaP (acellular component)

Question 7

What can agar environment can Legionella pneumonophila grow on?

Answer 7

BCYE agar that contains buffer, charcoal, yeast extract, iron, cysteine and antibiotics. Will not even grow on just chocolate agar.

Question 8

What diagnostic measure should a MD take when suspecting a patient infected with Legionella pneumophila?

Answer 8

Doc should prepare a culture and Urine Ag test to cover bases of the many disease-causing serotypes of Legionella pneumophila.

Question 9

How is Legionella pneumophila able to grow inside warm-water environments (when there’s no nutrients there)?

Answer 9

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.

Question 10

Describe the transmission and MOA of Francisella tularensis.

Answer 10

Small Gram-negative zoonotic coccobacillus that is transmitted from wild animals. Evades phagosome in macrophages and causes them to undergo apoptosis.

Question 11

What is the cause of and vector or Black Death (bubonic plague)? What is needed for diagnosis?

Answer 11

Yersinia pestis is transmitted from rodents (i.e. rats/ prairie dogs) via flea vectors to humans. Travel history is needed for diagnosis.

Question 12

Describe the MOA for Yersinia pestis.

Answer 12

1. Flea feeds on infected rodent
2. Bacteria in flea gut cause blood to clot
3. Flea regurgitates this on human during bite
4. Bacteria enter human host via bit wound.

Question 13

What is the clinical and histological presentation of Yersinia pestis infection?

Answer 13

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.

Question 14

In what rare instance can a zoonotic disease lead to human to human transmission?

Answer 14

Yersinia pestis when in the lung causes pneumonic plague with a higher tendency to be transmitted between humans.

Question 15

What microbe is an opportunistic gram (-) bacteria that forms biofilms?

Answer 15

Pseudomonas aeruginosa forms biofilms in environment and in CF patients. They are multi-drug resistant and common in hospitals.

Question 16

Describe the MOA by which Pseudomonas aeruginosa can infect cells.

Answer 16

P aeruginosa can secrete exotoxins A virulence factor into macrophages to directly kill them. They act as molecular syringes.

Question 17

Describe how P. aeruignosa can present in culture in patients with Cystic Fibrosis.

Answer 17

They have a mucous morphology to which they adapt in living in CF lung.

Question 18

What bacterial infection is a feared complication of burn injury patients?

Answer 18

Pseudomonas aeroginosa

Question 19

What is the significance Pseudomonas virulence factor?

Answer 19

Represents Exotoxins A which is also seen in pertussis

Question 20

What Gram-negative, nosocomial pathogen is highly encapsulated, the causes necrotizing pneumonia and presents bloody sputum in infected patients? Name 2 important clinical features.

Answer 20

Klebsiella - ferment lactose and resist antibiotics via ESBL and carbapenemases

Question 21

Describe some features and the growth requirements for Haemophilus influenza. List at least 2 diseases associated with this.

Answer 21

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)

Question 22

Name the 2 treatments that can be used to treat Haemophilus influenzae.

Answer 22

1. Hib-vaccine at 2-18 months of age to stimulate an IgG response
2. 3rd generation cephalosporins (Ceftriaxone)

Question 23

Describe some clinical features of Legionella pneumophila (morphology, clinical features, tests, treatments)

Answer 23

1. Slender, Gram-negative rods that are oxidase-positive
2. Legionnaires Disease - hyponatremia, lung infiltrate pneumonia, diarrhea and headache
3. Rapid Urine Ag test
4. Macrolide and Fluoroquinolones

Question 24

Describe some clinical features of Pseudomonas aeroginosa (morphology, clinical features, tests, treatments).

Answer 24

1. Gram-negative opportunistic rod that’s catalase and oxidase-positive.
2. Respiratory failure in CF patients, nosocomial pneumonia and otitis externa
3. Mucoid morphology of cultured bacteria in CF patient
4. Piperacillin, aminoglycosides and fluoroquinolones

Question 25

This bacterial species is facultative intracellular, a reservoir in farm animals and causes Systemic febrile illness (fever and anorexia). What is it? Describe a common infected food and treatments.

Answer 25

Brucella species;

Found in unpasteurized milk and treatments include Doxycycline and Rifampin (adjunctive therapy)

Question 26

This bacterial species is facultative intracellular, a reservoir in rabbits and causes ulcers and lymphadenopathy. What is it? Describe the mode of transmission and treatments.

Answer 26

Francisella tularensis;
Transmitted by ticks and can be aerosolized (report to CDC when infected);
Treatments include streptomycin and aminoglycosides

Question 27

This small gram-negative coccobacillary bacterial species is transmitted by cats and dog bites. What is it? Describe the symptoms and treatments.

Answer 27

Pasteurella multocida;
Cellulitis and osteomyelitis after animal bites; It grows well on sheep’s blood agar and is catalase positive. Empiric treatment is amoxicillin (penicillin).