Genus Francisella

Question 1

Classification

Answer 1

Family: Francisellaceae

Genus: francisella

Only one pathogenic species:

• Francisella tularensis

Reservoir: Rabbit
Transmission: directly, tick bite, aerosols (potential bioweapon)

Two main types: A (more virulent) and B

Question 2

Morphology

Answer 2

• gram-negative rods

Question 3

Growth characteristics

Answer 3

• obligate aerobes
• facultative intracellular parasites (macrophages)
• Fastidious: require cysteine for growth

Question 4

Antigenic structure

Answer 4

Somatic O antigens

Question 5

Virulence factors

Answer 5

• no exotoxins
• hemolysin
• T6SS
• Francisella pathogenicity island (FPI)

Question 6

Disease

Answer 6

Tularemia

• after tick bite -> painful ulcer at bite site
• spread through macrophages
• granulomas with caseous necrosis are mainly at the lymph nodes

Question 7

Microbiological diagnosis

Answer 7

• culture is rarely done because special media are required and there is a high risk of infection of laboratory personnel
• diagnosis is usually made by serologic tests that detect antibodies in patient’s serum

Question 8

Treatment and prevention

Answer 8

• streptomycin = aminoglycoside

Prevention:

• live, attenuated vaccine for person in high-risk occupations
• protection against tick bites