Genus Brucella

Question 1

Classification

Answer 1

Family: brucellaceae

Genus: brucella

3 medically important species:

• B. Melitensis
• B. Abortus (Cow)
• B. Suis

Domestic livestock are reservoirs (cow, pigs etc.)
Transmitted via unpasteurized milk and cheese
Direct contact with infected animal

Question 2

Morphology

Answer 2

Gram negative coccobacilli

Question 3

Growth characteristics

Answer 3

• aerobic
• non-fastidious
• facultatively intracellular organism
  »> able to multiple inside macrophages by preventing phagolysosome fusion)
• Br.abortus is capnophilic (requiring 5 - 10% CO2)
• slow and scanty growth (growth improved by addition of serum or liver extract)
• does not ferment carbohydrate
• generally oxidase, catalase and urease positive

Question 4

Antigenic structure

Answer 4

Two main antigens: A and M
-part of the LPS

The three main Brucella differ from one another in the amount of the two main antigen they have in common

B.abortus-> A:M = 20:1
B.melitensis -> A:M = 1:20
B.suis -> A:M=2:1

Question 5

Virulence factors

Answer 5

Endotoxin

Question 6

Disease

Answer 6

Brucellosis (undulant fever):

• fever
• anorexia
• chills

Complications:

• osteomyelitis
• splenomegaly
• hepatomegaly

Question 7

Microbiological diagnosis

Answer 7

• Microscopy: no use

Gram staining is not useful from clinical specimens due to their small size and intracellular location

• culture on blood agar plate
• identification: biochemical tests & rapid slide agglutination tests
• serological diagnosis: rise in antibody titer in patient’s serum.

Question 8

Treatment and prevention

Answer 8

Treatment:
Tetracycline (doxycline) + rifampin

Prevention:
Pasteurize milk
Vaccinate cattle