Lesson 2b: Streptococcus species

Question 1

General description

Answer 1

• Gram-positive cocci are approximately 1.0 μm in diameter and form chains of different lengths
   catalase-negative, facultative anaerobes, non- motile
   Fastidious requiring enriched media, colonies are small usually hemolytic and translucent
   Streptococcus pneumoniae (pneumococcus)
  occurs as slightly pear-shaped cocci in pairs.
   Pathogenic strains have thick capsules and
  produce mucoid colonies

Question 2

an anaerobic Gram-positive coccus, which is
aetiologically implicated in bovine ‘summer mastitis’ in association with
Arcanobacterium pyogenes

Answer 2

Peptoniphilus indolicus

Question 3

Usual habitat:

Answer 3

: commensals on the mucosae of the upper respiratory tract and lower urogenital tract; susceptible to dessication

Question 4

Laboratory differentiation:

Answer 4

hemolysis,
Lancefield grouping, and
biochemical
testing

Question 4

Type of haemolysis on sheep or ox blood agar:

Answer 4

Beta-haemolysis
Alpha-haemolysis
– Gamma-haemolysis

Question 4

partial or incomplete haemolysis indicated by
greenish or hazy zones around colonies

Answer 4

Alpha-haemolysis

Question 5

complete haemolysis indicated by clear zones
around colonies

Answer 5

Beta-haemolysis

Question 6

denotes no observable changes in the blood agar around colonies.

Answer 6

Gamma-haemolysis

Question 7

Pyogenic characteristics causes streptococcus

Answer 7

abscess formation, suppurative lesions and
septicemia

Question 7

which is non-pyogenic, is a major pathogen of pigs, causing septicaemia, meningitis and pneumonia among other condition

Answer 7

Streptococcus suis

Question 7

are generally more pathogenic than those
producing alpha-haemolysis

Answer 7

Beta-haemolytic streptococci

Question 8

Virulence factors include

Answer 8

enzymes and exotoxins such as streptolysins
(haemolysins), hyaluronidase, DNase,
NADase, streptokinase and protease

Question 8

which are major virulence factors of S. pyogenes, S. pneumoniae and most strains of S. equi, are antiphagocytic that protects them
from phagocyte

Answer 8

Polysaccharide capsules

Question 8

(dx)

Answer 8

• Gram staining
  -Specimens should be cultured on blood agar, selective blood agar and
  MacConkey aga

Question 9

Identification criteria:

Answer 9

Small, translucent colonies, some of which may be mucoid
– Type of haemolysis on blood agar
– Chains of Gram-positive cocci
– No growth on MacConkey agar with the exception of Enterococcus
species –
Negative catalase test
–> Lancefield grouping or Biochemical test
profile.

Question 9

Swab samples collected from pus or exudates should be processed immediately as it is easily destroyed by dessication

Question 10

. Disease outbreaks are most common in intensively reared pigs
when they are subjected to o

Answer 10

Overcrowding, poor ventilation and other stress factors.

Question 10

horses; a febrile disease
involving the upper respiratory tract with abscessation of regional lymph nodes

Tx: Penicillin, vaccine,

Answer 10

Strangles: Streptococcus equi

Question 10

Asymptomatic carrier pigs harbour S. suis in
tonsillar tissue

Answer 10

Streptococcus suis infections

Question 11

are the principal pathogens involved in streptococcal mastitis;

Answer 11

Bovine streptococcal mastitis:
Streptococcus agalactiae, S. dysgalactiae and
S. uberis

Question 11

which is often fatal, is characterized by fever, tremors incoordination, opisthotonos and convulsions

Answer 11

Meningitis

Question 12

Dx:
clinical signs, sugar fermentation test; molecular identification of organism by
real-time PCR