Lesson 2b: Streptococcus species Flashcards
General description
- 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
an anaerobic Gram-positive coccus, which is
aetiologically implicated in bovine ‘summer mastitis’ in association with
Arcanobacterium pyogenes
Peptoniphilus indolicus
Usual habitat:
: commensals on the mucosae of the upper respiratory tract and lower urogenital tract; susceptible to dessication
Laboratory differentiation:
hemolysis,
Lancefield grouping, and
biochemical
testing
Type of haemolysis on sheep or ox blood agar:
Beta-haemolysis
Alpha-haemolysis
– Gamma-haemolysis
partial or incomplete haemolysis indicated by
greenish or hazy zones around colonies
Alpha-haemolysis
complete haemolysis indicated by clear zones
around colonies
Beta-haemolysis
denotes no observable changes in the blood agar around colonies.
Gamma-haemolysis
Pyogenic characteristics causes streptococcus
abscess formation, suppurative lesions and
septicemia
which is non-pyogenic, is a major pathogen of pigs, causing septicaemia, meningitis and pneumonia among other condition
Streptococcus suis
are generally more pathogenic than those
producing alpha-haemolysis
Beta-haemolytic streptococci
Virulence factors include
enzymes and exotoxins such as streptolysins
(haemolysins), hyaluronidase, DNase,
NADase, streptokinase and protease
which are major virulence factors of S. pyogenes, S. pneumoniae and most strains of S. equi, are antiphagocytic that protects them
from phagocyte
Polysaccharide capsules
(dx)
- Gram staining
-Specimens should be cultured on blood agar, selective blood agar and
MacConkey aga
Identification criteria:
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.
Swab samples collected from pus or exudates should be processed immediately as it is easily destroyed by dessication
. Disease outbreaks are most common in intensively reared pigs
when they are subjected to o
Overcrowding, poor ventilation and other stress factors.
horses; a febrile disease
involving the upper respiratory tract with abscessation of regional lymph nodes
Tx: Penicillin, vaccine,
Strangles: Streptococcus equi
Asymptomatic carrier pigs harbour S. suis in
tonsillar tissue
Streptococcus suis infections
are the principal pathogens involved in streptococcal mastitis;
Bovine streptococcal mastitis:
Streptococcus agalactiae, S. dysgalactiae and
S. uberis
which is often fatal, is characterized by fever, tremors incoordination, opisthotonos and convulsions
Meningitis
Dx:
clinical signs, sugar fermentation test; molecular identification of organism by
real-time PCR
