Streptococci

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BACTERIA



Overview

  • Cause suppurative infections in many different animals
  • Cause abscess formation and septicaemia
  • Cause mastitis, metritis, polyarthritis, meningitis
  • Primary or secondary infections following viral infection
  • Neonatal septicaemia related to maternal genital tract infection
  • Often commensals on mucous membranes of upper respiratory and lower urogenital tract
  • Opportunistic infections


Characteristics

  • Gram positive cocci forming chains
  • Catalase negative, facultative anaerobes
  • Fastitidious - require enriched media such as blood or serum
  • Small haemolytic, translucent colonies, some mucoid
  • Catalase negative
  • Susceptible to desiccation


Identification

  • Beta haemolysis (complete with clear zones surrounding colonies)
  • Alpha haemolysis (partial with green zones surrounding colonies)
  • Lancefield grouping - serology based on group-specific polysaccharide in cell wall
  • Biochemical testing


Pathogensis and Pathogenicity

  • Beta-haemolytic strains more pathogenic than alpha-haemolytic strains
  • Virulence factors include streptolysins, hyaluronidase, DNase, streptokinase and proteases
  • S. pyogenes, S. pneumoniae and some strains of S. equi have polysaccharide capsules which are antiphagocytic
  • S. pyogenes and S. equi have antiphagocytic cell wall M proteins


Strangles

  • Epidemiology
    • strangles is a highly infectious disease of horses caused by Streptococcus equi subsp. equi
    • Upper respiratory tract disease with fever and abscessation of regional lymph nodes
    • Outbreaks in groups of young horses
    • Transmitted via purulent exudate discharging from upper respiratory tract or from lymph nodes
    • Chronic, carrier state can occur with bacteria im the guttural pouch
    • A mild, atypical form can occur
    • S. equi shed for 4 weeks beyond clinical resolution
  • Clinical signs
    • Incubation period 3 to 6 days
    • Fever, depression, anorexia
    • Purulent nasal discharge
    • Swollen, painful regional lymph nodes, especially submandibular
    • Abscessation and rupture of lymph nodes
    • Guttural pouch empyema
    • 100% morbidity; 5% mortality
    • Death can occur from pneumonia, breathing difficulties from swollen lymph nodes or purpura haemorrhagica (an immune-mediated disease)
    • Bastard strangle may occasionally occur, with abscessaation in many organs of the body
  • Diagnosis
    • Clinical signs and history
    • Mucoid colonies with beta-haemolysis
    • Sugar fermentation allows differentiation of S. equi from S. zooepidemicus and S. equisimilis
    • PCR to detect asymptomatic carriers
  • Treatment and control
    • Penicillin administration to in-contact animals
    • Isolation of affected animals
    • Quaranteen in-coming animals
    • Avoid overcrowding and mixing different age groups
    • Disinfection of equipment

Streptococcus suis

Diagnosis

  • Swabs of pus or exudate cultured on blood agar and MacConkey agar
  • No growth on MacConkey except S. faecalis
  • PCR, Lancefield grouping and biochemical tests


Treatment

Control

  • Haemolytic streptococci of Lancefield group C are common inhabitants of the equine nasopharynx
  • Streptococcus zooepidemicus and S. equisimilis are usually non-pathogenic
  • S. equi is more pathogenic and is the cause of strangles with rhinitis, pharyngitis, lymphadenitis, myositis
  • S. equi may be involved in cutaneous lesions

URT inflammation in horses