Streptococci

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
• Haemolytic streptococci of Lancefield group C are common inhabitants of the equine nasopharynx
• Streptococcus zooepidemicus and S. equisimilis are usually non-pathogenic
• Involved in peritonitis in pigs, pyothorax, osteomyelitis, catarrhal stomatitis
• In infectious arthritis of sheep, arthritis in calves, arthritis in horses and arthritis in pigs
• 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

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

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 of horses with fever and abscessation of regional lymph nodes
  • Causes rhinitis, pharyngitis, lymphadenitis and myositis
  • 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
  • S. equi may be involved in cutaneous lesions

• 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

• Meningitis, arthritis, septicaemia and pneumonia of pigs
• Sporadic cases of endocarditis, neonatal deaths and abortion
• Carried in tonsils and nasal cavity of carrier pigs
• Outbreaks occur in intensively-reared herds with poor hygiene
• Carrier sows infect litters causing neonatal deaths
• Meningitis with fever, tremors, incoordination, opisthotonos and convulsions
• Treatment with penicillin; prophylactic long-acting penicillin for sows and piglets
• Suppurative conditions in cattle, sheep, horses, cats
• Septicaemia and meningitis in humans

Bovine streptococcal mastitis

• S. agalactiae, S. dysgalactiae and S. uberis primarily cause mastitis
• Also S. pyogenes, S. zooepidemicus and Enterococcus faecalis can be involved
• S. agalactiae colonises milk ducts causing persistent infections with acute outbreaks
• S. dysgalactiae found in the oral cavity and on the skin of the udder causes acute mastitis
• S. uberis inhabits normal skin, tonsils and vaginal mucosa, and causes mastitis without systemic signs
• Cause inflammation of mammary tissue and clots form in milk
• Milk samples are cultured on blood agar, Edward's medium and MacConkey agar for diagnosis

S. equisimilis

• Found on skin and vagina of horses
• Causes abscesses, endometritis and mastitis in horses
• Suppurative conditions in pigs, cattle, dogs, birds

S. zooepidemicus

• Colonises mucous membranes
• Causes mastitis, pneumonia, sinusitis and navel infections in horses
• S. zooepidemicus can cause similar signs to strangles in horses and may accompany COPD
• Secondary invador after equine influenza
• Colonises skin and mucous membranes of cattle, lambs, pigs and poultry and causes suppurative infections and septicaemia
• Can cause vascular fragility, leading to haemorrhagic disease

Enterococcus faecalis

• Colonises intestinal tract
• Causes opportunistic suppurative infections in many species

S. canis

• Found in vagina and anal mucosa of carnivores
• Neonatal septicaemia, suppurative infections, toxic shock syndrome
• In deep pyoderma and subcutaneous abscesses

S. pneumoniae

• Found in upper respiratory tract of primates
• Causes septicaemia, pneumonia and meningitis
• Pneumonia in guinea-pigs and rats

S. porcinus

• Submandibular lymphadenitis in pigs