Category:Streptococcus species

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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

Pathogenesis 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

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