Streptococci

Streptococci are gram +ve cocci that form chains of different lengths.. Streptococci are facultative anaerobes and require the addition of blood or serum to culture media. Streptococci are a group of bacteria which can cause pyogenic infections in many animal species.. Strephtococci have translucent and non motile greyish colonies. It does not use catalase and is sensitive to bile salts so therefore does not grow on MacConckey agar. Generally streptococci does not grow on simple media and generally survive poorly in the environment.

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There are 3 laboratory procedures that are used for differentiating streptococcu. Type of haemolysis, lancefield grouping and biochemical testing. On sheep or ox blood agar, beta haemolussi refers to complete haemolysis indicated by clear zones around colonies. Alpha haemoloysi is partial haemolusis indicated by a greenish zone around the colonies.
Lancefield grouping is a serological methos based on group specific c substance in the cell wall. Pyogenic streptococci is associated with abscess formation, suppurative conditions and septicaemias. Beta haemolytic streptococci are normally  more pathogenic.

Streptococci are often commensals on mucosus membranes and many streptococci infections are opportunistic. Infections might be primary (strangles) or secondary like in streptococcal pneumonia following viral infection. Strangles (s.equi), porcine steptoccal meningitis and bovine streptococcal mastitis are important specific infections. Strangles is an important contagious disease in young horses caused by s.equi. it involved the upper respiratory tract with abscessation of regional lymph nodes. Streptococcus suis recognized to cause huge losses in the pig industry with meningitis, arthritis, septicaemia and bronchopneumonia in pigs of all ages. Streptococci agalactiae, s.dysgalactiae, and s.uberis are the principal pathogens involved in streptococcal mastitis. The difference between these is the type of haemolyssi produced on blood agar in adwards medium, id with lancefield groups and results of CAMP test. S.agalactiae is the only one that produces a beta hemolossi. And gives a positive CAMP test.

Adherence to epithelium, causing cytotaxis and adherence factors bind to extracellylar matrix proteins, just like staphylococcus. They produce inhibit hemotaxis (anti chemotaxis). Anti opsonic and anti phagocytic factors makes capsules, haemolsis streptococci are very haemolytic that act on white cells to inhibit phagolysis. M protein in unique to stephtococci. Can also produce superantigens that give toxic shock syndrome. Streptococci produce a range of DNA degrading enzymes like DNAase, and is therefore good at spreading in tissue.

 

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About Annettevet

I'm a Norwegian practicing as a veterinarian in Durham, England. I`ve recently qualified as a veterinarian at Glasgow University. This is a blog about my experiences as a vet student and now as a veterinarian. “The greatness of a nation and its moral progress can be judged by the way its animals are treated”
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