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“Bacteria can be divided into gram negative or gram positive depending on their cell wall/peptidoglycan make up. Gram positive implies thick peptidoglycan layer and stain a purple colour.

There are two main spp of gram positive cocci that causes human infections. These are Streptococci and staphylococci, they are differentiated by two main criteria: first their ability to produce the enzyme catalase. Streptococci are catalase negative. Staphylococci are catalase positive, which allow them to convert hydrogen peroxide to water and oxygen gas. Hence on a slide or tube bubbles are formed. Second criteria to differentiate staph and strep is based on microscopic appearance. Staphylococcus spp are usually in clusters, where as streptococci are arranged in pairs, or chains.

Streptococcal infections remain a serious health problem worldwide.
The streptococci are divided based on their oxygen requirement are classified into aerobes/facultative anaerobes and obligate anaerobes. Here we are focusing on the aerobic and facultative anaerobes which make up majority of strep spp. I am writing aerobic here because facultative anaerobes are able to survive in oxygen.

The Gram- positive streptococci are then further divided into the haemolytic properties in blood. The streptococcus spp. are smeared in blood agar which is a plate containing blood. Haemolytic property of the bacteria mean the bacteria ability to haemolyse, breakdown red blood cells. Streptococci are divided into three haemolytic groups:
· Alpha haemolytic
· Beta haemolytic
· Gamma haemolytic

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Streptococcus pyogenes – Microbiology for Medical Students

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