Group A streptococci is best diagnosed by -
Ans. is 'b' i.e., Bacitracin sensitivity Streptococci are classified according to the type of hemolysis on when cultured on blood Agar namely a, b or v hemolysis. b HemolysisThese streptococci undergo complete hemolysis of sheep red blood cells in agar and therefore shows a clear zone around colonies. Hemolysis is caused by the enzyme hemolysins. a HemolysisIncomplete hemolysis producing greenish discolouration around colonies. g HemolvsisNon hemolysis b hemolytic streptococcibHemolytic streptococci are further classified into lancefied groups (A-H K-V) based on the antigenic carbohydrate in the cell wallGroup A, B, C, D and G are the groups most commonly associated with human infections.Group A streptococci (streptococcus pyogenic) is responsible for a wide range of superficial and deep infections and are further classified according to M protein an antiphagocytic fibrillar molecule that interferes with deposition of complement C3b.Group A streptococci is also classified using bacitracin sensitivity test: - BACITRACIN SENSITIVITY TESTThe bacitracin sensitivity test is useful for the differentiation of B hemolytic Group A streptococci from b hemolytic non Group A streptococciThis is important because most streptococcal diseases are caused by Group A streptococci."Streptococcus A (pyogenes) is bacitracin sensitive while streptococcus agalactiae is bacitracin resistantCAMP TESTThis test is used for the presumptive identification of Group B streptococcus (streptococcus agalactiae) and to differentiate it from streptococcus pyogenes group A.Group B is the only B hemolytic streptococcus which yields a positive CAMP testThis test detects a diffusible heat stable extracellular protein produced by Group B streptococcus that enhances the hemolysis of sheep erythrocytes by staphylococcus aureus.The CAMP factor acts synergistically with the beta hemolysin produced by staphylococcus aureus to induce enhanced hemolysis of sheep or bovine RBL.A known hemolytic strain of S. aureus is streaked in a straight line across the centre of the sheep blood agar plate.The test material is streaked in a straight line perpendicular to staphylococcus aureus streak but without touching it.The plate is incubated at 37deg C for 18-24 hours.A positive test for CAMP factor appears as arrowhead hemolysis between the junction of growth of staphylococcus aureus and Group B streptococcus.There is no enhanced or arrowhead hemolysis if the test isolate is not Group B streptococcus. OPTOCHINTESTOptochin sensitivity test is used to differentiate pneumococcus from other a hemolytic streptococci.a hemolytic streptococci may be pathogens such as streptococcus pneumonia or they may be a part of the flora of the upper respiratory tract i.e. viridans streptococci.Streptococcus pneumonia is sensitive to optochin therefore it does not grow around the optochin disc while bacterias that are optochin resistant will be unaffected.Bile solubility test * Bile solubility test is used to distinguish streptococcus pneumoniae from other d hemolytic streptococci.Bile will selectively lyse colonies of streptococcus pneumoniae while other streptococci are immune to bile's activity.When a bile salt such as deoxycholate is added directly to streptococcus pneumoniae growing on an agar plate or in a broth culture the bacteria will lyse and the area becomes clear. Other 5 hemolytic streptococci are resistant to (not lysed by bile) and will stay viable or turbidClassification of Streptococci
Optochin sensitivity
Bacitracin sensitivity
Catalase negative
Bile solubility
Bacteria