The Streptococci by keralaguest


									Microbiology – MCB 2010
The Streptococci
       Differ from staphyloccoci in 2 ways:
             o   Occur in chains rather than clusters
             o   Lack enzyme catalase
       Can cause mixed infections with staph
       Diseases: pneumonia, meningitis, endocarditis, pharyngitis, erysipelas, glomerulonephritis
       Normal inhabitants of human pharynx and mouth, found on skin and in vagina
       Several systems have been used to classify the streptococci
             o   Hemolysis
                          The bacteria are grown on blood agar plate
                          One of 3 things can happen:
                                    Beta-hemolysis
                                          o     Bacteria completely destroy red blood cells and produce clear ring around colony
                                          o     This is due to the production of streptolysin O or S that causes the RBC to lyse
                                    Alpha-hemolysis
                                          o     Bacteria produce greenish or brownish zone around colonies
                                          o     Partial hemolysis
                                          o     Discoloration due to loss of potassium from RBCs
                                    Gamma-hemolysis
                                          o     None
             o   Serological testing separating groups into A, B, C, and so on
                          Based on carbohydrate antigens associated with cell membranes of the organism
             o   Based on both of these systems, the following groups are as follows:
                          Beta-hemolytic Groups
                                    Serologic groups: A, B, C, and a few D
                                    Differentiated by different biochemical tests and colony morphology
                                    Group A Streptococci
                                          o     Streptococcus pyrogenes
                                          o     25% upper respiratory infections
                                          o     Asymptomatic carriers are common; can cause outbreaks in post-operative situations
                                          o     Produce hemolysins: streptolysin S and streptolysin O
                                          o     Sensitive to Bacitracin
                                    Group B Streptococci
                                          o     Streptococcus agalactiae
                                          o     Frequently found in milk
                                          o     Can be found in vaginal cultures of 3rd trimester pregnancy
                                          o     Not usually sensitive to bacitracin
                                    Group C Streptococci
                                          o     S. equisimilis, S. equi, S. zooepidemicus
                                          o     Diseases not as grave as groups A and B
                          Alpha-hemolytic Groups
                                    Zone must be looked at under microscope to determine if RBCs are still present
                                    Grouping of these groups are not as clear cut as it is for beta-hemolysis
                                          o     Some alpha-hemolytic types may have beta or gamma-hemolytic strains
                                    Again, differentiated by biochemical tests and colony morphology
                                    Groupings:
                                          o     Streptococcus pneumonia
                                          o     Viridans Group
                                                         Approximately 10 species
                                                         Parasites of upper respiratory tract
                                                         Low pathogenicity but opportunistic
                                                         S. mutans, dental caries
                                          o     Group D Streptococci
                                                         Most are from genus Enterococcus
                                                                   E. faecalis, E. faecium, E. durans, E avium

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