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MLT-Streptococcus

Microbiology

QuestionAnswer
What is Staphylococcus aureus? 金黄色葡萄球菌
Streptococcus pyogenes causes? Scarlet fever
What is Streptococcus penumoniae? 肺炎鏈球菌
What is Vancomycin resistant enterococci(VRE)? 抗萬古黴素腸球菌
Morphology of Streptococcus? Gram positive cocci, catalase negative, facultative anaerobic, non-moltile
Haemolytic pattern of Streptococcus? alpha haemolysis, beta haemolysis, gamma haemolysis
What is alpha haemolysis? Partial lysis, green discoloration around the colonies.
What is Beta haemolysis? Complete lysis, clear and colourless zone the colonies, due to sterptolysin.
What is gamma haemolysis Non-haemolytic, no effect on RBC.
What could cause false catalase positive in Streptococcocus? 1. Isolate from blood agar 2.Some Enterococci which has pseudocatalase activity, weak positive.
What is Lancefied classification for Streptococcus? Based on carbohydrate antigen on bacterial cell wall, Streptococci classified into many groups from A to U.
Which group could cause human infection? 1.A,B,D more frequent 2.C,G,F less frequent
Which Streptococcus is non-groupable? S.pneumoniae and Viridans streptococci
Which is Group A Streptococci and its characteristic on blood agar? Only S.pyogenes, wide clear zone of Beta hemolysis
What are the virulence factors of S.pyogenes? M protein, Hyaluronidase, Pyrogenic toxins, StreptolysinO, StreptolysinS
What are the diseases caused by GAS? 1.Localised superficial infection ->90% of cases of bacterial pharyngitis 2.Invasion infection ->Necrotizing fasciitis 3.Systemic infections -> Scarlet fever 4.Complication -> Rheumatic fever
What are the presumative tests for GAS? 1. wide clear zone Beta hemolysis 2. catalase negative 3. PYR test positive (red colour) 4. Bacitricin sensitive
What are the confirmative test for GAS? Streptrex
What is Streptrex? 1.Latex beads coated with antibodies against specific carbohydrate antigens of streptococcal groups A, B, C, D, F and G. 2.If the antigen is present, it will react with the antibodies causing the latex beads to clump.
What is the treatment for GAS? Penicillin
Which is Group B Streptococci and its characteristic on blood agar? S.agalactiae, narrow clear zone of Beta hemolysis.
What are the diseases caused by GBS? One of the major cause of invasive disease in the newborn 1.Early onset infection(<7 days): as pneumonia 2.late onset infection(>7days): as meningitis
What are the presumative tests for GBS? 1. narrow clear zone of beta hemolysis 2. catalase negative. 3. Hippurate hydrolysis positive 4. CAMP test positive
What is Hippurate hydrolysis test? 1.Incubating a turbid suspension of bacterial cell in 1% aqueous sodium hippurate for 2h at 35℃. 2.Glycine is the end product, which develop purple colour by adding ninhydrin reagent.
What is CAMP test? 1.GBS produces CAMP factor. 2.It acts synergistically with beta-haemolysin of Staphylococcus aureus to cause enhanced lysis of RBCs.
What is the confirmatory test for GBS? Streptrex
What is the treatment for GBS? Penicillin
Which is Group C/G Streptococci? Streptococcus dysgalactiae
Streptococcus dysgalactiae subdivided into which two subspecies? 1.S. dysgalactiae subspecies equisimilis (Human pathogen) 2.S. dysgalactiae subspecies dysgalactiae (Animal pathogen)
Compared to GAS, Group C/G Streptococci is resistant to ? Bacitricin
Which are Group D Streptococci? 1.Enterococci (More clinically important) 2.Non-enterococci, e.g. S. bovis(Less clinically important)
What is the mode hemolysis? Could be alpha, beta or gamma
What are the two major pathogens in GDS? 1.E.faecalis–account for 80-90% clinical cases 2.E.faecium–account for 5%-10% clinical cases
What are the common specimen for GDS? 1.Urine 2.Wound swab 3.Blood culture
What are the tests for Enterococci? 1. catalase negative 2. Bile esculin positive (black)
What is esculin? A plant sugar, can be hydrolysed and the product will react with Ferric salt to form black iron compound.
GDS could be subdivided into ? 1.Enterococci 2.Non-enterococci, eg, S.bovis
What is the function of Bile in Bile esculin test? It is a selective agent, it can lyse various bacterial cells but not enterococci and GDS.
How to differentiate enterococci and non-enterococci? 1. Enterococci grows in 6.5% NaCl, non-enterococci no growth 2. Enterococci PYR test positive, non-enterococci negative
The % of vancomycin resistance in GDS? 98% VRE are E.faecium and 2% are E.faecalis
What are the pathogens cannot be grouped under Lancefield classification 1.Enterococci 2.Viridans streptococci 3.Streptococcus pneumoniae
What is Streptococcus pneumoniae? 1.Gram-positive diplococcus, slightly elongated 2.Two forms: i.Encapsulated, virulent form ii.Avirulentform
What are the virulence factors for S.pneumoniae? 1.Capsular polysaccharide 2.‘C’ Carbohydrate antigen
What are the tests for S.pneumoniae? 1.α-haemolysis on Blood agar after 18-24 hrs, at 37℃ and 5% CO2 2.Optochin sensitive (>14mm clear zone) 3.Bile solubility test positive (test tube clearing)
What is Bile solubility test? S.pneumoniae produces a self-lysing enzyme to inhibit the growth, bile salt accelerates it. Incubate at 37℃for 15 min.
Can MALDI-TOF be used to differentiate S.pneumoniae? 1.No, it cannot differentiate S. pneumoniae from two viridans streptococci –S. mitis and S. oralis. 2.Optochin test and Bile solubility test are further required.
What is the treatment for S.pneumoniae? 1. Penicillin 2. if penicillin resistant, then cefotaxime 3. Vancomycine at last 4.Vaccine, capsular polysaccharide material of most commonly 13 serotypes
Created by: kencho
 

 



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