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MLT-Streptococcus
Microbiology
| Question | Answer |
|---|---|
| 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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