Microbiology CVS Lecture 2 & 3 PDF
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Mansoura University
Dr. Ziad Mahana
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This document is a lecture on microbiology, focusing on streptococci. It covers key characteristics, classification, and virulence factors. The information is presented in a detailed format, with diagrams and tables included.
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LECTURE (2&3) STREPTOCOCCI ① Gram positive cocci. ② Catalase negative (differentiate them from staphylococcoi) ③ Arranged in chains or pairs. ④ Facultative anaerobe ① Typable: Lancefield classification α - Hemolytic β- Hemolytic...
LECTURE (2&3) STREPTOCOCCI ① Gram positive cocci. ② Catalase negative (differentiate them from staphylococcoi) ③ Arranged in chains or pairs. ④ Facultative anaerobe ① Typable: Lancefield classification α - Hemolytic β- Hemolytic y - Hemolytic Partial Complete No hemolysis ② Non Typable: hemolysis hemolysis S. Viridians Green Clear -- S. pneumoniae S. Viridians S. Pyogens S. faecalis S. pneumoniae S. agalactia Serological classification of streptococci, based on carbohydrate antigen (C-antigen) on cell wall → 18 different sero-groups (A→ U) Group A = S. Pyogenes Group B = S. Agalactia Capsular polysaccharides antigens: used to classify group B streptococci ( ≥ 5) and S.pneumoniae (80). Surface protein antigens: as M-protein used for typing of S.pyogens ( ≥ 50). – SHAPE & GRAM STAIN Gram positive cocci ARRANGEMENT Long chains MOTILITY Non motile SPORE FORMATION Non spore forming CAPSULE Capsulated ① Carbohydrate (c) antigen of group A. ② Protein antigens: M, R, and T-proteins. M PROTEINS R & T PROTEINS Virulence factors Used as epidemiologic markers. > 50 types of S. pyogens. Have no role in virulence. The capsule of S. pyogena: Non antigenic. Composed of hyaluronic acid, which is chemically similar to that of host CT ① CELL WALL ASSOCIATED PROTEINS AND POLYMERS: M-PROTEIN & LIPOTEICHOIC ACID M-PROTEIN & HYALURONIC ACID CAPSULE Adherence to cells. Inhibit phagocytosis. ② ENZYMES : STREPTOKINASE Lysis of fibrin. STREPTODORNASE Lysis of nucleic acid. HYALURONIDASE Spreading factor which digests hyaluronic acid. ③ TOXINS: Streptolysin S: oxygen-stable, non antigenic homolysin STREPTOLYSIN S & Streptolysin O : oxygen-labile, antigenic hemolysin STREPTOLYSIN O Antibodies to Streptolysin O Used in diagnosis of streptococcal diseases. EXOTOXINS Causes rash of scarlet fever (ERYTHROGENIC TOXIN) Has been associated with a toxic shock-like syndrome ① SUPPURATIVE INFECTIONS: RESPIRATORY As tonsillitis, sinusitis, otitis media and pneumonia. INFECTIONS SKIN INFECTIONS Superficial (impetigo) or Deep (cellulitis). Bacteremia, osteomyelitis, wound infections, meningitis, INVASIVE INFECTIONS endocarditis, puerperal sepsis and erysipelas. ② TOXOGENIC DISEASES: Streptococcal toxic shock-like syndrome: similar in C/P to staphylococcal TSS. Scarlet fever: Affects children, Clinical picture: fever, skin rash and stomatitis (Strawberry tongue). ③ POST-STREPTOCOCCAL SEQUELAE: Infection with S. pyogenes can give rise to sequelae (e.g., acute DEFINITION rheumatic fever and acute glomerulonephritis). TIMING Begin 1-3 weeks after an acute streptococcal illness period. Not well understood, but the mechanism is immune mediated. e.g., acute rheumatic fever: antibodies produced during streptococcal PATHOGENESIS infections may cross-react with certain host tissues (autoimmune responses). 1 Diagnosis of suppurative infection Differs according to the clinical presentation. ① Blood: puerperal sepsis, erysipelas, endocarditis, bacteremia SAMPLES ② Throat swab: pharyngitis, scarlet fever ③ Sputum: pneumonia GRAM STAIN Direct film stained with Gram stain for characteristic morphology. a) Culture requirements: O2: Facultative anaerobes Optimum temperature: 37C CO2: grow in normal atmospheric CO2 concentration, but 10% CULTURE CO2 enhances growth. b) Culture media: ① Ordinary media : Cannot grow on it. ② Enriched media: grow on blood agar, colonies are small (pin point) and translucent surrounded by zones of β-hemolysis. ① Film stained by Gram stain to show the morphology. ② Biochemical reactions: Catalase negative. IDENTIFICATION ③ Bacitracin sensitivity: sensitive (differs them from other beta OF GROWTH BY hemolytic streptococci which are bacitracin resistant). “ AS: group A= Sensitive” ④ Specific identification of S. pyogens : by reaction with specific Ab. Clumping of the latex particles is seen in the "A" circle (arrow) indicating that this is a Lancofield group A Stroptococcus SEROLOGY (Streptococcus pyogenes). A negative test is milky in appearance SEROLOGY GRAM STAIN CULTURE 2 Diagnosis of scarlet fever ① Specimen: Throat swab, examined as mentioned before. ② Schultz-Charlton reaction: PRINCIPLE Neutralization of the toxin with specific antitoxins Injection of the antierythrogenic toxin in rash → disappearance of PROCEDURE rash within 6-12 hours. ③ Dick test (Test of susceptibility): USES Assess the susceptibility to scarlet fever. Erythrogenic toxin is irritating and causes local reaction when PRINCIPLE injected intradermal unless it is neutralized by specific antitoxin. 0.1 ml of toxin is injected intradermal in one forearm (test) METHOD Same amount of heated toxin (detoxified) is injected in the other forearm (control) the test is read within 4-7 days. ① Positive test (susceptible): Redness and swelling in the test arm that reaches maximum after 4-7 days and disappear gradually. INTERPRETATION No reaction in the control arm. ② Negative test (immune): No reaction on both arms. ③ Pseudo- reaction (hypersensitivity): reaction that appears and disappears in both arms at the same time. 3 Diagnosis of rheumatic fever CLINICAL Clinical picture and history of preceding streptococcal infections. C-reactive protein (CRP) high ESR. NON SPECIFIC CRP: Non specific protein that appears in serum in active TESTS rheumatic fever as well as other inflammatory conditions. By detection of increase in the titer of ① Anti-streptolysin O (ASO). Done to determine the titer of antibodios to streptolysin O toxin. SPECIFIC TESTS A titer of 200 or more Todd units is significant. ② Anti-DNase. ③ Anti-hyaluronidase ④ Anti-streptokinase. No vaccine is currently available. Long acting penicillin can be used to prevent recurrent pharyngitis and its immune- mediated sequelae. – GROUP B STREPTOCOCCI GROUP D STREPTOCOCCI (STREPTOCOCCUS AGALACTIAE) STREPTOCOCCUS FAECALIS (ENTEROCOCCI) Normal vaginal, oral and Present in GIT HABITAT gastric flora Considered as indication of faecal pollution of water. Neonatal septicemia Urinary tract infections DISEASES: Pneumonia Wound infections Meningitis DIFFERENTIAL TESTS CAMP test positive Bile esculin hydrolysis test: FROM OTHER Bacitracin resistant positive STREPTOCOCCI CAMP TEST S. agalactiae produces a protein called the CAMP factor which acts to amplify the beta hemolytic activity of S. aureus. SHAPE & GRAM STAIN Gram positive lancet shaped cocci ARRANGEMENT Diplococci MOTILITY Non motile SPORE FORMATION Non spore forming Capsulated, the capsules appears as unstained halos around CAPSULE the cocci. The main virulence factor is Polysaccharide capsule as it resists phagocytosis. It is classified into 80 serotypes according to antigenic structure of the capsule. Can be detected by a serological test (Quellung reaction =Capsular swelling reaction). The most frequent cause of pneumonia and its complications as bacteremia, meningitis, septic arthritis and endocarditis. It is common cause of sinusitis, acute otitis media and conjunctivitis. SAMPLES Sputum GRAM STAIN Direct film stained with Gram stain for characteristic morphology. a) Culture requirements: O2: Facultative anaerobes Optimum temperature: 37C CO2: grow in normal CO2 concentration, but grows better in excess CO2. CULTURE b) Culture media: ③ Ordinary media : Cannot grow on it. ④ Enriched media: Grow on blood agar, colonies are small with central depression (Draughtsman appearance) surrounded by zones of α-hemolysis. ① Film stained by Gram stain to show the morphology. ② Biochemical reactions: Ferment inulin, bile soluble. ③ Sensitive to optochin. IDENTIFICATION ④ Pathogenicity to mice: Intraperitoneal injection of culture into mice OF GROWTH BY → death in 18-48 hours due to septicaemia. ⑤ Capsular swelling reaction (Quellung reaction): Swelling of the capsule after addition of specific polyvalent antibodies. Pnumococcal Vaccine: Contains: purified capsular material from most pathogenic 23 strains. Recommended for: young children, elderly and debilitated persons. HABITAT Normal oral flora. Gram positive cocci arranged in pairs or short chains. Non spore forming. MORPHOLOGY Non motile. Non capsulated. Produces α-hemolytic small colonies on blood agar. CULTURE Resistant to optochin & Not bile soluble. Bacterial endocarditis : Especially if heart valves have been damaged by previous DISEASE rheumatic fever or by congenital heart disease. Dental manipulation associated with transient bacteremia are the most common predisposing factors. CHARACTER S. PNEUMONIAE S. VIRIDANS INULIN FERMENTATION Positive Negative BILE SOLUBILITY Soluble Not soluble OPTOCHIN SENSITIVITY Sensitive Resistant CAPSULE AND QUELLING REACTION Positive Negative MICE PATHOGENICITY Pathogenic Non pathogenic RHEUMATIC ENDOCARDITIS SUBACUTE BACTERIAL ACUTE ULCERATIVE ENDOCARDITIS ENDOCARDITIS Post-streptococcal infection by group A beta hemolytic Streptococci S. viridans S. pyogenes No organisms are present in blood or on the S. faecalis valve