Gram Positive Bacteria (2) 2022 PDF

‫ميحرلا نمحرلا هللا‬ ‫بسم‬ International University of Africa Faculty of Medicine Microbiology Department Gram positive Gocci bacteria (2) : Streptococci Introduction to study of diseases (213) Batch: 24 Semester 3 (2022)...

‫ميحرلا نمحرلا هللا‬ ‫بسم‬ International University of Africa Faculty of Medicine Microbiology Department Gram positive Gocci bacteria (2) : Streptococci Introduction to study of diseases (213) Batch: 24 Semester 3 (2022) Sara Mirghani Elmuzzamil Assistant professor IUA MSc Microbiology UofK  Objectives By the end of this lecture you should be able to:  Classify the streptococcus  Describe medically important Streptococci & their characteristics  Describe antigenic structure of Streptococci  describe the laboratory diagnosis of Know the Streptococcus spp.(S, S.pyogenes, S.agalactiae,.pneumoniae ,,..) microbiology, pathogenesis, epidemiology, laboratory diagnosis, treatment, prevention and control  Gram positive Gocci bacteria Streptococci Overview: S. pyogenes S. agalactiae S. pneumoniae Viridans streptococci Enterococcus faecalis  General Characteristics of Streptococci  Gram-positive spherical/cocci arranged in long chains; commonly in pairs  Non-spore-forming, non motile  Can form capsules and slime layers  Facultative anaerobes  Do not form catalase, but have a peroxidase system  Most parasitic forms are fastidious and require enriched media.  Small, non pigmented colonies  Sensitive to drying, heat and disinfectants  Streptococci  Lancefield classification system based on the nature of a carbohydrate (C) antigen on the cell wall Ag – 17 groups (A,B,C,….)  Another classification system is based on hemolysis reactions.  b-hemolysis – A,B,C,G and some D strains  a – hemolysis – S. pneumoniae and others collectively called viridans  Classification of Streptococci Streptococci are first divided into obligate anaerobes and facultative anaerobes. The former are designated peptostreptococci and The aerobic and facultative anaerobic streptococci are classified on the basis of their hemolytic properties. Brown (1919) categorized them into three varieties based on the growth in 5% horse blood agar pour plate cultures.  Human Streptococcal Pathogens S. pyogenes S. agalactiae Viridans streptococci S. pneumoniae Enterococcus faecalis 8  Streptococci cultures S. pyogenes S. pneumonae S.viridans  b-hemolytic S. pyogenes  Most serious streptococcal pathogen  Strict parasite  Inhabits throat, nasopharynx, occasionally skin  S. pyogenes Laboratory characteristics  Culture: blood agar with small, typically matt or dry colonies surrounded by b-haemolysis.  Capsule: some strains produce a hyaluronic acid capsule during the logarithmic phase of growth, and develop mucoid colonies on blood agar.  Catalase negative.  Bacitracin all strains are susceptible; detection of group- specific carbohydrate (A antigen); detection of L- pyrrolidonyl arylamidase enzyme (PYR)  Virulence Factors of b-hemolyticS. pyogenes Produces surface antigens:  C-carbohydrates – protect against lysozyme  Lipoteichoic acid, protein F cause adherence of the streptococci to buccal epithelial cells; this adherence is mediated by fibronectin, which acts as the host cell receptor molecule.  M protein(class I &class II) is a major virulence factor of S pyogenes. M protein appears as hairlike projections of the streptococcal cell wall. acts as an antiphagocytic molecule. can cause suppurative infections and also M proteins cause rheumatic fever and glomerulonephritis  Hyaluronic acid capsule – provokes no immune response, capsule can protect the bacteria from phagocytic 13  Virulence Factors of b-hemolytic S. pyogenes Extracellular enzymes 1. Streptokinase: protease which lyses fibrin. 2. Hyaluronidase: attacks hyaluronic a acid - the cement of connective tissue - causing increased permeability. Antibodies to this enzyme are produced after infection. 3. DNAases (deoxyribonucleases): four immunologically distinct types - A, B, C and D, B enzyme is the most common. Antibodies to DNAse - especially B enzyme – are demonstrable in most patients after recent infection with S. pyogenes. 4. NADase (nicotinamide adenine dinucleotidase): kills leucocytes. Antibody formed after infection  Virulence Factors of b-hemolytic S. pyogenes Extracellular toxins:  Streptolysins – hemolysins; streptolysin O and streptolysin S – both cause cell and tissue injury  pyogenic toxin (erythrogenic) – induces fever and typical red rash responsible for the characteristic erythematous rash in scarlet fever.  Superantigens – strong monocyte and lymphocyte stimulants; erythrogenic rash cause the release of tissue necrotic factor Haemolysin Stability to Active Active Antigenic oxygen aerobically anaerobically Streptolysin O - - + + Strawberry tongue Streptolysin S + + + -  Streptococcus pyogenes Pathogenecity  Infections of upper respiratory tract and of skin and soft tissue (e.g. pharyngitis, cellulitis, erysipelas, lymphadenitis).  Toxic manifestations include scarlet fever.  Non-suppurative sequelae (acute glomerulonephritis and rheumatic fever) are important complications of both skin and throat infections.  Streptococcus pyogenes (Group A) Suppurative Infections  Pharyngitis: reddened pharynx with exudates generally present; cervical lymphadenopathy can be prominent  Scarlet fever: diffuse erythematous rash beginning on the Impetigo chest and spreading to the extremities; complication of streptococcal pharyngitis  Impetigo (pyoderma) - localized skin infection with vesicles progressing to pustules; no evidence of systemic disease Erysipilus  Erysipelas –: localized skin infection with pain, inflammation, lymph node enlargement, and systemic symptoms  S. pyogenes (Group A) Suppurative Infections  Cellulitis: infection of the skin that involves the subcutaneous tissues  Necrotizing fasciitis: deep infection of skin that Cellulitis  involves destruction of muscle and fat layers  Streptococcal toxic shock syndrome: multiorgan Necrotizing systemic infection, resembling staphylococcal toxic shock fasciitis syndrome; however, most patients are bacteremic and with evidence of fasciitis  Other suppurative diseases: variety of other  infections recognized including puerperal sepsis, lymphangitis, and pneumonia  Nonsuppurative Infections (Post streptococcal infection)  Rheumatic fever: characterized by inflammatory changes of the heart (pancarditis), joints (arthralgias to arthritis), blood vessels, and subcutaneous tissues  Acute glomerulonephritis: acute inflammation of the renal glomeruli with edema, hypertension, hematuria, and proteinuria  S.Pyogenes (Group A Streptococcus) Epidemiology  The incidence of both respiratory and skin infections peaks in childhood.  Infection can be transmitted by asymptomatic carriers. Acute rheumatic fever was previously common among the poor; susceptibility may be partly genetic.  Portal of entry generally skin or pharynx  Children predominant group affected for cutaneous and throat infections  Systemic infections and progressive sequelae possible if untreated  S.pyogenes host defenses  Antibody to M protein gives type-specific immunity to group A streptococci.  Antibody to erythrogenic toxin prevents the rash of scarlet fever.  Immune mechanisms are important in the pathogenesis of acute rheumatic fever and Glomerulonephritis.  Laboratory identification  Grown on blood agar. Pronounced haemolytic activity (enhanced anaerobically).  Catalase negative.  Bacitracin (0.04 units); all strains are susceptible;  Detection of group-specific carbohydrate (A antigen);  Detection of L-pyrrolidonyl arylamidase (PYR)  Anti streptolysin O test(ASO test) is useful for confirming rheumatic fever or glomerulonephritis associated with streptococcal pharyngitis;  Anti-DNase B test should be performed for glomerulonephritis associated with pharyngitis or soft-tissue infections  Laboratory diagnosis of Streptococci Lancefield grouping test CAMP test S.pyogens are, catalase-negative (ASO test β haemolytic colonies sensitive to the Bacitracin disc This bacterium is belong to group A Lancefield grouping PYR test 24  S. pyogenes- Treatment and Prevention Antibiotic sensitivity The drug of choice is penicillin. In patients hypersensitive to penicillin, use erythromycin.  Antibiotic resistance: all strains are sensitive to penicillin but there is often resistance to tetracycline.  Resistance to erythromycin, although uncommon, is increasing.  No vaccines available  Group B: Streptococcus agalactiae  Regularly resides in human vagina, pharynx and large intestine  Can be transferred to infant during delivery and cause severe infection  most prevalent cause of neonatal pneumonia, sepsis, and meningitis  15,000 infections and 5,000 deaths in US  Pregnant women should be screened and treated.  Wound and skin infections and endocarditis in debilitated people  Streptococcus pneumoniae: The Pneumococcus  Causes 60-70% of all bacterial pneumonias  Gram positive diplococci, small, lancet- shaped cells arranged in pairs and short chains  Culture requires blood or chocolate agar.  Growth improved by 5-10% CO2  It also forms short chains, particularly following culture.  Pneumococci are non motile.  All pathogenic strains form large capsules – major virulence factor.  S. pneumoniae Pathogenicity:  Pneumococci are important pathogens and cause a considerable amount of both morbidity and mortality today, despite their sensitivity to penicillin. They may cause: Lobar pneumonia Acute exacerbation of chronic bronchitis (often with Haemophilus influenzae). Meningitis. Otitis media. Sinusitis.  Conjunctivitis. Septicaemia (especially in splenectomized patients).  S. pneumoniae Epidemiology & Pathology  5-50% of all people carry it as normal flora in the nasopharynx; infections are usually endogenous.  Very delicate, does not survive long outside of its habitat  Young children, elderly, immune compromised, those with other lung diseases or viral infections, persons living in close quarters are predisposed to pneumonia  Pneumonia occurs when cells are aspirated into the lungs of susceptible individuals.  Pneumococci multiply and induce an overwhelming inflammatory response.  Gains access to middle ear by way of eustachian tube 29  S. pneumoniae laboratory Diagnosis  Gram stain of specimen – presumptive identification  α hemolytic; optochin sensitivity  Quellung test or capsular swelling reaction quellung reaction is a good test Culture of S. pneumonia on for rapid microscopic S. pneumoniae (lancet-shaped blood agar showing alpha- determination of whether or not gram-positive diplococci.) haemolytic colonies sensitive pneumococci are present in fresh Mucus and amorphous debris to optochin disc sputum. are present in the background. 30  S. pneumoniae: Treatment and Prevention  Traditionally treated with penicillin G or V  Increased drug resistance  Two vaccines available for high risk individuals: -capsular antigen vaccine for older adults and other high risk individuals-effective 5years(PPSV23)Pneumococcal polysaccharide polyvalent vaccine against 23 serotypes)(Pneumovax) -conjugate vaccine for children 2 to 23 months (PPV13) 31  Alpha-Hemolytic Streptococci: The Viridans Group  Alpha-hemolytic (“viridans = green”)  No Lancefield group Lack group-specific carbohydrates  Normal microbiota mouth, pharynx, GI tract, GU tract  Opportunistic Disease: One of the causes of dental caries and dental plaques; Can cause meningitis and endocarditis Group D Enterococci and Groups C and G Streptococci  Group D:  Enterococcus faecalis, E. faecium, E. durans  normal colonists of human large intestine  cause opportunistic urinary, wound, and skin infections, particularly in debilitated persons Groups C and G:  common animal flora, frequently isolated from upper respiratory; pharyngitis, glomerulonephritis, bacteremia group D non-enterococci (S. bovis group) has undergone significant taxonomic reclassification. These organisms are PYR negative and Enterococcus faecalis on bile esculin positive MacConky,