Download as PDF, PPTX
5 Streptococci & Enterococci.pdf
- 1. Streptococci & Enterococci CollegeApplied Medical Sciences Department Medical Laboratory Sciences
- 2. Objectives: • Describe themorphological and physiological characteristics of genus Streptococcus • List the features by which Streptococcus pyogenes, Streptococcus agalactiae, Viridans Streptococci, and Entrococcus can be identified. • Describe the spectrum of diseases caused by various Streptococcus. • Describe different laboratory diagnostic techniques for Sterptococcus.
- 5. Streptococcaceae General Characteristics: • TheStreptococcaceae consist of a large family of medically important species including Streptococcus spp. and Enterococcus spp, many of these organisms are commonly found as part of normal human flora • Streptococci are Gram-positive cocci arranged in chains or pairs and non motile • Streptococci are catalase negative
- 6. • This groupof organisms are differentiated based on cell wall structure, hemolytic patterns on blood agar (beta, alpha, or gamma), the reaction of antibodies to specific bacterial antigen, Lancefield classification scheme, and , and biochemical identification relating to physiologic characteristics. • Most commonly encountered in infections in humans include Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, Enterococcus faecalis, and the viridans streptococci group.
- 7. Streptococci classification: ➢According tohemolysis: Some streptococcal species can completely hemolyze red blood cells, while other species partially hemolyze the RBC’s, therefore Streptococci are divided into 3 groups based on their hemolytic ability. ▪ Beta hemolytic streptococci: Completely lyse the RBCs, leaving a clear zone of hemolysis around the colonies. ▪ Alpha hemolytic streptococci: Partially lyse the RBCs, leaving greenish coloration surrounding the colonies. ▪ Gamma hemolytic (non-hemolytic) streptococci: They cannot lyse the RBCs
- 8. ➢According to carbohydratesantigens on the cell wall: These antigens are called Lancefield antigens, and they are given letter names (A- H, and K-U) is used to divide streptococci into stereological group Lancefield groups. Typing is done only for A, B,C,F and G. group A or S.pyogenes is the most important as it causes several human diseases
- 9. Streptococcus pyogenes Group AStreptococci (Beta hemolytic) • Rosenbach (1884) isolated the cocci from human suppurative lesions and gave them the name Streptococcus pyogenes. Normal habitat: S. pyogenes may be carried in the upper respiratory tract of humans, it is not considered to be normal flora and should be deemed clinically important whenever it is encountered Mode of transmission: Direct contact: person to person Indirect contact: aerosolized droplets from coughs or sneezes
- 10. Virulence factors: ▪ M-Protein:antiphagocytic ▪ Protein F mediates epithelial cell attachment (fibronectin-binding) ▪ Pyrogenic exotoxin: • Pyrogenic exotoxin A (erythrogenic toxin ) This is a toxin produced by group A streptococci, and it causes scarlet fever • Pyrogenic exotoxin B: destroy tissue(necrotizing) Pathogenicity
- 11. ➢Enzymes: ▪ Haemolysins: thereare two types Streptolysin S: It is oxygen stable, also responsible of beta hemolysis, but it is not immunogenic capable of lysing erythrocytes, leukocytes, and platelets in the presence of oxygen. Streptolysin O: This is oxygen labile enzyme(is broken down by oxygen), capable of lysing the erythrocytes, leukocytes, and platelets, and will produce haemolysis only in the absence of oxygen It is immunogenic after infection anti-streptolysin O antibodies were developed.
- 12. Diseases and infections: ➢Pyogeniclocal infections: • Streptococcal throat infection or pharyngitis: enlarged tonsils with purulent exudate. Pyoderma (impetigo): skin infection characterized by the formation of blisters ➢Invasive disease: • Acute bacterial endocarditis • Puerperal sepsis infection of the uterus after delivery associated with septicemia
- 13. ➢Toxigenic disease: • Scarletfever in children associated with pharyngitis and rash due to erythrogenic toxin • Streptococcus toxic shock syndrome ➢Post streptococcal immunogenic infection: • Acute rheumatic fever (Cross-reactions of antibodies produced against streptococcal antigens and human heart tissue) • Acute glomerulonephritis (Deposition of antibody- streptococcal antigen complexes in the kidney)
- 14. Identification: ❖Specimens according tothe site of infection • Blood for blood culture (bacteriemia, septicemia, and endocarditis) • Throat swab from the lesion (pus) ❖Antigen detection test: using Enzyme-linked immunosorbent assay(ELISA) or agglutination test. ❖Serological test: Antistreptolysin O (ASO) titer is high soon after group A streptococcal infection. An elevated ASO titer of more than 200 units indicates a recent streptococcal infection
- 15. ❖ Cultural characteristics: Culturemedia: • Culture on blood agar, chocolate blood agar • Selective media crystal violet blood agar Incubation condition optimum temperature 37°C. they are aerobic bacteria or facultative anaerobic. Colonial appearance: • On blood agar colonies show complete hemolysis(Beta hamolysis).
- 16. Biochemical reactions: ▪ Catalasenegative ▪ Bacitracin sensitivity test: sensitive to bacitracin Treatment: Penicillin G is the drug of choice if the patient has an allergy to clindamycin or erythromycin is used
- 17. Group B streptococci(streptococcus agalactiae) Normal habitat: Inhibit about 25% of the normal adult vaginaand lower gastrointestinal tract Mode of transmission: • Endogenous strain: gaining access to the sterile site(s) probable • Direct contact: person to person from mother in utero or during delivery • Nosocomial transmission by unwashed hands of mother or health care personnel
- 18. Pathogenicity: Virulence factors: Uncertain; capsularmaterial interferes with phagocytic activity Diseases and infection: • Neonatal meningitis, pneumonia, and septicemia (infants can acquire S.agalactiae during delivery ) • Pneumonia and endocarditis (in adult)
- 19. Identification: • Specimens VaginalSwab, blood, CSF, ear swab • Beta hemolytic on blood agar • Bacitracin resist • Hydrolyses Hippurate and are CAMP factor positive
- 20. Streptococcus pneumoniae Alpha hemolytic(No Lancefield antigen) Morphology: Gram positive cocci arranged in pairs (diplococci),have lancet shape (fusiform pointed ends) they are capsulated, capsules may appear as unstained haloes around the organism Inhabitant: normally carried in upper respiratory tract of healthy persons
- 21. Pathogenicity: Virulence factors: • Themajor virulence factor of S. pneumonia is its polysaccharide capsule which protects the bacteria from phagocytosis. • secretory IgA protease Diseases and infection: • Bacterial pneumonia • Meningitis • Sinusitis and otitis media
- 22. Viridans streptococci (Alphahemolytic) • This is a large group with no Lancefield antigen, including S. mutans, S.mitis. • Inhabitant: They are normal flora of the oral cavity, gastrointestinal tract, and female genital tract
- 23. • Pathogenicity : •Virulence factors: Generally considered to be of low virulence; • production of extracellular complex polysaccharides (e.g., glucans and dextrans) enhances attachment to host cell surfaces, such as cardiac endothelial cells or tooth surfaces in the case of dental caries • Diseases and infection: dental infections and endocarditis.
- 24. Identification of Streptococcuspneumoniae and Viridans streptococci • Both are alpha-hemolytic • Differentiated by: Bile solubility test and optochin disc sensitivity test • Streptococcus pneumoniae: soluble in bile, sensitive to optochin antibiotic disc. • Viridans streptococci: not soluble in bile, resist optochin antibiotic disc
- 25. Group D streptococci (Entrococciand non-entrococci) • These are alpha-hemolytic, eg. Enterococcus faecalis Inhabitant: It is a normal flora of the intestine Pathogenicity : • Virulence factors: • Adhesions, cytolysins, and other metabolic capabilities may allow these organisms to proliferate as nosocomial/healthcare-associated pathogens • Diseases and infection: • Most infections are healthcare–associated and include urinary tract infection, wound infection, and endocarditis.,
- 26. Identification: • Grow inMacConkey gives pink colonies, and it can grow in the presence of 40% bile. grow in 6.5% NaCl • Hydrolyze polysaccharide esculin(bile esculin positive)
- 27. Questions ➢Describe Morphology &physiological characteristics of Streptococcus? ➢Classify the streptococcus on the basis of Hemolysis? ➢Describe medically important Streptococci & their characteristics? ➢Describe Lab Diagnosis of Streptococci? ➢Differentiate between Streptococci and Staphylococci? ➢List virulence factors or Streptococci? ➢Group D streptococci is ……………hemolytic. ➢Viridans streptococci is …………hemolytic. ➢Why streptolysin S cannot be used for diagnosis? ➢How can we differentiate between Streptococcus pneumoniae and Viridans streptococci? ➢25% of women carry this type of Streptococci in their reproductive systems ?…………………. ➢……………Streptococci cause similar infections as Staphylococcus aureus?