bacteriology 9. Streptococci-1.pptx at IUIU-KIBULI

microbiology

1. Streptococci Dr. Okoche Deo

2. Outline General characteristics Cell wall structure Hemolysis Classification Clinically important streptococci Streptococcus pyogenes Streptococcus agalactiae Streptococcus pneumoniae Viridans streptococci

3. General characteristics Streptococcus & Enterococcus spp. belong to the family Streptococcaceae Members of both genera are: Gram-Positive cocci C atalase-negative , Gram-positive cocci usually arranged in pairs or chains A negative catalase test differentiates streptococci & enterococci from staphylococci Weak false-positive catalase reactions occur when growth is taken from blood agar, owing to peroxidase activity of hemoglobin

4. Most members are facultative anaerobes Metabolize Carbohydrates fermentatively producing lactic acid; gas is not produced Some species are capnophilic , requiring increased concentration of carbon dioxide ( CO 2 )

5. Classification Cell wall structure Streptococci possess a gram-positive cell wall with peptidoglycan & teichoic acid Most streptococci, except many of viridans , have a common C carbohydrate (polysaccharide), used to classify an isolate serologically This classification scheme was developed in the 1930’s by Rebecca Lancefield Some species can also produce a type-specific polysaccharide capsule

6. Conie R.M, et al.Textbook of diagnostic microbiology, 5 th Edn Schematic representation of streptococcal cell wall

7. After first recognizing the antigen in ß-hemolytic streptococci, Lancefield was able to divide the streptococci into serologic groups, designated by letters (A, B,C , etc ) Hemolysis Streptococci can produce numerous exotoxins that damage intact red blood cells (RBCs)

8. Conie R.M, et al.Textbook of diagnostic microbiology, 5 th Edn

9. Hemolysis Patterns of Streptococci ob blood agar

10. Conie R.M, et al.Textbook of diagnostic microbiology, 5 th Edn

11. Streptococcus pyogenes Group A Strep (GAS); human-restricted pathogen Colonizes throat & skin on humans, making these sites, primary sources of transmission Antigenic Structure Similar to that of other streptococci & gram-positive bacteria Belong to Lancefield group A M protein is attached to peptidoglycan of the cell wall, extends to cell surface & is essential for virulence

12. Virulence factor of GAS Cell-associated virulence factors M protein ( > 80 serotypes; M1, M2, etc ), encoded by the genes emm Causes streptococcal cell to resist phagocytosis Helps in adherence of bacterial cell to mucosal cells Resistance to infection with S. pyogenes appears to be related to the presence of type-specific antibodies to the M protein Fibronectin -binding protein (protein F ) Adhesion molecules that mediate attachment to host epithelial cells Lipoteichoic acid Adherence to host epithelial cells

13. Hyaluronic acid capsule Weakly (non) immunogenic; Allows the bacterium to mask its antigens & remain unrecognized by its host Prevents opsonized phagocytosis by phagocytes Extracellular products Streptolysin O ( SLO) O refers to this hemolysin being oxygen labile Its active only in reduced form, which is achieved in an anaerobic environment Lyses leukocytes, platelets , and other cells as well as RBCs H ighly immunogenic , & infected individuals readily form antibodies to it. Antistreptolysin O (ASO) Abs can be tested to determine whether a recent infection has occurred with GAS

14. Streptolysin S; is oxygen stable Lyses RBCs, leukocytes & other host cells Non-immunogenic Hemolysis seen around colonies that have been incubated aerobically is due to streptolysin S Streptokinase Cause lysis of fibrin clots through action of streptokinase on plasminogen Plasminogen is converted into a protease (plasmin), which lyses the fibrin clot Antibodies to streptokinase, detected after infection but not specific indicators of GAS infection because groups C & G also form streptokinase

15. Hyaluronidase A n enzyme that solubilizes ground substance of mammalian connective tissues (hyaluronic acid ) B acteria use it to separate tissue & spread infection S treptococcal pyrogenic exotoxins Causes a red spreading rash ( scarlet fever) 4 immunologically distinct exotoxin types in S. pyogenes are SpeA , SpeB , SpeC , and SpeF ( superantigens ) These stimulate T-lymphocyte proliferation by interaction with class II MHC molecules on APCs specific variable ß-chains of TCR Leading to production of IL-1, TNF- α , which mediate disease processes associated with these toxins

16. Clinical Infections Bacterial Pharyngitis (“Strep throat”) Together with tonsillitis, most common O ften seen in children betwn 5 & 15 yrs After incubation period of 1 - 4 days; illness ensues with; S ore throat, malaise, fever & headache. Nausea, vomiting & abdominal pain may occur T onsils & pharynx are inflamed; cervical lymph nodes are swollen & tender Some individuals have mild disease S ymptoms subside within 3-5 days unless complications, like peritonsillar abscesses, occur The disease is spread by droplets & close contact

17. Pyodermal (skin) Infections These result in impetigo, cellulitis, erysipelas, wound infection , or arthritis Impetigo A localized skin disease, begins as small vesicles that progress to weeping lesions lesions crust over after several days Occurs mainly in children btn 2-5yrs Inoculation of organism occurs through minor abrasions or insect bites

18. Impetigo

19. Erysipelas I nfection of the skin and subcutaneous tissues, common in elderly C haracterized by an acute spreading skin lesion that is intensely erythematous with a plainly demarcated but irregular edge

20. Cellulitis Develops following deeper invasion by streptococci Can be serious or life-threatening with bacteremia or sepsis. In patients with peripheral vascular disease or diabetes, cellulitis may lead to gangrene Source: MSD Manuals Source: Merck Manuals

21. S carlet fever Caused by streptococcal pyrogenic exotoxins Appears within 1-2 days after bacterial infection C haracterized by a diffuse red rash that appears on the upper chest and spreads to the trunk & extremities The rash disappears over the next 5 to 7 days and is followed by desquamation Source: NHS

22. Necrotizing Fasciitis (NF) “Flesh eating” bacteria Life-threatening invasive infection characterized by rapidly progressing inflammation and necrosis of the skin, subcutaneous fat & fascia M ortality rate may reach greater than 70% if left untreated

23. Streptococcal Toxic Shock Syndrome A condition in which entire organ system collapses, leading to death Develops after a severe initial streptococcal infection severe ( e.g .,pharyngitis , peritonitis, cellulitis, wound infections ) Patients are often bacteremic & have NF A streptococcal pyrogenic exotoxin , notably SpeA superantigens are produced leading to over-simulation of the immune response

24. Post-streptococcal Sequelae R heumatic fever F ollows S. pyogenes pharyngitis C haracterized by fever and inflammation of the heart, joints, blood vessels, & subcutaneous tissues Occurs within 1 month after infection Caused by Antibody cross-reactivity between streptococcal antigens & heart tissue Major complication : chronic, progressive damage to the heart valves For patients with history of Rheumatic fever; Prophylactic penicillin is given to prevent recurrent infections & additional damage to the heart valves

25. Acute glomerulonephritis Occurs after a cutaneous or pharyngeal infection C ommon in children than in adults Caused by deposition of antigen-antibody complexes in the glomeruli leading to Complement activation, & an inflammatory response causes; D amage to the glomeruli, resulting in impairment of kidney function

26. Streptococcus agalactiae (GBS)

27. All strains of S. agalactiae have the group B–specific antigen, A n acid-stable polysaccharide located in the cell wall S . agalactiae is the only species that expresses group B antigen The organism is encapsulated Serotypes Ia , Ib & II contain a terminal residue of sialic acid (weakly immunogenic & inhibit activation of alternative complement pathway

28. Virulence Factors A capsule P revents phagocytosis mainly due to presence of Sialic acid Other virulence factors: Hemolysin , CAMP factor, neuraminidase, DNase , hyaluronidase & protease

29. Clinical infections Two clinical syndromes are associated with neonatal GBS disease : E arly-onset infection (<7 days old) & late-onset infection (at least 7 days old to about 3 months old ) Early-onset disease is caused by vertical transmission of organism from the mother during birth Colonization of vagina & rectal area with GBS is found in 10-30 % of pregnant women I nfection associated with obstetric complications, prolonged rupture of membranes & premature birth

30. Early onset infection often manifests as pneumonia & sepsis R ecommended that all pregnant women be screened for GBS at 35 to 37 weeks’ gestation Late-onset infection Occurs betwn 1 week & 3 months after birth and usually manifests as sepsis & meningitis O rganism is rarely found in the mother’s vagina before birth M ortality rate is considerably less than the mortality of early-onset disease incidence of GBS infections decreases dramatically after the neonatal period

31. In adults, causes; Endometritis especially after abortion or child birth Wound infections T ricuspid valve endocarditis in women undergoing obstetric procedures

32. Schematic diagram for differentiation of GAS from GBS

33. Streptococcus pneumoniae Identified by α -hemolysis , catalase negative, susceptible to Optochin & dissolved by bile acids Polysaccharide capsule: approx. 90 different capsular types Antibody directed against capsular antigen is protective In the presence of specific anti-capsular serum, the capsule swells ( quellung reaction )

34. Virulence Factors Capsule ; Most important virulence factors; its anti-phagocytic Other virulence factors: hemolysin , an IgA protease , neuraminidase & hyaluronidase

35. Factors that Predispose to Pneumococcal Disease Extremes of age Defective Antibody formation HIV/AIDS Complement defects Few or ineffective PMNs (steroids, EtOH , DM) Asplenia ( e.g sickle cell disease) Excess exposure (daycare, prison, shelter) Prior respiratory infxn , esp flu Pulmonary inflammatory (smoking, COPD)

36. Pneumococcal Pneumonia R isk factors ; Alcoholism , anesthesia, malnutrition, extremes of age, viral infections of upper respiratory tract Leads to lobar pneumonia characterized by sudden onset with chills, dyspnea, cough, DIB I nfection begins with aspiration of respiratory secretions, with pneumococci I nfecting organisms in alveoli stimulate an outpouring of fluid , which serves to facilitate spread of organisms to adjacent alveoli till septa of lung lobe Most common isolates in lobar pneumonia capsular serotypes 1, 2 & 3 Clinical Infections

37. W ithout therapy, mortality rate approaches 50 %; reduces to 5-10% with antimicrobial therapy Complication: P leural effusion, usually sterile ( empyema )

38. B acterial meningitis Occurs in age all groups Usually follows other S. pneumoniae infections , like otitis media or pneumonia D isease is rapid & mortality rate is near 40% Direct smears of CSF often reveal leukocytes & numerous gram-positive cocci in pairs Other infections Exacerbation of chronic bronchitis 2 nd to H. influenzae

39. Conjunctivitis Endocarditis (uncommon) Purulent pericarditis (rare) Septic arthritis Osteomyelitis ( esp of vertebrae) Otitis media Usually #1 or #2 to H. influenzae Sinusitis Usually #1 or #2 to H. influenzae

40. Prevention Three pneumococcal vaccines are available; Heptavalent pneumococcal conjugate vaccine (PCV7 ) used in children <5 yrs 13-valent product that contains six additional serotypes (1, 3, 5, 6A, 7F, and 19A) used in children <5 yrs 23-valent vaccine (PS23), has 23 purified capsular polysaccharides , used for adults

41. Viridans Streptococci A re constituents of normal microbiota of upper respiratory tract, female genital tract & GIT The term viridans means “green,” referring to α -hemolysis many species exhibit However, ß-hemolytic & nonhemolytic species are also classified as viridans Viridans are classified into 5 groups: S. mitis group ( S . mitis , S. pneumoniae , S . sanguis , S. oralis ) S. mutans group ( S. mutans & S . sobrinus )

42. S. salivarius group ( S . salivarius & S. vestibularis ) S . bovis group ( S . equinus , S. gallolyticus , S. infantarius & S. alactolyticus ) S. anginosus group ( S . anginosus , S. constellatus & S. intermedius ) A nginosus group can possess Lancefield group A, C, F, G, or N antigen and in some instances may not be groupable O rganisms also can cross-react with other grouping antisera

43. S. bovis group & enterococci possess group D antigen ( enterococcal and nonenterococcal ) Both groups were bile esculin -positive, but non- enterococcal don’t grow in a nutrient broth with 6.5% NaCl Oropharyngeal normal flora regarded as opportunistic pathogens Virulence is low

44. Clinical Infection Subacute bacterial endocarditis A ssociated with a transient bacteremia Often occurs Individuals whose heart valves have been damaged by rheumatic fever Signs & symptoms: Fever , malaise, anorexia Low-grade bacteremia (1-30 CFU per mL blood)

45. Other Manifestations of Strep viridans Bacteremia Account for 2.6% of all positive blood cultures After toothbrushing , 25-50% of people have bacteremia If transient, may consider limited clinical significance Bacteremia is more common in children than in adults & in patients with hematologic malignancies Bad outcomes (maybe just marker of bad mucosal barriers?) Meningitis Rare: 0.3 to 5% of culture-positive meningitis However, concern about contamination Pneumonia Very rarely the sole, instigating pathogen

46. Lab Diagnosis of Streptococcal infection Source: Sherries Medical Microb

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