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Non-suppurative sequelae

  1. S. pyogenes is responsible for causing acute rheumatic fever and acute glomerulonephritis.
  2. These conditions appear 1-3weeks after infection with S. pyogenes.
  3. Many cases are preceded by subclinical streptococcal infection. In such cases high titres of antibodies to streptococcal antigens are demonstrable.
  4. Streptococci are not directly demonstrable in the lesions
  5. Acute rheumatic fever: Develops in about 3% of individuals, 2-3weeks after acute streptococcal pharyngitis. It is linked to certain M types (1,3,5,6,12,14,17,19,24,27,29,30,32 and 41). Recovery from ARF occurs without residual injury to joints, but permanent damage to heart valves may occur.
  6. Acute glomerulonephritis: Apart from group A, group C streptococci may also be involved. It is preceded by streptococcal upper respiratory tract infection or skin infection. Types of group A streptococci associated with acute glomerulonephritis are 1,3,4,25,49,52-55 and 57-61.

A. Laboratory diagnosis

  1. Specimens: Suppurative diseases are diagnosed by isolation and identification of ß-hemolytic streptococci from the lesions while non-suppurative complication are diagnosed by demonstrating rising titre of antibody to streptococcal antigens. Specimens collected are throat swabs from cases and carriers, pus or pus swabs from suppurative lesions, blood from cases of systemic infections.
  2. Direct examination: Gram stained smears are prepared from pus and wound exudates and are examined for presence of gram positive cocci in chains.     
  3. Culture: Specimens are inoculated on blood agar plate and are incubated at 37°C. Next day plates are examined for typical colonies. Transport medium which can be used is Pike’s medium (Blood agar with crystal violet and sodium azide). Selective media which can be used are crystal violet blood agar and PNF medium. ß-hemolytic streptococci are subjected to Lancefield grouping. If it belongs to group A it is further subjected to M typing. Group A streptococci can be presumptively identified by bacitracin sensitivity test using 0.04U bacitracin disc. S. pyogenes is sensitive to bacitracin giving a zone of inhibition around the disc. However, other non group A streptococci (B, C and G) may give a positive test.
  4. Serological tests: Non-suppurative complication can be diagnosed by demonstrating rise in antibody titre to one or more extra cellular products of S. pyogenes. Antistreptolysin O (ASO) titres higher than 200 Todd units/ml is indicative of recent infection while anti-DNAase B titers higher than 300 are considered as significant.    

A child develops pustule on front of his leg. Which on culture is found bacitracin sensitive beta hemolytic streptococci. A similar stain is found by school doctor in students causing pharyngitis. Which test can differentiate between two strains? AIIMS 2010 Question
A. M. Protein            
B. mec A gene         
C. Capsule               


Ans- A


B. Treatment

Group B Streptococcus
  1. Also called S. agalactiae
  2. Etiological agent of bovine mastitis
  3. Infection of neonates and children
A. Infection of neonates
  1. Eearly onset type :
    1. Acquired from genital tract of mother onset < 5 days after delivery
    2. Septicemia, pneumonia, meningitis. Mortality rate 50-70%
  2. Late onset type: 
    1. 2-4 wk of life. Infection acquired from hospital personnel
B.  Infection in adults
  1. Septicemia, endocarditis, meningitis, pneumonia
    1. Blood Agar: ß hemolysis on blood agar; orange colonies on Columbia, or starch/serum agar
    2. Camp test +and Hippurate hydrolysis +

Group D Streptococci:

  1. S. bovis, S.equinus
  2. Grow in 40% Bile, Hydrolyze aesculin- together tested on bile-esculin agar
  3. Fails to grow in 6.5% NaCl broth, PYRase-ve –differentiation from enterococcus which is also bile-esculin +
  4. Diseases:
    1. Bacterial endocarditis,
    2. UTI,
    3. septicemia,
    4. associated with polyps and carcinoma of colon.
  5. Susceptible to penicillin:


Previously referred as enterococcal group D streptococci

A. Characteristic:
  1. Normal flora of lower intestinal tract
  2. Non motile, non capsulated, gram + cocci in pairs, short chains
  3. a , ß or non- hemolytic on sheep blood agar
  4. MacConkey’s agar: tiny magenta colored colonies (LF)
  5. Grow in presence of 6.5% NaCl, pH 9.6, at 10°C & 45°C
  6. Grow in presence of 40% bile, hydrolyze aesculin
  7. PYRase test +
  8. Survive 60°c for 30 min
  9. Resistant to penicillin
    1. E. faecalis: most common; E. faecium , E. durans
    2. UTI, wound infection, endocarditis, Peritonitis, Septicemia

Viridans Streptococci

  1. a Hemolysis on sheep blood agar
  2. Commensal of mouth/ oropharynx
  3. S. salivarius, S. sanguis, S. mutans, S. mitis, S. milleri
  4. Dental caries (S. mutans), infective endocarditis (most common cause of SABE)
  5. Fail to grow on the MacConkey’s agar, sensitive to penicillin

Streptococcus Pneumoniae (Pneumococcus)

  1. Non motile non-sporing, gram + coccus
  2. Pairs of flame-shaped / lanceolate cocci, 1µm diameter
  3. Capsulated – India ink, quellung reaction
  4. Aerobe, facultative anaerobe, capnophilic, temp 37°c , pH 7.4, grows on enriched media
  5. Blood agar: 0.5-1mm, moist, mucoid, transparent colonies. Zone of a hemolysis, further incubation draughtsman colony. Anaerobic conditions- ß hemolysis (Pneumolysin)
A. Biochemical Reactions:
  1. Ferment glucose, sucrose, lactose, inulin ? acid no gas
  2. Bile soluble: activates autolytic enzymes
    1. Tube: 10% sodium deoxycholate
    2. Plate: 2% sodium deoxycholate
Features S. pneumoniae Viridans streptococci
Morphology shape
Round/ oval
Cultural characteristic
Blood agar
Liquid medium
Draughtsman colonies
Uniform turbidity
Dome shaped, opaque
Granular turbidity
Bile solubility + -
Inulin fermentation + -
Optochin sensitivity + -
Animal Pathogenicity (mouse) Fatal Non-pathogenic
B.  Sensitivity To Physical And Chemical Agents:
  1. Delicate organism. Killed at 55°c in 10 min and most disinfectants
  2. Sensitive to wide range of antimicrobials: penicillin, cephalosporin, erythromycin
  3. Some strains resistant to ß-lactam antibiotics and erythromycin
  4. Sensitive to Optochin: 5 µg, 6 mm disc = 14 mm zone of inhibition                                           
C.  Antigenic Structure:
  1. Capsular antigen: 85 types, Serum Soluble Substance, essential for virulence, typing by Quellung reaction
  2. Somatic antigens: carbohydrate antigens- ribitol teichoic acid
  3. M protein
  4. C-reactive protein, ß globulin
  5. Smooth ? rough variation. R forms: non-capsulated, autoagglutinable, avirulent
  6. Pneumolysin: hemolysin similar to (group A streptococcus, C. tetanus, C. perfringens, Listeria) 
D. Pathogenicity:
  1. 5-70% humans carry S. pneumoniae in throat
  2. Pneumococcal pneumonia, most common cause of community acquired pneumonia: Risk factors: Chilling, GA, convulsions, CVA, epilepsy, morphine, alcoholic intoxication, viral infections CHF, CAD, CRF, COPD, DM, HIV; Lobar pneumonia (most common cause)
  3. Impair epiglottal reflex, mucociliary escalator, cough reflex
  4. In adults type 1-8, 18 and in children capsular types 6,14,19,23
  5. Lobar pneumonia: 10-50 yrs. Broncho pneumonia: young children, adults > 50 yrs
  6. Acute bronchitis, sinusitis, otitis media (most common cause in children), mastoiditis, meningitis, suppurative arthritis
E.  Lab Diagnosis:
  1. Demonstration in sputum, exudate, blood, CSF by gram staining, culture, Ag (COA, LA, CIEP)
  2. Blood culture
F.  Chemotherapy:
Penicillin: penicillin resistance (chromosomal). Due to alteration in PBP (cephalosporin, erythromycin etc)
Recent advances
  1. S. pn. Vaccine-Pneumovax 23- contains polysaccharide component of 23 capsular serotypes responsible foe 90% of S. pn. Bacteremias. Single dose gives protection for 5-10 yrs. This vaccine fails to mount an adequate response in children less than 2 yrs.
  2. Prevnar and Prevnar 23 is a conjugate vaccine containing capsular antigen of 7 and 13 serotypes responsible for 75% of invasive infections conjugated with diphtheria proteins.

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