Streptococcus and Enterococcus

They member of family streptococcacea. Catalase and cytochrome enzyme (oxidase) differentiated them from other micrococal and staphylococci. Elongated cocci (more than spherical) arranged in chains when grown in broth. Facultative anaerobic, fastidious (require special condition and enriched media) and some spp are capnophilic (require CO2 for growth

Genus Streptococci Classification schemes: Four commonly used classification schemes are: 1. Hemolytic pattern on SBA. There are 3 type of hemolytic pattern: a. Alpha α-hemolysis greenish discoloration around the colony (AH). b. Beta hemolysis clear zone around the colony(BH). c. Non haemolytic (NH).

2. Serological grouping of C CHO (Lancefield classification) &capsular polysaccharide. Lancefield classification depend on extraction of C CHO from the cell by heating or acid. The Lancefield gp seen in human infection (A,B,C,D,F,G,N). Viridians streptococci do not posses any of the recognized Lancefield grouping antigen.

Physiological characteristics. Biochemical characteristics.

Group A B hemolytic streptococci (S. pyogenes) Virulence factors : M- protein: is the best defined virulence factor. There are more than 80 serotype of M protein . it play a role in resistance to phagocytosis and adherence of mo to mucosal cells. Fibronectin binding proteins (FBPs): these proteins play a role in adherence of mo to keratinocyte. Capsule: which is composed of hyaluronic acid it is indistinguishable from the ground substance of connective tissue which explain it is lack of immunogensity. Streptolysin O SLO (O2 labile and antigenic ) & Streptolysin S SLS (O2 stable and non antigenic).

Streptococcal pyrogenic exotoxin (SPE A , B & C) responsible for the rash of scarlet fever and pathogensity in streptococcal toxic shock syndrome, SPE A & C act as superantigens that cause hypotension and shock. Other immunological active substances are: a. hyaluronidase deploymerizes connective tissue b. streptokinase hydrolyse fibrin clot c. deoxy ribonucleases (DNAase used in debridement) d. SIC protein that inhibit complements.

Clinical significant : Human is natural reservoir of S. pyogenes transmitted from person to person. 1. streptococcal pharyngitis is most common infection caused by S. pyogenes children (5-15 years). 2. Pyodermal infection including a. Impetigo: local infection of superficial layers of skin, especially in children. It consists of superficial vesicles that break down and eroded areas whose denuded surface is covered with pus and later is encrusted. It spreads by continuity and is highly communicable.  b. Erysiplus : results with massive brawny edema and a rapidly advancing margin of infection. c. Cellulitis: Streptococcal cellulitis is an acute, rapidly spreading infection of the skin and subcutaneous tissues.  

3. Scarlet fever which is red spreading rash caused by SPE A 3. Scarlet fever which is red spreading rash caused by SPE A. it commonly affects children. Signs and symptoms include sore throat, fever, and a characteristic red rash.   4. Necrotizing fasciitis This is infection of the subcutaneous tissues and fascia. There is extensive and very rapidly spreading necrosis of the skin and subcutaneous tissues. it is called “flesh-eating bacteria.”  5. Streptococcal toxic shock syndrome resemble staphylococcal toxic shock syndrome.

6. Post streptococcal diseases : a. Rheumatic fever (after pharyngitis) This is the most serious sequela of S pyogenes because it results in damage to heart muscle and valves. Certain strains of group A streptococci contain cell membrane antigens that cross-react with human heart tissue antigens. Sera from patients with rheumatic fever contain antibodies to these antigens. Typical symptoms and signs of rheumatic fever include fever, malaise, a migratory nonsuppurative polyarthritis, and evidence of inflammation of all parts of the heart (endocardium, myocardium, pericardium).  

b. Acute glamerulonephritis ( after skin infection and pharyngitis) b. Acute glamerulonephritis ( after skin infection and pharyngitis) . Glomerulonephritis may be initiated by antigen-antibody complexes on the glomerular basement membrane. In acute nephritis, there is blood and protein in the urine, edema, high blood pressure, and urea nitrogen retention; serum complement levels are also low. A few patients die; some develop chronic glomerulonephritis with ultimate kidney failure and the majority recover completely.

Treatment of Streptococcal infection pencillin is the drug of choice erythromycin is alternative in allergic patients. Routine susceptibility testing for BH is not required (sensitive to penicillin).  

Group B streptococci (S. agalactiae) 1. Virulence factor : the capsule is important virulence of group B it prevent phagocytosis. 2. Clinical infection: S. agalactiae cause invasive disease in newborn . two clinical syndrome: a. Early onset appear(less than 7 days old) 80% of clinical case of new born in the form of bactermia , pneumonia and meningitis. b. Late onset infection occur between 1 week- 3month mainly in the form of meningitis. 3. The treatment of choice is ampicillin +aminoglycoside

Viridans streptococci: They are constituents of the normal flora of the URT , female genital tract and GIT. (viridans mean green). Many spp are α hemolytic and few spp are non hemolytic and very rarely beta hemolytic. They do not posses any recognized Lancefield grouping antigen lack of C CHO. Virulence factors include polysaccharide capsule and adhesions implicated in adherence and colonization in endocarditis.

Clinical infection : It is the most common cause of subacute bacterial endocarditis, bacterimia, gingivitis and dental caries, abscess formation. Viridians are general susceptible to penicillin, over the last 2 decade there is increase resistance to penicillin, cephalosporin and aminoglycoside. Accurate susceptibility to penicillin is required to viridians when isolated from serious infection.

Streptococcus pneumonia Virulence factor: 1. Capsular polysaccharide is main virulence factor by which the mo resist opsonization and phagocytosis. There at least 90 capsular type ,23 of these type account for over 88% of pneumoncoccal meningitis and bacterimia.   2. Several toxin produced include hemolysin, IgA1 proteases, neuraminidase , hyaluronidases, pneumolysin, teichoic acid and lipotiechoic acid.

Clinical infection: It causes pneumonia (2ry pneumonia), otitis media (recurrent infection in children under 3years of age) ,sinusitis , meningitis 2ry to otitis media affect all age group and bactermia. Antimicrobial resistance:Over the last three decades S pneumoniae have become increasingly resistant to penicillin and generally treat with erythromycin.

Genus Enterococci 1. These mo are normal residents of GIT and in lower number of the vagina and male urethra. 2. E. feacalis is the most common isolate being associated with 80-90% of human enterococcal infection. E. faecium ranks second and is isolated from 10-15% of infection. 3. It is the second most common cause of nosocomial UTI and wound infection and the third most common cause of bacterimia. Unlike streptococci ,enterococci have the ability to grow under extreme conditions (the presence of 6.5% NaCl, the presence of bile or at 45C or alkaline PH). 4. The ability of enterococci to hydrolyse esculin differentiated it from non hemolytic or alpha hemolytic streptococci other than gp D.

5. The ability of enterococci to hydrolyse PYR and growth at 6 5. The ability of enterococci to hydrolyse PYR and growth at 6.5 NaCl is useful in differentiate them from group D streptococci (S. bovis bile esculin +). 6. Isolates that fit the criteria for diagnosis of enterococci ( bile esculin +, PYR +, growth at 6.5% NaCl growth at 10- 45 C). 7. E.faecalis differentiated from faecium) by hippurate hydrolysis ( faecalis + faecium _-) .   8. They are generally resistant to penicillin and cephalosporin. Also resistant to aminoglycoside and now emergence of vancomycin resistance.

. Laboratory diagnosis of Streptococci: 1. Direct detection: Gram stain of clinical specimen show gram positive cocci arranged in chains or pairs. Direct detection of Ag of group A, B and pneumococcal capsular Ag. by slide agglutination or latex or EIA. Quelling reaction for capsular type of pneumococcus seldom used. DNA probe has been used for direct detection of gp A.

. 2. Culture: a. SBA 5% is suitable media for isolation where we can evaluate hemolysis . group A, B, C, F and G Beta hemolytic (hemolysis is enhanced under anaerobic condition e.g inoculation by stabbing inside the media ), while majority of group D and enterococci are either non hemolytic or AH. S. pneumoniae Surrounded with intense green AH. Viridans streptococci are AH or NH. b.Other media used Columbia base medium. c. The colonies is then tested for catalase.

3. Biochemical activities: Presumptive identification can be accomplished using few biochemical test which are selected depending on the hemolytic pattern. a. Bacitracin susceptibility : This test used to identify Beta Haemolytic gp A (Streptococcus pyogens) which sensitive to Bacitracin while BH gp is resistant (S. agalactiae). Bacitacin disk contain 0.04 unit of bacitracin any zone of inhibition considered sensitive. b. Susceptibility to trimethoprim and sulfamethoxazole (STX) used to improve the accuracy of gp A identification both groups A&B are resistant, while BH gp C& G are sensitive to STX.

c. CAMP test used to differentiate gp B from other BH streptococci c. CAMP test used to differentiate gp B from other BH streptococci. Arrowhead shaped area of enhanced hemolysis are formed when 2 streak staph aureus and gp B streptococci approach each other. d. Hippurate hydrolysis : differentiate agalactia (+) from other beta hemolytic strep. Some isolates of gp D give +ve hippurate hydrolysis but are not BH. e. PYR hydrolysis (pyrrolidonyl aminopeptidase) to identify gp A. f. Bile esculin hydrolysis to differentiate gp D & Enterococcus from other Strep (viridans gp) . g. Salt tolerance test : to differentiate gram positive cocci that grow 6.5% (enterococci) from those inhibited by it ( gp D). h. Optochin Susceptibility and bile solubility : used to differentiate S. pneumoniae from viridians gp.