Streptococci

1. Streptococci

2. Streptococcus • Gram positive spherical or ovoid cells, arranged in chains or pairs • Non spore forming, • Non-motile • Some species form capsules of polysaccharides or hyaluronic acid • Small, non pigmented colonies • Most streptococci are facultative anaerobes, and some are obligate (strict) anaerobes. • Do not form catalase

3. Freshly isolated Streptococcus 3

4. Classification • Based on their hemolytic properties on blood agar • Lancefield Grouping • species-specific CHO cell wall antigens • groups designated A-H, K-V • some not groupable (e.g., Streptococcus pneumoniae and viridians streptococci).

5. Human Streptococcal Pathogens • S. pyogenes • S. agalactiae • Viridans streptococci • S. pneumoniae • Enterococcus faecalis

6. Streptococcus pyogenesPyogenes means pus producing • Inhabits throat, nasopharynx, occasionally skin • It is the main human pathogen associated with local or systemic invasion and poststreptococcal immunologic disorder. • Gram positive cocci in chains • Lancefield Serological Group A • Beta Hemolytic on blood agar

9. Clinical disease: • pharyngitis (streptococcal sore throat), osteomyelitis, endocarditis, septic arthritis, and meningitis. • It may also infect the skin, causing erysipelas, impetigo, or cellulitis. • two autoimmune diseases, rheumatic fever and acute glomerulonephritis. • Other toxigenic S. pyogenes infections may lead to streptococcal toxic shock syndrome, scarlet fever.

10. Laboratory diagnosis 1-Blood agar: very small, white to grey colonies approximately 1mm in diameter surrounded by a zone of beta hemolysis. 2- Sensitive to bacitracin. 3-Serological test: streptolysin O stimulate Anti- streptolysin O (ASO) antibody:ASO test) is indicative of previous pharyngeal infection.

11. 2-Group B streptococci (GBS or Streptococcus agalactiae): • Often found in the upper respiratory tract and genitourinary tract of healthy adults • Gram-positive cocci • Typically form short chains in clinical specimens and longer chains in laboratory media. • A small zone of beta hemolysis on Blood agar, although some strains are non-hemolytic. • Resist to bacitracin.

12. Streptococcus Pneumonia • Gram positive, They typically appear as a diplococcus • Alpha hemolytic, • Not of lancefield serotype • Often part of normal flora of respiratory track and becomes infective once hosts resistance is lowered. Classified as an endogenous infection.

14. Strep Pneumonia

15. Cultivation and Diagnosis • Gram stain of specimen – presumptive identification • a-hemolytic • optochin sensitivity • Quellung test or capsular swelling reaction   The test consists of mixing a loopful of colony with equal quantity of specific antiserum and then examining microscopically at 1000X for capsular swelling. • bile solubility

16. Hemolysis patterns on blood agar

17. Identification Not optochin sensitive Optochin sensitive

18. 4-The Viridans Streptococci: • Normal flora in the upper respiratory tract. • alpha hemolysis or no hemolysis on Blood agar • Do not possess Lancefield group antigens. • Cases 50% and 70% of the bacterial endocarditis, especially in people with previously damaged heart valves. They are also frequently associated with bacteremia, deep wound infections, dental abscesses

19. 5-The Genus Enterococcus (Enterococcus faecalis): • Enterococci are streptococci typically occurring in pairs and short chains • Lancefield group D streptococci, these are non-hemolytic (gamma) • Normal colonists of human large intestine • Cause opportunistic urinary, wound, septicemia and endocarditis • hydrolyze esculin and grow in the presence of 40% bile salts

20. Laboratory diagnosis: • To distinguish group D streptococci, the Bile Esculin agar method is performed. • Enterococci grow in the presence of the bile salts in the medium. They hydrolyze the esculin, producing esculetin which reacts with the iron salts in the medium turning the agar black