A Hemo. Stre.

α HEMOLYTIC STREPTOCOCCI

KELVIN B. SUREJA ROLL NO. 87

CLASSIFICATION • 3 types of streptococci – α HEMOLYTIC - STREPTOCOCCI – β HEMOLYTIC - STREPTOCOCCI – γ HEMOLYTIC - STREPTOCOCCI

α HEMOLYTIC STREPTOCOCCI • •

Exhibit incomplete hemolysis which impairs greenish discoloration around the colony. It includes 2 species 1. Streptococci pneumoniae (Pneumococci) 2. Viridans streptococci

Streptococcus pneumoniae ( Diplococcus pneumoniae)

Pathogenesis of S. pneumoniae infections

lobar pneumonia otitis media sinusitis bacteremia meningitis arthritis Streptococcus pneumoniae is currently the leading cause of invasive bacterial disease in children and the elderly.

Morphological Characteristics of S. pneumoniae • Gram-positive, lancet-shaped cocci (elongated cocci with a slightly pointed outer curvature)

• Usually seen as pairs (diplococci) • Individual cells range from 0.5 to 1.25 micrometers in diameter • Non motile; non spore-forming • Capsulated

• Catalase-negative

Cultural characteristics: • Fastidious bacterium,aerobic and facultatively anaerobic grows best in 5% carbon dioxide • Enriched medium :Usually cultivated in blood broth or on blood agar • Some fresh clinical isolates require fully anaerobic conditions • Growth requires a source of catalase (e.g. blood) to neutralize the large amount of H2O2 produced by the bacteria.

Cultural characteristics: • A zone of alpha (green) hemolysis seen on blood agar

• Serotype 3 and 7 produce mucoid colonies Production of excessive capsular polysaccharides • Liquid medium - uniform turbidity Cotton wool deposit by non capsulated variants

Identification of pneumococci from other streptococci • Gram-positive staining • alpha hemolysis • bile solubility (deoxycholate lysis) • optochin sensitivity

Cell Surface Structure Capsule • composed of polysaccharide • interferes with phagocytosis by preventing C3b opsonization

Cell Surface Structure

Surface Proteins • Five penicillin binding proteins (PBPs) • Two neuraminidases • IgA protease : organisms colonize pharyngeal mucosa

Pathogenicity Capsule : Viulence Common Infecting types: Types 1-12 in adults Types 6,14,19,23 in children Types 1,3,7,8 and 12 : Invasive types,serious infections 3 : most virulent Predisposing factors: Abnormality of respiratory tract : Viral infection etc… Alcohol or Anesthesia :Convulsions decrease cough reflex Circulatory problems: Pulmonary oedema Others: Malnutrition,Sickle cell anemia,Hyposplenism..

Complications Death occurs in 14% of hospitalized adults with invasive disease.

Transmission Person to person, by aerosol

Treatment

Prompt treatment with beta lactam antibiotics is usually effective. However, the number of penicillin-resistant pneumococcal infections is increasing. These cases require treatment with more powerful antibiotics or combinations of antimicrobial agents.

VIRIDANS STREPTOCOCCI • •

It typically shows α hemolysis on blood agar but some strains are non-haemolytic. General property – –

Micro aerophilic Protein rich medium is required for growth

• Principal species 1. S. mitis – Endocarditis 2.S. sanguis - Endocarditis 3.S. mutans – Endocarditis & Dental carries 4.S. salivarius – rarely Endocarditis