STREPTOCOCCUS

Gram positive cocci arranged in chains or pairs.
They cause pyogenic infections with a characteristic tendency to spread unlike staph(which typically localize)
Billroth called them streptococci (Strepto meaning twisted or coiled)
They cause Non Suppurative lesions, acute rheumatic fever & glomerulonephritis.
Streptococci are first divided into obligate anaerobes & facultative anaerobes.
Streptococci are classified on basis of hemolytic properties; Alpha , Beta , Gamma.
Most pathogenic strepto fall into group Beta & called as hemolytic strepto cocci.
Alpha strepto cocci are generally commensals in throat and produce opportunistic infections called as viridance group(green).
Gamma strepto cocci include fecal strepto cocci.

MORPHOLOGY
Gram positive cocci in chains , 0.5 – 1 um in diameter.
They are non motile and non sporing.
Group C strains have some capsules.

CULTURE
Aerobic and facultative anaerobe.
Grows best at 37 degrees C (range – 22 to 42 degree C)
They have exact nutritive requirements, growth occurring in media with blood ,serum or sugars.
Colonies are small (0.5 to 1 mm) circular ,semi transparent & low convex with a wide zone of beta hemolysis.
Hemolysis is promoted by 10% CO2.
Virulent strains form “matt” colonies,
Avirulent strains form glossy colonies.

RESISTANCE
Delicate organisms and inactivated by heat at 56 degree C for 30 minutes.
They survive in dust for several weeks if protected from sunlight.
It is rapidly inactivated by antiseptics.
Its more resistant to crystal violet than many other bacteria.
They do not develop resistance to drugs. (unlike staph)
They are sensitive to bacitracin.

ANTIGENIC STUCTURE
1) Capsular Hyaluronic Acid
2)Group Specific Polysaccharide Antigen
3)Type Specific Antigen
M,T&R proteins

TOXINS AND OTHER VIRULENCE FACTORS
Hemolysins
There are two types of hemolysins: O and S
Streptolysin O:
Lyses red cells ,cytotoxic for neutrophils platelets and cardiac tissue.
It is antigenic and antistreptolysin O appears in sera post streptococal infection.

Estimation (ASO titre) standard serological procedure for the retrospective diagnosis.
ASO titre > 200 units suggest either recent or recurrent streptococcal infection.
Streptolysin S:
Oxygen stable.
Responsible for haemolysis in blood agar.
It is a protein but not antigenic.
Pyrogenic exotoxin (erythrogenic, dick, scarlatinal toxin)
Three types of streptococcal pyrogenic exotoxin (S P E) A,B & C
SPE ‘s are SUPERANTIGENS (induce massive release of cytokines causing fever, shock & tissue damage)
Streptokinase(Fibrinolysin)
It breaks down fibrin barrier around lesions and spreads the infection.
Streptokinase IV given as RX in early myocardial infarction and other thromboembolic disoders.

Deoxyribonucleases(stretodornase,DNAase)
Stretodornase liquefies the thick pus.
This property apply therapeutically in liquefying thick exudates as in empyema.
There are four types of DNAases A,B,C &D.
Nicotinamide adenine dinucleotidase (NADase, formerly diphosphopyridine nucleotidase, DPNase)
It is leucotoxic.
It is antigenic.
Hyaluronidase
Breaks down hyaluronic acid of tissues and spread the infection along intercellular spaces.
It is semingly self destructive process.
It is antigenic.
Serum opacity factor (SOP
PATHOGENICITY
Streptococcus pyogenes is intrinsically much more dangerous organism than staph aureus and has much greater tendency to spread in the tissues.
It is more likely to give septicaemia.
Carriers(5% )of general population carry S pyogenes in resp tract , mouth & skin.
Carrier rate is higher in children between 1 to 15 years of age.
Carriers and patients with acute infections are the sources of infection.