Streptococcus Bacteria

Streptococcus Bacteria Dr.Younis A.Al-Khafaji
Streptococci are gram positive , spherical, pair or chain in form, wide distributed in nature, some of them are members of normal human flora, other are associated with important human disease.
Other characteristic …….>* Most group A, B, and C strains produce capsules.
*Streptococci grow on solid media as discoid colonies, 1-2mm in diameter , but colonies of capsule producing strains are often mucoid
*Peptostreptococci is an obligatory anaerobes
*Streptococci need enriched media which contain blood or tissue fluid .
* Streptococci need 10 % CO2 for its growth and hemolysis at 37 •c, whereas group D streptococci ,(Enterococci) grow well at between 15 – 45•c.
Enterococci also grow in high (6.5%)NaCl concentration , 0.1% methylen blue and in bile esculin agar.
Most streptococci are facultative anaerobes.
Streptococci are catalase negative , one of the most important characteristic of Streptococci used for identification is the type of hemolysis. There are three type of hemolysis:
a- Alpha hemolysis (?) mean incomplete lysis of RBC, characterized by ((green zone)) round colony on blood agar culture.
b- Beta Hemolysis (?) mean complete lysis of RBC, characterized by (( clear zone)) round colony on blood agar culture.
c- Gamma hemolysis ( ?) ornon hemolysisClassification of ***Lancefield classification of Streptococci according to type of hemolysis***
A - Beta hemolytic streptococci: Which are arranged into groups (A-U) (A-H and K-U ) on the basis of antigenic difference in C The carbohydrate of the cell wall , for example group A- streptococci
….Streptococcus pyogenes …...causing pharyngitis .
Group B – streptococci ……..S.agalactia causing newnatal meningitis, normaly present ingenetal tract of monen.
Group D – streptococci Which include:
a- Enterococci , for example Enterococcus fecalis
b-Non Enterococci for example Streptococcus bovis
*Enterococci grow in 6.5 % NaCl , while non Enterococci inhibit.
* Enterococci not killed by penicillin G while non Enterococci killed.
B-Non- Beta –Hemolytic Streptococci
Some produce no hemolysis , other produce alpha hemolysis example Streptococcus pneumonia and viridance group of streptococci ( S.mitis,
The following table showing the main differences between Streptococcus pneumonia and viridance group of streptococci
S. pneumonia viridance group of streptococci
1- Arranged in pairs 1- arranged in long or short chain
2- Bile soluble (in 2%sodium 2- non bile soluble
deoxycholate)
3- Sensitive to optichin 3- non inhibited by optichin
4- Capsulated 4- non capsulated
5- Cause pneumonia , meningitis; 5- non pathogenic mostly, and
Respiratory tract infection. some of them are normal flora
of oral cavity
6- Alpha hemolysis 6- alpha hemolysis

C-Peptostreptococci : They are grow under anaerobic or microaerophilic condition, produce variable hemolysis; they are member of normal flora of gut and female genital tract.
Transmission : Most Streptococci are part of microflora of human throat , skin , and intestine but produce disease when gain access to tissue or blood .
Pathogenesis : Group - A Streptococci (S.pyogenes) cause disease by three mechanisms:-
1- Inflammation 2- Exotoxin production 3- Immunologic
Streptococci causes different type of disease but the most common disease diseases are :-
1- Rhomatoid fever
2-Scarlet fever
3-Endocarditis
4-Pharyngitis
5-Various skin disease ( examples Erysiplas, necrotizing fasciitis and impetigo ).
6-Glumerulonephritis and other urogenetal tract infection like endometritis, and urinary tract infection.
Diagnosis :
Laboratory diagnosis of Streptococcal infection include :-
1- Specimens collection , which depend upon the nature of streptococcal infection …., throat swab, pus; or blood for culture.
2- direct smear for Gram staining , in which the presence of Gram positive cocci is indicative in specimens collection from site of infection other than regions of normal flora.
3- serological test are use for estimation of anti- streptolysin – O (ASO- titer ) and titer of anti- DNase B which are indicative of previous infection in patient suspected having acute glomerulonephritis .
4- Isolation of the microorganism by using culture media.
The most important species of Streptococci
Streptococcus pyogenes They are aerobic bacteria , on blood agar culture we see beta hemolysis , this microorganism produce several enzymes and toxins which include :-
a- Erythrogenic toxin ,which cause scarlet fever.
b-Streptolysin, which are on two types :-
1-Streptolysin –O (oxygen Labile)
2-Streptolysin –S (oxygen stable)
c-Hyalurodinase which act as a spreading factor
d- Pyrogenic exotoxin A causing Streptococcal toxic shock syndrome
e- Exotoxin B , a protease that rapidly destroy tissue causing necrotizing fasciitis .
2- Streptococcal agalactia ……., They are Beta hemolytic bacteria but with narrow zone of hemolysis.
*Normally inhibit genital tract of women but under certain circumstances they induce disease in human, like neonate meningitis and endocarditis.
* It produce pigments under certain circumstances on certain media ( Colombia media).
3- Streptococcus fecalis ( Enterococcus fecalis) ** This bacteria are member of flora of the gut so it is a friendly bacteria.
** They are non hemolytic
*** Also produce sex pheromone which stimulate bacterial aggregation which can be used for differentiation between bacteremia and septicemia.