Streptococci

1. Streptococci & Enterococci
College Applied Medical Sciences
Department Medical Laboratory Sciences

2. Objectives:
• Describe the morphological and physiological characteristics of genus
Streptococcus
• List the features by which Streptococcus pyogenes, Streptococcus
agalactiae, Viridans Streptococci, and Entrococcus can be identified.
• Describe the spectrum of diseases caused by various Streptococcus.
• Describe different laboratory diagnostic techniques for Sterptococcus.

5. Streptococcaceae
General Characteristics:
• The Streptococcaceae consist of a large family of medically important
species including Streptococcus spp. and Enterococcus spp, many of
these organisms are commonly found as part of normal human flora
• Streptococci are Gram-positive cocci arranged in chains or pairs and
non motile
• Streptococci are catalase negative

6. • This group of organisms are differentiated based on cell wall structure,
hemolytic patterns on blood agar (beta, alpha, or gamma), the reaction
of antibodies to specific bacterial antigen, Lancefield classification
scheme, and , and biochemical identification relating to physiologic
characteristics.
• Most commonly encountered in infections in humans include
Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus
pneumoniae, Enterococcus faecalis, and the viridans streptococci
group.

7. Streptococci classification:
➢According to hemolysis: Some streptococcal species can completely
hemolyze red blood cells, while other species partially hemolyze the
RBC’s, therefore Streptococci are divided into 3 groups based on their
hemolytic ability.
▪ Beta hemolytic streptococci:
Completely lyse the RBCs, leaving a clear zone
of hemolysis around the colonies.
▪ Alpha hemolytic streptococci: Partially lyse
the RBCs, leaving greenish coloration surrounding the colonies.
▪ Gamma hemolytic (non-hemolytic) streptococci:
They cannot lyse the RBCs

8. ➢According to carbohydrates antigens on the cell wall:
These antigens are called Lancefield antigens, and they are given letter names (A-
H, and K-U) is used to divide streptococci into stereological group Lancefield
groups. Typing is done only for A, B,C,F and G. group A or S.pyogenes is the most
important as it causes several human diseases

9. Streptococcus pyogenes
Group A Streptococci (Beta hemolytic)
• Rosenbach (1884) isolated the cocci from human suppurative lesions
and gave them the name Streptococcus pyogenes.
Normal habitat:
S. pyogenes may be carried in the upper respiratory tract of humans, it is
not considered to be normal flora and should be deemed clinically
important whenever it is encountered
Mode of transmission:
Direct contact: person to person
Indirect contact: aerosolized droplets from coughs or sneezes

10. Virulence factors:
▪ M-Protein: antiphagocytic
▪ Protein F mediates epithelial cell attachment (fibronectin-binding)
▪ Pyrogenic exotoxin:
• Pyrogenic exotoxin A (erythrogenic toxin ) This is a toxin
produced by group A streptococci, and it causes scarlet fever
• Pyrogenic exotoxin B: destroy tissue(necrotizing)
Pathogenicity

11. ➢Enzymes:
▪ Haemolysins: there are two types
Streptolysin S: It is oxygen stable, also responsible of beta
hemolysis, but it is not immunogenic capable of lysing erythrocytes,
leukocytes, and platelets in the presence of oxygen.
Streptolysin O: This is oxygen labile enzyme(is broken down by
oxygen), capable of lysing the erythrocytes, leukocytes, and platelets,
and will produce haemolysis only in the absence of oxygen It is
immunogenic after infection anti-streptolysin O antibodies were
developed.

12. Diseases and infections:
➢Pyogenic local infections:
• Streptococcal throat infection or pharyngitis: enlarged
tonsils with purulent exudate. Pyoderma (impetigo): skin
infection characterized by the formation of blisters
➢Invasive disease:
• Acute bacterial endocarditis
• Puerperal sepsis infection of the uterus after delivery
associated with septicemia

13. ➢Toxigenic disease:
• Scarlet fever in children associated with pharyngitis and
rash due to erythrogenic toxin
• Streptococcus toxic shock syndrome
➢Post streptococcal immunogenic infection:
• Acute rheumatic fever (Cross-reactions of antibodies
produced against streptococcal antigens and human heart
tissue)
• Acute glomerulonephritis (Deposition of antibody-
streptococcal antigen complexes in the kidney)

14. Identification:
❖Specimens according to the site of infection
• Blood for blood culture (bacteriemia, septicemia, and endocarditis)
• Throat swab from the lesion (pus)
❖Antigen detection test: using Enzyme-linked immunosorbent
assay(ELISA) or agglutination test.
❖Serological test: Antistreptolysin O (ASO) titer is high soon after
group A streptococcal infection. An elevated ASO titer of more than
200 units indicates a recent streptococcal infection

15. ❖ Cultural characteristics:
Culture media:
• Culture on blood agar, chocolate blood agar
• Selective media crystal violet blood agar
Incubation condition optimum temperature 37°C. they are aerobic
bacteria or facultative anaerobic.
Colonial appearance:
• On blood agar colonies show complete hemolysis(Beta
hamolysis).

16. Biochemical reactions:
▪ Catalase negative
▪ Bacitracin sensitivity test: sensitive to bacitracin
Treatment: Penicillin G is the drug of choice if the patient has an
allergy to clindamycin or erythromycin is used

17. Group B streptococci (streptococcus agalactiae)
Normal habitat:
Inhibit about 25% of the normal adult vaginaand lower gastrointestinal tract
Mode of transmission:
• Endogenous strain: gaining access to the sterile site(s) probable
• Direct contact: person to person from mother in utero or during delivery
• Nosocomial transmission by unwashed hands of mother or health care
personnel

18. Pathogenicity:
Virulence factors:
Uncertain; capsular material interferes with phagocytic activity
Diseases and infection:
• Neonatal meningitis, pneumonia, and septicemia (infants can acquire
S.agalactiae during delivery )
• Pneumonia and endocarditis (in adult)

19. Identification:
• Specimens Vaginal Swab, blood, CSF, ear swab
• Beta hemolytic on blood agar
• Bacitracin resist
• Hydrolyses Hippurate and are CAMP factor positive

20. Streptococcus pneumoniae
Alpha hemolytic (No Lancefield antigen)
Morphology: Gram positive cocci arranged in pairs (diplococci),have
lancet shape (fusiform pointed ends) they are capsulated, capsules may
appear as unstained haloes around the organism
Inhabitant: normally carried in upper respiratory tract of healthy
persons

21. Pathogenicity:
Virulence factors:
• The major virulence factor of S. pneumonia is its polysaccharide
capsule which protects the bacteria from phagocytosis.
• secretory IgA protease
Diseases and infection:
• Bacterial pneumonia
• Meningitis
• Sinusitis and otitis media

22. Viridans streptococci (Alpha hemolytic)
• This is a large group with no Lancefield antigen, including S.
mutans, S.mitis.
• Inhabitant: They are normal flora of the oral cavity,
gastrointestinal tract, and female genital tract

23. • Pathogenicity :
• Virulence factors: Generally considered to be of low virulence;
• production of extracellular complex polysaccharides (e.g., glucans and
dextrans) enhances attachment to host cell surfaces, such as cardiac
endothelial cells or tooth surfaces in the case of dental caries
• Diseases and infection: dental infections and endocarditis.

24. Identification of Streptococcus pneumoniae and Viridans streptococci
• Both are alpha-hemolytic
• Differentiated by: Bile solubility test and optochin disc sensitivity
test
• Streptococcus pneumoniae: soluble in bile, sensitive to optochin
antibiotic disc.
• Viridans streptococci: not soluble in bile, resist optochin antibiotic
disc

25. Group D streptococci
(Entrococci and non-entrococci)
• These are alpha-hemolytic, eg. Enterococcus faecalis
Inhabitant: It is a normal flora of the intestine
Pathogenicity :
• Virulence factors:
• Adhesions, cytolysins, and other metabolic capabilities may allow these
organisms to proliferate as nosocomial/healthcare-associated pathogens
• Diseases and infection:
• Most infections are healthcare–associated and include urinary tract
infection, wound infection, and endocarditis.,

26. Identification:
• Grow in MacConkey gives pink colonies, and it can grow in the
presence of 40% bile. grow in 6.5% NaCl
• Hydrolyze polysaccharide esculin(bile esculin positive)

27. Questions
➢Describe Morphology & physiological characteristics of Streptococcus?
➢Classify the streptococcus on the basis of Hemolysis?
➢Describe medically important Streptococci & their characteristics?
➢Describe Lab Diagnosis of Streptococci?
➢Differentiate between Streptococci and Staphylococci?
➢List virulence factors or Streptococci?
➢Group D streptococci is ……………hemolytic.
➢Viridans streptococci is …………hemolytic.
➢Why streptolysin S cannot be used for diagnosis?
➢How can we differentiate between Streptococcus pneumoniae and Viridans
streptococci?
➢25% of women carry this type of Streptococci in their reproductive
systems ?………………….
➢……………Streptococci cause similar infections as Staphylococcus aureus?