STREPTOCOCCI

y Definition: Gram +ve cocciarranged in chains.

y All Catalase test -ve #

y [ staphylococci] .

y All Oxidase negative #[Neisseria]

 

STREPTOCOCCI

 F-hemolytic streptococci E-hemolysis streptococci Non-hemolytic streptococci

Complete hemolysis of RBCs. Incomplete hemolysis of RBCs

(E-hemolysis)

1- Str. pyogenes (grp A)

y Follicular tonsillitis.

y Scarlet fever.

y ABE (acute bacterial endocarditis)

y Rheumatic fever.

y Post streptococcal glomerulonephritis.

y Streptococcal TSS.

1- Str.viridans.

y Normal oral flora (s subacute BE (SABE))

2- Str. pneumoniae.

y Pneumonia.

3- Strep. faecalis (D)

Strep. faecalis (D)

2- Strep. agalactiae (B)y flora in o genital tractNeonatalsepsis & meningitis.y Pneumonia, endocarditis,arthritis.

3- Strep. faecalis (D)

 

Gram positive cocci in chainsstreptococci

 

Gram positive cocci in chainsstreptococci

 

Gram positive lanceolated diplococci(pneumococci)

 

Staphylococci streptococci pneumococci

 

White coloniesPigmented goldenyellow

 

-- hemolytic streptococci on BAhemolytic streptococci on BA

- hemolytic streptococci on BA

 

- hemolytic streptococci on BA

 

- hemolytic streptococci on BA

 

- hemolytic streptococci on BA

 

- hemolytic streptococci on BA

 

Hemolytic staphylococci on BA

 

Hemolytic staphylococci on BA-- hemolytic streptococci on BAhemolytic streptococci on BA

 

OxidaseCatalase

-ve+ve

 

Catalase

2H2O2 O2 + 2H2OStreptococci vs. Staphylococci

Differential Characteristics

 

Catalase POS

Staphylococcus

Catalase NEG

 

Different i al 

Char act eri st i cs

Optochin test-

bacitr acin test

 

Optochin test

 

Heat resistance test+vestrept faecalis

 

ASO titre

 

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STREPTOCOCCI

 F-hemolytic streptococci E-hemolysis streptococci Non-hemolytic streptococci

Complete hemolysis of RBCs. Incomplete hemolysis of RBCs

(E-hemolysis)

1- Str. pyogenes (grp A)

y Follicular tonsillitis.

y Scarlet fever.

y ABE (acute bacterial endocarditis)

y Rheumatic fever.

y Post streptococcal glomerulonephritis.

y Streptococcal TSS.

1- Str.viridans.

y Normal oral flora (s subacute BE (SABE))

2- Str. pneumoniae.

y Pneumonia.

3- Strep. faecalis (D)

Strep. faecalis (D)

2- Strep. agalactiae (B)y flora in o genital tractNeonatalsepsis & meningitis.y Pneumonia, endocarditis,arthritis.

3- Strep. faecalis (D)

 

2-Serology ( Lancefield ) grouping : 

Antigenic composition of group specific cell wall carbohydrates andbiochemical reactions.

3- DNA  ±DNA hybridization 

- Peptostreptococci (anaerobic)

Normal flora in gut &female genital tract.

Anaerobic infections in abdomen, pelvis, lung, brain.

-Strep. faecalis (D)---enterococcus

 

Pharyngitis and tonsillitis

25

 

Scarlet FeverCaused by Erythrogenic

Toxin secreted by

S. pyogenes

 

C. Schultz-Charlton Reaction

Used for the diagnosis of scarlet fever.

27

 

Streptococcal skin infections

28

 

Antigenic structure

Beta-haemolytic streptococci can be divided into 20

different serologic groups according to C antigen andcertain groups can be subdivided into types according to Mand T protein-antigens:

1- CapsuleThe hyaluronic acid of the capsule is nonantigenic presumably because of its similarityto hyaluronic acid of the animal connectivetissue. So no anticapsular antibodies areformed.

 

2- C ell wall 

a- Group specific carbohydrate (C-Ag)

This antigen is contained in the cell wall of many streptococci and

forms the basis of serologic grouping known as Lancefield

groups A-H and K-U.

b- Proteins

Streptococcus pyogenes produces 3 surface protein antigens (M,T

and R) that are useful in serotyping. Of these three, M proteins

is the most important. It acts as a virulent factor by inhibiting

phagocytosis and is also immunogenic with the formation of anti

M antibody after infection which then enhances phagocytosis.

 

Toxins* & enzymes of  F-strept

1- Streptokinase

2-Streptodornase (Streptococcal DNAase)

It depolymerizes DNA. Mixture of streptodornaseand streptokinaese help to liquefy exudates andfacilitate removal of pus and necrotic tissue,antimicrobial drugs thus gain better access andinfected surface recover more quickly.

3- Hyaluronidase (spreading factor)

It splits hyaluronic acid, an important component of the ground substance of connective tissue. Thus,hyaluronidase aids in spreading infecting microorganisms.

 

4- Streptococcal pyrogenic exotoxin (SPE)

There are 3 antigenically distinct toxins: A, Band C. Type A corresponds to the classicerythrogenic toxin which is associated with therash in scarlet fever. Both types A and C areencoded by bacteriophage gene duringlysogenic conversion, while type B is encodedby chromosomal genes.

These 3 toxins are superantigens, in addition toscarlet fever they have been associated withstreptococcal toxic shock syndrome andnecrotizing fasciitis.

 

Scarlet FeverCaused by Erythrogenic

Toxin secreted by

S. pyogenes

 

Scarlet Fever

y The erythrogenic

toxin is coded by a gene

lysogenic bacteriophage

within the genome of 

S. pyogenes

yRash is an inflammatory reaction tothe toxin

 

5 - H aemolysins

 F-haemolytic group A streptococci elaborate twohaemolysins (streptolysins).

(a) Streptolysin O (SLO)

It is inactivated in the presence of oxygen (oxygenlabile), it is antigenic and antibody to streptolysin Odevelops after infection.

An antistreptolysin O (ASO) serum titre in excess of 160-200 units is considered abnormally high and suggestseither recent infection with streptococci or persistentlyhigh antibody levels due to an exaggerated immuneresponse to an earlier exposure in a hypersensitiveperson. ASO titre helps in the diagnosis of rheumatic fever.

 

Streptococcal tests

36

 

b) Streptolysin S (SLS)

y it is not inactivated by oxygen (oxygenstable), it is responsible for the haemolyticzones around streptococcal colonies onblood agar plate incubated aerobically. It isnot antigenic.

 

Group A Strep

yCapsule -resistantto phagocytosis

y Enzymes damagehost cells

yM protein adhesin

The M protein has many antigenic varieties

and thus, different str ain of S.pyog enes

cause repeat infections

 

Character Pneumococci Viridans streptococci

Morphology Lanceolated diplococci.Short or long chains of 

rounded cocci

Capsule Present Usually absent

Optochin sensitivity Sensitive viR idans R esistant

Bile solubility +ve -

Inulin fermentation +ve -

Mice pathogenicity

+veIntraperitoneal die in

48 hour.-

 

InfectedMiddleEar(otitismedia)

 

Bacterial PneumoniaBacterial, vir al or f ungal infection can cause

Inflammation of the lung with fluid filled

alveoli

 

42

 

The course of bacterialpneumonia

43

 

View of ear anatomy indicatingroute of infection

44

 

Figure 23.4

Bacterial Endocarditis