Streptococci pdf - ...

True bacteria – Cocci- Gram positive cocci

Streptococci

Most of Strep. species are commensal resident of mouth, throat, so

several may act as opportunistic pathogens, also few spp. like

Strep. pyogenes and Strep. agalactiae act as primary pathogen.

Classification of Streptoccoci

Strep. are classified by 2 major methods:

1- Classification by hemolytic activity:

The initial classification of the Strep. depends on the type of

hemolysin produced on blood agar (under anaerobic conditions about

(5-10 % Co

): (Figure 1).

a- Strains that produce soluble hemolysin(Streptolysin O or S)

colonies that produce streptolysin causing complete clearness around
the colony in blood agar are called β-hemolytic Streptococci e.g
Strep. pyogenes, Strep. agalactiae.

b- Strains that produce insoluble hemolysin which causes partial lysis
called α-hemolytic Streptococci e.g Strep. pneumonia, Strep.viridans.
c- Starins that are non-hemolytic, give no change around the colonies
called γ-hemolytic streptococci e.g Strep. faecalis.

2- Serological classification (Lancefield classification).: (Figure 2)

Made by Lancefield, based on the presence of polysaccharide

antigen

called

"C-substance" or "C-carbohydrate" present in the cell wall which differ

from group to another .A,B,C,D which are implicated in human

infections, and E,F,H,G and K-U which are implicated in animal

infections.

 Group A causes tonsillitis in human.
 Group B causes mastitis which is transmitted from cows to human

through contaminated milk.

 Group C causes strangles disease which transmitted to human from

horses.

 Group D which are enterococci present as normal flora in intestine

of human.

All above are β- hemolytic Strep. and the clinical important groups

are types A and B.

Antigenic Structure of Streptococci:

Several antigentic substances are formed in the hemolytic Strep. cells:

1- Group-Specific cell wall antigen

This carbohydrate is contained in the cell wall of many

Streptococci and forms the basis of serologic grouping

(Lancefield A-U)which is determined by an amino sugar which

are:

 Group A Rhamnose-N- acetylucosamine.
 Group B Rhamnose-glucosamine polysaccharide.
 Group C Rhamnose-N-acetylgatasamine.
 Group D glycerol techoic acid containing D-alanine and glucose.
2- M-protein

This protein is associated with virulence of group A and occurs

in organisms producing mucoid colonies.This protein resists the

phagocytosis.

3- T- substance

This antigen has no relationship to virulence of Strep. and used

to differentiate between certain types of Strep. by agglutination

with specific antisera.

4- Nucleoproteins (P-substance)

That make up most of the Strep. cell body and a little of serologic

specificity.

Groups of Streptococci

A- β-hemolytic Streptococci

1) Group A Streptococcus pyogenes

is the human pathogen of primary importance, produce human

respiratory infection, such as Tonsillitis, bronchopneumoniae, scarlet

fever, erysipelas, cellulitis, glomerulonephritis and rheumatic fever.

Group A are usually bacitracin sensitive.

2) Group B Streptococcus agalactiae

are endogenous to the vaginal mucosa and been responsible for

puerperal fever, fatal neonatal meningitis and endocarditis.This group is

rarely bacitracin sensitive.

3) Group C and G

Causes erysipelas, puerperal fever, throat infection, sinusitis,
bacteremia or endocarditis, occur sometimes in pharynx and produce β-
hemolysin on sheep blood agar e.g. Strep. equisimilis and Strep.equi

4) Group D

Includes Enterococci, e.g. Strep. faecalis and non-Enterococci,e.g.,

Strep. bovis produces α and γ hemolysin which may causes UTI or

endocarditis.

5) Group E, F, H and K, U

Occur primarily in animals others can infect humans.

B- Non β-hemolytic Streptococci

These usually produce α-hemolysis or no hemolysis on blood agar.

This group includes:

1- Strep. pneumoniae (pneumococci)

(1) bile soluble , (2) inhibited by optochin disks , (3) Quellung

reaction positive (capsule swelling test) (4) can cause pneumomia and

other infection processes.

2- Strep. viridans

(1) not bile soluble , (2) not inhibited by optochinn disks , (3) Quellung

reaction negative, (4) they are normal flora in upper respiratory tract in

human and may cause endocarditis.

C- Peptostreptococci

They are members of the normal flora of the gut and female genital

tract, grow under aerobic or microaerophilic condition and produce

variable hemolysin.

Group A Hemolytic Streptococci :

The most clinically important species of this group is Strep.

pyogenes it can invade in the skin or mucous membrane and cause

infection .

Structural Features :

These are involved in the identification of Group A Streptococci:

Capsule:

Hyaluronic acid resemble to that found in human connective tissue,

it is not recognized as foreign by the body, so it is non-immunogenic.

Cell wall:

Contains no. of clinically important components:

a. Fimbriae: contain the major Strep. pyogenes virulence factor,

the M protein .

b. Group A specific C-carbohydrate: composed of rhamnose &

N-acetylglucoseamine (all gp A Strep. contain this antigen).

c. Protein F (Fibronectin binding protein): which mediated

attachment to fibronectin in pharyngeal epithelium .

Extracellular products play a role in the pathogenesis (Figure3)

More than 20 extracellular products (exotoxins) that are antigenic are

produced by group A Strep. including :-

1- Streptokinase (Fibrinolysin)

produced by many strains of group A hemolytic Strep. Transforms

the plasminogen of human plasma into plasmin, which is an active

proteolytic enzyme that digests fibrin and other proteins.

2- Streptodornase (DNase)

This E. depolymerizes DNA in exduates and purulent exudates,

their viscosity to deoxyribonucleoprotein, both streptokinase and DNase

help to liquefy exudates and facilitate removal of pus and necrotic tissue,

both enzymes are used for diagnosis test of Strep. in general.

3-Hyaluronidase

E. splits hyaluronic acid, an important component of connective

tissue. This hyaluronidase aids in spreading infecting microorganisms

(Spreading factor), it's antigenic.

4- Diphosphopyridine Nucleotidase

E is kill leukocytes. Proteinase and

amylase are produced by some strains.

5-Erythrogenic Toxin (Pyrogenic exotoxins)

It causes the rash in scarlet fever and

elaborated

lysogenic

Strep.

(Strep.

pyogenes) also called Dick toxin, and detected

by dick test (anti toxin).

6- Hemolysin

β-hemolytic group A Strep.

pyogenes

elaborates

two

hemolysins

(streptolysins):

a- Streptolysin O= labile and inactivated in

, this antigen is responsible for the produce

of Ab called (antistreptolysin O) (ASO) in

human following infection and act as a titers

for diagnosis if the serum titers of 160-200

units suggests recent infection.

b- Streptolysin S=stable in O

and causes

hemolytic zones around Strep. colonies on

blood agar this is not antigenic.

Clinical Findings

A- Disease due to invasion : by β-hemolytic

group

(A)

such

Strep. pyogenes : Pathogenicity is determined

by (1) portal of entry of the Strep., (2)

diffusion of spreading of Strep. to different parts of the body (3) extend

along lymphatic pathways → to the blood stream.

1- Erysipelas

If the portal of entry is the skin, erysipelas results with massive

brawny edema, and rapidly advancing margin of infection.

2- Puerperal fever

If the Strep. enters the uterus after delivery, puerperal fever

develops which is essentially a septicemia originating in the infected

wound.

3- Sepsis/ bacteremia

Infection of traumatic or surgical wounds with Strep. results in

bacteremia/ sepsis, which can be fatal rapidly.

B- Diseases due to local infection: by



-hemolytic group (A)

1- Streptococcal sore throat

Patients have intensive nasopharyngitis, tonsillitis and intense redness

and edema of the mucous membrane, with purulent exudates, and usually

a high fever.If the infecting Streptococci produce erythrogenic toxin

scarlet fever rash will be produced.

2- Streptococcal pyoderma

Local infection of superficial layers of skin, in children, called
“impetigo”.

C- Infection of endocarditis

1- Acute endocarditis

Rapid destruction of the valves leads to fatal cardiac failure.

2- Subacute endocarditis

Due to members of the normal flora of respiratory or intestinal tract

that have accidently reached the blood.

D- Other infection

Various

Strep.,

such

Enterococci

can

cause

UTI,

Peptostreptococci which occurs in the female genital tract, the gut and

intestine causes suppurative lesion in the genital tract of the female.

E- Post streptococcal disease

1- Acute glomerulonephritis

occurs after 3 weeks of the infection by Strep. group A and about

23% of children with skin infection with type 49 strain develops nephritis

or hematuria.

2- Rheumatic fever

This is the most serious of Strep. group A infections, because it

results in damage to heart muscles and valves, appears after 1-4 weeks of

infection, causes a complex infection all parts of the heart (endocardium
– mycocardium – pericardium).

Diagnostic laboratory tests

Specimens : depend upon the nature of Strep. infection, as swab, pus,

blood is obtained for culture. Serum is obtained for Ab determination.

Microscopic examination

: G+ spherical or ovoid bacteria that are

arranged in chains of varying length, nonsporing , nonmotile

,noncapsulated .

Macroscopic examination

: facultative anaerobes require enriched

media as blood agar for growth. On blood agar incubated aerobically

and anaerobically to show the type of hemolysis and colonial

appearance. catalase negative

Strep. group A sensitive for bacitracin .

Serologic test : by using ELISA, or Agglutination test, also

antistreptolysin

(anti

ASO)

respiratory

infections,

antihyaluronidase in skin infection. Antistreptokinase, anti-M type –

specific Abs and others of these. The anti ASO titer is most widely

used.

Treatment

All



-hemolytic group A Strep. are still susceptible to penicillin G

and most are sensitive to erythromycin.

In endocarditis, which caused by enterococci, a combination of

penicillin G and aminoglycoside is used as treatment.

Penicillin prophylacticin is given to person with rheumatic fever, to

prevent recurrence of the disease (monthly for several years).

Amoxicillin is used for dental procedure.

Streptococcus agalactiae (group B,



-hemolytic)

Found as normal flora in vagina in 5-25% of woman and in

urethral mucous membranes of male carriers as well as in the G.I.T.

Their colonies on blood agar are larger and less hemolysis than Group



-hemolytic Strepococci (Strep. pyogenes).

It can transfer from infected mothers to infants at birth and may cause

(1) meningitis and septicemia in neonates with high mortality rate,

(2) endocarditis endometritis,

(3) septicemia or pneumonia in impaired immune systems individuals .

(4) diabetic foot infections.

Sensitive to penicillin G and ampicilline. Strep. group B resistant

for bacitracin .

Streptococcus pneumonia

Antigenic Structures

It posses a number of Ags:

A- The capsular polysaccharides (SSS)

Specific

Soluble

Substance

capsulated

form.

Capsular

polysaccharides are used to determine the type specificity of organisms

and virulence.Typing can carried out by:

1- Agglutination of cocci with type – specific antisera (Ag + Ab

reaction).

2- Precipitation of capsular polysaccharide with specific serum.

3- Capsular swelling reaction (Quellung reaction). Suspension of

pneumococci is mixed with specific anti-polysaccharide serum of

the same type or the polyvalent antiserum on slide, the capsule

swells.This reaction useful for rapid identification and for typing of

the microorganism (Figure 4).

B- M- Protein

It's characteristic for each type of Strep. pneumonia

C- Group – Specific Carbohydrate

This is common in all pneumococci , which it can be precipitated by

(c-reactive proten) in the serum of patients.

Toxin and Virulence Factors

1- Pneumolysin O

an oxygen sensitive toxin, cytolytic for cells.

2- Neuraminidase

E degrades surface structure of host tissues.

3- Capsular polysaccharide
It’s  SSS  which  protects  the  microorganism  from
phagocytosis and has association with virulence.

4- C- substance

The cell wall of pneumococci contain teichoic acid

(C-sub) that react with a certain antiserum protein,

C- reactive protein (CRP) and causes activation of

some nonspecific host immune response.

5- Leucocidin

Kills leukocytes W.B.C.

Pathogenesis

It’s a normal flora of nasopharynx and

oropharynx in 15% of children and 5% of adults.

They produce disease through their ability

to  multiply  in  the  tissues  and  the  virulence  of
pneumococci  is  a  function  of  it’s  capsule  which
prevents ingestion  by phagocytes.

The normal respiratory mucosa posses

natural resistance to the pneuomococci, many

factors lower this resistance and predispose to

infection, like:

1- Respiratory viral infection, bronchial obstruction, respiratory tract

injury, alcohol or drug intoxication .

2- Organism passes from person to another via respiratory secretions and

aerosols.

Clinical Findings

The onset of pneumococcal pneumonia is usually sudden with

fever, chills and sharp pleural pain, with blood or rusty sputum. In the

early disease, when the fever is high, bacteremia is present in about 10-

20% of cases, causes severe complication as meningitis, which is the

most serious infection common in children, endocarditis, septic arthritis.

1- Acute bacterial pneumonia

A leading causes of death in the aged and those whose resistance is

impaired. This disease caused mostly by Strep. pneumonia. Pneumonia is

preceded by an upper or middle respiratory viral infection, which

predisposes to Strep. pneumonia infection of pulmonary parenchyma, by

the mechanisms of:

1) increased volume and viscosity of secretions that are more difficult to

clear,

2) Secondary, inhibition of the action of bronchial cilia by viral infection.

2- Otitis media

Which is the most common bacterial infection of children, is most

caused by pneumococcus,followed by Haemophils influenza and

Moraxella catarrhalis

The traditional treatment of it with a



-lactam antibiotics (with or

without a penicillinase – inhibitor) has been threatened by the spread of

penicillin – resistant pneumococci.

3- Bacteremia/ sepsis

In the absence of a focus of infection is commonly caused by

pneumococcus, especially in splenectomized individuals.

4- Meningitis

H. influenzae was leading cause of bacterial meningitis in U.S.

After a vaccine was developed against this organism, Strep. pneumonia

became the most common cause, which is high mortality rate even when

treated.

Laboratory identification (Table 1) :

Specimens → nasopharyngeal swab, pus, sputum or spinal fluid.

Microscopic examination

: show many polymorphonuclear

neutrophiles and many RBC. (1) G + , (2) lancet shaped (3) diplococci,

(4) nonmotile, (5) nonsporing, (6) capsulated.

Macroscopic examination : need enriched media with blood or

serum for growth, produce



-hemolysin on blood agar growth is

enhanced by 5-10% CO

. On solid media → form a small round colonies

dome-shaped at first, few hours later it undergoes some autolysis in the

center of the colony and become flat while the edges are arised.

Biochemical tests →

1- Optochin sensitivity

2- Lysis the cell by bile acids

3- Capsular swelling (the Quellung reaction, see figure 4) is observed

when sputum treated by type– specific antisera as immunological

test.

4- Inuline fermentation to different from Sterp. viridans

Animal pathogenicity → mice are most susceptible to

pneumococcal infection and used for diagnosis, animal will die in 18-

48h.

Treatment and Prevention

Pneumococci are sensitive to sulfonamides and penicillin.

Amoxicillin, cephalosporins, erythromycin, cortimoxazole ,vancomycin

and penicillin G. Recently some drug resistance has appeared, e.g.

tetracycline, erythromycin and lincomycin.

Prevention

pneumococcal polysaccharides vaccine ppv,

immunizes against 23 serotype of Sterp. pneumoniae and is indicated for

the protection of high risk individuals older than 2 years, for 85-90% of

infections, including prominent penicillin-resistant strains.

Pneumococcal conjugate vaccine pcv7, is effective in infants (6

weeks – 5 years of age). Its made up of 7 pneumococci Ags conjugated to

CRM 197 (a mutant nontoxic diphtheria toxin). This vaccine protect

invasive pneumococcal disease, in older children and adults, effects on

pneumococci transmission (indirect effects on herd immunity) than
through it’s direct effect of protecting vaccinated children.

Streptococcus viridans

Include species : Sterp. nitis , Sterp. mutans and Sterp. salivarins

There growth is not inhibited by optochin disk , not soluble in bile

salt and not ferment Inuline (see table 1).

It’s a members of the normal flora of the upper respiratory tract, it

cause endocarditis, some like Strep. mutans produce large polysaccharide

which contribute to the genus of dental caries.

Table 1: Differentiation between Streptococcus pneumococcus and

Streptococcus viridans

Strepto. pneumonia

Strepto viridans

Microscopical

morphology

Capsulated

flame-

shaped diplococci

Non capsulated oval or

round

arranged

chains

Culture colonies

Initially dome-shaped

later flated colonies

Dome – shaped

Quelling test

Growth in liquid media Uniform turbidity

Granular turbidity and

powdery deposits

Bile solubility

Inuline fermentation

Optochin sensitivity

Sensitive

Resistant

Intraperitoneal

inoculation in mice

Cause fatal infection

non pathogenic