G - Streptococcus

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Streptococcus

J. Walter Sowell, R.Ph., Ph.D.



G2

General Characteristics of Genus

Diverse group of gram-positive cocci which grow

in chains in broth or individually, in pairs, or as

short chains on solid media

Some Streptococcus have capsules

Streptococcus pyogenes

Streptococcus pneumoniae Most species are facultative anaerobes but a few

range from anaerobic to capnophilic (requires

carbon dioxide)



G3

General Characteristics of Genus

Energy is derived by carbohydrate fermentation

with lactic acid production

Unlike Staphylococci, this genus is catalase

negative

Preliminary laboratory identification is based on

hemolytic reactions on 5% sheep blood agar plates



G4

Beta-Hemolytic Streptococci



G5

Serologic Classification for

Streptococcus species

Rebecca Lancefield (1933) developed technique

Based on immunoassay of group antigen in cell wall

Within cell wallGroup specific and Type-specific antigens

Group antigen = N-acetylglucosamine-Rhamnose

Group A Streptococci

Group antigen = Glucosamine polysaccharide-Rhamnose

Group B Streptococci

Group antigen = N-acetylgalactosamine ±Rhamnose

Group C Streptococci



G6

Importance of Lancefield

Classification Rapid identification of pathogenGroup

antigen within the cell wall

Immunoassay from a throat

swabQuick way to identify

Streptococcus pyogenes as the

pathogen in pharyngitis

Often used in physician¶s offices or the

hospital to identify pathogen



G7

Limitation of Lancefield

Classification

Many species of Streptococci lack a group

antigen Require other biochemical tests for

identification

Lancefield classification used for a few

species

Group A, B, C, F, and G



G8

Streptococcus pyogenes (Group A)

General Characteristics/Classification

Possesses a specific carbohydrate antigen inthe cell wall called the C antigen.

This antigen is used to separate the various

species of Streptococcus into multiple groups:

A,B

, C, D, F, andG

Serological Classification ± Group A

Hemolytic Pattern ± Beta hemolytic



G9

S. pyogenes

General Characteristics (cont¶)

M protein, a major surface antigen, is presenton the fimbriae of this pathogen

Subdivides Group A into multiple immunologic

types100+

Clinical importance?? Differ serotypes areassociated with causing disease. It is type specific.

Serves as a basis for preventing reinfection

Antiphagocytic

Immunity is type specific (based on M protein)

Important in epidemiological studies



G10

S. pyogenes

Habitat ± lives on human skin and mucous

membranes Transmission

> Respiratory tract droplets from a carrier

> Fomites (pens, paper, drinking glasses)



G11

S. pyogenes ± Virulence Factors

Structural Components

Capsule Some strains have a hyaluronic acid capsule

Nonimmunogenic and antiphagocytic

Hyaluronic acid is an important component of

connective tissue

Capsule is recognized as natural by the immune system

Encapsulated strains more likely to cause severe

systemic infections



G12


Structural Components (cont¶)

M Protein

The M protein on fimbriae serves as a major surface antigen and serves as the basis for thesubdivision within Streptococcus pyogenes

It is antiphagocytic and serves to degrade one of

the components of complement F Protein

May participate in tight binding of the pathogen tothe epithelial cells of the throat and skin



G13


Enzymes Secreted by the Pathogen

Streptolysin O (oxygen labile) Antigenic ± Antibodies formed against this

antigenhelpful when testing for a recent infection

by this pathogen

Antibodies against Streptolysin O (ASO) appear 3 to 4

weeks after initial infection and persist

Lyses blood cells (WBC, R BC, platelets)



G14


Enzymes Secreted by the Pathogen (cont¶)

Streptolysin S (oxygen stable) Nonantigenic

Lyses blood cells (WBC, R BC, platelets)

Streptokinase

Lyses blood clots Dissemination factor



G15


Enzymes Secreted by the Pathogen (cont¶)

DNases A

D Lyses DNA

Dissemination factor

Pus, which contains DNA, is more fluid with

Streptococcus infections in comparison toStaphylococcus infections



G16

S. pyogenes ± Virulence Factors Streptococcal Pyrogenic Exotoxins

(previously called Erythrogenic Toxins)

Four types (Toxin A, B, C, and F)

Possibly responsible for clinical manifestations seen in

severe reactions

Rash in Scarlet fever

Necrotizing fasciitis

Streptococcal toxic shock syndrome

Phage mediated

Toxins are classified as a superantigen

Bridge Macrophages to Helper T cells

Hyper response of the immune system

shock, organfailure and death



G17

Streptococcus pyogenes-CDC In 2005, CDC reports that 4700 cases of

invasive disease in the U.S.

Perhaps, 10 million cases of noninvasivedisease, mostly pharyngitis and pyoderma

Pharyngitis caused by Streptococcus

pyogenes is most often seen in children, ages

5 to 15 years, but certainly not limited to this

age range.



G18

S. pyogenes ± Suppurative Diseases

Pharyngitis (³Strep Throat´)

Fever, sore throat, redness, and edema of the mucous

membranes, purulent exudates, and enlargement of the cervical lymph nodes

May extend to middle ear, mastoid, and meninges

Pyoderma (Impetigo) ± Vesicles Pustules (pus

filled) Rupture Crust

Puerperal Sepsis ± postpartum infection of uterus



G19


Cellulitis of skin

Involves deeper subcutaneous tissue withrapid spread

Often the result of damage to skin (burn or wound)

Post-surgical WoundI

nfection ± Onset of symptoms of infection occur rapidly (6-12hours), while 48 hours or longer withStaphylococcus aureus



G20

S. pyogenes ± Suppurative Diseases Scarlet Fever

Complications of pharyngitis

Rash caused by pyrogenic exotoxins Within a couple of days after initial symptoms

of pharyngitis, a red rash appears on upper chest

and spreads to extremities

Erysipelas ± rash on skin as a complication of

pharyngitis

Pneumonia



G21

S. pyogenes ± Suppurative Diseases Necrotizing fasciitis(Streptococcal gangrene)

An infection that occurs in the deep

subcutaneous tissue

Very rapid movement

³Flesh eating bacteria´ that causes death to

fascia and destruction to muscle and fat



G22


Streptococcal Toxic Shock Syndrome

Typically occurs in association withnecrotizing fasciitis or bacteremia

Rapidly progresses to shock and death due to

organ failure (kidneys, lungs, liver, heart)

See Clinical Case 22-1 of Textbook-Page 231(Note how rapidly this patient declined!!)



G23

Erysipelas Necrotizing fasciitis



G24



G25

S. pyogenes ± Nonsuppurative Diseases

Acute Glomerulonephritis

Associated with untreated skin or respiratory tract

infections caused by nephritogenic strains of S. pyogenes, Group A

Onset of symptoms may be as short as one week after infection

Evidence strongly support a Type III hypersensitivity

reaction, where the antigen-antibody complex istrapped in the glomerular membranes

Symptoms include hypertension, edema, BUN, serum creatinine, blood and protein in urine



G26

S. pyogenes ± Nonsuppurative Diseases

Acute Rheumatic Fever

Greatly reduced incidence in U.S. (only 112 cases in 1994)

Far more prevalent in developing countries

Associated with untreated upper respiratory tract infections,usually pharyngitis

Onset of symptoms 14 weeks post S. pyogenes infection

M protein of the pathogen shares some common structural

features with certain cardiac tissue. M protein serves as anantigen which induces antibody formation. A Type II

hypersensitivity reaction may occur with the antibody

binding to cardiac tissue, causing inflammation and cardiac

damage



G27

S. pyogenes ± Diagnosis Rapid antigen detection from specimen

Release the C antigen by enzymatic or chemicalmeans

Detection of the C antigen with ELISA or latexagglutination

If rheumatic fever is suspected, high ASO titers(Antibody to Streptolysis O) would confirm arecent Streptococcus pyogenes infection

If acute glomerulonephritis is suspected, highanti-DNase B titers would confirm a recent

Streptococcus pyogenes skin infection



G28

Streptococcus agalactiae (Group B) General Characteristics/Classification

Serological classification ± Group B

Hemolytic pattern ± beta hemolytic, but narrowzone

Growth pattern ± short chainslong chains

Habitat ± GI

and female genital tracts Transmission ± Can be transmitted to unborn,

in utero, or to newborn during birth



G29

Streptococcus agalactiae (Cont¶d) Early-Onset Neonatal

Birth1st week of life

Bacteremia, pneumonia,

or meningitis Mortality rate-5% or so

Meningitis survival-

Significant neurological

effects (blindness,deafness, mental

retardation)

Late-Onset Neonatal

One week 3 months

Bacteremia with

meningitis

Neurological effects

high with meningitis

See Case 22-2-p 235



G30

S. agalactiae - Diseases

Adults

After deliver, the pathogen can cause

endometritis . Pathogen may cause UTI

Older adults with compromised immunity

Bacteremia, bone and joint, skin and soft-tissue,

pneumonia Mortality rate fairly high

G - Streptococcus

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