Lesson 1: STREPTOCOCCUS Flashcards by Zari Ami

Family Streptococcaceae 3 genera

Streptococcus
Enterococcus
Lactococcus

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Catalase negative

Streptoccoci

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Media used for Streptococci

BAP
CHOC
Todd-Hewitt Broth

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Streptococci

Facultative anaerobes and needs ? CO2 for growth

5-10%

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● Green discoloration

Alpha hemolytic

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Organisms w A-hemolysis

S. pneumoniae
S. viridans

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Clear or colorless zone of hemolysis surrounding bacterial colony

Beta hemolytic

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Organisms w B-hemolysis

S. pyogenes
S. agalactiae

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Non-hemolytic

Gamma hemolytic

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Organisms w Gamma hemolysis

Enterococcus spp.

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Physiologic divisions

Pyogenic division
Viridans division
Enterococcus division
Lactic division

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Found in Sherman 1937

Bergey’s/Academic Classification

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PHYSIOLOGIC DIVISION (Streptococci)

streptococcal organisms = diseases associated w PUS FORMATION

Pyogenic division

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PHYSIOLOGIC DIVISION (Streptococci)

Includes beta hemolytic strains

Pyogenic division

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Lancefield groups

A, B, C, E, F, and G

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PHYSIOLOGIC DIVISION (Streptococci)

Difference between Viridans and Enterococcus division

Viridans - not salt tolerant
Enterococcus - salt tolerant

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PHYSIOLOGIC DIVISION (Streptococci)

● Not beta hemolytic
● Not salt tolerant
● Grow at high pH

Viridans division

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PHYSIOLOGIC DIVISION (Streptococci)

● Salt tolerant
● Grow at high pH

Enterococcus division

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PHYSIOLOGIC DIVISION (Streptococci)
Enterococcus division

Temp range

10C-45C (optimal growth temp)

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PHYSIOLOGIC DIVISION (Streptococci)

● Not clinically significant
● Associated with dairy industry

Lactic division

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Developed Lancefield Grouping

Rebecca Lancefield (1933)

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Divides the Streptococci into serological groups; Based on antigenic properties of carbohydrate group antigens in their cell wall

Lancefield Grouping

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Lancefield grouping

Clinically significant; Mostly isolated and associated with human infections

A, B, C, D, F, and G

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Done to differentiate Streptococci into groups

Serological testing

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Lancefield group A

S. pyogenes

Lancefield group B

S. agalactiae

Lancefield group C and G

S. dysgalactiae and S. equi

Lancefield group A, C, F, and G

S. anginosus

Not a normal flora Most virulent for humans

GROUP A: STREPTOCOCCUS PYOGENES (GAS)

GAS Diseases

- Bacterial Pharyngitis - Skin infections - Invasive diseases

GAS Complications

Rheumatic heart disease Acute glomerulonephritis

GAS transmission

- person to person contact - aerosol droplets

GAS Major Virulence Factors - Anti-phagocytic: protects the organism from being phagocytosed - Reason for mucoid colonies

Hyaluronic acid Capsule

GAS Major Virulence Factors - Precipitates fibrinogen - Clumps platelets and WBCs - Inhibits migration of WBCs

M protein

GAS Major Virulence Factors Group-specific cell wall antigen

Grp. A sugar: rhamnose-N-acetylglucosamine

GAS Major Virulence Factors ● Equipped with structures that allow them to act like immune cells ● No antigen-antibody complex

IgG and IgA - binding proteins

important anaphylotoxin; Part of initiation of inflammatory process

C5a

GAS Major Virulence Factors Byproduct of complement cascade

C5a protease

GAS Major Virulence Factors Inhibits neutrophil chemotaxis in vitro

C5a protease

attach to mast cells and basophils → initiate the release of histamine → further inflammatory reaction

C5a

Allows binding to fibronectin in pharyngeal epithelium

F protein

binding site for organisms on membranes of host cells

Fibronectin

Attached to M protein; May allow binding to fibronectin

Lipoteichoic acid

● Fibrinolysin that lyses blood clots ● Similar function with staphylokinase

Streptokinase

Degrades host DNA & RNA

Streptodornase

● Can hydrolyze or break down hyaluronic acid which is part of the connective tissue ● Important in spreading the infection

Hyaluronidase

Associated with the organism’s ability to destroy WBCs

Diphosphopyridine nucleotidase

Most potent pyrogenic exotoxin

● Associated with fever and rashes in scarlet fever ● Responsible for the increase in temperature and rashes (especially in Scarlet fever) ● Associated with Streptococcal TSS

Pyrogenic exotoxins/ erythrogenic toxins

A, B, C

more fatal TSS

Staphylococcal TSS

Oxygen labile; Antigenic (Anti-Streptolysin O) ○ Can induce antibody response ○ Can be detected serologically

Streptolysin O

- Oxygen stable - Toxic to various types of human cells but non-antigenic - Do not trigger an immune response

Streptolysin S

Pyogenic disease

Erysipelas Cellulitis Impetigo Streptococcal pharyngitis

Erysipelas is also known as

St. Anthony’s Fire

● Spreading of rashes across the face, legs ● Itchy and hotter compared to other parts of the body ● NO PUS production, but exotoxin A production (increase temperature in the area) & rashes

Erysipelas

● Inflammation of deep tissues including the skin ● Common in middle-aged individuals

CELLULITIS

- Begins as fluid-filled blisters that usually erupts creating weeping lesions - Mouth and nose area; Common in children

Impetigo

● Red, swollen tonsils ● Pus formation

STREPTOCOCCAL PHARYNGITIS (STREP THROAT)

Strep throat lasts from

3-5 days

Toxigenic disease

Necrotizing Fasciitis Scarlet Fever Streptococcal Toxic Shock Syndrome

Made streptococcus pyogenes earn the name of “flesh-eating bacteria”

Necrotizing fasciitis

Process of removing necrotized skin = infection does not spread

Debridement

Nectrotizing fasciitis active component

Exotoxin A

Necrotizing fasciitis: cause the actual tissue damage

Macrophage

Necrotizing fasciitis: Destruction of tissue occur at a rate of -

2 inches per hour

- May occur after streptococcal pharyngitis or other infection; Pyrogenic exotoxin is present

Scarlet fever

Characteristic sign of scarlet fever

Strawberry tongue

- Toxin mediated - Hypotension, multi-organ failure, fever, erythema, swelling, tachycardia, acute respiratory distress, renal impairment and shock is observed

STREPTOCOCCAL TOXIC SHOCK SYNDROME

Proliferation of glomerular tissue that can result in damage to the basement membrane

Acute glomerulonephritis

Comprises a specific set of renal disease; immunologic mechanism; triggers inflammation

Acute glomerulonephritis

Cardiac inflammation and scarring; triggered by an autoimmune reaction to infection w GAS

Rheumatic heart disease

This condition in the acute stage may consist of pancarditis

Rheumatic heart disease

System disease that occur after an untreated strep throat due to GAS

Acute rheumatic fever

- Preceded by skin or respiratory infections - Represents a HYPERSENSITIVITY response - Immune-mediated

Post-Streptococcal Diseases

Streptococci culture incubation

Incubation for 18-24 hrs. @ 37C with 5-10% CO2 since they are fastidious

Streptococcal culture ● white to gray pinpoint colonies, translucent, opalescent. ● Wide zone of B-hemolysis

BAP

Streptococcal culture - is addedto BAP

trimethoprim/sulfamethoxazole

Most virulent strain in mucoid colonies

M protein 49

Biochemical test to differentiate Streptococcus from Staphylococcus

Catalase test

Lesson 1: STREPTOCOCCUS Flashcards

(80 cards)