Streptococci And Enterococci Flashcards by Ifeyinwa Ani

General characteristics of streptococci

Gram positive
Cocci or lancet-shaped
1µm in diameter
Chains or pairs
Usually capsulated (Except for viridians streptococci group)
Non motile
Non spore forming
Facultative anaerobes (Except Peptostreptococcus)
Fastidious, often
Oxidase-negative
Catalase negative (Staphylococci are catalase positive)

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Habitat

Indigenous respiratory tract microbial flora of animals and humans

Certain species are also found in the gastrointestinal and urogenital tracts of humans

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Clinical infections

Upper and lower respiratory tract infections
Urinary tract infections
Wound infections
Endocarditis

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Structure

Thick peptidoglycan layer
Teichoic acid
C=carbohydrate layer present except in viridans group
Capsule in S. pneumoniae and in young cultures of most species

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Criteria for Classification

Oxygen requirements
Serology
Hemolysis on Blood Agar (BA)
Biochemical Reaction

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Classification of Streptococci Based on Oxygen requirement

Anaerobic
Peptostreptococcus

Aerobic or facultative anaerobic
Streptococcus

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Classification of Streptococci Based on Serology

Many serogroups/ serotypes

Lanciefield Classification most popular
Based on carbohydrate antigen types in the cell wall
Two Major Divisions based on Lanciefield Classification :

Groupable streptococci
Has carbohydrate antigen used for classification

Non-groupable streptococci
Lack carbohydrate antigen used for classification

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two surface antigens on Streptococcal cell wall:

(a)Polysaccharide, or carbohydrate, called the C substance
(b) Protein M-protein)

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Precipitation Test (Reaction):

Soluble type-specific antigens is reacted with antisera
Positive test gives visible precipitates
Antisera is produced by injecting purified antigen into an animal
Antibodies produced upon stimulated immune response (antisera) is harvested.

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Significance of agglutination and precipitation test

Known antigens are reacted with unknown antibodies
Agglutination: when an insoluble antigen is mixed with a soluble antibody, the antibodies link the bacterial cells together forming an agglutinate

Precipitation: when a soluble antigen is mixed with a soluble antibody, it forms a precipitate

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Groupable and non-groupable streptococci

many groups, at least 20 serogroups
Labelled A-K & H-V
A,B,C,D,F,G - main human pathogens
A, B and D (more frequent)
C, G and F (Less frequent)

Non-groupable streptococci
S. pneumoniae (pneumonia)
Viridans streptococci group
e.g. S. mutans

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Examples of groupable

A - S.pyogenes
B - S. Agalctiae
C - S.esquisimilis and S.dysgalactiae
D - Enterococcus and S.bovis
E/U - Other

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Examples of non-groupable

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Classification of Streptococci Based on Haemolysis on Blood Agar

Hemolysis on Blood Agar (BA)
Best on Sheep blood agar

Types of heamolysis:

Alpha-hemolysis
Partial hemolysis
Green discoloration around the colonies
e.g. non-groupable streptococci (S. pneumoniae & Viridans group of streptococci)
Beta-hemolysis
Complete hemolysis
Clear zone of hemolysis around the colonies
e.g. Group A & B (S. pyogenes & S. agalactiae)
Gamma-hemolysis
No lysis
e.g. Group D (Enterococcus spp)

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Species table

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Classification of Streptococci Based on Biochemical Reactions

Susceptibility testing: Bacitracin, Optochin
Christie-Atkins, Munch-Petersen (CAMP) Test
Bile solubility test
PYR Hydrolysis
Hippurate hydrolysis
Bile Esculin hydrolysis
Growth in 6.5% NaCl broth (grows: enterococcus, no growth: streptococcus galluliticus)
Quelong test

Bacitracin sensitivity

Principle:
Bacitracin test is used for presumptive identification of group A
To distinguish between S. pyogenes (susceptible to B) & non group A such as S. agalactiae (Resistant to B)

Bacitracin will inhibit the growth of gp A Strep. pyogenes giving zone of inhibition around the disk

Procedure:
Inoculate BAP with heavy suspension of tested organism
Bacitracin disk (0.04 U) is applied to inoculated BAP
After incubation, any zone of inhibition around the disk is considered as susceptible

Optochin Susceptibility Test

Principle:
Optochin (OP) test is presumptive test that is used to identify S. pneumoniae
S. pneumoniae is inhibited by Optochin reagent (<5 µg/ml) giving a inhibition zone ≥14 mm in diameter.
( undergoes alpha hemolysis)

Procedure:
BAP inoculated with organism to be tested
OP disk is placed on the center of inoculated BAP
After incubation at 37oC for 18 hrs, accurately measure the diameter of the inhibition zone by the ruler
≥14 mm zone of inhibition around the disk is considered as positive and ≤13 mm is considered negative
S. pneumoniae is positive (S) while Viridans are negative (R)

Bile solubility test

Principle:
S. pneumoniae produce a self-lysing enzyme to inhibit the growth
The presence of bile salt accelerate this process

Procedure:
Add ten parts (10 ml) of the broth culture of the organism to be tested to one part (1 ml) of 2% Na deoxycholate (bile) into the test tube
Negative control is made by adding saline instead of bile to the culture
Incubate at 37oC for 15 min
Record the result after 15 min

Results:
Positive test appears as clearing in the presence of bile while negative test appears as turbid
S. pneumoniae soluble in bile whereas Viridans streptococciinsoluble

Clinically Significant Streptococci

Streptococcus pyogenes
(Group A Beta-Hemolytic Streptococci)
2. Streptococcus agalactiae
(Group B b-Hemolytic Streptococcus)
3. Streptococcus Group D and Enterococcus Species
4. Viridian group of streptococci
5. Streptococcus pneumoniae

Clinically significant Streptococcus-Like Organisms

Aerococcus
Leuconostoc
Pediococcus

Clinically significant Streptococcus-Like Organisms

Aerococcus
Leuconostoc
Pediococcus

Virulence Factors

Structural Elements/ factors

Capsule (Hyaluronic acid ): nonimmunogenic, antiphagocytic

Fimbrae (F-protein): attachment and adherence to epithel. cells

M protein: major virulence factor, antiphagocytic, anticomplement

Teichoic acid (lipoteichoic acid): adherence to epithelial Cells

Exo products

Streptococcal Infections: Strept Throat

Strept Throat = Acute bacterial pharyngitis/ tonsilitis Most common of all Strep diseases 90% of all pharyngitis/ tonsilitis is due to Grp A strep infection Affect all ages, peak incidence at 5-15 years Incubation period 2-4 days Characterized by Sore throat Malaise Fever/headache pus in back of throat Important to treat immediately to avoid post strep diseases

Post–Group-A Post-Streptococcal Infections Rheumatic fever

Rheumatic fever from pharyngeal infections only Fever Inflammation of the heart, joints, blood vessels, and subcutaneous tissues Chronic, progressive damage to the heart valves Most common cause of permanent heart valve damage in children Exact cause not yet known but there appears to be some antibody cross reactivity between the cell wall of S. pyogenes and heart muscle autoimmune disease Occurs most frequently between ages of 6 and 15 100x more frequent in tropical countries

Post–Group-A Post-Streptococcal Infections Acute glomerulonephritis

from either cutaneous or pharyngeal infections More common in children than adults Antigen-antibody complexes deposit in the glomerulus Inflammatory response causes damage to the glomerulus and impairs the kidneys Diagnosis based on history of Strep throat and clinical findings. Symptoms include fever, malaise,edema, hypertension and blood or protein in urine Occurs in 0.5% of those having strep throat 80-90% of cases recover with bed rest lasting for months Kidney damage in the remainder is often permanent resulting in chronic glomerular nephritis

Erysipelas

Acute infection and inflammation of the dermal layer of skin. Painful red patches which enlarge and thicken

Invasive Group A Streptococcal Infections:Streptococcal toxic shock syndrome

Streptococcal toxic shock syndrome Multi-organ system failure similar to staphylococcal toxic shock Initial infection may have been pharyngitis, cellulitis, peritonitis, or other wound infections Due to lysogenic S. pyogenes (infected by a particular phage making it express erythrogenic toxin) Erythrogenic toxin responsible for Scarlet fever Scarlet fever characterized by peculiar rash and strawberry colored tongue

What bacteria can cause strep throat?

Streptococcus pyogenes

Write short notes on catalase test based on: I. Principle II. Uses/purpose III. Materials and reagents IV. Techniques/method V. 2 bacteria identifiable with the laboratory test/ procedure

Write short notes on coagulase test based on: I. Principle II. Uses/purpose III. Materials and reagents IV. Techniques/method V. 2 bacteria identifiable with the laboratory test/ procedure

Write short notes on oxidase test based on: I. Principle II. Uses/purpose III. Materials and reagents IV. Techniques/method V. 2 bacteria identifiable with the laboratory test/ procedure

Write short notes on harmolysis on blood/chocolate agar based on: I. Principle II. Uses/purpose III. Materials and reagents IV. Techniques/method V. 2 bacteria identifiable with the laboratory test/ procedure

Alpha hemolysis is best on what agar?

Chocolate agar

Describe the pathogenesis of post-streptococcal infections

List post streptococcal diseases

Acute proliferative glomerulonephritis Rheumatic fever

What is the full meaning of ASO?

Antistreptolysin O

List and briefly discuss the role of ASO titre in microbiology?

Role of ASO titre: 1. Diagnosis: ASO titre helps confirm recent streptococcal infection. 2. Monitoring: Serial ASO titre measurements track the immune response and treatment efficacy. 3. Prognosis: High ASO titre levels indicate increased risk of complications.