Streptococci And Enterococci Flashcards
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)
Habitat
Indigenous respiratory tract microbial flora of animals and humans
Certain species are also found in the gastrointestinal and urogenital tracts of humans
Clinical infections
Upper and lower respiratory tract infections
Urinary tract infections
Wound infections
Endocarditis
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
Criteria for Classification
Oxygen requirements
Serology
Hemolysis on Blood Agar (BA)
Biochemical Reaction
Classification of Streptococci Based on Oxygen requirement
Anaerobic
Peptostreptococcus
Aerobic or facultative anaerobic
Streptococcus
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
two surface antigens on Streptococcal cell wall:
(a)Polysaccharide, or carbohydrate, called the C substance
(b) Protein M-protein)
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.
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
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
Examples of groupable
A - S.pyogenes
B - S. Agalctiae
C - S.esquisimilis and S.dysgalactiae
D - Enterococcus and S.bovis
E/U - Other
Examples of non-groupable
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)
Species table
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:
- Diagnosis: ASO titre helps confirm recent streptococcal infection.
- Monitoring: Serial ASO titre measurements track the immune response and treatment efficacy.
- Prognosis: High ASO titre levels indicate increased risk of complications.
