Microbiology Lab 1: Strep Classification

Questions and Answers

Which test differentiates staphylococci from streptococci?

Catalase Test

Which microbe species is weakly catalase positive but may not always test positive due to its weak properties?

Enterococci

How are the Streptococcus species separated into different groups?

Immunologic properties, hemolytic properties, biochemical properties

What is the immunologic classification system used to organize streptococci?

Lancefield grouping Signup and view all the answers

Lancefield groupings originally applied only to beta-hemolytic streptococci, but later discoveries extended classification to other non-hemolytic streptococci.

True Signup and view all the answers

Lancefield antigens define a particularly virulent group of streptococci regardless of their hemolytic patterns.

True Signup and view all the answers

What are the three distinct hemolysis patterns used to separate streptococci?

Beta hemolytic, alpha hemolytic, gamma hemolytic Signup and view all the answers

Which strep classification utilizes immunologic testing?

Lancefield groups Signup and view all the answers

__________; using antibodies to identify an unknown organism.

Serology/immunodiagnostics Signup and view all the answers

The commercially available strep typing kits contain vials of ________ directed against the various groups of streptococcal antigens.

Antibodies Signup and view all the answers

Sequelae resulting from infection with Strep pyogenes include __ and .

Rheumatic fever and glomerulonephritis Signup and view all the answers

What type of hemolysis does strep pyogenes carry out?

Beta hemolysis Signup and view all the answers

Streptolysin O produced by strep pyogenes has what properties?

Is oxygen labile Signup and view all the answers

People with infections caused by strep pyogenes produce _________ in response to the antigens produced by the microbes.

Anti-streptolysin O Signup and view all the answers

What are some other virulence factors produced by strep pyogenes besides streptolysin O?

Streptolysin S, streptokinase, fibrinolysin, hyaluronidase, proteases, erythrogenic toxins, strep pyrogenic exotoxins, exotoxin A, deoxyribonucleases Signup and view all the answers

Which organisms are PYR positive?

Group A streptococci and enterococcus Signup and view all the answers

Describe the basic science behind a rapid screening test for strep.

The kit contains antibody bound to a solid matrix which captures the strep bacterial antigen, then it is washed and exposed to specific anti-group A antibody, resulting in a detectable color change. Signup and view all the answers

The rapid screening test for strep is quite (specific/sensitive) but is lacking in (specificity/sensitivity).

Very specific, but is lacking in sensitivity Signup and view all the answers

Study Notes

Identification Tests and Characteristics

Catalase Test distinguishes staphylococci (positive) from streptococci (negative).
Enterococci are weakly catalase positive, leading to potential false negatives in testing.

Streptococcus Classification

Streptococcus species are categorized by:
- Immunologic properties (Lancefield groupings)
- Hemolytic properties
- Biochemical properties
Lancefield Grouping: Classifies streptococci into groups A to O (excluding I and J) based on carbohydrate antigenic differences in cell walls.

Hemolysis Patterns

Three groups based on hemolysis:
- Beta-hemolytic: Destroys red blood cells (RBCs), changing hemoglobin into a colorless form.
- Alpha-hemolytic: Causes green/brown discoloration by converting hemoglobin to methemoglobin without lysing RBCs.
- Gamma-hemolytic: Non-hemolytic, showing no effect on RBCs or hemoglobin.

Immunologic Testing

Lancefield Groups utilize immunologic testing for precise identification of streptococci.
Serology/Immunodiagnostics: Antibodies are used to identify unknown organisms.

Strep Pyogenes and Its Infections

Streptococcus pyogenes is linked to multiple conditions: strep throat, scarlet fever, childbed fever, impetigo, septicemia, and necrotizing fasciitis.
Sequelae from S. pyogenes infections include rheumatic fever and glomerulonephritis.

Hemolysis and Testing Properties

S. pyogenes exhibits beta hemolysis and is sensitive to bacitracin.
Streptolysin O is oxygen labile; weak hemolysis may occur under aerobic conditions but can be enhanced by reducing oxygen tension in blood agar.

Antibody Response

Patients infected with S. pyogenes produce anti-streptolysin O antibodies. A high titer indicates recent or past infection.

Virulence Factors of S. Pyogenes

Other virulence factors include:
- Streptolysin S: Lyses RBCs and non-erythrocyte cells
- Streptokinase, Fibrinolysin, Hyaluronidase, Proteases
- Erythrogenic toxins: Includes streptococcal pyrogenic exotoxins and exotoxin A
- Deoxyribonucleases

PYR Test Results

PYR positive organisms include group A streptococci and enterococcus.

Rapid Screening Tests

A rapid screening test for strep utilizes antibodies bound to a solid matrix to capture streptococcal antigens from a patient sample, followed by detection through colorimetric measures.

Sensitivity and Specificity

The rapid strep screening test is very specific but lacks sensitivity in identifying all cases.

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Description

Test your knowledge on the classification and identification of streptococci in this micro lab quiz. You will explore essential differentiation tests, properties of various species, and grouping based on immunologic characteristics.