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State the gram reaction and morphology of the streptococci.
- All Streptococci are Gram positive.
- Appear in pairs and chains.
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State 2 ways the streptcocci are classified.
- Hemolytic properties on blood agar.
- Serologic group
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Describe alpha hemolysis on blood agar plates.
Appears as a zone of partial hemolysis surrounding colony, often accompanied by a greenish discoloration of the agar.
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Describe beta hemolysis on blood agar plates.
Clear, red blood cell free zone surrounding colony, where a complete lysis of the red blood cells has occurred. Best seen in subsurface colonies where the agar has been stabbed.
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Describe gamma reaction on blood agar plates.
No hemolysis or discoloration of the agar.
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What is meant by the Lancefield system?
A classification of streptococci into serologic groups on the basis of carbohydrate antigens in their cell wall.
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What Lancefield serologic groups of streptococci that may show beta hemolysis on blood agar?
Groups A, B, C, D, F, and G
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State the Lancefield group of streptococcus that is the most common cause of acute streptococcal infections in humans.
Group A beta streptococci because they belong to Lancefield serologic group A and show beta hemolysis on blood agar.
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Name 5 other Lancefield groups, other than Group A, that frequently cause human infections.
- Group B
- Group C
- Group D
- Group F
- Group G
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State what the term "group A beta" means when referring to streptococci.
Group A beta means the streptococcal bacteria belong to the Lancefield serological group A and they show beta hemolysis on blood agar plates.
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State the genus and species of the group A beta streptococci.
Streptococcus pyogenes
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State the most common infection caused by Streptococcus pyogenes and name 6 other infections it may cause.
- pharyngitis (most common infection)
- Spreads to other areas of the respiratory tract, and causes
- -laryngitis
- -pneumonia
- -otis media (ear infection)
- It may enter the lymphatic vessels or the blood and disseminate to other areas causing
- -septicemia
- -osteomyelitis
- -endocarditis
- -septic arthritis
- -meningitis
- It can also infect the skin causing
- -erysipelas
- -impetigo
- -cellulitis.
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Name 2 autoimmune diseases associated with the group A beta streptococci.
- rheumatic fever
- acute glomerulonephritis
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Certain strains of Streptococcus pyogenes cause invasive group A streptococcal infections by producing protease called Exotoxin B. Name 3 of these infections.
- necrotizing fasciitis
- Scarlet fever
- toxic shock-like syndrome (TSLS)
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Describe the appearance of group A streptococci on blood agar.
- Very small, white to grey colonies approximately 1mm in diameter.
- A zone of beta hemolysis around 2-3mm in diamter surrounding each colony.
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Describe the reaction of group A beta streptococci to a Taxo A disc containing bacitracin.
Zone of growth inhibition around a Taxo A disc (sensitivity to the antibiotic bacitracin).
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State the genus and species of the pneumococcus.
Streptococcus pneumoniae
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State the gram reaction and morphology of Streptococcus pneumoniae.
- Gram positive
- lancet shaped (pointed like a lance) coccus
- 0.5 - 1.2µm in diameter
- Appears as diplococcus, but occasionally appear singularly or in short chains.
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State the natural habitat of Streptococcus pneumoniae.
- Found as normal flora of the nasopharynx of healthy carriers.
- 5-10% of healthy adults
- 20-40% of healthy children
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Name 4 infections Streptococcus pneumoniae may cause in humans.
- otitis media (ear infection)
- sinusitis
- bacteremia
- meningitis
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Describe the appearance of Streptococcus pneumoniae on blood agar with a Taxo P disc containing the drug optochin.
- Wet/shiny growth (due to capsules)
- Zone of alpha hemolysis
- Zone of growth inhibition around Taxo P disc
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Name the most common enterococcus that infects humans.
Enterococcus faecalis
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State the normal habitat of Enterococcus faecalis.
Normal flora of the intestinal tract.
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State the Lancefield group of the enterococci.
group D
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Name 5 infections commonly caused by Enterococcus faecalis.
- Infections within the peritoneal cavity (especially following penetrating trauma)
- Urinary tract infections
- Kidney infections
- Prostate infections
- Infections of damaged or compromised skin (diabetic or decubitus ulcers, burns, surgical wounds)
- *Note 1 - Enterococci are the 2nd most common bacterium isolated from nosocomial urinary and wound infections, and the 3rd most common cause of nosocomial bacteremia.
- *Note 2 - Enterococci are among the most antibiotic resistant of all bacteria.
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Describe the reaction of enterococci in SF broth.
Enterococci will grow in SF broth and ferment the dextrose, turning the pH indicator from violet to a yellow-brown color.
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Describe the reaction of enterococci on Bile Esculin agar.
Enterococci will grow in the presence of the bile salts in the medium. They hydrolyze teh esculin, turning the agar black.
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State the gram reaction and morphology of the enterococci.
- Gram positive streptococci
- Occur in pairs and short chains
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Name 5 common clinically important species of Staphylococcus and state which species is most pathogenic.
- Staphylococcus aureus (most pathgenic)
- Staphylococcus epidermidis
- Staphylococcus haemolyticus
- Staphylococcus hominis
- Staphylococcus saprophyticus
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State 2 sources for most Staphylococcus aureus infections.
- healthy nasal carrier
- contact with an abscess
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State the portal of entry for most Staphylococcus aureus infections.
usually the skin
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Name 6 systemic Staphylococcus aureus infections.
- septicemia
- septic arthritis
- endocarditis
- meningitis
- osteomyelitis
- abscesses in the lungs, spleen, liver, and kidneys
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State the gram reaction and morphology of all staphylococci.
- Gram positive cocci 0.5-1.0µm in diameter
- irregular grape-like clusters
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Describe the typical reactions of Staphylococcus aureus on:
a. Blood agar w/ Novobiocin disc
b. Mannitol Salt agar (phenol red pH indicator)
c. DNase agar
d. Coagulase test w/ citrated rabbit plasma
- a. creamy gold colonies, beta hemolysis, disc sensitive
- b. positive; turns from red to yellow
- c. positive; cleared zone around colonies after adding 1M HCl
- d. positive; plasma coagulates
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Describe the typical reactions of Staphylococcus epidermidis on:
a. Blood agar w/ Novobiocin disc
b. Mannitol Salt agar (phenol red pH indicator)
c. DNase agar
d. Coagulase test w/ citrated rabbit plasma
- a. white colonies, gamma reaction (no hemolysis), disc sensitive
- b. negative; indicator stays red
- c. negative; no cleared zone around colonies after adding 1M HCl
- d. negative; plasma does not coagulate
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Describe the typical reactions of Staphylococcus saprophyticus on:
a. Blood agar w/ Novobiocin disc
b. Mannitol Salt agar (phenol red pH indicator)
c. DNase agar
d. Coagulase test w/ citrated rabbit plasma
- a. white colonies, gamma reaction (no hemolysis), disc resistant
- b. positive; turns from red to yellow
- c. negative; no cleared zone around colonies after adding 1M HCl
- d. negative; plasma does not coagulate
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State the gram reaction and the morphology of the neisseriae.
- Gram negative
- diplococci
- 0.6-1.5µm in diameter
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State the correct scientific names for the gonococcus and the meningococcus and indicate what disease each causes.
- Neisseria gonorrhoeae causes gonorrhea
- Neisseria meningitidis causes meningococcal (epidemic) meningitis
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Give the normal habitat for Neisseria meningitidis and briefly descibe how it reaches the meninges.
- Infects the nasopharynx of humans causing mild or subclinical infections.
- In about 15% of these individuals, the organism invades the blood and disseminates, leading to septicemia and/or meningitis.
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What is a GC smear (gonococcus smear)?
A gram stain of urethral exudates in men and endocervical secretions in women.
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Describe the appearance of a positive GC smear (gonococcus smear) and indicate its significance in the diagnosis of gonorrhea.
Gram negative diplococci with flattened adjacent walls that are seen both inside and outside of polymorphonuclear leukocytes.
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State where clinical specimens are obtained in the male and in the female for the isolation of Neisseria gonorrhoeae.
- From urethra in males.
- From cervix and rectum in females.
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State where clinical specimens are obtained for the isolation of Neisseria meningitidis when it is causing meningitis.
- nasopharynx
- blood
- cerebrospinal fluid
- skin lesions
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Name selective medium useful for the isolation of pathogenic Neisseria and describe how the resulting colonies will appear.
- Modified Thayer Martin (MTM) Chocolate agar is selective for Neisseria.
- N. gonorrhoeae - small, convex, grayish-white to colorless, mucoid colonies.
- N. meningitidis - medium to large, blue-gray, mucoid, convex colonies
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State the results Neisseria gonorrhoeae for
a. oxidase test (Taxo N disc)
b. acid production in glucose (phenol red)
c. acid production in maltose (phenol red)
d. acid production in sucrose (phenol red)
- a. positive; blackened colonies surround disc
- b. positive; phenol red turns yellow
- c. negative; phenol remains red
- d. negative; phonol remains red
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State the results Neisseria meningitidis for
a. oxidase test (Taxo N disc)
b. acid production in glucose (phenol red)
c. acid production in maltose (phenol red)
d. acid production in sucrose (phenol red)
- a. positive; blackened colonies surround disc
- b. positive; phenol red turns yellow
- c. positive; phenol red turns yellow
- d. negative; phenol remains red
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Discuss one characteristic common to the genus Mycobacterium which allows us to distinguish this organism from most other genera of bacteria.
Mycobacterium are acid-fast. When they are stained by the acid-fast procedure they will resist decolorization with acid-alcohol and stain red, the color of carbol fuchsin. All other bacteria will be decolorized and stain blue.
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List 3 pathogenic species of Mycobacterium and name the infection that each causes.
- Mycobacterium tuberculosis causes tuberculosis
- Mycobacterium leprae causes leprosy
- Mycobacterium avium complex causes systemic infections in people with HIV/AIDS
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State 3 presumptive tests for the diagnosis of tuberculosis.
- PPD skin test
- chest x-rays
- acid-fast stain of sputum
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State 2 methods used for confirmation of active tuberculosis.
- Culturing the organism on Lowenstein-Jensen agar slants, Middlebrook agar, or 7H 10 Oleic acid agar
- Nucleic acid test
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Describe the appearance of a positive acid-fast stain for tuberculosis.
rod-shaped bacteria stained red
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Name the most common obligate anaerobe to cause infections in humans, state its normal habitat, and name the most common type of infections it causes.
- Bacteroides fragilis
- normal flora of human intestinal tract
- wound infections
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State the normal habitat of Clostridium perfringes and name an infection it may cause.
- normal flora of intestinal tract of animals
- gas gangrene
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Describe the appearance of Clostridium perfringes when it is anaerobically-grown on blood agar.
Smooth, glossy colonies surrounded by double-zone hemolysis (both alpha and beta hemolysis).
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Describe the appearance of Clostridium perfringes when it is anaerobically-grown in litmus milk.
Stormy fermentation with acid production (litmus turns pink), clotting of milk proteins, and gas formation.
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Define serology.
Using antigen-antibody reactions in the laboratory for diagnostic purposes.
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Define antigen and state what my act as an antigen.
- A substance that reacts with antibody molecules and antigen receptors on lymphocytes.
- Anything that the body does not recognize as "self" and stimulates an adaptive immune response.
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Define antibody and state where they are primarily found in the body.
- Antibodies are specific protein configurations produced by B-lymphocytes and plasma cells in response to a specific antigen and capable of reacting with that antigen.
- Antibodies are found in the plasma portion of the blood.
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Define direct serologic testing.
Uses a preparation of known antibodies to identify an unknown antigen.
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Define indirect serologic testing.
Antibodies in a person's serum being made by that individual against an antigen associated with a particular disease are detected by using a known antigen.
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Define antiserum.
Serum containing specific known antibodies.
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Describe the concept for using serologic testing to identify unknown antigens (direct serologic testing).
Antigen-Antibody reactions are very specific. Antibodies react only with antigens that stimulated their production. Because of this you can use known antiserum to identify unknown antigens such as a microorganism.
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Describe the general procedure for using serologic testing to identify unknown antigens (direct serologic testing).
A suspension of the unknown antigen to be identified is mixed with known antiserum for that antigen. Then look for an antigen-antibody reaction.
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Describe how to determine serologically whether an organism is a subgroup A, B, C, or D Shigella.
Shigella has 4 serological subgroups (A, B, C, and D). The unknown Shigella is placed in each of 4 circles on a slide, and different known antiserum (A, B, C, or D) is placed in each circle. A positive antigen-antibody reaction appears as a clumping or agglutination of the Shigella.
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Describe how to serologically identify Lancefield group A Streptococcus causing phyrangitis.
- The Rapid Response Strep A Test
- A membrane strip is coated with rabbit anti-Strep A antibody-red latex conjugate and immobilized rabbit anti-Strep A antibody.
- When the strip is immersed in the sample the Group A Streptococcal antigen moves up the strip, binds to the red-colored known antibody-latex conjugate. This complex continues up the strip until it contacts the immobilized rabbit anti-Strep A antibodies.
- If Group A Streptococcal antigen is present a red-colored sandwich of antibody/Strep A antigen/red latex conjugate antibody forms in the test area of the strip.
- The red color in the control region lets you know the test is complete.
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Describe how to diagnose pregnancy serologically.
Similar to the Strep test but detects the presence of human chorionic gonadotropin (HCG). (see page 208 of lab book)
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