Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
31 Cards in this Set
- Front
- Back
|
Stretococci are Gram positive cocci and arranged in chains. TRUE/FALSE
|
TRUE.
|
|
|
Where are a number of these species normally found?
|
Among the normal flora of human and animal skin and on mucus membranes. Especially the upper respiratory tract.
|
|
|
What are their growth requirements like?
|
Fastidious growth needs, especially for blood enriched media.
|
|
|
Are they facultative?
|
Yes. Most grow in air, but also in the absence of O2. Some prefer reduced o2 tension, and increased CO2(microaerophilic).
|
|
|
In what genus are the anerobic strep placed?
|
Peptostreptococcus. 35C is optimal for most streptococci.
|
|
|
What are hemolysins?
|
A number of species produce toxins that destroy red blood cells, they lyse the red cell wall with the resultant release of hemoglobin. These toxins are also called streptolysins. These can be observed on a blood agar plate.
|
|
|
What is alpha hemolytic streptococci?
|
Different strep. produce different effects on RBCs in blood agar. Those that produce incomplete hemolysis with partial destruction of the cells around the colonies are alpha hemolytic strep.
|
|
|
How is the alpha toxin observed or visualized?
|
This type of hemolysis is seen as distinct greening of the agar in the hemolytic zone. This is called the viridans group.
|
|
|
What is Strep. pneumoniae also known as?
|
Pneumococcus. It is a pathogen that also produces alpha hemolysis.
|
|
|
Where is Strep. pneumoniae found?
|
Normal flora in the throats of some persons, but is considered pathogenic when isolated in large numbers from the sputum and blood of patients with pneumonia.
|
|
|
What is meant by beta hemolytic?
|
Species whose hemolysins cause complete destruction of RBCs in the agar zones surrounding their colonies.
|
|
|
In reference to the above,these strep are small opaque or semitranslucent colonies surrounded by clear zones in an otherwise red opaque medium. TRUE/FALSE
|
TRUE.
|
|
|
Some strains of Staph, E. coli and other bacteria may also demonstarte beta-hemolysis. TRUE/FALSE
|
TRUE.
|
|
|
What is nonhemolytic streptococci?
|
Some species do not produce hemolysins. When grown in agar, no change is seen in the red blood cells around them. They were once referred to as gamma strep.
|
|
|
What is the danger to persons with heart valve abnormalities?
|
In tese patients, alpha hemolytic streptococci may be deposited on the valves, usually at the time of dental work, when they have the opportunity, and untreated may be fatal.
|
|
|
What is considered diagnostic for endocarditis?
|
In these patients, isolation of viridans strep. from multiple blood cultures is considered diagnostic of endocarditis.
|
|
|
What must be done when beta hemolytic strep. are found in throat cultures?
|
The laboratory must proceed with further testing to determine the antigenic group.
|
|
|
How is the above done?
|
By extracting the CHO antigen from the strep cell wall and reacting it with specific antibodies in a latex agglutination test or enzyme immune assay.
|
|
|
Which is the most important strep group?
|
Strep. grpoup A, which is responsible for strep pharyngitis(strep throat), as well as a variety of other serious skin and and depp tissue infections.
|
|
|
What is the species name given to group A streptococci?
|
Pyogenes group, pus producing. Certai toxins and extracellular products of S. pyogenes are responsible for Scarlet fever, a toxic shock syndrome similar to that produced by Staph. aureus, and the flesh eating disease(necrotizing fascitis).
|
|
|
What is the cause of Rheumatic fever?
|
It is caused by immunologic reactions between strep antibodies and heart tissue antigens, and glomerulonephritis occurs as a result of antigen antibody complex deposition in the kidney glomeruli.
|
|
|
What about group B streptococci?
|
Strep. agalactiae were considered primarily animal pathogens. Now, they are known to colonize the human female genital tract. This organism has been known to cause sepsis and meningitis in the newborn child.
|
|
|
Pregnant women are routinely screened for vaginal carriage of the group B Strep a few weeks before term and treated with antimicrobial agents during labor if they are colonized. TRUE/FALSE
|
TRUE.
|
|
|
Are there other groups recognized?
|
Other beta hemolytic strep are placed in groups C through V, but most do not cause disease. Groups C, F and G may cause mild pharyngitis but do not have serious side effects.
|
|
|
What is Enterococcus?
|
Strep like bacteria with group D antigen were first classified in the Strep. genus, but studies have revealed that they differ in many biological respects. They have now been placed in their own genus: Enterococcus.
|
|
|
Alpha hemolytic colonies from upper respiratory specimens are not identified further because they are considered normal flora. TRUE/FALSE
|
TRUE.
|
|
|
What is the approach when Beta hemolytic colonies are identified?
|
They must be further identified to determine whether or not they are group A, or group B(genital specimens).
|
|
|
What type of in house testing is available?
|
Alternative presumptive tests are commonly used in the lab for identifying groups A and B..
|
|
|
Give an example of the above statement.
|
Group A strep, but not other beta hemolytic strep. are susceptible to low concentration of te drug bacitracin. By using a bacitracin disk diffusion assay, the susceptibility of suspected strains can be tested.
|
|
|
How do the group A strep react?
|
These like the enterococci, hydrolyze the reagent PYR(L-pyrrolidonyl-beta-napthylamide). This rapid assay test may be used to identify group A strep.
|
|
|
What do group B produce?
|
These produce a substance called the CAMP factor that enhances the effect of beta hemolysins possessed by some strains of S. aureus. All other groups of beta hemolytic strep must be identified serologically, but determining the absence of group A and b strains is usually sufficient for clinical purposes.
|
