Lab 8: Diagnostic Microbiology - Staphylococcus, Streptococcus, And Enterococcus Flashcards
(23 cards)
What are enteric bacteria?
Gram negative, rod-shaped bacteria in the Enterobacteriaceae family, commonly found in animal intestines
What are the second most frequently encountered bacteria recovered from animal specimens after enteric bacteria?
Gram positive cocci
How do staphylococci typically appear under a microscope?
As grape like clusters of immobile spherical gram positive cells
How do streptococci differ in arrangement from staphylococci?
Streptococci form chains due to division in one plane, staphylococci divide in two planes and form clusters
What metabolic feature do staphylococci possess?
They are facultative anaerobes — can grow aerobically or via fermentation
Where are staphylococci commonly found?
On the skin and mucous membranes of humans and animals
Name at least three diseases caused by staphylococcus aureus.
Skin infections, food poisoning, toxic shock syndrome, bacteremia, impetigo, abscesses, carbuncles
How do streptococci metabolize nutrients?
They are lactic acid bacteria — grow by fermentation only, even in the presence of oxygen
What are some industrial or natural roles of streptococci?
Used in the production of buttermilk, silage, and other fermented products
What serious diseases can streptococci cause in dogs and humans?
In dogs: abortion, pneumonia, septicemia
In humans: strep throat, necrotizing fasciitis
What is hemolysis, and why is it important in identifying streptococci?
Breakdown of red blood cells, used to classify streptococcal species on blood agar plates
What is alpha hemolysis?
Partial hemolysis producing green discoloration on blood agar
What is beta hemolysis?
Complete hemolysis creating clear zones on blood agar
What is gamma hemolysis?
No hemolysis — no change in the agar around colonies
What test distinguishes staphylococci from streptococci and enterococci?
The catalase test
What is the result of a postive catalase test?
Immediate and vigorous bubbling
Which bacteria are catalase positive?
Staphylococci
Which bacteria are catalase negative?
Streptococci and enterococci
How can enterococci be differentiated from streptococci?
By their ability to grow and hydrolyze esculin on bile esculin azide (BEA) agar, producing a black precipitate
What is the purpose of the API staph identification test?
To identify species of staphylococcus, micrococcus, and kocuria using biochemical reactions
What media is used to culture and test for enterococcus?
Bile esculin azide (BEA) agar
What is the expected BEA agar result for enterococcus?
Blackening of the medium around colonies (positive test)
Why should you avoid taking colonies from SBA plates for the catalase test?
Red blood cells may cause a false positive result
