Quiz 4 Flashcards
What is the purpose of each test used? (Coliform Bacteria)
- The presumptive Test - Used to detect the presence of coliforms in a water sample
- The Confirmed Test - Confirm the presence of coliforms and eliminate false positives caused by non-coliform bacteria.
- The Completed Test - Provide further verification that the bacteria present is coliform.
What is the difference between each test (think media components and what they tell you
about the bacterial physiology for positive and negative results)
- Presumptive Test - Uses Lauryl- tryptose broth broth. Broth contains SLS. Lactose promotes the growth of SLS-tolerant enteric bacteria
- Confirmed Test - Lauryl-tryptose broth inoculates brilliant green lactose bile (BGLB) broth. The green dye inhibits gram (+) bacteria.
- Completed Test - BGLB broth is used to streak a plate of EMB agar. EMB plate contains Eosin and Methylene blue which passes through the peptidoglycan layer of gram (+) bacteria and inhibits their growth - it cannot pass the outer wall of gram (-) bacteria. E.coli produces a dark green metallic sheen. Enterobacter aerogenes produce light pink or colorless colonies
What is an indicator species and why is it used in this context? (Coliform)
Indicator species test for organisms always present in feces rather than testing for pathogenic feces-borne organisms. We use indicators because they signal the presence of pathogenic microorganisms that pose high risks.
What are the characteristics of a coliform?
- Small, Gram (-) Rods
- Don’t produce endospores
- Ferment lactose in the presence of bile producing acid and gas
-Produce metallic green sheen on EMB plates
What is a nosocomial infection and how is it acquired?
Nosocomial infections are infections acquired in a medical facility. They can be acquired through direct contact (Person to Person) , indirect contact (Contaminated Surfaces)
What are the differences between endogenous and exogenous infections?
- Endogenous - Body’s normal microorganisms may become pathogenic
- Exogenous - Pathogen enters a body from the environment (Contact with contaminated surface)
What is a fomite and what type of transmission is it involved in?
Fomites are nonliving objects capable of transferring. Surface and skin transmission
What is coagulase and why does it matter in the context of bacterial infections?
Coagulase is an enzyme that causes a clot to form around the bacteria and essentially protects it from being attacked by the hosts phagocytes
What test is done to detect it? How does the test work? (Coagulase production by pathogenic staphylococci)
Coagulase Test is conducted to detect it. Take Staph Epidermidis and aureus and inculate cardboard cut out. Add reagent on inoculated area (Blue latex beads). With staph aureus, you will notice agglutination (Presence of bound coagulase (clumping factor))
What types of hemolysis exist? What do they look like? (Hemolysis of red blood cells)
- Alpha - Causes greenish/brownish region around the colonies. Partial lysis of red blood cells
- Beta - Causes distinct zone of clearing. Complete lysis of red blood cells
- Gamma - Only growth present
What is blood agar and how does it work to detect hemolysis?
Blood agar plate is used to determine if a microbe has hemolytic properties.
What are the implications of each type of hemolysis on host organisms?
Beta - Beta-complete hemolysis (Clear zone around colonies)
Alpha - Partial Hemolysis (Opaque zone around colonies)
Gamma - No Hemolysis
What species are normally found on human skin?
Bacteria, Fungi, and viruses
What defenses does the body have for fighting off pathogenic organisms on the skin?
Mechanical,Chemical, and Microbial
Where are you most likely to find skin organisms?
Epidermis
What characteristics might you expect from species that live on skin?
- They are resident
- They live in conditions that have moisture and in chemicals that are naturally occur in our bodies
What is the importance of normal flora in the urinary tract?
The normal flora is important for defense against infectious diseases.
How can you determine if a person has a urinary tract infection?
Laboratory examination of urine. I am using midstream urine specimen.
What does dark metallic growth on an EMB plate mean about a urine sample? What
about a halo of clearing around a colony on a blood agar plate?
- Dark metallic growth on EMB: EMB media contains lactose. This means the urine sample contains a bacterium that is gram-negative, ferments lactose
- Halo of clearing around a colony on Blood Agar (BA) plate: Halo represents Beta hemolysis as complete lysis of RBCs. Beta Hemolysins are associated with pathogenic bacteria.
What is the purpose of collecting a mid-stream sample?
Mid-stream catch is so you get only the urine sample. If you start at the beginning, you could include bacteria from external genitalia which you want to avoid.
What is the difference between an antiseptic and a disinfectant?
Antiseptics are chemicals that are meant to be applied to living tissue. Disinfectants are chemicals that are intended to be applied to surfaces of nonliving
What is the difference between a bactericidal and a bacteriostatic compound?
Bacteriostatic means that the agent prevents the growth of bacteria.
Bactericidal means that it kills the bacteria
How can you determine which species are sensitive to an antiseptic?
Less clear because there is no specific range for ZOI for antiseptics to determine if bacteria are resistant or sensitive. The greater the ZOI for the antiseptic, the more sensitive the species is to the antiseptic.
Why is it important to standardize this test? What parts of the test are standardized?
It is important to standardize this test because it ensures consistent and accurate results. All aspects of the Kirby test are standardized
