Quiz 4

Question 1

What is the purpose of each test used? (Coliform Bacteria)

Answer 1

• 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.

Question 2

What is the difference between each test (think media components and what they tell you
about the bacterial physiology for positive and negative results)

Answer 2

• 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

Question 3

What is an indicator species and why is it used in this context? (Coliform)

Answer 3

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.

Question 4

What are the characteristics of a coliform?

Answer 4

• 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

Question 5

What is a nosocomial infection and how is it acquired?

Answer 5

Nosocomial infections are infections acquired in a medical facility. They can be acquired through direct contact (Person to Person) , indirect contact (Contaminated Surfaces)

Question 6

What are the differences between endogenous and exogenous infections?

Answer 6

• Endogenous - Body’s normal microorganisms may become pathogenic
• Exogenous - Pathogen enters a body from the environment (Contact with contaminated surface)

Question 7

What is a fomite and what type of transmission is it involved in?

Answer 7

Fomites are nonliving objects capable of transferring. Surface and skin transmission

Question 8

What is coagulase and why does it matter in the context of bacterial infections?

Answer 8

Coagulase is an enzyme that causes a clot to form around the bacteria and essentially protects it from being attacked by the hosts phagocytes

Question 9

What test is done to detect it? How does the test work? (Coagulase production by pathogenic staphylococci)

Answer 9

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))

Question 10

What types of hemolysis exist? What do they look like? (Hemolysis of red blood cells)

Answer 10

• 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

Question 11

What is blood agar and how does it work to detect hemolysis?

Answer 11

Blood agar plate is used to determine if a microbe has hemolytic properties.

Question 12

What are the implications of each type of hemolysis on host organisms?

Answer 12

Beta - Beta-complete hemolysis (Clear zone around colonies)

Alpha - Partial Hemolysis (Opaque zone around colonies)

Gamma - No Hemolysis

Question 13

What species are normally found on human skin?

Answer 13

Bacteria, Fungi, and viruses

Question 14

What defenses does the body have for fighting off pathogenic organisms on the skin?

Answer 14

Mechanical,Chemical, and Microbial

Question 15

Where are you most likely to find skin organisms?

Answer 15

Epidermis

Question 16

What characteristics might you expect from species that live on skin?

Answer 16

• They are resident
• They live in conditions that have moisture and in chemicals that are naturally occur in our bodies

Question 17

What is the importance of normal flora in the urinary tract?

Answer 17

The normal flora is important for defense against infectious diseases.

Question 18

How can you determine if a person has a urinary tract infection?

Answer 18

Laboratory examination of urine. I am using midstream urine specimen.

Question 19

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?

Answer 19

• 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.

Question 20

What is the purpose of collecting a mid-stream sample?

Answer 20

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.

Question 21

What is the difference between an antiseptic and a disinfectant?

Answer 21

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

Question 22

What is the difference between a bactericidal and a bacteriostatic compound?

Answer 22

Bacteriostatic means that the agent prevents the growth of bacteria.

Bactericidal means that it kills the bacteria

Question 23

How can you determine which species are sensitive to an antiseptic?

Answer 23

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.

Question 24

Why is it important to standardize this test? What parts of the test are standardized?

Answer 24

It is important to standardize this test because it ensures consistent and accurate results. All aspects of the Kirby test are standardized

Question 25

What makes the Mueller Hinton agar especially useful for this test?

Answer 25

helps to mediate the rate of diffusion of the antimicrobial more effectively than other types of media

Question 26

How can you determine if an organism is sensitive/resistant to an antibiotic?

Answer 26

• To determine if an organism is sensitive or resistant to an antibiotic, you measure the diameter of the zone of inhibition. Then look at the specific range for the unique antibiotic to see what value range is considered sensitive or resistant.
• If there is no zone of inhibition, this tells you that it is likely resistant to an antibiotic.

Question 27

Which species are identified by this stain? Are these species of medical importance?
What do these species have to do with armadillos?

Answer 27

• Most acid-fast bacteria fall in the genus Mycobacterium, not gram (+ or -), rod-shaped, causes Leprosy and tuberculosis
• When looking at medical importance, mycobacterium tuberculosis is important to look at. Affects people with immune deficiencies such as aids
• Leprosy, Mycobacterium leprae, Some armadillos are naturally infected with the bacteria that cause Leprosy, only other hosts besides humans

Question 28

Why is gram staining a poor choice for acid fast organisms?

Answer 28

• You can’t gram stain acid-fast bacteria because it has a different cell wall structure, the stain won’t pass through
• Difficult for water-based dyes to enter the cell so must be forced in, typically with heat

Question 29

What are the characteristics of an acid-fast bacterial cell wall?

Answer 29

waxy since the high lipid amount makes them very hydrophobic and impenetrable

Question 30

What reagents are used and what were their purposes?

Answer 30

• Carbol fuchsin - lipid soluble and contains phenol which helps the stain penetrate the cell wall (all pink)
• Acid alcohol- removes stain from non-acid fast cells; fuchsin complex stays in acid-fast cells b/c the high lipid content does not allow decolorizer to enter their cells
• Methyl blue- stain non acid-fast bacteria (blue)