Agars & Antibiotics (Lab Only)

Question 1

what is microbiological media?

Answer 1

(AKA bacterial culture media)
growth medium used to grow bacteria

Question 2

when is bacterial culture media used?

Answer 2

when a specific bacterium must be grown in order to confirm the presence of an infection or study a specific bacterium further

Question 3

chemical media

Answer 3

• uses chemicals in precise amounts to provide needed nutrients to an organism
• AKA chemically defined & can be duplicated exactly

Question 4

organic media

Answer 4

• contains organic material (blood, egg yolk) that a certain bacterium may need to grow
• AKA complex, and cannot be duplicated exactly due to hormones & other factors based on the source & host of additive

Question 5

selective media allows for…

Answer 5

growth of certain organisms while excluding others

Question 6

differential media allows for…

Answer 6

determination of certain types or strains of bacteria based on a reaction

Question 7

name 5 types of selective media

Answer 7

• eosin methylene blue
• YM (yeast extract, malt extract agar)
• MacConkey agar
• mannitol salt agar
• sabouraud’s agar

Question 8

name 4 types of differential media

Answer 8

• blood agar
• eosin methylene blue
• MacConkey agar
• mannitol salt agar

Question 9

define selective toxicity

Answer 9

selectively finding and destroying pathogens without damaging the host

Question 10

define antibiotic

Answer 10

a substance produced by a microbe that, in small amounts, inhibits another microbe

Question 11

define antimicrobial drugs

Answer 11

synthetic substances that interfere with growth of microbes

Question 12

define narrow spectrum of microbial activity

Answer 12

drugs that affect a narrow range of microbial types (given first to avoid resistance)

Question 13

define broad-spectrum antibiotics

Answer 13

affect a broad range of gram+ or gram- bacteria (what we worry about for antibiotic resistance)

Question 14

name 2 actions of antimicrobial drugs

Answer 14

bactericidal
bacteriostatic

Question 15

define bactericidal

Answer 15

kill microbes directly (eg. cooking)

Question 16

define bacteriostatic

Answer 16

prevent microbes from growing (eg. freezing)

Question 17

Name 5 actions of antibiotics upon bacteria

Answer 17

• inhibit cell wall synthesis
• inhibit protein synthesis
• injure plasma membrane
• inhibit nucleic acid synthesis
• inhibit synthesis of essential metabolites

Question 18

why are the best antibiotics for humans ones that act by inhibiting cell wall synthesis?

Answer 18

humans have no cell walls

Question 19

what effect do antibiotics that inhibit protein synthesis have on males and females?

Answer 19

Males: sterilization (should avoid giving to young men)
Females: stops activity of birth control pills

Question 20

How do antimycotics act to kill fungi? Which human cell is impacted the most by this?

Answer 20

• injures the plasma membrane (very permeable)
• RBCs

Question 21

why do we avoid giving Cipro (quinolone) to people of childbearing age?

Answer 21

inhibits nucleic acid synthesis, which impacts human cell division

Question 22

antibiotics that inhibit synthesis of essential metabolites are often used to treat ____

Answer 22

UTI’s
(eg. sulfanilimide)

Question 23

the “-cillin” antibiotics inhibit cell wall synthesis because they contain a ____

Answer 23

B-lactam ring

Question 24

Over the counter drugs/ointments such as Neosporin should not be used long term because…

Answer 24

they cause injury to the plasma membrane

Question 25

the quinolones, particularly Cipro, are very potent, and can cause what negative effects to humans?

Answer 25

• phototoxicity (eyes)
• neurotoxicity (nerve endings)
• cardiotoxicity
• glucose metabolism dysfunction (^diabetes risk)
• increased risk (400x) for tendon rupture (achilles)

Question 26

the disk-diffusion method (Kirby-Bauer test) tests the effectiveness of ____

Answer 26

chemotherapeutic agents

Question 27

in the disk-diffusion method, a zone of inhibition (clearing) around the disk determines…

Answer 27

sensitivity of the organism to the antibiotic and/or antiseptics/disinfectants
(no clearing = resistant)

Question 28

name 4 mechanisms of resistance (i.e., how bacteria get rid of an antibiotic)

Answer 28

• enzymatic destruction/inactivation of the drug
• prevention of penetration to target site within the microbe (seal off)
• alteration of drug’s target site
• rapid efflux (ejection) of antibiotic

Question 29

name 5 examples of misuse of antibiotics

Answer 29

• using outdated/weakened antibiotics
• using antibiotics for common cold and other inappropriate conditions
• using antibiotics in animal feed
• failing to complete prescribed regimen
• using someone else’s leftover prescription

Question 30

name 3 sources for mannitol salt agar?

Answer 30

skin
nose
fomites (surfaces)

Question 31

what effect does staphylococcus epidermidis have on any media? why?

Answer 31

• no effect on any media (may turn slightly purple)
• has NO TOXINS!

Question 32

A boil was sampled from the leg of a 27-year-old student. It was plated onto mannitol salt agar and turned the media yellow. What is the most likely organism seen here?

Answer 32

staphylococcus aureus
(source: skin)

Question 33

A toddler comes into your practice with a weepy eye. You gather a sample and send it to a testing lab where it is grown out. It grew on mannitol salt and did not cause any change to the media.

Answer 33

staphylococcus epidermidis

Question 34

The terms “complete or incomplete” hemolysis on blood agar are used to indicate a sample of what organism?

Answer 34

staphylococcus aureus

Question 35

The terms “beta or alpha” hemolysis on blood agar are used to indicate a sample of what organism?

Answer 35

Streptococcus

Question 36

A sample taken from a throat swab is plated on blood agar. You see complete clearing. What type of hemolytic activity is most likely seen here? Why?

Answer 36

throat (source) = most likely streptococcus pyogenes, which has beta hemolytic activity

Question 37

A sample taken from a boil is plated on blood agar. You see complete clearing. What hemolytic activity is seen here? Why?

Answer 37

skin (source) = most likely staphylococcus aureus which has complete hemolytic activity

Question 38

What is the difference between complete and incomplete hemolysis?

Answer 38

complete = can see through it
incomplete = cannot see through it

Question 39

A sample is taken from skin/nose/surface and plated on blood agar. When grown out, you cannot see through the media. What is the most likely organism and what hemolytic activity is seen?

Answer 39

staphylococcus aureus will cause incomplete hemolysis
(staph epi doesn’t change media, just grows)

Question 40

A sample is taken from a throat swab and plated on blood agar. When grown out, you see incomplete clearing and a greenish change to the media. What is/are the most likely organism(s) and what hemolytic activity is seen?

Answer 40

• any other streptococcus (eg. strep viridans, strep pneumonaie)
• alpha hemolysis

Question 41

How does E. Coli appear when grown on Eosin methylene blue agar? What diagnosis is this method commonly used for?

Answer 41

• GREEN SHEEEEEEEN!!!!!!
• UTI’s

Question 42

What will grow on MacConkey agar?

Answer 42

feces (enterics)

Question 43

What will grow on Sab Dextrose agar? Why?

Answer 43

selective for fungi due to presence of sugar and acid
(will rarely grow bacteria)

Question 44

How do yeast and molds differ in appearance when grown on Sab Dextrose agar?

Answer 44

yeast = slimy colonies
molds = fuzzy/hairy

Question 45

Chromagar MRSA II is selective/differential for ____, which will grow as ____ colonies

Answer 45

• methicillin-resistant staphylococcus aureus (MRSA)
• reddish-pigmented