Agars & Antibiotics (Lab Only) Flashcards
what is microbiological media?
(AKA bacterial culture media)
growth medium used to grow bacteria
when is bacterial culture media used?
when a specific bacterium must be grown in order to confirm the presence of an infection or study a specific bacterium further
chemical media
- uses chemicals in precise amounts to provide needed nutrients to an organism
- AKA chemically defined & can be duplicated exactly
organic media
- 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
selective media allows for…
growth of certain organisms while excluding others
differential media allows for…
determination of certain types or strains of bacteria based on a reaction
name 5 types of selective media
- eosin methylene blue
- YM (yeast extract, malt extract agar)
- MacConkey agar
- mannitol salt agar
- sabouraud’s agar
name 4 types of differential media
- blood agar
- eosin methylene blue
- MacConkey agar
- mannitol salt agar
define selective toxicity
selectively finding and destroying pathogens without damaging the host
define antibiotic
a substance produced by a microbe that, in small amounts, inhibits another microbe
define antimicrobial drugs
synthetic substances that interfere with growth of microbes
define narrow spectrum of microbial activity
drugs that affect a narrow range of microbial types (given first to avoid resistance)
define broad-spectrum antibiotics
affect a broad range of gram+ or gram- bacteria (what we worry about for antibiotic resistance)
name 2 actions of antimicrobial drugs
bactericidal
bacteriostatic
define bactericidal
kill microbes directly (eg. cooking)
define bacteriostatic
prevent microbes from growing (eg. freezing)
Name 5 actions of antibiotics upon bacteria
- inhibit cell wall synthesis
- inhibit protein synthesis
- injure plasma membrane
- inhibit nucleic acid synthesis
- inhibit synthesis of essential metabolites
why are the best antibiotics for humans ones that act by inhibiting cell wall synthesis?
humans have no cell walls
what effect do antibiotics that inhibit protein synthesis have on males and females?
Males: sterilization (should avoid giving to young men)
Females: stops activity of birth control pills
How do antimycotics act to kill fungi? Which human cell is impacted the most by this?
- injures the plasma membrane (very permeable)
- RBCs
why do we avoid giving Cipro (quinolone) to people of childbearing age?
inhibits nucleic acid synthesis, which impacts human cell division
antibiotics that inhibit synthesis of essential metabolites are often used to treat ____
UTI’s
(eg. sulfanilimide)
the “-cillin” antibiotics inhibit cell wall synthesis because they contain a ____
B-lactam ring
Over the counter drugs/ointments such as Neosporin should not be used long term because…
they cause injury to the plasma membrane
the quinolones, particularly Cipro, are very potent, and can cause what negative effects to humans?
- phototoxicity (eyes)
- neurotoxicity (nerve endings)
- cardiotoxicity
- glucose metabolism dysfunction (^diabetes risk)
- increased risk (400x) for tendon rupture (achilles)
the disk-diffusion method (Kirby-Bauer test) tests the effectiveness of ____
chemotherapeutic agents
in the disk-diffusion method, a zone of inhibition (clearing) around the disk determines…
sensitivity of the organism to the antibiotic and/or antiseptics/disinfectants
(no clearing = resistant)
name 4 mechanisms of resistance (i.e., how bacteria get rid of an antibiotic)
- 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
name 5 examples of misuse of antibiotics
- 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
name 3 sources for mannitol salt agar?
skin
nose
fomites (surfaces)
what effect does staphylococcus epidermidis have on any media? why?
- no effect on any media (may turn slightly purple)
- has NO TOXINS!
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?
staphylococcus aureus
(source: skin)
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.
staphylococcus epidermidis
The terms “complete or incomplete” hemolysis on blood agar are used to indicate a sample of what organism?
staphylococcus aureus
The terms “beta or alpha” hemolysis on blood agar are used to indicate a sample of what organism?
Streptococcus
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?
throat (source) = most likely streptococcus pyogenes, which has beta hemolytic activity
A sample taken from a boil is plated on blood agar. You see complete clearing. What hemolytic activity is seen here? Why?
skin (source) = most likely staphylococcus aureus which has complete hemolytic activity
What is the difference between complete and incomplete hemolysis?
complete = can see through it
incomplete = cannot see through it
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?
staphylococcus aureus will cause incomplete hemolysis
(staph epi doesn’t change media, just grows)
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?
- any other streptococcus (eg. strep viridans, strep pneumonaie)
- alpha hemolysis
How does E. Coli appear when grown on Eosin methylene blue agar? What diagnosis is this method commonly used for?
- GREEN SHEEEEEEEN!!!!!!
- UTI’s
What will grow on MacConkey agar?
feces (enterics)
What will grow on Sab Dextrose agar? Why?
selective for fungi due to presence of sugar and acid
(will rarely grow bacteria)
How do yeast and molds differ in appearance when grown on Sab Dextrose agar?
yeast = slimy colonies
molds = fuzzy/hairy
Chromagar MRSA II is selective/differential for ____, which will grow as ____ colonies
- methicillin-resistant staphylococcus aureus (MRSA)
- reddish-pigmented
