Exam 2 deck 2

Question 1

Disk Diffusion method

Answer 1

Put filter paper soaked in a chemical on a culture

The bigger the zone of inhibition, the more affective the chemical agent

Question 2

Phenols

Answer 2

• Injure lipids in plasma membranes
• can be bacteriostatic or bactericidal
• active for a long time–> doesn’t break down fast
• antiseptic, but burns
• e.g. lysol

Question 3

Bisphenols

Answer 3

• disrupt plasma membrane
• Hexachlorophene is affective against G-
• Triclosan used to be common, but it leaves behind super resistant bacteria with no competition

Question 4

Essential Oils

Answer 4

• hydrocarbon mixtures from plants
• effective due to phenolics and terpenes
• e.g. oregano and oranges (flavor + preservatives)
• weaken cell wall of bacteria?

Question 5

2 Halogens discussed in class

Answer 5

Iodine and chlorine

Question 6

Iodine

Answer 6

• Impairs protein synthesis and alters membrane
• Tincture Iodine is a solution in aqueous alcohol
• Iodophor is combined with organic molecules (doesn’t stain)

Question 7

Chlorine

Answer 7

• oxidizing agent –> shuts down cellular enzyme systems
• bleach easily enters cell wall (HOCl)
• chloramine = chlorine and ammonia

Question 8

Alcohol

Answer 8

• denatures proteins and dissolves lipids
• no effect on endospores or non-enveloped viruses
• ethanol and isopropyl require water to be affective
• methanol is toxic

Question 9

Heavy metals

Answer 9

• Ag, Hg, Cu, Zn
• very small amount exert antimicrobial activity
• They denature proteins and act on -SH groups of proteins
• e.g. put silver nitrate in babies’ eyes

Question 10

Surface-Active Agents

Answer 10

Soap

-degerming through emulsification (not really antiseptic)

Question 11

Quaternary Ammonium Compounds

Answer 11

• Quats
• Denature proteins and disrupt the membrane
• effective on most things except endospores

Question 12

Chemical Food Preservatives

• what do they do?
• what are some examples?

Answer 12

• they inhibit metabolism in microbes, but humans can metabolize them
• sorbic acid, benzoic acid, and calcium propionate
• sodium nitrate
• nisin and natamycin

Question 13

Sorbic acid, benzoic acid, calcium propionate

Answer 13

control molds and bacteria in food and cosmetics

Question 14

sodium nitrate

Answer 14

prevents endospore germination

• in hot dogs, sausage, bacon, ham
• there’s some worry that it reacts with amino acids to cause cancer

Question 15

Nisin and natamycin

Answer 15

antibiotics solely used to prevent cheese spoilage

Question 16

Aldehydes

Answer 16

• one of the most affective antimicrobials
• inactivate proteins by cross-linking their functional groups
• formaldehyde preserves specimen
• glutaraldehyde is one of a few liquid chemical sterilizing agents (used for medical equipment)

Question 17

Chemical sterilization

Answer 17

• gaseous sterilant cause alkylation which replaces proteins’ hydrogen atoms with free radicals
• cross links nucleic acids and proteins
• used for heat-sensitive materials
• e.g. ethylene oxide which is affective, but toxic and explosive

Question 18

Are chemical and physical methods of microbial control specific?

Answer 18

NO! chemotherapeutic drugs are, though