Lecture 12: Antimicrobials

Question 1

How is sterilization and pasteurization different?

Answer 1

Sterilization must eliminate the most heat-resistant organisms, usually bacterial endospores.

Pasteurization does not sterilize liquids, but reduces microbial load, killing most pathogens and inhibiting the growth of spoilage microorganisms.

Question 2

What are typical uses for sterilization and pasteurization?

Answer 2

sterilization - hospital, surgery room
pasteurization - food, diary products

Question 3

What is the decimal reduction time and how is it affected by temperature?

define

Answer 3

The decimal reduction time (D-value) is the time required, at a specific temperature, to reduce a microbial population by 90% (one log cycle), and it’s significantly affected by temperature; higher temperatures lead to shorter D-values, meaning faster microbial inactivation

Question 4

What is the difference between antimicrobial activities of ionizing radiation vs. UV radiation?

Answer 4

UV Radiation - 220-300 nm wavelengths, causes DNA damage, surface decontamination (non-penetrating)

Ionizing radiation - damage through generation of highly reactive ions (OH dot), absorbed radition (rads or grays), decimal dosage can be calculated

Question 5

What is a decimal reduction dose and how does it relate to a lethal dose of radiation?

Answer 5

In practice, the lethal dose (amount of radiation to kills whole population) used to kill organisms is sufficient to reduce populations by a factor of 10-12 (i.e., 12 D10 values)

Question 6

What are the three classes of filters described in class?

Answer 6

Depth Filters - fibrous nature, used to pre-filter liquids, sterilization of air (HEPA)

Standard Membrane Filter - ~80% open pore, traps filtrate on surface, common heat-sensitive liquid sterilization filter

Nucleopore Membrane Filter - formed by etching polycarbonate film after nuclear radiation

Question 7

How to HEPA filters fit into this classification?

Answer 7

HEPA is commonly used in operating room and patient and exmaination room

Question 8

What is the difference between bactericidal, bacteriostatic and bacteriolytic chemicals?

Answer 8

Bactericidal chemicals kill bacteria, bacteriostatic chemicals inhibit bacterial growth, and bacteriolytic chemicals cause bacteria to burst and release their contents

Question 9

Compare and contrast MIC and disc diffusion assays for assessment of chemical antimicrobial activity.

Answer 9

Minimum Inhibitory Concentration - Make serial dilutions of that chemical –> Inoculum –> incubate –> look at growth –> tube has hasn’t concentration can kill everything –> then you see growth at some dilution

Disc-Diffusion - microbial lawn (a uniform growth of bacteria) –> Paper disks, each containing a specific antibiotic –> incubated –> presence and size of zones of inhibition (areas where bacterial growth is inhibited) around the disks are measured.

Question 10

Compare and contrast antispetics and chemotherapeutic agents.

Answer 10

Sterilants - gaseous infusion of chemicals (e.g., formaldehyde, ethelene oxide), sterilization of heat sensitive materials

Disinfectants - kill most organisms (not endospores) (e.g., cationic detergents)

Sanitizers - reduce microbial populations to “safe” levels (e.g., weak solutions of cholorine and iodine compounds)

Antiseptics (germicides) - antimicrobial agents that are safe for application to living tissue (e.g., alcohol solutions, hand santizers)

Question 11

Define and give examples

Synthetic agents

Answer 11

Growth Factor Analogs - Sulfa Drugs, Isoniazid, Nucleic Acid Analogs​

Quinolones - DNA gyrase inhibitors (e.g., nalidixic acid, Ciprofloxin)

Question 12

Define and give examples

Semi-synthetic agents

Answer 12

• chemically modified derivatives of antibiotics
• possess properties that increased their efficacy
• ex: penicillin

Question 13

Define and give examples

Antibiotics

Answer 13

• can be natural or semi-synthetic
• natural - produced by fungi and bacteria, most are not useable as chemotherapeutics
• ex: tetracycline, doxycycline

Question 14

Outline activity

Sulfa drugs

Answer 14

• sulfamides inhibit folic acid synthesis
• Bacteria can’t produce folic acid, which is essential for nucleotide synthesis → inhibits DNA/RNA synthesis

Question 15

Outline activity

Penicillin

Answer 15

• Inhibits cell wall synthesis
• Target: Penicillin-binding proteins (PBPs), specifically transpeptidase
• Prevents cross-linking of peptidoglycan → weakens cell wall → cell lysis

Question 16

Outline activity

Rifampin

Answer 16

• Inhibits RNA synthesis
• Binds to bacterial RNA polymerase –> Prevents initiation of transcription

Question 17

Outline activity

Quinolones

Answer 17

• ex: cirpofloxacin
• Inhibit DNA gyrase and topoisomerase IV (DNA replication)

Question 18

Outline activity

Tetracycline

Answer 18

Inhibits protein synthesis