Mechanisms of antimicrobial action

Question 1

Define antiseptic

Answer 1

disinfecting agents with sufficiently low toxicity for host cells that they can be used directly on skin, mucous membranes, or wounds

Question 2

Define disinfectant

Answer 2

strong chemical agents that inhibit or kill microorganisms

Question 3

Define sterilant

Answer 3

kill both vegetative cells and spores when applied to materials for appropriate times and temperatures

Question 4

What is of primary importance for antiseptics

Answer 4

selective toxicity (toxicity to microorganisms but not to human cells)

Question 5

use of antiseptics

Answer 5

• treatment of skin infections
• prevention of infections in cuts and wounds
• cleaning the skin area of surgery from microorganisms
• prophylaxis and treatment of infections in mucosal areas such as mouth, nose and vagina that are open to environment
• as a scrub for surgeons and the medical personnel

Question 6

Classification of antiseptics

Answer 6

1. Those that denature proteins (cidal)
2. Those that cause osmostic disruption of the cell (cidal)
3. Those that interfere with specific metabolic processes (growth arrest/ static)

Question 7

What is the mechanism of action of phenols, iodine, alcohols, aldehydes and metallic compounds

Answer 7

denature proteins and DNA bases

Question 8

What is the mechanism of action cationic detergents

Answer 8

• interfere with plasma membrane’s
• permeability and cause leakage of
• enzyme, coenzyme and metabolites

Question 9

What is the mechanism of action oxidizing compounds

Answer 9

oxidize functional molecules in the microorganisms

Question 10

how do iodophores work

Answer 10

• iodine and other free halogens oxidize the -SH groups of proteins and enzymes
• antiseptic or disinfectant
• kill vegativitive bacteria, mycobacteria, fungi, lipid containing viruses (spores on prolonged use)

Question 11

how do alcohols work as antiseptics and disinfectants

Answer 11

• reduce bacterial numbers 90% when applied to skin
• rapidly kill vegetative bacteria, fungi and inactivate lipophilic viruses
• denature proteins and disturb the membrane permeability of bacteria
• limited antibacterial spectrum

Question 12

How does chlorhexidine work

Answer 12

• water soluble chlorhexidine diglouconate is used as an antiseptic
• spore germination inhibitied
• strongly adsorbs to bacterial membranes and causes leakage of small molecules and precipitation of cytoplasmic proteins
• resistant to inhibition by blood or organic material

Question 13

what types of bacteria is chlorhexidine most effective against

Answer 13

gram positive cocci

Question 14

what are the targets of action for antibiotics plus examples

Answer 14

1. inhibition of cell wall synthesis e.g. penicillins
2. inhibition of protein synthesis e.g. tetracyclins
3. inhibition of nucleic acid replication and transcription e.g. rifampin
4. injury to plasma membrane e.g. polymyxinB
5. inhibition of synthesis of essential metabolites e.g. trimethoprim

Question 15

by what mechanisms does antibiotic resistance occur

Answer 15

1. blocked entry by cell wall
2. inactivating enzymes
3. alteration of target molecules
4. Efflux of antibiotic