INF1 - F. CLASSES OF ANTIMICROBIALS-COVERED

Question 1

what does bacteriostatic mean

Answer 1

cells stop dividing but remain viable

Question 2

what does bactericidal mean

Answer 2

cells are killed but dead cells remain

Question 3

what does bacteriolytic mean

Answer 3

cells are killed and broken down

Question 4

what is minimum bactericidal concentration (MBC)

Answer 4

lowest conc of an antimicrobial agent that kills 99.9% original inoculum

Question 5

what is minimum inhibitory concentration (MIC)

Answer 5

highest dilution antibiotic prevents overnight visible growth

Question 6

properties of an antibiotic

Answer 6

systemic antimicrobial action
low host toxicity
targeted selective toxicity
naturally occurring or synthetic
bacteriostatic or bactericidal

Question 7

properties of a non-antibiotic antimicrobial (antiseptic/disinfectant/preservative)

Answer 7

ex vivo use only
high host toxicity (gloves to protect skin)
broad, non-selective toxicity
chemical agents - biocides
bacteriostatic, bactericidal, bacteriolytic

Question 8

properties of antiseptic

Answer 8

• against sepsis: prevent systemic infection
• destruction or inhibition of micro-organism on living tissues
• non-toxic to host
• for ex-vivo use (preoperative, wounds, mouth)
• can be effective disinfectants at higher concentrations eg - alcohol

hand sanitiser
sudocream
iodine for pre-surgery

Question 9

properties of disinfectants

Answer 9

• remove microorganisms from inanimate objects/surfaces
• kill or reduce numbers to a suitable level
• most are too toxic for use on body tissues
• aka germicides or sterilants/cold sterilisation

alcohol based gel scrubs

Question 10

properties of preservatives

Answer 10

• prevent microbial contamination
• non-toxic to humans
• low antimicrobial effect ‘at use’ concentrations (‘static’ behaviour)
• lower levels of activity than antiseptics/disinfectants
• BP says must be effective against 2 bacteria, yeast and a mould

Question 11

what microorganisms are most susceptible to biocides

Answer 11

fungi
gram -ve bacteria
cocci
lipid enveloped viruses

Question 12

what stages of life cycle are most susceptible to biocides

Answer 12

vegetative cell

Question 13

how does biocides reach their target

Answer 13

• interaction with cell wall via electrostatic or hydrophobic interactions
• entry via porin channels or diffusion
• no specific receptor/uptake mechanisms

*higher the pH, more electronegative cell surface so quaternary NH3+ compounds are more effective (biocide)

Question 14

what is antimicrobial activity of biocides influenced by and how do they exert their activity

Answer 14

• affinity of biocide to cell which is influenced by environmental factors - conc, temp, pH, solubility
• structural damage of cell wall/membrane or interactions with cellular components
• progress from bacteriostatic to bactericidal as biocide concentration increases
• selective permeability changes, reverse enzyme inhibition, structural damage, leakage, autolysis, lysis, cytoplasm coagulation

Question 15

can a cell be resistant to biocides

Answer 15

• yes, but not often seen as biocide is short lasting
• cause: inappropriate use eg - dilution
  (gram -ve bacteria more reistant to bicodes)