Biocides

Question 1

What are Biocides?

Answer 1

Agents that kill microbes, or inhibit their growth (Biostatics)

Question 2

What are the two classes of antimicrobial agents?

Answer 2

Class A: Biocides
-broad spectrum, they kill bacteria, fungi, viruses
-Mechanism is non-specific: primary way is through the cell membrane, and destroy proteins, lipids, DNA

Class B: Antibiotics
-narrow spectrum, only kills bacteria
-MOA is specific: Penicillin inhibits cell wall synthesis, and Tetracycline inhibits protein synthesis -> Bacteria can develop resistance to ANTIBIOTICS

Question 3

What are the different types of BIOCIDES?

Answer 3

Antiseptic: broad-spectrum, non-toxic for skin and mucosal membrane (lower concentration than disinfectant and higher than preservatives)

Disinfectant: broad spectrum, chemicals toxic to our skin, only for objects (higher concentration than Antiseptics and preservatives)

Preservatives: broad spectrum, used in pharmaceutical products to prevent the growth of microorganisms (low concentration)

Question 4

What do different BIOCIDES have in common?

Answer 4

Some ingredients are commonly used in BIOCIDES, but with different concentrations (f.e. chlorhexidine, iodine)

Question 5

How do BIOCIDES work?

Answer 5

-Disruption of the cell wall (phospholipids) and proteins there -> LYSIS
-Intracellular coagulation
-chemical modification of proteins and nucleic acid

Question 6

What is the difference between a Sanitizer and a Disinfectant?

Answer 6

Sanitizer
-reduce microorganisms to a number acceptable for public health
-antiseptic -> skin
-kills 99.9 3-log or 99.999 4-log in about 30s
-mostly 70% alcohol

Disinfectants
-kills 99.9999% 6 log reduction, in less than 10 min (stronger than Sanitizer)
-for objects
-can contain other chemicals

Question 7

What is the Dwell time?

Answer 7

Length time of which the product stays on the surface before it evaporates

Question 8

What affects BIOCIDAL ACTIVITY?
TEMPERATURE

Answer 8

-Temperature: Speed of reaction increases with temperature

-Temperature coefficient (Q10)= change in rate of kill for 10°C rise
Q10 = 4 -> rate of kill will be times 4, for each 10°C raise

Question 9

What affects BIOCIDAL ACTIVITY?
pH

Answer 9

-pH: only the unionized form can enter the plasma membrane of a microbe, for acidic agents an acidic pH is required, for basics a basic pH

-Solubility: some lipid-solubility is needed

Question 10

What affects BIOCIDAL ACTIVITY?
CONCENTRATION

Answer 10

-Increase in concentration will increase the rate of kill, but the increase is NOT linear

-increase in concentration will reduce the time required to kill (log)

Question 11

What does eta as exponent means?

Answer 11

-Eta (exponent) describes how the rate of kill changes, with the rate of concentration

Example: if the concentration is tripled, you take the value of eta as an exponent (Eta = 2) -> 3^2 = 9 -> rate of kill increases by 9, it takes 9x less time to kill

(Dilution of the concentration will reduce the rate of kill -> it takes more time)

Question 12

2What is the Broth-dilution method?

Answer 12

QUANTITATIVE METHOD
-assay to find the lowest concentration of biocide that inhibits
growth of the population of cells = Minimum inhibitory concentration (MIC) in mg/L

-bacteria is inoculated in different concentrations and incubated over-night -> observe the lowest concentration where no microbial growth has occurred

Question 13

What is the Agar diffusion method?

Answer 13

QUALITATIVE METHOD
-take a filter paper disc and soak it into the BIOCIDE -> put it on different spots of the agar plate and inoculate it with the microbe -> observe the Zone of inhibition

-Biocide dissolves and diffuses through the aqueous phase of agar

The size of the zone of inhibition is dependent on biocide concentration, solubility, diffusion coefficients, concentration exponent

Question 14

What affects BIOCIDAL ACTIVITY?
pH

Answer 14

-pH: only the unionized form can enter the plasma membrane of a microbe, for acidic agents an acidic pH is required, for basics a basic pH

-Solubility: some lipid-solubility is needed, and the length of C chains (f.e. parabens - preservatives) will increase lipophilicity (decreases hydrophilicity), but as lipophilicity increases, the ability to get into a solution of the product decreases
-> so you need a mix of more lipophilic and more hydrophilic preservatives

-problematic for emulsions bc the chance of contamination

Question 15

What affects BIOCIDAL ACTIVITY?
Interaction between excipients and packaging materials

Answer 15

f.e. preservatives should not interact with anything
-charged agents cause the adsorption of ingredients
-adsorption to the container -> decreasing concentration of biocide
-adsorption to polymers (suspending agents: starch, PEG)
-Adsorption of preservatives to suspended oils

Question 16

What are compounds that are incompatible with certain preservatives?

Answer 16

Chlorhexidine -> inorganic anions and anionic surfactants
Benzoates and parabens -> Iron salts
Chlorocresol -> Phosphates
Phenyl mercury salts -> Chloride ions
Bronopol -> Aluminum

Question 17

What affects BIOCIDAL ACTIVITY?
Photodegradation and volatility

Answer 17

Phenolics, Mercury, or ammonium compounds preservatives are prone to photodegradation -> colored bottles used

-Volatile preservatives can be lost through evaporation -> Benzoic acids, Benzyl alcohol -> tight container

Question 18

Kill curves:

Answer 18

-Quantitative information about the rate of cell death (decreasing Colony forming units CFU after time)

-Inoculate biocides with the known concentration of microbes and take samples over time and determine the number of surviving cells

Question 19

Preservative efficacy testing

Answer 19

-Similar to the Kill curve
-The product is tested with the preservative in its final container to ensure it works in real world
-Microbes inoculated and samples are observed in different intervals

Question 20

Disinfectant Testing:

Answer 20

-Must possess bactericidal, sporicidal, fungicidal, and virucidal properties

-Suspension test (disinfectant in suspension form): Inoculation and sampling over time (CFU)

-Capacity test: reapplying the microbes repeatedly to see what the maximum capacity of the disinfectant is

-Surface test: microbes are dried to the surface of cylinders to simulate a real situation -> then put into disinfectants -> after some time it is checked for microbial growth

Question 21

REMINDER: What efficacy standards are required for Disinfectants

Answer 21

6-log (1 million-fold) reduction of microbes in 10 minutes