Lecture 5: chemical control methods Flashcards
chemical control methods
- disinfectants
- preservatives
- antiseptics
disinfectants
- chemicals that are capable of killing microorganisms
- cannot be applied to tissues
- in the lab they are applied to inanimate surfaces and used in discard jars and buckets
antiseptics
- chemical agents that kill or inhibit growth of microorganisms
- are sufficiently non toxic to be applied to living tissues
preservatives
- included in pharmaceutical preparations or foods to prevent microbial spoilage of the product
chemical control methods are used for:
- antisepsis of skin
- disinfection of equipment which cannot be sterilised by other methods
- cleaning up spills of cultures or infected clinical material
- disinfection of surfaces
- as preservatives
conditions influencing the effectiveness of antimicrobial agents
- population size
- properties of the chemical agent
- types of microbe
- environmental factors
- toxicity of the agent
population size
- only a fraction of the microorganisms die during a given time interval
eg: 90% in the first minute and 90% of the remaining die in the next minute - therefore the time it takes to achieve sterility depends in part on the number of organisms present at the beginning of sterilisation
properties of the chemical agent
- dilution
- higher concentrations are sometimes inhibitory
- all chemicals should have a concentration which is within their optimal range
eg: ethanol is used at 70% bc activity of ethanol is enhanced by the presence of water - pH
- all chemicals have an ideal pH
type of microbe
- phase of growth
actively growing phase = taking up chemicals from the external environment rapidly, will take up harmful chemicals, more likely to kill microbes - polymer, capsule or liquid production
- may act to limit the diffusion of chemicals from the external environment into the cell - altered cell wall or membrane or modified sensitive sites
- especially if there is a chemical which will be harmful, they can change the resistance in that area of the cell to protect it - cellular aggregation/biofilms
- microbes like to stick together to from aggregations/biofilms, so bacterial cells in the middle get protection from chemicals in the environment - resistant structures
- bacterial endospores, have a higher resistance to chemicals in the environment
descending order of resistance to germicidal chemicals (most resistant –> least resistant)
bacterial endospores, mycobacteria, nonlipid or small viruses, fungi, vegetative bacteria, enveloped or medium sized viruses
environmental factors
- neutralisation by organic material
- all body fluids are organic material
- they can neutralise the active ingredients of the disinfectants
- lots of organic material in the environment so need a disinfectant which in not inactivated by that fact - temperature
- strongly influences the action of disinfecting agents
- tend to work better at higher temps, but not always
toxicity of the agent
- we want our disinfectant to be toxic enough to kill the microbes, but not to toxic for living tissue and the environment
- we have to match our chemical agent to the specific microbe that could be present
ideal chemical control agent
- high antimicrobial activity
- broad spectrum of antimicrobial activity
- stability
- homogeneity
- adequate solubility
- minimum toxicity
- detergent activity
- minimum material effects
- minimum inactivation by organic material
- activity at ordinary temperatures
- deodorising ability
- low costb
use of specific agents to control microbial growth
- alcohol
- aldehydes
- quaternary ammonium compounds
- halogens and hydrogen peroxide
- heavy metals
- phenols and phenolic derivatives
- sterilising gases
chemical agent = alcohol
advantages = non toxic
disadvantages = endospores not killed, poor penetration
major use = skin swab prior to injection
mode of action = denatures proteins and membranes (by denaturing lipids in cell membrane)
chemical agent = aldehydes
advantages = kills endospores and vegetative cells
disadvantages = toxic
major use = preserving tissues
mode of action = inactivates enzymes by adding alkyl grp (adds small chain of carbon atoms into bacterial proteins which inactivates them and kills the cell )
chemical agent =quaternary ammonium compounds
advantages = non irritant, detergent action
disadvantages = endospores not killed, inactivated by organic matter
major use = soaps, detergents, skin antiseptics
mode of action = physical removal, disrupts membranes (penetrating and destroying cytoplasmic membrane)
chemical agent = halogens and hydrogen peroxide
advantages = wide activity
disadvantages = inactivated by organic matter, short life
major use = water chlorination, skin antiseptic
mode of action = oxidises vital biochemicals
- hydrogen peroxide used at 3%
chemical agent =heavy metals
advantages = none
disadvantages = toxic
major use = drops in eyes of newborns, silver dressings
mode of action = reacts with sulpydral groups
chemical agent = phenols and phenolic derivatives
advantages = wide spectrum of activity
disadvantages = endospores not killed, some toxic, skin irritant
major use = home and hospital use, mouthwashes
mode of action = denatures proteins, disrupts membranes
chemical agent = sterilising gases
advantages= kills endospores
disadvantages = explosive and toxic to humans
major use = pre wrapped disposable items
mode of action = strong alkylating agent
