Disinfection, Sterilisation & Antibiotics Flashcards
Why control the growth of bacteria? (3)
- Prevent infection of humans, other animals and plants
- Prevent spoilage of food
- Prevent contamination of industrial processes & products
Define; -
- Sterilization
- Disinfection
- Preservation
- Antiseptic
Sterilization: An absolute term meaning destruction or removal of all life forms - esp. microorganisms
-something is either sterile or not
Disinfection: Killing or removal of organisms capable of causing infection (reduce load so that not a problem)
-focuses on pathogenic organisms
-usu on inanimate objects & surfaces w/ chem. agent
Preservation: Treatment or condition that prevents growth of microbes
-usu used for food
Antiseptic: Chem. agent (milder action) used on skin or in living tissues that kills or inhibits microbes
-has to be milder so doesnt damage living tissues
How bacteria die on exposure to physical or chemical factors
-D Value
- Populations of bacteria die at an exponential rate
- not all bacteria are equally sensitive due to different metabolic states, mutations etc.
- Most sensitive bacteria die first, most resistant bacteria die last
D Value: Time taken for a 10 fold reduction in a population
- shorter the time = more effective/efficient the treatment is
- is the way rate of death is measured
Physical Agents for sterilisation (4)
- Heat
i) Incineration
ii) Dry heat
iii) Wet heat - UV radiation
- Ionizing radiation
- Filtration
Sterilisation using heat
-effects of heat
Incineration - what it is and what it’s used for
-Heat degrades nucleic acids, causes disruption and melting of cell membranes and coagulation/denaturation of proteins
i) Incineration: Flame sterilisation, commonly used in laboratory for glass spreaders, wire loops and metal spatulas
- also used for clinical waste and farm buildings
Sterilization using heat; Dry heat
- What it is and does
- what it’s used for - how long & temp
- 2 requirement for it to work
-Dry heat oxidizes cytoplasm as it heats in the absence of water (i.e. in an oven)
*This method requires long times of exposure and very hot temperatures
-not that effective
Used for glassware in lab - 170 degrees Celsius for 2 hours
Sterilization using heat; Wet heat
- what is it
- 3 ways to achieve wet heat
-Moist heat is more efficient than dry heat because tends to coagulate microbial protein
Ways to achieve wet heat;
- Boiling
- Pasteurization
- Tyndallization
Wet heat; Boiling
- What it is effective & ineffective on
- Downfall
(100 degrees Celsius)
-Rapidly kills vegetative bacterial cells, altho viruses can survive longer and spores can survive very long periods (i.e. 20 hours)
*Boiling doesn’t sterilize - therefore inadequate for surgical instruments
Wet heat; Pasteurisation
- What it is used for
- 3 types
-Common for milk products; kills pathogens but not spores
i) LTH = low temp holding (63 deg. for 30 mins)
ii) HTST - “flasth methods” (7 deg for 15-30 secs)
iii) UHT - Ultra - heat treated (150 deg for 3-4 secs)
Wet heat; Tyndallization
- Process & what it targets
- what it doesn’t guarantee
- Is the process of heating material in hydrated state, let material cool so spores germinate and then heat up again before bacteria can sporate. Repeat
- sequential three day cycle of 100 deg for 20 mins used to treat soils (kills spores)
*Doesn’t guarantee sterility in many situations
How to achieve sterility w/ Wet Heat?
- What steam usu works agains
- 4 ways to increase the efficiency of killing by moist heat
- Way steam is altered to be most efficient
-Steam (100 deg) rapidly kills vegetative bacteria, but not viruses & spores
Efficiency of killing by moist heat affected by:
1. Hydration
2. Time of exposure
3. Temp of exposure
4. pH
- Steam under pressure leads to higher temperatures -> rapidly kills bacteria, destroys viruses and spores
- is the most efficient and effective process for routine sterilization
-Carried out using autoclave
Sterilization using UV radiation
- What dose is lethal
- effects
- what it is used for and what it can’t penetrate
- Lethal at 260nm
- Affects DNA: causes thymine dimers that result in mutations and misreading of genes
- Used to sterilize surfaces, atmospheres
- Doesn’t penetrate glass, plastic, paper, water
Sterilization using Ionising Radiation
- E.g.
- What it is good for, not good for
- What it is used for
- Gamma rays
- Excellent for sterilizing agent for bacteria and spores, but not effective for viruses
- Used to sterilize plastics, petri dishes, gloves, syringes; cold sterilization for antibiotics, hormones
Sterilization using Filtration
- What is it & how achieved
- What it is effective and not so effective for
- What it used to sterilize
- Physical removal of microbes using cellulose acetate filters
- achieved by air flow in laminar flow cabinets
- Effective process for bacteria and spores but not so effective for viruses
- Used to sterilize heat sensitive solutions such as serums (vaccines, antibiotics, vitamins)
Techniques for Preservation (3)
- inhibition of bacterial growth*
1. Low temp (freezing, refridgeration)- microbiologists use ultra cold storage to store microbes for years
- Dehydration: Makes water unavailable to bacteria - bacteria need water to grow
- e.g. jams (high sugar content), salted foods - both have high osmotic potential
- Preservatives
- e.g. Chemicals that inhibit bacteria, nitrite in ham, bacon and cured meats, sulfites in dried fruits, wine
- microbiologists use ultra cold storage to store microbes for years
Chemical methods for Sterilization
- comparison to physical sterilization
- e.g.
- Are slower and less effective than physical sterilization and w/ side effects such as mess, staining, toxicity
e. g. Vapourised and gaseous agents, Disinfectants and antiseptics and antimicrobial agents
Disinfectants and antiseptics
- Soaps
- Alcohols - most effective conc., effects
- Aldehydes - effects, cons, e.g.
- Soaps (i.e. used in handwashing) - key action is more physical (mechanical removal of bacteria)
- antiseptics such as triclosan can be added to inhibit or kill bacteria
- Alcohols: 70 % (v/v) conc. most effective (30% water helps absorption into membranes
- causes membrane damage, protein denaturation
- not effective for spores
- Aldehydes: Very toxic compounds; strong irritants, strong reducing agents (adverse effects on living)
- inactivate enyzmes, proteins, nucleic acid, will kill spores
i. e. formaldehyde: need long exposure as is poor at penetrating
- inactivate enyzmes, proteins, nucleic acid, will kill spores
Disinfectants & Antibiotics; Ethylene oxide gas
- challenge
- what it is used for
-Is a toxic gas; useful for sterilizing large materials (i.e. buildings)
-key challenge: removing gas
Used for;
-Plastics
-medical equip
-surgical supplies
-vaccines
-buildings
Disinfectants & antibiotics; Halogens (3 types)
*Are oxidising agents - oxidise cell components
- Chlorine - water supplies
- Hypochlorite (i.e. household bleach) - cheap, corrosive
- used for: dairy utensils, pools, nappies
- Iodine (used as antiseptic) - binds to proteins and is an oxidant
- e.g. betadine
Disinfectants & antibiotics; Phenolics
- features
- 1 eg
- Are very toxic compounds - are irritants
- denature proteins, disrupt membranes
- Neurotoxin when absorbed
e.g. hexachlorophene good for Staphylococcus
Disinfectants & antibiotics; Heavy Metals; Cationic Detergents; Acids & alkalis
Heavy metals: inactivate proteins
e.g. silver, mercury, copper
Cationic detergents: quaternary ammonium compounds - destroys cell membranes, denatures proteins
-e.g. Benzalkonium chloride
-low toxicity, biocidal effect, better at killing gram neg. bacteria
Acids & Alkalis: detergents and germinides
Factors that affect chemical killing (interactions determine effectiveness of treatment) (7)
- Nature of chemical used - mechanism of action
- Population size - larger populations take longer to kill
- Contact time - death proportional to contact time
- Cell physiology - young cells more sensitive (log phase vs stationary phase)
- Temp - rate of killing increases w/ temp
- Local enviro - organic matter decreases effectiveness (chem. binds to organic matter - effectively decreases the conc. of chemical available to bind to bacteria)
- Conc. of chemical
Criteria for effective Antibiotics (7)
- Active at high dilution
- selective toxicity (affects microbes, not host)
- Non-allergic to host cells
- Stable in storage and in body
- Soluble in body fluids (blood - means it can be injected)
- Retained in body at effective conc (otherwise excreted rapidly in urine)
- Target micro-organism and slow for microorganisms to develop resistance
Action of antibiotics (2)
Bacteria either have a;
- Bacteriostatic effect (Only inhibits growth of bacteria - does NOT kill)
- Bactericidal effect (kills bacteria)
