L16- Microbial Death; Physical & Chemical Control Methods Flashcards
Sterilisation
Removes or kills all loving organisms
Disinfection
Treatment of materials with disinfectants to kill, inhibit or remove disease-causing microorganisms
May be residual living organisms present after treatment
Disinfectant
Chemicals employed to kill, inhibit or remove microorganisms present on inanimate objects
Sanitisation
Reduction of microbial pop on inanimate object to low level so safe by public health standards
Antiseptic
Chemical agents applied to tissue/body surfaces to prevent infection by killing or inhibiting pathogens
Aseptic techniques
Procedures to prevent contamination of previously uncontaminated materials to obtain pure cultures of microorganisms and to prevent infection
Chemotherapy
Use of chemical agents to kill or inhibit growth of microorganisms within host tissue
Bactericidal
Type of antimicrobial agents
Kills bacteria
Bacteriostatic
Type of antimicrobial agents
Inhibit bacterial growth
Viricidal
Type of antimicrobial agents
Kills viruses
Fungicidal
Type of antimicrobial agents
Kills fungi
Fungistatic
Type of antimicrobial
Inhibits fungal growth
Algicidal
Type of antimicrobial agents
Kills algae
Antimicrobial
Types of antimicrobial agents
Agents which kills or inhibits microbes
Selective toxicity
Types of antimicrobial agents
Activity against microbial pathogen but damages host as little as possible
Chemotherapeutic
Antimicrobial agent with selective toxicity
Compound used in treatment of disease
Microbial pop death
Not killed instantly when exposed to lethal agent
Generally exponential (log). Pop is reduced by same fraction at constant intervals
Essential to have precise measure of agent’s killing efficiency. One measure: decimal reduction time (time required to kill 90^ of microbes in sample under specific conditions)
Factors influencing effectiveness of control agents
Pop size (larger size -> takes longer to achieve sterility. Death rate exponential, time it takes directly proportional to no of organisms initially present)
Contact time (longer pop is exposed to agent, more organisms killed)
Pop susceptibility (different microorganisms die at different rates. Endospores more resistant than vegetative, acid fast more resistant than most, capsulated bacteria, enveloped viruses, Gram -ve more resistant). Actively growing bacteria more susceptible (increased uptake of agent)
Antimicrobial conc (more concentrated an agent, more rapidly destroyed. Some more effective at low conc)
Temp (mild heat enhances activity of disinfectant by promoting chemical reactions. Every 10 degree rise in temp increases disinfectant activity by 2-3 fold)
Local environment (some environmental factors are protective)e.g chlorine is bound by organic matter (protect against disinfection) -> more chlorine must be added
Heat
Physical agent
Kills by:
protein denaturation & nucleic acid degradation -> membrane becomes more fluid -> contents leak out -> prevent nutrient transport
High heat most efficient & cost effective sterilant
Dry heat
Dehydrates cell
Tends to preserve cells -> greater amt of heat is required to kill in dry than in moist
Incineration: exposed to heat -> burnt. E.g. used to sterilise inoculating loops.
Hot air ovens: for glassware, metal instruments. 160-170degrees, 2-3 hrs. Advantages: doesn’t corrode, can be used for metal, powders, oils. Disadvantages: slow, not suitable for heat-sensitive materials like plastic &rubber
Moist heat: Steam sterilisation
Carried out with autoclave (~pressure cooker)
Chamber filled with hot, saturated steam until reaches desired temp & pressure
Moist heat heats porous substances quickly. At elevated pressures steam (temp:100degrees). Increase in steam temp proportional to pressure
Routine lab sterilisation: 121degrees, 15psi for 15-30mins
Advantages: fast, convenient, reliable. Disadvantages: corrodes metal, may damage heat sensitive material, leaves glass ware wet
Moist heat: boiling
Inexpensive & relatively effective disinfectant
100degree (boiling water) for 10 min
Kills vegetative cells and eukaryotic spores. Will not destroy bacterial endospores -> not sterilant
Application: home disinfection use
Moist heat: cooking
60-80 degrees
Kills all but spores
Moist heat: pasteurisation
Reduces microbial pop of liquid
Heating liquids to temps below 100 degrees -> kill disease and spoiling-causing microorganisms
Extends shelf life of products but doesn’t sterilise
Examples: Batch pasteurised (in large tanks at 63degrees for 30 mins), ultrahigh temp (140-150degrees for 1-3 sec. no refrigeration needed & stored at room temp) & high temp short time (liquid forced through metal plates or pipes at 72 degrees for 15 degrees)
Radiation: ionising radiation
Example: x rays and gamma rays. Damage cell by reacting with proteins and nucleic acids
Used to sterilise heat sensitive medical supplies like plastic syringes, antibiotics, drugs and food
Cobalt 60: source of gamma rays
Advantages: penetrates deeply, kills all cells including endospores. Disadvantages: expensive & dangerous.
Radiation: UV
Electromagnetic radiation ~260nm absorbed by nucleic acids altering DNA structure
2 adjacent thymine nucleotides bind together -> thymine dimers -> distorts DNA preventing DNA replication
UV doesnt readily penetrate glass, opaque solids and liquids -> used in UV lamps to sterilise air in rooms. Used in biological safety cabinets to sterilise air and surfaces
Not usually listed as sterilising agent (lack of penetrating ability)
Filtration
Advantages: effective & economical for liquids & gases which cannot be autoclaved
Applications: use to sterilise pharmaceuticals, culture media, oils, antibiotics. Laminar flow biological safety cabinets : air forced through filters, projects vertical curtain of sterile air cabinet opening
Chemical control agents
Some agents used in laboratories & hospitals
Decontaminate or disinfect work areas like surgical suits & media preparation rooms
Other chemicals used as antiseptics to prevent infection
Effectiveness of chemical disinfectants and antiseptics influenced by..
Conc & nature of disinfectant/ antiseptic
Length of treatment
Kinds of microorganisms present. Many chemical agents are effective against vegetation bacteria, viruses, fungi but few are effective against bacterial endospores. TB and hepatitis viruses, rhinoviruses (colds), enteroviruses (e.g polio), highly resistant to chemical control
Chemical control agents: phenols (phenolics)?
First widely used antiseptic and disinfectant. Joseph Lister used to reduce risk of infection during operation
Phenol derivatives (phenolics) used in lab & hospitals. Phenol derivatives such as Lysol used as disinfectants
Bisphenols (2 phenolic groups) used as antiseptics. E.g. triclosan- antibacterial soaps, toothpaste, kitchenware.
Advantages: effective in presence of organic matter, long lasting — good for disinfecting pus, saliva, faeces. Tuberculocidal. Disadvantages: strong odour, irritating skin. Not sporicidal
Chemical control agents: alcohols
Most widely used disinfectants & antiseptics. Bactericidal & fungicidal, but not sporicidal
Most popular: ethanol and isopropanol (70-80%). Antiseptic for wound cleaning, disinfecting skin, hand rubs. Disinfectant for small instruments, bench tops.
100% ethanol: dehydrating agent. Can extract cellular water & preserve cells -> 70% more effective
Advantages: cheap, stable, nontoxic
Chemical control agents: halogens
Fluorine, bromine, chlorine, iodine, astatine
High affinity for electrons -> very reactive & toxic
Chlorine (halogen)
Disadvantages: high affinity for organic matter, too harsh for use as antiseptic, reacts with organic compounds -> carcinogenic trihalomethanes
Advantages: very effective disinfectants in water supplies, swimming pools, dairy & food industries.
Iodine (halogens)
Antiseptic for superficial wounds. Dissolved in 70% ethanol -> tincture of iodine
Advantages: sporicidal at high conc. Disadvantages: may damage skin, leaves stain, may cause allergic response
Betadine (halogen)
Iodine + organic carrier -> iodophore
Advantages: water soluble, stable, nonstainjng, releases iodine slowly to minimise skin burns and irritation. Used as antiseptic in hospitals and labs.
Heavy metals (chemical control agents)
Heavy metal ions of arsenic, copper, mercury, silver used.
Toxic to most life forms because they combine with cell proteins and denature them.
Still used:
Silver sulfadiazine: used on patient with burns
Silver nitrate: antiseptic used on newborns. Eye drops to prevent eye infection with Neisseria gonorrhoeae. Superseded in some hospitals by antibiotic erythromycin
Copper sulfate. Algicide- algal blooms in lakes, stock ponds, reservoirs. Fungicide
Quarternary ammonium compounds ( chemical control agents)
Detergents: have both (polar) hydrophilic and (nonpolar) hydrophobic ends (-> amphipathic)
Only cationic detergents are disinfectants: disrupt bacterial membranes
Advantages: stable & nontoxic, often used as disinfectants for food utensils and small items, and as antiseptics
Disadvantages: inactivated by hard water by soap. Kill most bacteria but not m.tuberculosis or pseudomonas aeruginosa i.e. low activity. Not sporicidal
Aldehydes (chemical control agents)
Highly reactive molecules that cross-link & alkylate nucleic acids and proteins
Formaldehyde- 7% aqueous or alcohol solution
Glutaraldehyde- 2% aqueous solution. The most effective. Used on hospital & lab equipment e.g. anaesthesis tubing. Items must be rinsed in sterile water after sterilisation.
Both sporidical, tuberculocidal, virucidal, bactericidal, funcgicidal
Sterilising gases (chemical control agents)
Ethylene oxide: used inside ethylene oxide steriliser (5-8hrs). Sterilises disposable plasticware, syringes, catheters, packing material. Sporicidal, tuberculocidal, virucidal, bactericidal, fungicidal
Advantages: rapidly penetrates packing material. E.g. paper, plastics. No heat required, so suitable for heat-sensitive items
Disadvantages: ethylene oxide is hazardous because flammable, explosive & toxic. Items must be well-aired after sterilisation
Vaporised hydrogen peroxide: can be used to decontaminate operating rooms, other facilities
