L16- Microbial Death; Physical & Chemical Control Methods

Question 1

Sterilisation

Answer 1

Removes or kills all loving organisms

Question 2

Disinfection

Answer 2

Treatment of materials with disinfectants to kill, inhibit or remove disease-causing microorganisms

May be residual living organisms present after treatment

Question 3

Disinfectant

Answer 3

Chemicals employed to kill, inhibit or remove microorganisms present on inanimate objects

Question 4

Sanitisation

Answer 4

Reduction of microbial pop on inanimate object to low level so safe by public health standards

Question 5

Antiseptic

Answer 5

Chemical agents applied to tissue/body surfaces to prevent infection by killing or inhibiting pathogens

Question 6

Aseptic techniques

Answer 6

Procedures to prevent contamination of previously uncontaminated materials to obtain pure cultures of microorganisms and to prevent infection

Question 7

Chemotherapy

Answer 7

Use of chemical agents to kill or inhibit growth of microorganisms within host tissue

Question 8

Bactericidal

Answer 8

Type of antimicrobial agents

Kills bacteria

Question 9

Bacteriostatic

Answer 9

Type of antimicrobial agents

Inhibit bacterial growth

Question 10

Viricidal

Answer 10

Type of antimicrobial agents

Kills viruses

Question 11

Fungicidal

Answer 11

Type of antimicrobial agents

Kills fungi

Question 12

Fungistatic

Answer 12

Type of antimicrobial

Inhibits fungal growth

Question 13

Algicidal

Answer 13

Type of antimicrobial agents

Kills algae

Question 14

Antimicrobial

Answer 14

Types of antimicrobial agents

Agents which kills or inhibits microbes

Question 15

Selective toxicity

Answer 15

Types of antimicrobial agents

Activity against microbial pathogen but damages host as little as possible

Question 16

Chemotherapeutic

Answer 16

Antimicrobial agent with selective toxicity

Compound used in treatment of disease

Question 17

Microbial pop death

Answer 17

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)

Question 18

Factors influencing effectiveness of control agents

Answer 18

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

Question 19

Heat

Answer 19

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

Question 20

Dry heat

Answer 20

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

Question 21

Moist heat: Steam sterilisation

Answer 21

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

Question 22

Moist heat: boiling

Answer 22

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

Question 23

Moist heat: cooking

Answer 23

60-80 degrees

Kills all but spores

Question 24

Moist heat: pasteurisation

Answer 24

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)

Question 25

Radiation: ionising radiation

Answer 25

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.

Question 26

Radiation: UV

Answer 26

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)

Question 27

Filtration

Answer 27

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

Question 28

Chemical control agents

Answer 28

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

Question 29

Effectiveness of chemical disinfectants and antiseptics influenced by..

Answer 29

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

Question 30

Chemical control agents: phenols (phenolics)?

Answer 30

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

Question 31

Chemical control agents: alcohols

Answer 31

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

Question 32

Chemical control agents: halogens

Answer 32

Fluorine, bromine, chlorine, iodine, astatine

High affinity for electrons -> very reactive & toxic

Question 33

Chlorine (halogen)

Answer 33

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.

Question 34

Iodine (halogens)

Answer 34

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

Question 35

Betadine (halogen)

Answer 35

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.

Question 36

Heavy metals (chemical control agents)

Answer 36

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

Question 37

Quarternary ammonium compounds ( chemical control agents)

Answer 37

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

Question 38

Aldehydes (chemical control agents)

Answer 38

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

Question 39

Sterilising gases (chemical control agents)

Answer 39

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