ANSWERS

1. Why must organic material such as dirt, dust, grease, faeces, urine, blood and vomit be physically removed from surfaces prior to disinfection for efficient results?
   The effective action of disinfectants is dependent upon the direct contact with the target micro-organisms. Therefore surface debris must be removed prior to use.
2. List the precautions that should be taken when using disinfectants.
   • Wear protective gloves and aprons when handling (avoid contact with the skin).
   • Use at the correct concentration.
   • Use as for the purpose as recommended by the manufacturer.
   • Store in the original container, ensuring that the lid is secure.
   • Store away from children and animals.
3. What is meant by the "recommended routine strength" of a disinfectant?
   The strength used for normal daily cleaning, where no specific problems exist. The efficiency of a disinfectant may be increased by using a higher concentration of disinfectant or by use at a higher temperature. Always refer to the manufacturer's instructions.
4. Why is it potentially dangerous to mix disinfectants or detergents together?
   • They may negate the active ingredient in either or both of the products.
   • Harmful, noxious gases may be produced.
   • The combination of chemicals may have a corrosive action.
5. List 6 criteria that affect the action of disinfectants.
   • The freshness of the disinfectant solution.
   • Contact time with the surface to be disinfected.
   • Water quality used for dilution.
   • The presence of organic material.
   • The temperature of the disinfectant solution.
   • The concentration of the disinfectant solution.
6. What regulations govern the control of disinfectants used in veterinary practice?
   The COSHH (Control of Substances Hazardous to Health) 1994.
7. Many disinfectants, if used incorrectly, may represent a risk to personnel. List factors relevant to the safe use of disinfectants in practice.
   • Adorn protective clothing (gloves, apron and mask before use).
   • Ensure adequate ventilation.
   • Use only according to the manufacturer's directions.
   • Establish ease and economy of use.
   • Never mix chemicals.
8. List disadvantages of the use of chemical disinfectants.
   • Malodorous smell.
   • Sensitivity to certain types (e.g. cats and phenols).
   • Staining of any porous materials.
   • Ineffectivity due to the presence of organic material.
9. State the tests made upon disinfectants against specific significant organisms; of these stated - which is the most efficient?
   • Chick-Martin.
   • Rideal-Walker.
   • Kelsey-Sykes (this is more up to date than the previous 2 examples and therefore more relevant to disinfectants used in practice).
10. Bacteria may be classified as gram positive, gram negative, acid fast or spore formation. List their resistance against disinfection in order, with the most resistant listed first.
    • Bacterial spores.
    • Acid fast bacteria.
    • Gram negative bacteria.
    • Gram positive bacteria.
11. What is the difference between bactericidal and bacteriostatic disinfectants?
    A bactericide kills bacteria, while a bacteriostat prevents or inhibits the growth of bacteria. The former is preferable in the selection of disinfectants for use in practice.
12. What species are allergic to phenols?
    Cats.
13. What are hypochlorites commonly called?
    Bleach.
14. What is meant by surfactants?
    Chemical compounds that commonly lower the surface tension of an aqueous solution. They are commonly used as wetting agents, detergents and emulsifiers.
15. What are the main disadvantages of aldehydes?
    High irritancy to the eyes, skin and mucosae.
16. What is the difference between an antiseptic and a disinfectant?
    • Antiseptic = A chemical used upon the skin for the destruction or inhibition of micro-organisms, without damaging the animal's cells.
    • Disinfectant = A chemical for the treatment of inanimate objects (and sometimes a live animal) against micro-organisms.

Note: Two Key Notes tables - Antiseptics and Disinfectants - accompany this module.