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Flashcards in MicroBiology- Control of Microbial Growth Deck (10)
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1

WHAT ARE CONTROLS OF MICROBIAL GROWTH?

- Any measures taken to greatly reduce number of microorganisms

Processes used in microbial control (3 types)
- Sterilisation→ removal/destruction of all living cells (including spores) and other ineffective material (viruses) from an object
- Disinfection→ Killing/ inactivation of large number of organisms (agent is disinfectant, e.g. chlorine in pools)
- Antisepsis→ Prevention of tissue infection: Agent used is antiseptic (e.g. dettol)

2

PHYSICAL AGENTS (1) HEAT: Incineration

- Total destruction of contaminated material by fire
- Only for single- use objects (needles, syringes, dressings)

3

PHYSICAL AGENTS (1) HEAT: Dry Heat Sterilisation (“Baking”)

- Heating items at 160℃ for 1 hour→ kills all microorganism forms (including endospores)
- However many items needing to be sterilised wont tolerate this condition: e.g. plastic ware

4

PHYSICAL AGENTS (1) HEAT: Boiling

- Putting item in water at 100℃ for 10 mins is disinfection only→ won't kill endospores
- Effectiveness as a microbial control agent relies on thorough cleaning beforehand
- Remains a simple means of microbial control available to everyone
- “Boiled water alert” issued when disinfection at water supplier is compromised

5

PHYSICAL AGENTS (1) HEAT: Wet Heat Sterilisation: Autoclaving

- Autoclave: Water in autoclave chamber is subjected to pressure 2x that of atmospheric levels→ water must be heated to 121℃ to boil and produce steam
- Steam must be able to penetrate whatever is being sterilised
- When performed for 15 mins→ can kill vegetative cells and endospores

6

PHYSICAL AGENTS (2) RADIATION: Ionising Radiation

- Gamma rays from radioactive source will disrupt DNA→ sufficient to sterilise objects
- Common method in commercial suppliers of clinical and surgical disposables which wouldn't withstand heat sterilisation

7

PHYSICAL AGENTS (2) RADIATION: Ultraviolet Radiation

- UV rays disrupt DNA but poor level of penetration of UV light→ means this is primarily used to disinfect surfaces
- E.g. communal kitchens in nursing homes may have UV lights left on when not in use

8

PHYSICAL AGENTS (3) FILTRATION

- Processes which rely on physical barrier that excludes particles of a specific size or greater
- Ideal process for liquids sensitive to other agents (e.g. water can be treated in this way)
- Size of holes (pores) in barrier determines level of sterility

9

CHEMICAL AGENTS

- Agents work via restrictions between agent and components of infection agent
- Reaction modifies the component so organisms is no longer viable
- Hypochlorous acid→ “bleach” and is chemical disinfectant
- 70% v/v alcohol swabs and hand washes
- Chemical sterilants and disinfectants work on dosage basis
- Dirtier an item; the more agent you would need
- In a clinical situation; important that where it's safe to the handler→ equipment cleaned prior to sterilization or disinfection

10

ANTIBIOTICS AND ANTIVIRALS

- Drugs with selective toxicity
- They target chemical/metabolic pathways unique to pathogen which are critical for growth/replication
- E.g. Penicillin (antibacterial drug) blocks cell wall synthesis
- Zidovudine→ Anti HIV drug; targets a unique viral enzyme