Week 2 Flashcards
Sterilisation
The removal of all microbial life
Decontamination
Treatment that renders an object or surface safe to handle
Disinfection
The removal of pathogens from an inanimate object or surface
Antisepsis
The removal of pathogens from living tissue
Sanitation
The reduction of the number of microbes in water or on an object
Measuring Bacterial Growth
Direct Cell Counts > count cells in a microscope chamber
Culture Turbidity > measure the culture’s absorbance
Viable Cell Plating > count colony-forming units
Microbial Growth Curve
Lag phase (Flat start) Log phase (Exponential) Stationary phase (Flat straight) Death phase (Decline)
Microbial Growth Curve causes of death
In the Death (Decline) phase, more cells are dying than are being replaced by new cells.
One cause of death are by-products of metabolism which are often acidic and therefore, lower the pH causing cell death
Moist Heat
Pattern of thermal damage is multi-factorial
– single strand breaks occur in DNA due to nuclease activation
– functional integrity of membrane is lost
– small molecules of ribosomal origin leak
Moist heat is more effective than dry heat
– achieves sterilisation at a lower temperature for a given time
– achieves sterilisation more quickly at given temperature
The killing of resistant spores
– moist heat at 121oC for 15 minutes
– dry heat at 160oC for 60 minutes
Autoclave
Uses a combination of high temperature (to 121oC / 135 oC) and increased pressure
The high temperature and pressure is effective in killing moist micro-organisms, in particular human viral, bacterial, fungal, protozoan and metazoan pathogens
Stages of the Autoclave Cycle
Autoclave is loaded with items appropriately spaced to allow steam to penetrate
Cycle is started and the air inside the inner chamber is replaced by steam
The chamber is allowed to reach the target temperature and pressure
Desired temperature and pressure held for appropriate length of time
Steam released from the inner chamber, but the surrounding jacket continues to contain steam so the chamber remains hot
Air is returned to the chamber and when normal air pressure is restored and the temperature is lowered, the door can be opened to allow the load to be removed
Halogens
These oxidize cell components and so kill microbes
Examples are iodine and chlorine
Hydrogen peroxide
Also a strong oxidizing agent, mainly used today in disinfection of contact lenses
Formaldehyde and gluteraldehyde
Alkylating agents that are highly toxic
Used to sterilize some devices that cannot be heat-treated
Ethylene oxide gas
This inflammable and explosive gas can be used to achieve sterility. It is an alkylating agent
Phenolics
Phenolics are toxic to human cells but short exposures
are tolerated
Surface-active compounds (surfactants)
These have hydrophobic and hydrophilic groups that attach to and solubilize
bacterial membranes and other complexes
Conditions that affect Antimicrobial Activity
Size of microbial population
Intensity or concentration of microbicidal agent
Time of exposure to microbicidal agent
Temperature at which micro-organisms are exposed to microbicidal agent
Nature of the material containing the micro-organisms
Characteristics of micro-organisms which are present
Chemotherapy
The use of chemical substances to treat a disease
Antibiotic
Strict Definition
A chemotherapeutic substance naturally-produced by a microbe which in small amounts kills or inhibits the growth of another microbe.
Broader definition
A chemotherapeutic substance which in small amounts kills or inhibits the growth of microbial cells.
physical methods of microbial control purpose
Sterilisation, decontamination,
disinfection, and sanitation.
Chemical methods of microbial control can also be used for
antisepsis and chemotherapy
Paul Ehrlich main work
In his quest for a magic bullet, Paul Ehrlich chemically-synthesised salvarsan which was effective
against Treponema pallidum. Salvarsan however, had significant side effects on the patient.
first naturally-produced antibiotic was discovered by
Alexander Fleming
Wonder drug
Penicillin was effective against a range of human pathogens and had very low levels of toxicity. Penicillin therefore became known as the wonder drug.
