Control Of Microbial Growth Flashcards by Rebecca Treacy

Why do we need microbial growth?

prevent cross contamination of cultures in a laboratory
prevent contamination of equipment used in medical and food preparation procedures
to increase the shelf life of food and beverages
to limit the detrimental effect the microbes or their metabolic products would have on us and/or our food

How well did you know this?

Not at all

Perfectly

What is sterilisation?

Killing or removal of all microorganisms

How well did you know this?

Not at all

Perfectly

What is commercial sterilisation?

Killing clostridium botulinum endospores (no pathogens left, growth stopped)

How well did you know this?

Not at all

Perfectly

What is disinfection?

Removing pathogens from inanimate objects

How well did you know this?

Not at all

Perfectly

What is antisepsis?

Removing pathogens from living tissue

How well did you know this?

Not at all

Perfectly

What is degerming?

Removing microbes in a limited area

How well did you know this?

Not at all

Perfectly

What is sanitisation?

Lowering microbial counts e.g. On eating utensils

How well did you know this?

Not at all

Perfectly

What is a biocide/germicide?

Kills microbes, inactivated viruses

How well did you know this?

Not at all

Perfectly

What is bacteriostasis?

Inhibiting, not killing, microbes

How well did you know this?

Not at all

Perfectly

What is sepsis?

Refers to microbial contamination

How well did you know this?

Not at all

Perfectly

What is asepsis?

Is the absence of significant contamination.

Asceptic techniques prevent microbial contamination of wounds

How well did you know this?

Not at all

Perfectly

Describe some patterns of microbial death.

Population death rate is constant.

90% of population will be reduced after I minute

How well did you know this?

Not at all

Perfectly

What are some of the factors that affect microbial death?

Number of microbes. More time may need to be applied
Environment. Organic matter, temperature, biofilms.
Time of exposure
Microbial characteristics

How well did you know this?

Not at all

Perfectly

What are the 3 actions of microbial control actions?

Alteration of membrane permeability
Damage to proteins
Damage to nucleic acids

How well did you know this?

Not at all

Perfectly

What are the 6 microbial physical control mechanisms?

Temperature +/- moisture
Filtration
Desiccation (drying)
Osmotic pressure
High pressure
Radiation

How well did you know this?

Not at all

Perfectly

Explain the importance of heat as a microbial control mechanism

Heat denatures and coagulates proteins

Microbes differ in their resistance to the affects of temperature

What is thermal death point?

TDP. Lowest temperature at which ALL cells in a culture are killed in 10min

What is thermal death time?

TDT . Time during which ALL cells in a culture are killed

What is decimal reduction time?

DRT. Time (in minutes) to kill 90% of a population at a given temperature

Describe autoclaving

Moist heat (steam) under pressure. Steam must contact the items surface
- temperature acting on items is raised by increasing the pressure around the item
15psi (103 kPa), 121 degrees centigrade for 15  minutes - kills all (except prions)
- sterilisation time depends on the volume. 10ml = 15 mins

Describe dry heat sterilisation and the techniques used.

Kills by oxidation
Dry heat
Flaming
Incineration
Hot air sterilisation

Explain the purpose of pasteurisation

Kills pathogens and reduces spoilage organisms.
Equivalent treatments
63 degrees Celsius for 30 min
High temp short time. 72 degrees for 15 sec
Ultra high temp. 140 degrees for less than 1 sec
Thermoduric (heat resistant) organisms can survive and cause spoilage

Describe how low temps suppress microbial growth

Refrigeration. Slows metabolic activity, generally bacteriostatic, rather than bacteriocidal
Freezing. Slow freezing more effective than flash freezing as forming ice crystal disrupt the cells, thawing more damaging than freezing
Freeze drying. Long term preservation, decreases water availability

Describe how filtration suppresses microbial growth

HEPA - removes microbes > 0.3 um
Membrane filtration removes microbes > 0.22 um
Does NOT inactivate any existing metabolic products (toxins)
Will not remove viruses

Describe the steps of making a disk diffusion plate?

1. Inoculate surface with bacteria 2. Add disc with inhibitor /antibiotic 3. Incubate to allow bacteria to grow while inhibitor diffuses out into medium

What is the importance of phenols and phenolics?

They disrupt the plasma membranes | Exert antimicrobial activity by injuring lipid containing plasma membranes - leakage of cellular contents

What is the importance of bisphenols?

Important ones are hexacholorophene and triclosan. They disrupt the plasma membranes

What is the importance of biguanides?

They can refer to a molecule, or to a class of drugs based upon a molecule with amine groups that are involved Acts on membranes by blocking lipid synthesis and disrupting plasma membranes Often used in combination with other agents Antiseptic uses Disinfectant uses Preservative uses

Describe quats and their importance.

Quarternary ammonium compounds Effective against bacteria, fungi, viruses (enveloped and non) and emoebae Do not kill endospores or mycobacterium Widely used in both the home an industry

Identify the appropriate uses for the surface acting agents

Soap Degerming (cleaning/washing) Acid-anionic detergents Quaternary ammonium compounds (cationic detergents) Sanitising Bactericidal, denature proteins, disrupt plasma membranes

From most resistant to least resistant, name the microbes that influence control methods

``` Prions Endospores of bacteria Mycobacterium Cysts of Protozoa Vegetative Protozoa Gram negative bacteria Fungi, including most fungal spores Viruses without envelopes Gram positive bacteria Viruses with lipid envelopes All depends on the presence of membranes being disrupted and the resistance of the membrane on what is trying to get through ```

What are asceptic techniques?

A set of practices and procedures performed under carefully controlled conditions with the aim of minimising contamination by unwanted pathogens or cells Eg. Culturing microorganisms, cell structure, surgery, wound care etc

What is the importance of Ehrlich?

Came up with the concept that different organisms have different types of cells and therefore should have unique drug targets within those cells. That's the magic bullet idea - kill an invading pathogen, but leave us humans alive

What is the importance of Fleming/ Florey and Chain?

Fleming - Discovered the most famous magic bullet, penicillin Florey and Chain - were able to develop this for use in the Second World War. Modern antibiotic era was born

Define broad spectrum and narrow spectrum.

In relation to antibiotics that affects a broad or narrow range of gram positive or gram negative bacteria. They are called broad spectrum antibiotics

List the 5 antibiotic modes of action

Can affect 5 main targets 1. Cell wall - inhibition of cell wall synthesis 2. Membrane - injuring the plasma membrane 3. Protein - inhibiting protein synthesis 4. Nucleic acids - inhibiting nucleic acid synthesis, interfere with process of DNA replication 5. Essential metabolite. Competitively inhibited by a substance that closely resembles normal substrate for the enzyme