Culturing microorganisms

why need to culture microorganisms?

• This grows enough microorganisms to make measurements during investigations

• E.g. bacteria reproduce by cloning themselves, so when they are grown on agar gel they form a colony of identical individuals that is visible to the naked eye

what do microorganisms need to grow?

• Nutrients

• Oxygen

  • Note that anaerobic microorganisms would require the absence of oxygen

• Optimum pH

• Favourable temperature

why need to take great care when growing a pure strain of microorganisms?

• the entry of any other microorganisms from the air or your skin into the culture will contaminate it

• always risk of mutant strain developing that may be pathogenic

• risk of contamination of the culture by pathogenic microorganisms from the environment

health and safety precautions when culturing?

• Ensure that all equipment are sterilised before culturing the bacteria

  • Sterilising involves killing microorganisms, e.g. by heating to a high temperature or the use of antimicrobial chemicals

• Keep the culture in the laboratory 

• Seal cultures in a plastic bag and sterilise at high temperature and pressure before disposal

steps to culture

• Obtain a supply of the type of microorganism to be cultured

• Provide them with the correct type of nutrients to facilitate growth

• Ensure that the nutrient medium is kept under sterile conditions until use

what type of nutrient growth medium is used to facilitate growth?

• A nutrient growth medium (plural media) containing carbon, nitrogen, and minerals is typically used

• The medium could be in the form of a liquid culture or a solid nutrient agar, a type of gel extracted from seaweed

• Microorganisms are introduced to a growth medium using inoculation with a sterilised inoculation loop 

• Inoculation can be used to transfer microorganisms between media, e.g.

  • From agar gel into a liquid culture flask

  • From a liquid culture flask onto agar gel

• The new medium should be sealed or covered to avoid contamination from microorganisms in the air; if growing aerobic microorganisms any seal or cover should not be airtight 

  • Flasks can be sealed with a sterile cotton wool stopper 

  • Petri dishes can be covered with a lid

• Label the medium clearly and incubate at around 20 °C to prevent the growth of pathogenic microorganisms

  • Microorganisms that are pathogenic to humans will grow best at around 37 °C 

  • In a hospital or research laboratory a higher temperature might be used to obtain faster results

what is a selective medium?

• created by adjusting the type of nutrients in the medium, conditions will be created for the optimal growth of a certain type of microorganism

benefit of selectrive medium

• create optimal growth of a certain type of microorganism

• Selective media can be used to identify mutant strains of microorganisms or those that are resistant to antibiotics

• They are also useful for identifying genetically modified microorganisms

how to grow a single type of microorganism

• In order to grow a single type of microorganism, or a pure culture, the specific microorganism must be isolated

• This can be done by using knowledge about the needs of the microorganism to be cultured or those of microorganisms that may contaminate the culture

• Examples include

  • Growing the culture under either aerobic or anaerobic conditions to reduce the variety of microorganisms in the culture

  • Using a selective medium that is tailored to the specific requirements of the desired microorganism

  • Indicator media can provide a colour change to distinguish desired colonies from the rest

• Being able to isolate pathogenic microorganisms is useful in the diagnosis and treatment of diseases

aseptic technique meaning

methods used to prevent contamination (of person / culture) (with other microorganisms) (1)

aseptic technique used

• carry out work beside {a bunsen burner / in a hood} (1) to create an updraft / to move the microorganisms in the air away / to prevent {bacteria / microorganisms / spores} falling into culture

• use sterilised {equipment / media} / sterilise equipment after use to kill any {bacteria / microorganisms / spores} present

• minimise the time that cultures are exposed to the air / do not open cultures at the end (1) to reduce chance of contamination

• washing hands flaming necks od bottles + to prevent transferring {bacteria / microorganisms / spores} into cultures

• close {doors / windows} + to avoid draughts

why aseptic technique important

 to prevent entry/contamination of bacteria in culture as they could {compete for nutrients / produce toxins (to the bacteria being cultured)} O

 to prevent entry of bacteria that may grow in different {types / concentrations} of microbial substances (than E. coli)/wont know if e coli or other bacteria are growing/could provide an overestimate of number of bacteria (1)

 to prevent infection (of person) with bacteria in the culture/ so that we don’t get pathogens transferred to ourselves that {is / maybe} pathogenic (1)