Microbiology Lecture 4 Flashcards
Define aseptic technique.
Ensure cultures are inoculated without contamination of unwanted microbes.
What is the first important step in aseptic technique?
Flame the loop to sterilise it.
What is the microbe loop made of and why?
Nichrome wire, as it is durable against repeated heating and cooling.
At what angle are the loops held against the flame, and why?
At a downward angle, to prevent any possible liquids from running downward to the hand.
How does a bunsen burner create an area of sterility?
Heats the air around the flame, preventing airborne microbes contaminating.
What is the problem with boiling the media to sterilise it before culturing? How can this be addressed? What is done with heat sensitive materials?
Boiling will kill microbes, but not endospores. Autoclaving is performed. If heat sensitive, is instead filtered to be made sterile, and added to cooled media.
Define chemoorganotroph.
microorganism requiring organic compounds for energy.
How can the requirements of a microorganism be determined?
Begin with minimal media, then sequentially supplement with nutrients to isolate requirements.
Describe nutrient media. Is this kind of media well defined?
Has a source of carbon, such as sugar, or complex like yeast extract/peptones.
Poorly defined as the source of nutrients can differ significantly.
Define peptone.
Oligopeptides obtained by boiling organic mass like blood, bones, and meat.
What is the problem with using gelatine as a media?
Isnt solid at 37 the grease.
Where is agar gel obtained from?
Red algae.
How is agar media prepared?
Dissolved in boiling water, and sets around 45C.
What temperature does agar melt after it has set?
98C.
What x% solution does agar form a strong gel?
1%.
Blood cant be filtered, as RBCs would be lost. How is blood agar made?
Blood is obtained aseptically, then warmed to 45C, and mixed with liquid agar, then cooled to set.
How are glass and plastic petri dishes sterilised?
Glass is autoclaved.
Plastic is gassed or irradiated.
What is the purpose of the larger dish in petri dishes? On what side are petri dishes incubated, and which side is labelled?
Larger dish acts as a lid to prevent contamination.
They are incubated with the large lid facing down.
Lids are never labelled.
Do petri dishes allow exposure to air, or are they airtight?
Allow exposure.
Describe the contents of nutrient agar.
Nutrient broth + agar
Describe the contents of horse blood agar (HBA).
Horse blood + nutrient agar
Describe the contents of chocolate agar (CHA).
Nutrient agar + cooked horse blood
How does CHA differ from HBA? Name a microbe that grows in CHA but not HBA.
RBCs in CHA are broken, and their contents released, where in HBA they are intact. Allows the growth of some organisms like gonorrhoea.
Define enriched media.
Basal media with extra nutrients added - HBA.
Define enrichment media.
Used to assist with the growth of a target organism in a mixed culture.
Contains additives which inhibits the growth of non-target organisms, and improves the growth of the target organism.
Define differential/indicator media.
Contains substances which produce a visible difference between organisms with different metabolism.
Describe the contents of Mac’Conkey agar.
Nutrient agar + bile salts + lactose + neutral red.
What colour do lactose digesting organisms turn Mac’Conkey agar?
Lactose digestion lowers pH, resulting in a pink colour.
Yellow indicates no fermentation.
Define selective media.
Similar to enrichment media, restricting the growth of non-target organisms. May improve target organism growth.
What is the purpose of bile salts in Mac’Conkey agar?
Inhibits the growth of many bacteria.
