4.4: Microbiology. Flashcards
What is a micro-organism?
Organisms too small to see with the naked eye such as bacteria, fungi, viruses and protoctists.
What is Microbiology?
The study of micro-organisms.
What are some of the defining characteristics of Bacteria?
They have no internal membranes - No ER/mitochondria etc They have small ribosomes 70S They have cell walls made of Murein.
What are the two different ways of classifying bacteria?
By their shape By gram staining.
What are the three main bacterial shapes?
Coccus: Sphere shaped. (Cocci plural) Bacillus: Rod shaped (Bacilli plural) Spirillum: Helical (Spirilla plural) NB you can also get Rectangular and Star shaped bacteria.
What are the different types of cocci and their defining features?
Micrococcus - a single cocci (in latin “single berry”) Diplococcus - two cocci joined together (in Latin “double berry”) Saphylococcus - an irregular bunch of cocci (in Latin “bunch of grapes”) Streptococcus - a chain of cocci (in Latin “twisted berries”) Nelsseiae - coffee-bean shape in pairs Tetrads - cocci in packets of four. Sarcinae - cocci in packets of 8,16,32 cells (cuboidal structure)
What happens when diplococci divide?
They remain in pairs
What happens when streptococci divide?
They remain in chains after dividing.
What happens when staphylococci divide?
They divide in all planes and remain grouped together.
What is staphylococcus aureus responsible for?
Causing food poisoning.
What does MRSA stand for and what is it?
Methicillin-resistant Staphylococcus aureus. It causes necrotising fasciitis (it’s a flesh eating bacteria)
Outline the rules of naming species
The name is written in italics (on PC) and underlined when handwritten Genus name has a Capitol letter and species name is all lower case. Bacteria often have the first genus name abbreviated e.g E. Coil.
What does Diplococcus pneumoniae cause?
This causes pneumonia.
What type of bacteria is salmonella typhi/enterica and what does it cause?
It is a bacillus and causes food poisoning.
What type of bacteria is Yersinia pestis and what does it cause?
Bacillus and causes The Bubonic plague
What type of bacteria is Escherichia coil?
It is a bacillus bacteria and allows you to digest your food. There are 10¹⁴ E.coli bacteria in your gut which is 10times more than the number of up an cells in your body.
What does bacillus anthracis cause?
Anthrax
What type of bacteria is Treponema pallidum and what does it cause?
Spirilla - It causes syphilis
What type of bacteria is Borrelia burgdorferi and what does it cause?
Spirilla - it causes Lyme disease.
Why do different bacteria have different shapes?
Because they have rigid cell walls with these unique shapes.
What are the advantages of using shape as a means of classification?
It’s quick, easy and cheap. There properties are useful if you’re trying to decide what disease someone has.
How else can bacteria be classified?
By their metabolic reactions.
What are SS agar (salmonella-shigella) plates?
SS agar plates contain lactose, bile salts, ferric citrate and neutral red. They allow you to tell the difference between bacterial species on the basis of their metabolism.
What is the purpose if the bile salts in the SS plates?
The bile salts select for Gram-Negative bacteria.
What is the purpouse of the other components of an SS Agar plate (all components excluding bile salts)?
The other components differentiate between different Gram Negative bacteria.
What are coliform bacteria?
These are rod-shaped Gram-negative non-spore forming bacteria which can ferment lactose with the production of acid and gas when incubated at 35–37°C.
What happens when coliform bacteria such as E.coli are grown on an SS plate?
Coliform bacteria ferment the lactose to give pink colonies. This is because they do not produce any hydrogen sulfide.
What happens when salmonella bacteria are grown on an SS plate?
These bacteria do not ferment lactose but do produce hydrogen sulfide gas which gives colourless colonies with black centres.
What happens when shigella bacteria are grown on an SS plate?
Shigella bacteria do not ferment lactose or produce hydrogen sulfide gas so the resulting colonies will be colourless.
What are the three types of bacteria in terms of their use/disuse of oxygen in their metabolism?
Obligate aerobes Obligate anaerobes Facultative anaerobes
What is an obligate aerobe?
These bacteria require oxygen for growth at all times. (Oxygen is obligatory) E.g Mycobacterium tuberculosis which causes TB.
What is an obligate anaerobe?
There require the absence of oxygen for growth at all times. They find oxygen toxic because it acts as a competitor to their respiratory reactions. They might respire by fermentation or by using methane as a substrate. E.g clostridium tetani (tetanus), clostridium botulinum (botulism), Clostridium perfringens (gas gangrene) and many soil bacteria.
What is a facultative anaerobe?
These bacteria grow rapidly in the presence of oxygen and can grow slowly in the absence of oxygen e.g E.coli can grow in your intestines where there is little/no oxygen but can also be grown in the lab.
What is Gram staining?
This was invented by Hans Christian Gram and was designed as a way of staining bacteria to make them easier to see but it also happens to distinguish between two different groups of bacteria.
How do gram positive bacteria appear after gram staining?
They retain the purple stain in their cell walls.
How do gram negative bacteria appear after gram staining?
They do not retain the purple stain in their cell walls and so are stained red by the counterstain.
How do you perform a gram stain?
1.) mount sample on a slide adding sterile saline if necessary 2.) heat the slide to kill the bacteria and make the slide safe to handle 3.) flood the slide with Crystal violet stain and leave for 1 minute - this stains all cells dark purple 4.) gently wash off crystal violet under running water 5.) flood the slide with lugol’s iodine and leave for 30 seconds. This reacts with crystal violet making all the cells appear blue-black. 6.) rinse the slide gently with acetone. This washes the iodine-dye complex out of gram negative cells. 7.) counter stain the slide with safranin/eosin/fuchsin.
Why do gram positive bacteria retain the Crystal violet stain?
Because of the structure if their cell walls: gram positive bacteria have a plasma membrane and then a thick peptidoglycan layer on the outside and so retain the stain.
Why do gram negative bacteria not retain the crystal violet stain?
Because of the structure of their cell wall: gram negative bacteria have a plasma membrane and then a thin peptidoglycan layer and then a lipopolysaccharide layer.
Do all bacteria stain with gram stain?
No because some bacteria have a waxy cell wall that resists the stain like the mycobacteria e.g mycobacteria tuberculosis.
What is the best way to classify bacteria?
By DNA sequencing. This is how the three domains (bacteria, Archaea and Eukaryota) were identified.
How are bacteria grown in liquid cultures?
In liquid culture bacteria under the surface may not get enough dissolved oxygen so they are usually grown in shaking incubators to aerate them.
What do bacteria need to grow?
Oxygen/no Oxygen (depending) Water (as all metabolic reactions occur in aqueous solution) A carbon source (usually organic (glucose)) A nitrogen source (organic or inorganic) to make amino acids. A phosphorus source (to make A.T.P) A respiratory substrate (energy source (glucose again)) Other nutrients: vitamins, growth factors, minerals.
What is LB (Luria-Bertani) broth?
It is a mixture of chemicals which provide the nutrients necessary for bacteria to grow: In 1 litre: 10g tryptone 5g yeast extract 10g NaCl 2g glucose (1.5% agar for plates)
How can galactose be useful in bacterial culture?
If you want to artificially give your bacteria a new gene on a plasmid (transformation) you can tag it with a gene to use galactose as an energy source. This ensures that only the bacteria with the new galactosidase and gene of interest will survive.
Label this fermenter diagram
