Microbiology Flashcards
What is a bacterial cell wall made of?
Peptidoglycan/murein
What size are bacterial ribosomes?
70s
How would you describe bacterial DNA?
Circular, free in the cytoplasm, also in smaller plasmids
How do bacteria move?
The flagellum
What are the proper terms for rod shaped, spherical and spiral bacteria?
Bacillus, coccus, spirillum
How are eukaryotic cells different to prokaryotic cells?
They contain membrane bound organelles, including the nucleus. They have linear rather than circular DNA and larger 80s ribosomes
Describe the cell wall of a gram positive bacterium
A thick layer of peptidoglycan
Describe the cell wall of a gram negative bacterium
A thin layer of peptidoglycan with an outer layer of lipoprotein and lipopolysaccharide
What colour do gram positive and gram negative bacteria stain with a Gram Stain?
Gram positive purple, gram negative pink/red
What are the four steps in a gram stain?
Add crystal violet, add iodine, add ethanol, add safranin
What conditions are required for bacterial growth?
The correct oxygen levels, correct temperature, correct pH, a carbon source, a nitrogen source, minerals
Define obligate aerobe
Bacteria that can only survive/divide in the presence of oxygen
Define obligate anaerobe
Bacteria that can only survive/divide in the absence of oxygen
Define facultative anaerobe
Divide faster in the presence of oxygen but can survive in its absence
What is the purpose of aseptic technique?
To prevent contamination of the environment by the microbes being handled and contamination of microbial cultures by unwanted microbes from the environment
Give three examples of aseptic technique
Flame equipment until red hot to sterilise, use an autoclave to sterilise other equipment, keep roaring flame on desk to create updraft, open petri dish lid at angle to reduce contamination, do not put lids on desks to reduce contamination
Give two reasons it is difficult to count bacteria
They are small, there are too many, it’s hard to tell if they are alive or dead
What are total and viable counts?
A total count includes both living and dead bacteria, a viable count is only living bacteria
Give the advantages of a total cell count using a haemocytometer
It’s fast and can be used for several types of cell at once
Give the disadvantages of a total cell count using a haemocytometer
It includes dead bacteria, they may clump making it hard to count (still need to dilute), requires an oil immersion lens
Give the advantages of a viable count using serial dilution
You can count only the living bacteria
Give the disadvantages of a viable count using serial dilution
Could be an underestimate if each colony came from more than one bacterium (clumping occurs), takes time, some species may take longer to grow than others
What is the assumption when doing a viable count from plates that have undergone serial dilution?
Each colony only comes from one bacterium
