Intro To Microbial World Flashcards
Features of bacteria
Can live under extreme conditions of temp and pressure
Prokaryotic - no nucleus
No nuclear membrane
No membrane bound organelles
70S ribosomes
Reproduce by binary fission
Peptidoglycan cell wall
0.5-2 micrometers
What are the shapes of bacteria?
Spirals (vibrios), rods (bacilli), spheres (cocci), spirilla, flagellate rods, spirochaetes, spore-former
What allows bacteria to hold their shapes together?
The bacterial cell envelope
What is the bacterial cell envelope made of?
Cell membrane - phospholipid bilayer
Cell wall - peptidoglycan
What is gram positive bacteria?
Thick peptidoglycan with many layers of it. Has an inner membrane.
Examples of gram positive bacteria
Streptococci, staphylococci
What is gram-negative?
Thin layer of peptidoglycan in the middle of an inner and outer membrane
Examples of gram negative bacteria
E.coli, Fusobacterium, Porphyromonas
What are the steps of the stain to test for gram-positive and negative?
Take some bacteria
Crystal violet
Decolorise with acetone
Counter stain with pink or red dye
Describe what colour changes occur at each staining step and why?
Crystal violet will penetrate through for gram positive deep through the layers of peptidoglycan. Gram negative only has a thin layer so not much to penetrate. So both penetrated.
After acetone, for gram negative the purple colour will be washed off but for gram positive the colour will not all be washed away.
After counter stain, gram positive will look dark purple or blue whereas gram negative will be red or pink
What colour are gram positive and negative bacteria at the end of the staining process
Gram positive are dark purple or blue
Gram negative are red or pink
What do flagella allow and aid with?
Enable bacteria to swim in fluids, aiding chemotaxis
What is chemotaxis?
The movement of a motile cell or organism in response to a chemical signal
Do oral bacteria have them?
Not many oral bacteria have flagella
What are Fimbriae?
Fimbriae/pills are fine short hair-like filaments that extend from the cell surface. Contain the protein pillin.
What do pilli allow?
Attachment to surfaces. Adhesions mediate the adhesion of bacteria to receptors on the cell surface, teeth, medical devices etc. e.g., oral bacteria attach to teeth and each other, gyms, periodontal pockets etc etc
What kind of specimen collections are there?
Tissue biopsy, faeces, urine, swab
How does culturing bacteria work?
Agar / liquid medium has lots of nutrients to provide the bacteria, allowing them to grow/reproduce/culture
What are facultative anaerobic bacteria?
Normally use oxygen but can switch to anaerobic if needed
How to grow anaerobic bacteria since they live without oxygen?
In a gas jar
Put bacteria on Petri dishes in jar and add a catalyst which will convert all oxygen to water, making the atmosphere anaerobic.
Cabinets with tight cuffs around hands to handle bacteria used
What does differential media for culturing bacteria allow?
To discriminate between microorganisms. Will be selective to inhibit or promote growth of some bacteria, or grow in a different colour.
What is haemolysis?
The destruction of red blood cells
Describe haemolysis on blood agar?
Bacteria that can conduct haemolysis will cause a see-through agar since they will destroy the RBCs. Some will cause a greenish translucent colour since some RBCs will be broken down but not all. Some will remain red since they can’t perform haemolysis at all.
Why are biochemical tests conducted?
To differentiate bacteria based on which sugars they react with by forming different colours in test tubes.
What are some genetic methods of identification and describe them briefly?
PCR/RT-PCR methods - amplifies genes from bacteria
Ribosomal 16S RNA gene sequencing - makes use of small sequence differences in the 16S ribosomal RNA molecule
DNA detection - whole genome sequencing
Cepheid GeneXpert - automated system detecting bacterium from a swab
