Intro To Microbial World

Question 1

Features of bacteria

Answer 1

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

Question 2

What are the shapes of bacteria?

Answer 2

Spirals (vibrios), rods (bacilli), spheres (cocci), spirilla, flagellate rods, spirochaetes, spore-former

Question 3

What allows bacteria to hold their shapes together?

Answer 3

The bacterial cell envelope

Question 4

What is the bacterial cell envelope made of?

Answer 4

Cell membrane - phospholipid bilayer
Cell wall - peptidoglycan

Question 5

What is gram positive bacteria?

Answer 5

Thick peptidoglycan with many layers of it. Has an inner membrane.

Question 6

Examples of gram positive bacteria

Answer 6

Streptococci, staphylococci

Question 7

What is gram-negative?

Answer 7

Thin layer of peptidoglycan in the middle of an inner and outer membrane

Question 8

Examples of gram negative bacteria

Answer 8

E.coli, Fusobacterium, Porphyromonas

Question 9

What are the steps of the stain to test for gram-positive and negative?

Answer 9

Take some bacteria
Crystal violet
Decolorise with acetone
Counter stain with pink or red dye

Question 10

Describe what colour changes occur at each staining step and why?

Answer 10

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

Question 11

What colour are gram positive and negative bacteria at the end of the staining process

Answer 11

Gram positive are dark purple or blue
Gram negative are red or pink

Question 12

What do flagella allow and aid with?

Answer 12

Enable bacteria to swim in fluids, aiding chemotaxis

Question 13

What is chemotaxis?

Answer 13

The movement of a motile cell or organism in response to a chemical signal

Question 14

Do oral bacteria have them?

Answer 14

Not many oral bacteria have flagella

Question 15

What are Fimbriae?

Answer 15

Fimbriae/pills are fine short hair-like filaments that extend from the cell surface. Contain the protein pillin.

Question 16

What do pilli allow?

Answer 16

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

Question 17

What kind of specimen collections are there?

Answer 17

Tissue biopsy, faeces, urine, swab

Question 18

How does culturing bacteria work?

Answer 18

Agar / liquid medium has lots of nutrients to provide the bacteria, allowing them to grow/reproduce/culture

Question 19

What are facultative anaerobic bacteria?

Answer 19

Normally use oxygen but can switch to anaerobic if needed

Question 20

How to grow anaerobic bacteria since they live without oxygen?

Answer 20

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

Question 21

What does differential media for culturing bacteria allow?

Answer 21

To discriminate between microorganisms. Will be selective to inhibit or promote growth of some bacteria, or grow in a different colour.

Question 22

What is haemolysis?

Answer 22

The destruction of red blood cells

Question 23

Describe haemolysis on blood agar?

Answer 23

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.

Question 24

Why are biochemical tests conducted?

Answer 24

To differentiate bacteria based on which sugars they react with by forming different colours in test tubes.

Question 25

What are some genetic methods of identification and describe them briefly?

Answer 25

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