MMB02 Morphology And Microbial Counts

Question 1

What are the main shapes bacterial cells come in

Answer 1

Bacillus (rod), cocci (spherical), spirillum (spiral), spirochaete (corkscrew), vibrio (comma)

They exist as single cells (mono), in pairs (diplo), in clusters (staphyl) and chains (strepto)

Question 2

What is the purpose of flagella

Answer 2

They are used for cell mobility

Question 3

What is the purpose of fimbrae

Answer 3

Fimbrae and pilli are filamentous structures composed of proteins that enable cells to stick to surfaces as well as form biofilms on liquids surfaces

Question 4

What is the purpose of pili

Answer 4

Pili are similar to fimbrae but longer. The facilitate genetic exchange between cells as well as allow pathogens to stick to host tissues

Question 5

What cells create endopsores

Answer 5

Certain species of gram positive bacteria, often found in soil

Question 6

What is the structure of endospores

Answer 6

Highly differentiated cells

Core contains dehydrated cytoplasm, DNA, ribosomes and enzymes

Cortex protects the core, mainly composed of peptidoglycan

Spore coat contains many cross linked proteins making it impermeable to most chemicals

Endospores only need water to turn back into normal cells

Question 7

What is bacillus anthracis

Answer 7

A saprohytic soil bacterium

Gram positive

First bacterium shown to be the cause of a disease during Robert Koch experiment in 1890

Produces endospores (anthrax)

Question 8

What kind of phospholipid membrane do bacterial cells have

Answer 8

A phospholipid bilayer (like most cells)

Question 9

What kind of phospholipid membrane do archea cells have

Answer 9

Phospholipid mono layer

(These are extremely resistant to heat and allows Archea to live in extreme temperatures)

Question 10

What is the difference in cell walls between gram-positive and gram-negative bacteria

Answer 10

Gram-positive:
-a thick layer of peptidoglycan on top of the cytoplasmic membrane

Gram negative
-a thin layer of peptidoglycan above the cytoplasmic membrane, sandwiched between another outer phospholipid membrane

Question 11

What is a microscopic count

Answer 11

Counting cells through a microscope using a counting chamber

Question 12

What are the limitation of microscopic counts

Answer 12

Dead cells can’t be distinguished from live cells

Isn’t very precise since smaller cells are easy to miss

Cell suspensions of low density may have very few bacteria present in the microscope field

Most samples will need to be stained in order to count

Question 13

What are the limitations of viable counts

Answer 13

If two or more cells are in a clump they will grow to form one cell

Different microorganism may need different culture times or conditions so the count may underestimate sample numbers

Not suited for microorganisms that can’t be cultured on agar