MMB02 Morphology And Microbial Counts Flashcards
What are the main shapes bacterial cells come in
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)
What is the purpose of flagella
They are used for cell mobility
What is the purpose of fimbrae
Fimbrae and pilli are filamentous structures composed of proteins that enable cells to stick to surfaces as well as form biofilms on liquids surfaces
What is the purpose of pili
Pili are similar to fimbrae but longer. The facilitate genetic exchange between cells as well as allow pathogens to stick to host tissues
What cells create endopsores
Certain species of gram positive bacteria, often found in soil
What is the structure of endospores
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
What is bacillus anthracis
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)
What kind of phospholipid membrane do bacterial cells have
A phospholipid bilayer (like most cells)
What kind of phospholipid membrane do archea cells have
Phospholipid mono layer
(These are extremely resistant to heat and allows Archea to live in extreme temperatures)
What is the difference in cell walls between gram-positive and gram-negative bacteria
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
What is a microscopic count
Counting cells through a microscope using a counting chamber
What are the limitation of microscopic counts
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
What are the limitations of viable counts
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
