Microbiology Flashcards
What do genetic differences of bacteria produce?
Different metabolic features and different surfaces molecules, so they have different antigenic properties
What is the smallest bacterium?
Archaea
What is the largest bacterium?
The sulphur bacterium/ thiomargarita namibiensis.
What are the 3 shapes of bacteria?
Bacillus
Coccus
Spiral/spirillum
What are the types of grouping of bacteria and give examples
Single, Helicobacter
Pairs, Diplococcus pneumoniae
Chains, Streptococcus
Clusters, Staphylococcus
What does gram-staining allow?
Distinguishment between gram-positive and gram-negative bacteria
What colour do gram-negative go?
Red
What colour do gram-positive go?
Purple
Describe the first step in gram staining
Use crystal violet which is a basic dye, it binds to peptidoglycan so all bacteria stain purple
Describe the second step in gram staining
Use lugols iodine, it is a mordant.
It binds the crystal violet more strongly
Describe the third step in gram staining
Use ethanol, a decolouriser.
It removes unbound crystal violet and lipopolysaccharides.
Gram-positive stay purple.
Gram-negative become colourless
Describe the fourth step in gram staining
Use safranin, a counter-stain.
It dyes gram-negative red
What is the structure of gram positive bacteria and what does it mean?
Has no outer lipopolysaccharide layer so stain binds more efficiently.
Lack of lipopolysaccharide layer means bacteria is more susceptible to penicillin and lysozyme.
What does lysozyme do?
It is an antibacterial enzyme, it hydrolyses the bonds holding the peptidoglycan molecule together.
What does penicillin do?
Prevents the bonds inter-linking peptidoglycan molecules from forming.
Therefore makes cell walls weak and prone to collapse.
