Bacteriology

• Growth curve of bacteria showing lag phase, log phase, stationary phase and death phase.

  
• Conditions of growth:

  • Aerobe: Bacteria that need oxygen to grow. Tend to grow in open spaces.
  • Anaerobe: Cannot grow in presence of oxygen.
  • Temperature: Psychrophilic grow in -5 to 15 degrees, Mesophilic grow at room temperature and Thermophilic grow in 30 to 85 degrees.
  • Acidophilic grow in acidic conditions whilst alkaliphilic grow in high pH.
  • Halophilic grow in up to 25% salt concentrations.
• Bacteria reproduce via binary fission:

  • During cell division the DNA replicates
  • The cell elongates causing the chromosome to split into two and be in two daughter cells
  • When the cell is twice its original length, the plasma membrane grows inwards forming a cell wall which splits the two cells.
• Genetic mutation (horizontal gene mutations) can occur through conjugation, where bacteria with an F factor (fertility factor) inside its plasmid form a conjugation tube with a bacteria that does not contain an F factor.
• The F factor is replicated and passed through the conjugation tube.
• The F factor can contain genetic mutations that allow the bacteria to be antibiotic resistant or have hairs on its cell wall.
• Transformation is a process where bacteria picks up extracellular fragments of DNA released by dead bacteria and incorporates it into its own DNA.
• Transduction is a process where bacteriophage infects bacteria and replicates with some of the bacteria's DNA instead of its own viral DNA by mistake, therefore picking up the bacteria's genetic mutations.
• Bacteria survival:

  • Bacteria can form endospores under harsh conditions which are tough cell walls that encase DNA and cytoplasm.
• Penicillin works by inhibiting the synthesis of peptidoglycan. So it attacks it. This works against gram positive bacteria but not gram negative as it contains two lipid membranes and has a thin peptidoglycan layer.
• Gram positive bacteria have a lipid membrane layer and a thick peptidoglycan layer whilst gram negative bacteria have two lipid membrane layers and a thin peptidoglycan layer in between. This is the cause of gram positive showing up as a purple stain whilst gram negative show up as pink stains.

  
• Gram negative bacteria have a periplasmic space in their outer membrane that contains enzymes such as beta lactamase that can breakdown antibiotics giving them antibiotic resistance.

  
• DNA in bacteria can have mutations that modify penicillin binding proteins which don't allow penicillin to bind to them. An example is methicillin resistant staphylococcus aureus.