Introduction to Microbiology – Bacteria

Microbiology – Bacteria


v  Exist everywhere

v  Unicellular – single cell, have small ribosome, have cellular dna, have plasma dna, have rna

v  No membrane

v  Prokaryotic

v  Can be seen by a light microscope

v  Few are pathogenic

v  Free living


v  Cytoplasm

  • 80% water, contains ions, proteins, carbs and lipidsand some enzymes floating too.
  • Chromosome is double stranded dna and rna (live in cytoplasm)
  • Ribosomes (site for protein synthesis)
  • Plasmids:
    • Extrachromosomal circular structure
    • Carry genes against drug resistance (dna fragments)

v  DNA

v  Ribosomes

v  Plasmids

v  Cell Membrane

  • Separates internal from external environment
  • Phospholipid and protein only
  • Selectively permeable

v  Cell Wall

  • Lies above plasma membrane
  • Under capsual
  • Semi rigid (gives shape) – it is it’s shield, lysozomes found in tears and saliva will damage the cell wall and the bacteria will die
  • A bit like skin, prevents the cell bursting in regard to osmotic pressure
  • Grahn test will help determine the types of bacteria

v  Flagellum

  • Multiple or sinlge
  • Very long
  • Involved in motion
  • Requires ATP to move

v  Glycocalyx (capsual)

  • Only in some bacteria
  • Sticky so it allows bacteria to adhere really well, like a slime layer
  • Protects against phagocytes

Classification and Terminology

v  2 names: Genus + species,  Together they identify the species
eg. Staphylococcus Aureus.

v  Three Basic Shapes:

  • Spherical (cocci)purple on grahm stain
  • Rod (bacilli) pink on ghram stain
  • Spiral (spirochaete)

v  2 domains:

  • Arhaebateria
  • Eubacteria

v  Single: cocci

v  Pair: diplococci

v  Cluster:staphlococci

v  Chains: streptococci


Survival of Bacteria Inside The Host

  • Correct Temperature
    Most Bacteria need a constant stable Temp and pH balance to be able to thrive, opposed to those that live at the extreems
  • Correct pH
  • Correct osmotic pressure
  • Correct amount of Oxygen (some need and some dont)
    anaerobic = don’t need oxygen and aerobic = need oxygen

Bacteria have the same needs as all living things:

  • Obtain food
  • Breakdown the food using chemicals within their environment or consuming other substances (meat, milk, decaying material), to utilise the nutrients (THIS IS CALLED RESPIRATION – it usually requires oxygen)
  • Protect themselves from the environment



Asexual Reproduction = Binary Fission

  • Cell membrane grows between the 2 DNA molecules
  • The bacteria  almost doubles in size and the original cell membrane pinches outwards (cant grow double its normal size)
  • Cell wall forms between the two dna molecules =  two identical daughter cell
  • The time takes for this to occur is called the generation time, the time varies from a few minutes to a few hours depending on the type of bacteria = that’s why food poisoning  takes time to sink in. Like no growth (lag phase) them BAM (exponential phase)! Then the nutrients are depleted after all the bacteria population has risen, and then death of bacteria or they find a new place to call home.

What affects the growth of bacteria:

  • Insufficient nutrients
  • Oxygen levels = some are anaerobic and some are aerobic
  • Changes in pH or temp

Normal flora

Most normal flora is bacteria, it is acquired on the skin moments after birth, the organisms present reflect the age, nutrition and environment of the person.

  • Dry areas on the skin usually have less flora, where as moister areas will support a large population.
  • The majority Bacteria is Anaerobic flora, which occur bellow the skin surface, they also live in the nose and mouth. Staphylococci and Streptococci live there (potentially pathogenic)
  • The gut usually provides a barrier as the  pH is acidic, so only those capable of living do.
  • The vagina houses a large population of flora.


  • Discourage potential pathogens from setting up shop
  • In the gut, the bacteria that are friendly help metabolise and breakdown the food


  • Potential pathogenic
  • Normal flora can turn nasty if the skin is an open wound
  • Antibiotics can change the tables letting not nice pathogens take over from normal flora

Important pathogens

Gram Positives: staphylococci (skin infection)and streptococci (sore throat)

Gram negatives: Neisseria (STI) and Bordetella perussis (Whopping Cough)

Cellulitus, Impetigo, Scarlet Fever, Leprosy


  • Antibiotics/ antimicrobials = damage the bacteria and not the host

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