Theme 2: Morphology of bacteria
Bacteria are prokaryotic cells that play an important role in human disease and health.
They can cause disease but are also part of the human microbiota and live on our skin,
body and on everyday objects in our environment.
When compared to eukaryotic cells, the structure of bacteria is less complex due to a
lack of nucleus and membrane-bound organelles such as mitochondria, endoplasmic
reticulum and Golgi complexes.
The cell wall
The cell wall which is found on the outer surface of the cell membrane and its most
important role is to protect the bacteria.
It consists of peptidoglycan which usually helps differentiate whether bacteria are
Gram positive or Gram negative.
Gram positive bacteria have a single thick layer of peptidoglycan above the plasma
membrane, which allows them to retain the staining dye, and Gram negative bacteria
have a thinner layer of peptidoglycan sandwiched between the surface membrane and
the plasma membrane, so they can’t retain the dye.
Additionally, the cell wall helps maintain their shape.
The round shaped bacteria are called cocci, the rod shaped ones are called bacilli,
spiral shaped ones are spirilla, and sometimes the same bacteria can have multiple
forms, in which case they’re called pleomorphic.
Some bacteria are covered by a capsule, which acts as a shield that protects the
bacteria against phagocytosis, and also helps the bacteria adhere to surfaces.
The capsule is considered an important virulence factor since the strains that lack a
capsule are less virulent.
Bacteria are prokaryotic cells that play an important role in human disease and health.
They can cause disease but are also part of the human microbiota and live on our skin,
body and on everyday objects in our environment.
When compared to eukaryotic cells, the structure of bacteria is less complex due to a
lack of nucleus and membrane-bound organelles such as mitochondria, endoplasmic
reticulum and Golgi complexes.
The cell wall
The cell wall which is found on the outer surface of the cell membrane and its most
important role is to protect the bacteria.
It consists of peptidoglycan which usually helps differentiate whether bacteria are
Gram positive or Gram negative.
Gram positive bacteria have a single thick layer of peptidoglycan above the plasma
membrane, which allows them to retain the staining dye, and Gram negative bacteria
have a thinner layer of peptidoglycan sandwiched between the surface membrane and
the plasma membrane, so they can’t retain the dye.
Additionally, the cell wall helps maintain their shape.
The round shaped bacteria are called cocci, the rod shaped ones are called bacilli,
spiral shaped ones are spirilla, and sometimes the same bacteria can have multiple
forms, in which case they’re called pleomorphic.
Some bacteria are covered by a capsule, which acts as a shield that protects the
bacteria against phagocytosis, and also helps the bacteria adhere to surfaces.
The capsule is considered an important virulence factor since the strains that lack a
capsule are less virulent.
