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What is the difference between gram positive and negative bacteria in gram staining appearance and in their shape?

Gram positve bacteria= purple 

Gram negative bacteria= red


Cocci - Spherical

Bacilli – Rod Shaped


Outline the differences between gram positive and negative bacteria in terms of the cell wall?

Gram positive

  • plasma membrane
  • periplasmic space
  • thick peptidogylcan. 

Gram negative

  • plasma membrane
  • periplasmic space
  • thin peptidogylcan
  • ♦ outer membrane consisting of lipopolysaccharide and protein.


Lipopolysaccharides (LPS)

Elicit strong immune responses in animals and humans.


What does peptidoglycan provide?

  • Strength and shape


What is the role of capsule ?

  • Prevents bacteria from phagocytosis


What is the role of flagellum?

  • Important for motility


What is the role of fimbriae?

  • Important for adherence


What is the role of spore?

  • Bacterial spores are highly resistant, dormant structures (i.e. no metabolic activity) formed in response to adverse environmental conditions.  
  • They help in the survival of the organisms during adverse environmental conditions; they do not have a role in reproduction.


What is the role of plasmids?

  • Contains a small, circular, double-stranded DNA molecule


What is a bacteriophage?

  • A virus that infects bacteria


Explain the classification of and nomenclature used for bacterial species

Name is based on genus(taxonomic rank) and species, first part refers to the genus and the second part refers to the species i.e Staphylococcus aureus

Strains of a species have similar characteristics so DNA typing techniques is used to identify specific strains.


Describe how bacteria replicate and create genetic variation?

  1. replicate by binary fission

–identical progeny (descendants)


     2. genetic variation by

–spontaneous mutation

transfer of DNA


Describe briefly the detection and culture of bacteria?

1. Individual bacteria

–can only be seen with a microscope


2. Colonies of individual bacteria

–cultured on solid medium (agar)

–bacterial colonies can be seen by eye



Strains of species 

Have a similar charecteristics so can only be differentiated using DNA typing technique.


Function of penicillin binding proteins

Involved in the final stages of the synthesis of peptidoglycan.