L07-Growth and nutrition of bacteria Flashcards
How is gram staining performed?
First bacteria are stained with crystal violet stain and iodine. The cells are then washed with alcohol and counterstained with safarin. If the cells remain iodine purple then they are gram positive and if the alcohol washes off the colour then they are gram negative.
What is the structure of gram positive bacteria?
They have a thick peptidoglycan outside the cell wall that retains the purple colour on staining.
What is the structure of gram negative bacteria?
They only have a thin peptidoglycan layer sandwiched between two cell membranes. The outer membrane is heavily modified with a molecule called lipopolysaccharide (LPS). This is a very potent activator of the immune system.
What is a common method by which antibiotics work?
They often target the biosynthetic pathway for the production of peptidoglycans.
How are bacteria identified in the laboratory?
Bacterial colonies are exposed to a laser beam which ionises the sample. The fragments of the sample are then analysed to determine the bacteria.
What are the 5 things bacteria need to do to cause disease?
Attach to the host Invade the tissue Acquire nutrients and grow Avoid the host immune response Cause disease (releasing toxins etc)
How do bacteria attach to host cells?
They use pili and also affect receptors on the cell surface to prevent them from being killed.
How do bacteria aquire nutrients e.g. iron?
They produce molecules called siderophores which have a high affinity for iron and retrieve it from host proteins.
what are the main mechanisms bacteria use to avoid the immune system?
Inhibit opsonisation
Inhibit antigen presentation
Inhibit phagocytosis
Inhibit t cell activation
What are the two mechanisms that mediate cell damage by bacteria?
Direct-usually mediated by production of toxins
Indirect-overactivation of inflammation
