Bacteria

Question 1

What are gram negative bacteria?

Answer 1

Outer membrane is heavily modified, with sugars to produce a molecule LPS or endotoxin. Thin layer of peptidoglycan sandwiched between two cell membrane layers doesn’t retain dye.

Question 2

What are gram positive bacteria?

Answer 2

Thick cell wall of peptidoglycan on the outside of the cell membrane which retains crystal violet dye.

Question 3

Do bacteria have a nucleus?

Answer 3

No nucleus, they are prokaryotes.

Question 4

Named a gram negative bacterial species?

Answer 4

E. Coli, Klebsiella

Question 5

Name a gram positive bacterial species?

Answer 5

Staphylococci, streptococci

Question 6

What does prokaryotes mean?

Answer 6

Lack membrane bound organelles. Usually have a cell wall. Can have protruding appendages (fimbriae, flagella)

Question 7

Name an opportunistic pathogen

Answer 7

Pseudomonas - most body sites if given a chance

Question 8

How do bacteria cause disease?

Answer 8

Varies. Some invade cells, occupy very different niches, disease is a function of: bacterial activity - production of toxins, direct tissue damage and host activity - immune response.
Bacteria products which cause disease: some are designed to damage the host - toxins. Some are immunogenic and result in damage indirectly - LPS, flagella

Question 9

What are some important cell wall components in bacteria?

Answer 9

Lipopolysaccharide (LPS): an endotoxin, gram negatives cause massive immunostimulation causing sepsis.

Peptidoglycan: give structure and shape to negative and positive gram cells. Synthesis target for cephalosporins, penicillins and vancomycin.

Lipotechoic acid: gram positive: immune irritant causes septic shock

Question 10

Describe the structure of LPS?

Answer 10

Firmly bound to cell and only released upon lysis. Only Lipid A is toxic –>major immune response. Polysaccharide is a major surface antigen - O antigen.

Question 11

What’s the difference between fimbriae (pili) and flagellae?

Answer 11

Pili are shorter and finer than flagella. Ordinary pili are colonisation antigens. This protein attaches to host cells e.g. UTI. Can be involved in host invasion e.g. N. meningitidis. There are sex pili which havea role in conjugation.

Flagella - molecular motors used to swim, important in pathogenesis, involved in motility and chemotaxis/ Often immunogenic and induce inflammation.

Question 12

What is the bacterial capsule?

Answer 12

condensed, well defined layer closely surrounding the cell which contributes to invasiveness of pathogenic bacteria by reducing opsonisation and protecting from phagocytosis. E.G. strep. pneumoniae.

Question 13

What are exotoxins?

Answer 13

protein secreted by bacteria used to destroy host cell and release contents or allow invasion
e.g. clostridium tetani - and clostridium botulinum

Question 14

How do bacteria cause disease?

Answer 14

To cause disease they need to do these 5 things:
	1) attach to the host: use appendages like pili or fimbriae to attach to host cells. By attaching to specific host receptors bacteria can induce their own uptake into pathways to allow intracellular survival rather than killing.
	2) invade the tissue: have specialised systems called type 3 secretion systems to promote their invasion into host cells
	3) acquire nutrients and grow: e.g. acquisition of iron, conc of free iron in human body low as bound to transferrin. Bacteria produce siderophores which have high affinity for iron and scavenge it from host proteins.
	4) avoid the host immune response: mechanisms to evade the immune system. Some include - inhibiting opsonisation, complement activation, antigen presentation, survival in phagocytes.
cause damage (symptoms): direct mechanisms: production of toxins or indirect mechanisms: overactivation of inflammation e.g. LPS, molecular mimicry - cross reaction of Abs.

The factors that allow bacteria to do this are called virulence factors.