first bacteriology

Question 1

what are the 3 types of outbreak?

Answer 1

1 - point source outbreak
2 - continuous source outbreak
3 - propagated (more complex) outbreaks

Question 2

what’s vertical transmission?

Answer 2

from mother to child ie transplacental (syphilis) or partuition/puerperal (gonorrhoea). also caled congenital

Question 3

what’s an obligate parasite?

Answer 3

An obligate parasite is a parasitic organism that cannot complete its life cycle without exploiting a suitable host.

Question 4

most bacteria are not obligate parasites, give an example of one that is

Answer 4

chlamydia. it replicates within human cells.

Question 5

what’s the mechanism of division of bacteria called?

Answer 5

binary fission

Question 6

are bacteria mRNA mono or polycistronic?

Answer 6

poly - (colinear genes)

Question 7

are bacteria pro or eukaryotes?

Answer 7

prokaryotes

Question 8

4 different shapes of bacteria?

Answer 8

1 - rods - bacilli - salmonella, E.coli
2 - cocci - spheres - staphylococcus
3 - curved/comma shaped - vibrio cholerae
4 - spiral shaped - treponaema pallidum (syphillis)

Question 9

name 4 bacteria that produce endospores

Answer 9

1 - clostridium tetani
2 - c. perfringes
3 - c. botulinium
4 - bacillus anthracis

Question 10

what stains do gram positive/negative bacteria hold? fundamental difference between the two bacteria?

Answer 10

+ve - crystal violet and iodine (complexed)
-ve - safranin (pink) - the others are washed out by ethanol
+ve - thicker peptidoglycan wall
-ve - an extra outer membrane

Question 11

what are PMNs?

Answer 11

polymorphonuclear leukocytes

Question 12

what medically important bacteria dont gram stain?

Answer 12

1 - Mycobacteria. inc M. tuberculosis. called acid fast bacteria as theyre difficult to stain/destain due to their waxy lipid coat.

2 -Mycoplasma. cause non-gonococcal urethritis (NGU) and pneumonia. lack a cell wall. are difficult to culture and are insensitive to many bacteria.

Question 13

what makes up the cell wall?

Answer 13

alternating N-acetylglucosamine (NAG), N-acetylmuramic acid (NAM). crosslinked by short oligopeptides.

thicker in gram positive. enzymes unpick it to add new strands during growth.
accounts for 90% of the dry weight.

Question 14

what does the cell membrane do?

Answer 14

lipid bilayer. osmotic barrier, signal reception, transport of nutrients, respiration.

Question 15

whats a periplasm?

Answer 15

• a layer between the two membranes of gram-negative bacteria containing hydrolytic enzymes inc beta-lactamases (breaks down lactam ring containing antibiotics eg penicillin or cephalosporin). also transport system components

Question 16

which bacteria have an outer membrane and what does it contain?

Answer 16

gram negative bacteria

- contains porin channels and lipopolysaccharides

Question 17

what’s an O antigen?

Answer 17

found on the outer part of bacterial LPS, highly variable - different antigens and serotypes.

Question 18

what is Lipid-A?

Answer 18

a component of bacterial LPS embedded in the outer membrane. called endotoxin. highly conserved across gram -ve so acts as a PAMP for TLRs.

Question 19

what’s a bacterial capsule made of and why is it there?

Answer 19

made of polysaccharide and prevents them drying and blocks complement and macrophages

Question 20

how do gram +ve and -ve bacteria typically transport stuff across the inner membrane?

Answer 20

using an N-terminal secretion signal and the standard secretion (Sec) pathway.
- ve also have other mechanisms for the periplasm and the outer membrane.

Question 21

what is bacterial binary fission?

Answer 21

genome duplication. segregation, cell septation thanks to FtsZ which is a tubulin ancestor that localises at the midpoint and ofrms a ring that tightens and divides the cell. lac cultures can double every 20-30 mins but take a lot longer in host.

Question 22

what are facultative anaerobes?

Answer 22

bacteria that dont need oxygen. most of which are pathogenic. some are strict anaerobes (clostridium, bacteroides) which typically ferment for energy.
only a few are aerobes ( pseudomonas aerginosa)

Question 23

how do bacteria move towards stimuli?

Answer 23

by chemotaxis. chemoreceptors at the nose sense and transmit info to the flagellar switch complex. this controls the direction in which the helical propeller rotates. counter clockwise to swim, clockwise to ‘tumble’ randomly. many also swarm as a coordinated population.

Question 24

how do bacteria alter transcription to adapt to environmental changes?

Answer 24

largely determined by changes in coupled transcription of continuous genes (operons) which is tightly coupled to translation and rapid mRNA turnover.

Question 25

how do bacteria sense the environment?

Answer 25

typically - histidine-aspartate phosphorelay (HAP) signalling pathways.
signals = temperature, pH, amino acids, osmolarity, stress.

can modulate expression of operon networks - global regulation.

Question 26

what is quorum sensing?

Answer 26

a special signal of cell density. it causes the pathogen to switch on its virulence geneswhen population is high. bacteria sense quorum by secreting a small signal molecule and sensing its concentration.

Question 27

how do bacteria alter their DNA to adapt?

Answer 27

1 - mutations in surface antigens ie O of LPS or K (capsular polysaccharide)

2 - DNA rearrangements. ie by insertion sequences and transposons.

3 - transfer between bacteria (transduction, transformation, conjugation)

Question 28

how do bacteria rearrange their DNA?

Answer 28

1 - random insertion of insertion sequences. a few hundred BP long moved by transposase. eg switching between 2 flagella antigens (phase variation) by salmonella, or between thousands of adhesion pili (antigenic variation) by neisseria.

• transposons are similar to IS but larger and often incorporate IS elements at their ends. convey useful genes ie antibiotic/heavy metal resistance or virulence factors ie toxins. can be picked up from plasmids which allow further flexibility and rapid spread of antibiotic resistance and virulence genes.

Question 29

functions of plasmids?

Answer 29

allow further flexibility and rapid spread of antibiotic resistance and virulence genes.

Question 30

how do bacteria transfer genes between each other?

Answer 30

1 - transduction - by bacteriophages

2 - transformation - uptake of DNA from lysed bacteria.

3 - conjugation - direct transfer requiring contact between two bacteria.

Question 31

what are pathogenicity islands?

Answer 31

groups of genes for infection and survival.
evolved by integration of transposons, plasmids and bacteriophage and incorporation of transformed DNA.

• typically have a G + C content different from surrounding areas.
• can include dozens of genes eg salmonella SPI-1 and -2 which determine entry into non-phagocytic cells and survival in macrophages respectively.
• these islands increase dissemination of virulence traits and facilitate virulence gene co-regulation.

Question 32

what are the physical and chemical barriers against bacterial infection?

Answer 32

1 - skin - sloughing cells (remove bac), etc

2 - mucous membranes - cillia, eyelid blinking, mucin, tight junctions
3 - lysozyme - splits bacterial peptidoglycan
4 - gastric acid,
5 - iron limitation - sequestration by lactoferrin and transferrin
6 - resident microflora - inhibits colonisation