biological agents of disease

Question 1

pathogen =

Answer 1

an organism that causes disease

e.g. viruses, bacteria, protozoan, fungi, worms

Question 2

not all microbes are ______ as lots are ______ to health

Answer 2

pathogens, beneficial

Question 3

this type of primary pathogen can only survive in host and have specific host species.

Answer 3

obligate pathogen

Question 4

this type of secondary pathogen is present in environmental reservoirs waiting for host

Answer 4

facultative pathogen

Question 5

this type of secondary pathogen is normally benign but can cause disease in compromised host

Answer 5

opportunistic pathogen

Question 6

2 closely related species can be pathogenic and harmless. they only differ by what type of genes?

Answer 6

virulence genes

Question 7

where are virulence genes found?

Answer 7

clustered together on the bacterial chromosome in large clusters called pathogenicity islands

they are then incorporated into bacterial DNA

Question 8

proteins that virulence genes encode are called?

Answer 8

virulence factors

Question 9

virulence genes can be carried on _______ by ________ gene transfer

Answer 9

bacteriophages

horizontal

Question 10

describe virulence genes in vibrio cholera

Answer 10

100s of different strains but only those infected by bacteriophages
→ bacteriophage transfer genes that encode the cholera toxin into bacterium
→ combination of the virus and bacteria that individually are harmless

Question 11

what does the cholera toxin do?

Answer 11

causes diarrhoea → dehydrates intestinal cells

→ spreads infected bacteria to new host

Question 12

have a complex life cycle and often show dimorphism

Answer 12

fungal pathogens

Question 13

histoplasmosis capsulatum

Answer 13

grows as mold in low temps in soil → switches to yeast when inhaled in warm lungs → engulfed by alveolar macrophages in yeast form

Question 14

why are anti fungal treatments less effective than antibiotics?

Answer 14

eukaryotic nature of fungal cells and dimorphism

Question 15

what type of pathogens often have more than 1 host?

Answer 15

protozoan pathogens

Question 16

describe how the malaria plasmodium falciparum parasite works

Answer 16

→ virus grows inside mosquito vector → sporozoites injected into human host when blood is sucked → replication in liver → infects RBCs → production of gametocytes in blood → gametocytes sucked up by new mosquito vector when fertilisation occurs → spreads the plasmodium falciparum

Question 17

what is a vector?

Answer 17

an insect that transmits disease

Question 18

what diseases caused by viruses need to replicate in insect cells to use them as vectors?

Answer 18

dengue and yellow fever

Question 19

how do successful pathogens work?

Answer 19

enter the host → find niche that is nutritionally compatible → deal with the hosts immune system → replicate → move from one host to another

Question 20

successful pathogens need to:

Answer 20

invade protective barriers and breach the cell membrane

Question 21

what are the protective barriers?

Answer 21

epithelia, flora, mucous

Question 22

how do epithelial cells work to protect against pathogens?

Answer 22

held together by tight junctions that prevent pathogens from squeezing between cells

Question 23

where is mucous secreted?

Answer 23

epithelial areas without flora secrete mucous e.g. lower lung, small intestines, bladder

Question 24

what are the different ways that pathogens overcome protective barriers?

Answer 24

open wounds in epithelial barriers give access to opportunistic pathogens (but breaks in epithelia are quickly recognised by WBCs)

some bacteria have P pili and special adhesin proteins → anchor them to epithelia
(adhesions have receptors on host cell that have other good functions so treatment can’t target these protein receptors)

breach the cell membrane → necessary to inject toxins or replicate inside the cell

toxins kill host cells

kill WBCs to evade the immune system

many bacteria have type 3 secretion systems → act like syringes to inject toxins or effector proteins

Question 25

both _____ mechanism and ______ mechanism cause _____________ (the active rearrangement of the cell)

Answer 25

zipper
trigger
actin polymerisation

Question 26

bacteria if inhaled is phagocytosed by macrophages. it then replicates inside them and camouflages itself. what type of diseases do this?

Answer 26

Legionnaires disease

Question 27

interaction of invasin protein with host cell receptors such as intergrins. causes membrane to curve and engulf pathogen. what type of mechanism is this?

Answer 27

zipper

Question 28

type 3 secretion apparatus causes polymerisation of actin which creates membrane ruffles that engulfs pathogen. what type of mechanism is this?

Answer 28

trigger

Question 29

explain how listeria monocytogenes enter their host and avoid destruction in host cells

Answer 29

→ enter by zipper mechanism by being engulfed by phagosome
→ listeriolysin O is secreted and breaks down the phagosome before it reaches the lysosome to form a phagolysosome
→ pH in cytoplasm = too high for listeriolysin O so is broken down
→ L monocytogenes can now replicate in host cell
→ L monocytogenes assemble actin tails that push them into neighbouring cells

→ bacterial protein ActA → initiates actin polymerisation at the tail end of L monocytogenes

Question 30

what are the 3 pathogens that you need to know that modify hosts behaviour to suit their needs

Answer 30

yersinia pestis, toxoplasma gondii, cordyseps sinesis

Question 31

how does yersinia pestis modify their hosts behaviour to suit its needs?

Answer 31

blocks fleas digestive tract so it starves and bites more → this spreads Y pestis to other hosts

Question 32

how does toxoplasma gondii modify their hosts behaviour to suit its needs?

Answer 32

can only complete its lifecycle in cats,
pathogen is transmitted via cysts in rat tissues
→ infected rats lose their fear towards cats and are even attracted to cats smell
→ cats catch and bite into rats more → helps transmit infection from rats to cats

Question 33

how does cord ceps sinesis modify their hosts behaviour to suit its needs?

Answer 33

infects ants → causes them to climb up branches → clamp on → die → body provides nutrients while fungus grows → fungus emerges from ant → spreads more spores

Question 34

what are the majority of antibiotics made from?

Answer 34

natural products produced by fungi or bacteria

e.g. penecillin, tetracycline

Question 35

why do antibiotics only work for bacteria and not viruses?

Answer 35

they don’t harm host eukaryotic cells (viruses invade host) so only target prokaryotic cells

Question 36

how does bacteria become resistant to antibiotics?

Answer 36

through mutations and lateral gene transfer

Question 37

how do antibiotics work?

Answer 37

disrupt bacterial growth by disrupting cellular processes

Question 38

how are new antibiotics developed when resistance occurs?

Answer 38

new side chains are added to give new generation of drugs