FUNGAL INFECTIONS

Question 1

What are the main differences between bacteria and fungi?

Answer 1

(b) are prokaryotes and (f) are eukaryotes
(b) are unicellular and (f) can be multicellular
(b) cell wall of peptidoglycan and (f) chitin
(b) 70s ribosomes and (f) 80s
(b) reproduce by binary fission and (f) reproduction can be sexual and asexual

Question 2

what are saphrophtes?

Answer 2

microorganisms that live on dead or decaying organic matter

Question 3

do fungal species intentionally colonise humans?

Answer 3

no theyre opportunistic hosts - none are primary pathogens but in some cases where someone is vulnerable/immunocompromised, they may colonise

Question 4

why is human infection of fungal species so rare?

Answer 4

they arent adapted to grow at 37 degrees
theyre poorly adapted to using human nutrients
they are slow growing
humans defence mechanisms are efficient as dealing with fungi
fungis enzymatic pathway is more efficient in non-living substrates eg. we are too acidic

Question 5

why are there more human-fungal infectiosn every year?

Answer 5

because there are increasing numbers of at-risk patients e.g. more immunocompressing drugs

Question 6

what are the main 3 types of fungi?

Answer 6

mold, yeast and dimorphic

Question 7

what are dimorphic fungi?

Answer 7

organisms that have the ability to switch between two morphologies during their lifecycle: yeast and hyphae

Question 8

what is a mycelium?

Answer 8

entangled masses of hyphae which can be visible to the naked eye

Question 9

how do molds grow?

Answer 9

by the formation of hyphae

Question 10

what are hyphae?

Answer 10

long, branching filamentous structures

Question 11

how do moulds reproduce?

Answer 11

asexually e.g. by hyphae touching other hyphae or sexually by spores from hyphae

Question 12

outline the key features of yeast?

Answer 12

unicellular, roung or ovoid

Question 13

how do yeast reproduce?

Answer 13

budding- a small bump protudes the parent cell, enlarges, matures and detaches

Question 14

what are pseudohyphae?

Answer 14

intermediate between a chain of budding cells and a true hyphae - seen in yeast when causing invasive disease

Question 15

which species are the only yeast which can form true hyphae?

Answer 15

candida species

Question 16

what can dimorphic fungi grow as?

Answer 16

yeast/moulds - and can change in their lifespan

Question 17

outline the epidemiology of dimorphic fungi?

Answer 17

they are geographically restricted and are not endemic in the UK.

Question 18

where is the dimorphic fungi’s natural habitat?

Answer 18

soil or plants where they grow as moulds

Question 19

how do dimorphic fungi cause infection?

Answer 19

by inhalation of spores into the pulmonary system

they can turn into yeasts in the lower respiratory tract

Question 20

what are mycoses and what are the 4 types?

Answer 20

a disease caused by any fungus that invades the tissues

superficial, cutaneous, subcutaneous and deep/systemic

Question 21

what are the features of superficial mycoses?

Answer 21

the fungus lives on the superficial layers of the skin and no living tissues is invaded so we dont get a cellular response from the host - may just cause a mild inflammatory reaction

Question 22

what are typical treatments for superficial mycoses?

Answer 22

topical antifungal creams

Question 23

what are the features of cutaneous mycoses?

Answer 23

when fungi extend deeper into the epidermis, inluding the appendiges. no living tissue is invaded because they stick to keratinised layers

Question 24

what are keratinophilic fungi?

Answer 24

fungi which can use keratin for growth

Question 25

what fungal species causes thrush?

Answer 25

candida

Question 26

what is candidiasis?

Answer 26

thrush

Question 27

outline the features of subcutaneous mycoses?

Answer 27

fungi invade the dermis, subcutaneous tissues, muscles and fascia
initiated by piercing trauma to the skin
tend to remain localised and slowly spread to surrounding tissues

Question 28

what are the features of deep mycoses?

Answer 28

involve the lungs, abdominal viscera, bones and or central nervous system.
The common entry points are the respiratory tract, gastrointestinal tract, and blood vessels

Question 29

how can you diagnose a yeast?

Answer 29

its seen in microscopy, grows slowly on normal culture plates, grows on blood cultures, seen on PCR

Question 30

how do you diagnose a mould?

Answer 30

seen mainly in tissues, grows very slowly on culture plates, doesnt, grow in blood culture

Question 31

when considering a fungal infection, how long of a travel history should you take from a patient?

Answer 31

3 years - most common to have picked up in past 3 months

Question 32

why are antifungal drugs usually toxic?

Answer 32

because fungal cells have similar properties to human cells

Question 33

why are there fewer antifungal drugs than antibacterial drugs?

Answer 33

because fungus are similar to host and they have many stages in life which can make them resistant/hard to treat

Question 34

what is amphotericin?

Answer 34

a broad spectrum antifungal drug

Question 35

how can you make amphotericin less toxic?

Answer 35

by wrapping the drug in a phospholipid bilayer so its less likely to be absorbed into the nephron

Question 36

how does amphotericin work?

Answer 36

it binds with ergosterol, forming pores in the cell membrane and causing rapid leakage of monovalent ions and subsequent fungal cell death.

Question 37

what are azoles?

Answer 37

antifungal drugs e.g. ketakonazole

Question 38

how do azoles work?

Answer 38

they inhibit lanosterol demythlase which means lanosterol cant be converted to ergosterol. a depletion in ergosterol disrupts fungal membrane strcuture and function, inhibiting growth

Question 39

what do fungi need ergosterol for?

Answer 39

maintaining cell membrane integrity

Question 40

what are echinocandins?

Answer 40

antifungal drugs e.g. caspofungin

Question 41

how do echinocandins work?

Answer 41

they inhibit glucan synthase = inhibits cell wall synthesis