Lect 9 - Introduction & Classification of Human Microbiota

Question 1

what percentage of cells in the human body are of human origin?

Answer 1

10 % of cells

Question 2

whats the name for cells that live in the body but are not human?

Answer 2

The remaining cells comprise the human commensal microbiota.

Certain viruses may also persist in the human body.

Question 3

are most bacteria harmful? how would you describe these bacteria?

Answer 3

No.

Microorgansims that do cause disease may be described as “virulent” or “pathogenic”.

Question 4

Historically, how would we define an organism as pathogenic?

Answer 4

using koch’s postulates.

Question 5

what are Koch’s Postulates?

Answer 5

The causative organism must be isolated from every individual suffering from the disease in question;

The causative organism must be cultivated artificially in pure culture;

When the causative organism is inoculated from pure culture, the typical symptoms of the infection must result;

The causative organism must be recoverable from individuals who are infected experimentally.

Question 6

how can koch’s postulates be applied to genetics?

Answer 6

the gene encoding the trait of interest should be present and transcribed/translated in a virulent strain;

the gene encoding the trait of interest should NOT be present or should be silent in a strain that does not cause disease;

disruption of the gene in a virulent strain should result in the formation of a strain that is incapable of casing disease;

Question 7

what comprises a virus?

Answer 7

They comprise of a nucleic acid core wrapped in a protein coat.

Some viruses have an envelope. other viruses are naked.

Question 8

do viruses carry DNA or RNA?

Answer 8

Viruses have a nucleic acid core, either DNA or RNA but not both.

Retroviruses (RNA) are unusual.

Question 9

what are the units that make up the protein coat of a virus called?

Answer 9

capsomeres.

Question 10

what is the class of virus that attacks bacteria called?

Answer 10

bacteriophages.

Question 11

what is the class of virus that attacks plants?

Answer 11

viroids: naked, infectious RNA molecules that are not associated with any proteins.

Question 12

whats the difference between a naked virus and a prion?

Answer 12

a prion has no genetic material

Question 13

are fungi all eukaryotic?

what is their cell wall made of?

Answer 13

All fungi are eukaryotic.

Most possess a cell wall made of chitin.

Question 14

what is the typical “hairy” type of fungi called?

Answer 14

moulds

Question 15

mould can grow tiny filaments, which form mats. what are these filaments and mats called?

Answer 15

hyphae (singular: hypha, Greek for a thread)

mycelia. (singular: mycelium, from the Greek mukes, meaning a mushroom).

Question 16

what are unicellular fungi called?

Answer 16

yeasts.

Question 17

what is the most common yeast infection?

Answer 17

“thrush” caused by Candida albicans.

Question 18

give some examples of infections caused y moulds

Answer 18

ringworm and athlete’s foot.

Question 19

What are protista?

Answer 19

a grouping of diverse unicellular eukaryotic organisms that are not animals, plants or fungi.

Question 20

what are the classes of protista?

Answer 20

apicomplxa (formerly sporozoa),

flagellate protista,

ciliate protista

and amoebae.

Question 21

give examples of diseases caused by protists

Answer 21

toxoplasmosis, 
amoebic meningitis, 
malaria, 
trypanosomiasis, 
leishmaniasis (Kala-Azar)
amoebic dysentery 
diarrhoea.

Question 22

What protista causes foul smelling vaginal discharge in women?

Answer 22

Trichomonas vaginalis. NOTE MEN CAN BE ASYMPTOMATIC CARRIERS.

Question 23

are bacteria pro or eukaryotes?

Answer 23

The bacterial cell lacks a membrane-bound nucleus. Because of this, bacteria are described as prokaryotes,

Question 24

what are the most common shapes of bacteria?

Answer 24

Most bacteria are either round (cocci) or rod-shaped (bacilli)

Question 25

how else do we divide bactera?

Answer 25

Gram reaction

Question 26

how do we do gram testing?

Answer 26

look at the ability to retain a crystal violet-iodine dye complex when cells are treated with acetone or alcohol.

(reveals fundamental differences in the structure of bacteria.)

Question 27

what is the difference between the structure of a gram + and - bacteria?

Answer 27

positive has a membrane of 30-40 layers of “peptidoglycan”, while a negative has far less of this.

negative bacteria have an extra, complex “outer membrane” instead.

Question 28

what do sugars form the surface antigen of gram negative bacteirum, along with the complex lipid known as lipid A cause?

Answer 28

they act as an endotoxin and cause Gram-negative shock

Question 29

what do bacteria use to increase their motility?

Answer 29

flagella

Question 30

what do gram neg bacteria use to aid adhesion onto surfaces?

Answer 30

hair-like structures known as fimbriae.

Some bacteria produce slime to help them to stick to surfaces. (like Streptococcus mutans on teeth, leading to plaque)

Question 31

what can gram negative bacteria use to exchange genetic material during conjugation?

Answer 31

sex pili (singular: pilus)

Question 32

what other feature have bacteria developed to prevent them from being phagocytosed?

Answer 32

capsules.

Question 33

what bacteria cause infections associated with implanted plastic medical devices.

Answer 33

‘Coagulase-negative’ staphylococci.

they live on the skin, and produce a slime that enables them to stick to plastics.

Question 34

what is the most resistant structure a bacterium can produce; resisting a range of hazardous environments by protecting against heat, radiation and desiccation?

Answer 34

endospores

Question 35

name some routes of infection

Answer 35

airborne
faecal-oral route (GI)
sexually transmissible 
direct inoculation (HIV)
via animals (MALARIA)
via Inanimate objects (known as fomites)

Question 36

how does one control infection?

Answer 36

by identifying the mode of spread and interrupting the cycle of infection, replication and spread.

Question 37

what term describes a pathogen’s ability to complete the cycle of infection?

Answer 37

“virulence factors”.

Question 38

what class of diseases can still spead without the victim encountering live microorganisms?

Answer 38

Intoxication illnesses, such as tetanus or botulism. these are unusual.

disease results from exposure to a toxin

Question 39

what are the different types of toxins?

Answer 39

exotoxins and endotoxin

Question 40

what are the mechanisms by which bacteria cause disease?

Answer 40

production of “aggressins”;

initiating undesirable consequences of the host defences.