Intro to microbes

Question 1

What are the 5 classes of microbial organisms?

Answer 1

Viruses, bacteria, fungi, protozoa, prions

Question 2

Describe viruses

Answer 2

20 nm – 1 μm in size​
RNA or DNA​
No independent metabolism and no organelles​
Simple protein coat (plus cell membrane from host cell)​
​
Examples :​
Influenza / Rhinovirus​
Rotavirus / Norovirus​
Herpes simplex / Chickenpox​
EBV / CMV​
HAV / HBV / HCV / HEV​
HIV​
Dengue / Zika​
Ebola / Lassa​
Smallpox

Question 3

Describe bacteria

Answer 3

1 – 10 μm in size​
DNA as a single chromosome (prokaryotes)​
Independent metabolism and no organelles​
Cell wall (distinct from cell membrane of host organism)​
​
​
Peptidoglycan cell wall = Gram stain +ve ​
Lipopolysaccharide cell wall = Gram stain –ve (stain pink)

Gram positive cocci e.g. Staphylococcus species, Streptococcus species​
​
Gram positive bacilli e.g. Bacillus anthracis, Lactobacilli species​
​
Gram negative cocci e.g. Neisseria meningitidis, Haemophilus influenzae​
​
Gram negative bacilli e.g. Escherichia coli, Salmonella species

Question 4

Describe fungi

Answer 4

5 – 10 μm in size​

• DNA as multiple chromosomes in a nucleus (eukaryotes)​
• Independent metabolism & organelles (no chloroplasts)​
• Cell wall (distinct from cell membrane of host organism)

Question 5

Describe protozoa

Answer 5

10 – 100 μm in size​
DNA as multiple chromosomes in a nucleus (eukaryotes)​
Independent metabolism and organelles​
Cell membrane (similar to host organism)

Question 6

Describe prions

Answer 6

~10 nm​
No RNA or DNA (just a protein enzyme)​
No independent metabolism & no organelles​
No protein coat, cell wall or cell membrane

Question 7

Define commensal

Answer 7

symbiotic relationship between two different species where one derives some benefit and the other is unaffected

Question 8

Define colonisation

Answer 8

when a microbe grows on or in another organism without causing any disease

Question 9

Define infection

Answer 9

the invasion and multiplication of microbes in an area of the body where they are not normally present – an infection may cause no symptoms and be sub-clinical or it may cause varying degrees of symptoms and be clinically apparent

Question 10

Define pathogen

Answer 10

a micro-organism that is able to cause disease

Question 11

Define obligate pathogen

Answer 11

a pathogen that must cause disease in order to be transmitted from one host to another – these pathogens must also infect a host in order to survive, in contrast to other pathogens that are capable of survival outside of a host

Question 12

Define opportunistic pathogen

Answer 12

a pathogen that takes advantage of an opportunity not normally available, such as a host with a weakened immune system, an altered microbiota (such as a disrupted gut flora), or breached integumentary barriers (eg. Cut in skin).

Question 13

Define parasite

Answer 13

old-fashioned term for pathogens that are protozoa or metazoa (worms and ecto-parasites)

Question 14

What are Koch’s postulates?

Answer 14

1) The micro-organism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.​
2) The micro-organism must be isolated from a diseased organism and grown in pure culture.​
3) The cultured micro-organism should cause disease when introduced into a healthy organism.​
4) The micro-organism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.