5.1 Types and properties of biological agents

Question 1

The main classes of harmful biological agent (micro-organisms) are: 5

Answer 1

  Bacteria 
  Viruses 
  Fungi 
  Protozoa 
  Macrobial parasites.

Question 2

Bacteria are

Answer 2

living microscopic organisms (typically < 1m), which lack cells with
internal membranes. Bacteria contain DNA, but this differs from cellular DNA in that
it has a circular arrangement, rather than linear. Bacteria are single celled and can
reproduce by duplicating themselves and they do not need a host to survive.
Bacteria (for example: tetanus and most forms of pneumonia) are responsive to
antibiotics.

Question 3

Bacteria may be classified in a number of ways: 3

Answer 3

 Their need for oxygen for growth. Aerobic bacteria (aerobes) can survive and
grow in an oxygenated environment, whereas anaerobic bacteria (anaerobes)
do not require oxygen for growth. Anaerobic, bacteria can survive in places
where there is less oxygen, such as human intestines and cause gastro enteric
illness.
 Their reaction to a gram stain test - gram positive or gram negative.
 Their morphology or shape

Question 4

A virus is

Answer 4

smaller than one cell. It lives within a cell (intracellular) to survive and
derives its ability to multiply from its host cell.

Viruses are 20 to 100 times smaller than bacteria and
cannot be seen by light microscopy. The largest viruses
(poxviruses) are about 450 nanometres in length and the
smallest viruses (polioviruses) are about 30 nm. (nm = one
billionth of a metre = 0.000000001metre).

Viruses are not really ‘alive’ as they cannot reproduce outside of a living cell. They
reproduce by transmitting their genetic information from one cell to another.
However, they can damage or kill the cells that they infect, causing disease in
infected organisms. Some cause cancers by stimulating cells to grow
uncontrollably.

Question 5

Antiviral treatments are difficult to create because

Answer 5

of the large number of variant
viruses that can cause the same disease. A further concern is the difficulty in
disabling a virus without disabling healthy cells.

Question 6

The main BBVs of concern are:

Answer 6

 Hepatitis B virus, hepatitis C virus and hepatitis D virus
 Human immunodeficiency virus (HIV).

Question 7

Fungi are

Answer 7

a diverse group of organisms that obtain food by direct absorption of
nutrients. The food is dissolved by enzymes that the fungi excrete and is then
absorbed through thin cell walls. This is then is distributed by simple circulation, or
streaming, of the protoplasm.

Fungi may be single-celled or multi-cellular.

Question 8

Protozoans are

Answer 8

living, motile, single-celled organisms that can live inside or outside
host cells or organisms. They can only divide within a host organism.

Most antibiotics, such as penicillin, don’t work on protozoan diseases. However,
they are susceptible to some antibiotics such as sulfonamides.

Question 9

Incubation period

Answer 9

Infection to Symptoms

Question 10

Latent period

Answer 10

Infection to Infectiousness

Question 11

The ‘infectious dose’ is

Answer 11

the amount of pathogen (measured in numbers of

organisms) required to cause infection in the host.

Question 12

The variables that can be manipulated to provide (or remove) optimal conditions
include: 6

Answer 12

the nutrients available; oxygen levels; water; temperature; pH; and light.