Microbes & Infection

Question 1

Microbes

Answer 1

fungi, protozoa, algae, bacteria and virus
Eukaryotic cells - True cells have membrane bound organelles/ nucleus
Prokaryotic cells - Simple cells have no membrane bound organelles

Question 2

Bacteria

Answer 2

derived from either dead organisms or a living host
Plasma membrane,cell wall, capsule, nucleoid, Ribosomes
reproduce by binary fission

Question 3

virus

Answer 3

Obligate parasite = can only reproduce inside a host cell
Naked virus = genetic material surrounded by a protein coat
Enveloped virus = naked virus plus an outer membrane taken derived from the
previous host cell

Attachment to target cell
Penetration
Replication
Maturation and release

Question 4

fungi

Answer 4

Eukaryotic cells with a cell wall containing chitin
Feed on organic matter and recycle organic matter in nature

Question 5

3 classes of microbes

Answer 5

Normal flora
Transient microbes
Pathogens

Question 6

3 types of relationship

Answer 6

Commensalism – one partner benefits, the other is unaffected
Mutualism – both partners benefit
Parasitism – one partner benefits at the expense of the other

Question 7

infection depends on

Answer 7

Pathogenicity depends on virulence = the
capacity of a pathogen to cause disease
host susceptibility (Extremes of age, Compromised barriers, Immunodeficiency, Poor immune status, Pre-existing poor health)
Environmental conditions= The health status of individuals, Reservoir of infection, Reservoir of infection

Question 8

conventional pathogens

Answer 8

A microbe which causes disease in previously healthy people with normal defences

Question 9

opportunistic pathogens

Answer 9

Microbes that don’t normally cause infectious disease but can do so under certain circumstances

Question 10

Opportunistic infections with
normal flora

Answer 10

Upset ecological balance
Relocation of the normal flora
Compromised host defences

Question 11

portals of entry

Answer 11

through skin or mucous membrane

Question 12

attachment

Answer 12

Many pathogens have adhesins on their surface bind surface receptors on host target cells
glycocalyx,a sticky substance that cements them to a body surface

Question 13

Multiplication and spread-

Answer 13

incubation period of an infectious disease pathogen is overcoming early host defences and utilising host resources to multiply

Strategies to spread include:
1. Overcoming innate defences:
* Overcoming surface barriers
* Resisting phagocytes
2. Overcoming adaptive defences
* Degrading antibodies
* Antigenic variation

Question 14

Pathogens can overcome host INNATE defences

Answer 14

killing phagocytes with toxins
using enzymes to break though surface barriers
degrading phagocyte digestive enzymes with their own enzymes
resisting phagocytosis via a slippery capsule
toxins that inactivate the mucociliary escalator

Question 15

Damage to the host can be caused:

Answer 15

through the lytic activity of viruses
by enzymes dervied from the pathogen or from host phagocytes
by perforins and granzymes from cytotoxic T cells or NK cells
by toxins that kill host cells

Question 16

portal of exit

Answer 16

Body fluids/wastes provide
excellent vehicles for exit
the respiratory and digestive tracts
The more pathogens that
are shed the greater the
chance of reaching a new
host

Question 17

course of acute

Answer 17

Incubation period - the time
between contact with the pathogen
and the appearance of signs and
symptoms. asymptomatic

Prodromal period – the time when
mild, non-specific symptoms appear. multiplying and evading host defences

Disease period - pathogen invasion and
tissue damage, specific signs and symptoms

Recovery period – immune response and other defences overcome the pathogen

Question 18

course of Chronic

Answer 18

An initial acute, symptomatic
disease period is followed
by apparent recovery

pathogen is not completely
eliminated and continues to multiply
slowly causing damage

it is eliminated/cleared very slowly or never eliminated

The host acts as a carrier, transmitting the pathogen even while appearing
healthy

Question 19

course of latent

Answer 19

An initial acute, symptomatic
disease period is followed
by apparent recovery without complete elimination

The pathogen does not multiply, “hides” inside cells from body defences – it cannot be transmitted as it is not multiplying= no symptoms

latent period may last for many years

The pathogen may be “reactivated”, grow and cause acute disease, symptoms may be quite different from the symptoms of
the initial disease