Microbiology

Question 1

What is an apparent infection?

What is a subclinical/inapparent/silent infection?

What is an inactive/dormant/latent infection?

Answer 1

An infection that produces symptoms is an apparent infection.

An infection that is active, but does not produce noticeable symptoms, may be called inapparent, silent, or subclinical.

An infection that is inactive or dormant is called a latent infection

Question 2

What is the chain of infection? Circular! 6parts

Answer 2

Causative agent>Reservoir>Portal of exit>Mode of transmission>Portal of entry>Susceptible host>>>(causative agent…. etc.

Question 3

Causative agents could be…

Answer 3

Microorganism/bsacteria/fungi/?virus/
ENDOgenous infections
EXOgenous infections

Question 4

where do most viral infections come from?
Where else can they come from and what stimulates virus reactivation?

Answer 4

Exogenous viruses usually
Endogenous viruses can be reactivated by age or immunosuppression, normally they are latent and controlled by immunosurveillance
e.g. Shingles (VZV), Recurrent oral & genital herpes (HSV), CMV infections

Question 5

what’s a reservoir (microbiology context)

Answer 5

A reservoir is the place where the agent survives, grows, and/or multiplies: e.g. human, animal or environment

Common examples include…

Environment
Soil: Clostridium tetani:Tetanus
Water: Legionella pnuemophilia:Legionnaires’ disease

Animals
Cow:Escherichia coli (toxigenic strains):Gastroenteritis
Poultry:Salmonella spp:Gastroenteritis

Humans
Respiratory tract:
Gut:

Question 6

What is a portal of exit? somexamples

Answer 6

the way the infectious agent leaves the reservoir

Aerosols/droplets; coughing sneezing
Bodily fluids; faeces, urine, mucous, blood, milk, semen, saliva

Question 7

Transmission; what are the two main modes of transmission?

Answer 7

The way the infectious agent can be passed on (through direct or indirect contact, ingestion, or inhalation)

Indirect contact: occurs when a susceptible person comes in contact with a contaminated object, a fomite. (can include pens, phones, work surfaces, countertops, tabletops, handrails, and doorknobs, stethoscopes! ties! sleeves!)

Airborne transmission possible when droplet nuclei are suspended in the air. Airborne dust or particles from soil is also capable of spreading pathogens when it is blown into the air. Droplet nuclei can travel long distances through the air, whereas respiratory droplets quickly fall to the ground.

Direct contact with; skin-to-skin contact, kissing, sexual, contaminated soil, fomites. Infection through respiratory droplets sneezing, coughing, or talking.

Question 8

Portal of entry

Answer 8

Open wounds/skin damage

Mucous membranes (eyes, genitals)

Question 9

What is a fomite?

Answer 9

A fomite is an object or surface that is capable of transmitting disease and infectious agents. Fomites can also be referred to as passive vectors.

Question 10

What makes a susceptible host?

Answer 10

A susceptible host is a person who can become infected by infectious agent

Question 11

How to break the chain of infection (9 examples)

Answer 11

Break the chain by

1 Wash hands

2 up to date vaccinations

3 Cover coughs and sneezes

4 Stay home when sick/Follow isolation rules

5 Use PPE correctly

6 Clean and disinfect surfaces/items correctly

7 Sterilize equipment properly

8 Safe infection technique

9 Careful antibiotic use

Question 12

After exposure to a pathogen, what two main types of infection can take their course?

Answer 12

Acute: Virus infects host, infection, recovery/cure. A non equilibrium process in which host response & virus infection change continually until resolution (host wins)

Chronic: infection continues beyond normal time frame when immune system should have cleared it (stalemate?)

Question 13

After exposure to a pathogen, what 6 outcomes/types of infection can take their course?

(Think win/lose/length of time of battle)

Answer 13

Asymptomatic inf: no signs or symptoms

Latent: full viral genome is retained in the host cell, but its expression is dramatically restricted, such that few viral antigens and no viral particles are produced

Acute: Virus infects host, infection, recovery/cure. A non equilibrium process in which host response & virus infection change continually until resolution (host wins)

Chronic: infection continues beyond normal time frame when immune system should have cleared it (stalemate?)

Recurrent: (Repeated replays of infection, neither really wins)

Death: A non equilibrium process in which host response & virus infection change continually until resolution, but NEGATIVE direction of change (pathogen wins)

Question 14

What forms the timeline of infection (4)

Answer 14

Latent>asymptomatic period (Also called incubation period)

Symptomatic period

• (outcome of infection win/lose/stalemate)*
• In many diseases the patient is considered infectious during the symptomatic*
• phase – this is not always the case though e.g. SARS-CoV2*

Question 15

What’s the difference betweena pathogen and a commensal?

Answer 15

Micro-organisms exist on a spectrum between:

Professional pathogens – almost always cause disease

Opportunistic pathogens – only cause disease in immunocompromised patients

this depends on their virulence

Question 16

What is virulence?

Answer 16

Virulence: The ability of an agent of infection to produce disease

Question 17

What is pathogenicity?

Answer 17

Pathogenicity is the capacity of an organism to cause disease/harm the host

Question 18

If a patient is immunocompromised what effect does this have on their susceptibility as a host?

Answer 18

They become much more suceptible to infection, either new acquired from environment or latent endogenous.

Microorganisms that would normally be commensals become pathogenic to a susceptible host

Question 19

WHich of the following statements best describes a Staphylococcus Areus infection?

a) S. Aureus is not a commmensal organism
b) S. Aureus is a coagulase negative baterium
c) Ricardo? should ideally be moved to side room and his bay deep cleaned
d) If he doesn’t approach any other patients he cannot pass on infection
e) S. Aureus has Protein A and a capsule which helps the bacterium to be detected by immue system

Answer 19

a) S. Aureus is not a commmensal organism
* Wrong - 20-60% of people are carriers so it is ‘normal’. 30% have S. Aureus on their skin, 10% have MRSA*
b) S. Aureus is a coagulase negative baterium
* Wrong - coagulase positive. Coagulase helps blood clot. Coagulase positive is normally a more serious infection than e.g. S epidermis wchi is coagulase -ve*
c) Ricardo? should ideally be moved to side room and his bay deep cleaned
* True*
d) If he doesn’t approach any other patients he cannot pass on infection
* No, other methods of transmission by fomites*
e) S. Aureus has Protein A and a capsule which helps the bacterium to be detected by immue system
* Wrong - these both help it avoid the immune system, evade immune clearance*

Question 20

Which receptors does lipopolysaccharide interact with on Immune cells

which cells?

Answer 20

LPS interacts with Toll-Like Receptors (esp. TLR4) on

Monocyte / macrophage lineage cells (white blood cells)

Endothelial

Question 21

TLR4 activation leads to…

Answer 21

Results in activation of

Inflammatory pathways

Coagulation and clotting pathways

Changes in endothelial integrity

Question 22

What is haemoptypsis

Answer 22

coughing up blood: Blood stained sputum

Question 23

Which is a stronger/more serious infection, gram -ve or gram +ve? (in blood at least)

Answer 23

Gram negative bacteria in the blood = Endotoxin in the blood

causes systemic activation of immune responses and is the main reason why people get very sick with gram negative infections

Gram positive bacteria don’t have endotoxin, can stimulate immune responses just like LPS but using different Toll-like receptors

Cell wall components: Lipoteichoic acid & Peptidoglycans

Question 24

What is in a gram -ve cell wall?

Answer 24

The cell wall of gram-negative bacteria is composed of thin layers of peptidoglycan, the outer membrane is composed of lipoproteins, phospholipids, and LPS

In the gram staining procedure, gram-negative cells do not retain the purple coloured stain

Gram-negative bacteria produce endotoxins

Question 25

What is in a gram +ve cell wall?

Answer 25

The cell wall of gram-positive bacteria is composed of thick layers peptidoglycan, Lipoteichoic acid, Peptidoglycans

In the gram staining procedure, gram-positive cells retain the purple coloured stain.

Gram-positive bacteria produce exotoxins.

Question 26

What’s the difference between an aerobe and anaerobe in bacterium?

Answer 26

Aerobe - use o2 as final electron acceptor (v efficient) to eg oxidise glucose into co2 and h2o Anaerobes - fermentation, final electron acceptor is an organic molecule eg glucose to lactic acid. Need plenty of substrates and oxygen usually toxic to these bacteria.

Question 27

What’s a facultative anaerobe?

Answer 27

Can switch between aerobe and anaerobe Aerobe - use o2 as final electron acceptor (v efficient) to eg oxidise glucose into co2 and h2o Anaerobes - fermentation, final electron acceptor is an organic molecule eg glucose to lactic acid. Need plenty of substrates and oxygen usually toxic to these bacteria.

Question 28

What’s a facultative anaerobe?

Answer 28

Can switch between aerobe and anaerobe Aerobe - use o2 as final electron acceptor (v efficient) to eg oxidise glucose into co2 and h2o Anaerobes - fermentation, final electron acceptor is an organic molecule eg glucose to lactic acid. Need plenty of substrates and oxygen usually toxic to these bacteria.