Lecture 2- Bacterial Diseases

Question 1

What are the two potential routes of infection by bacteria?

Answer 1

Extrinsic

Intrinsic

Question 2

Name some of the intrinsic sources of infection

Answer 2

• Nasal cavity and sinuses
• mouth
• upper respiratory tract
• stomach
• small intestine
• large intestine
• lower genital tract
• skin

Question 3

What are expected and unexpected portals of entry?

Answer 3

Expected= normal micobiota entering through an expected route (newborn and maternal microbiota)

Unexpected= normal microbiota entering an unusual site or entry of pathogenic microbes

Question 4

How are pathogens targeting the upper respiratory tract usually acquired?

Answer 4

Extrinsically

• droplets or airborne
• hand to hand transmission as intermediate

Question 5

Give some example of viruses which enter through the upper respiratory tract

Answer 5

Influenza 
Parainfluenza
Rhinovirus
Measles
VZV
Herpes viruses

Question 6

Give some examples of bacteria which enter through the upper respiratory tract

Answer 6

• streptococcus spp
• strep pneumoniae
• strep pyogenes
• neisseria meningitidis
• staph aureus

Question 7

What are the consequences of bacterial pathogens acquired by the upper respiratory tract?

Answer 7

1) upper respiratory tract infection
- pharyngitis
- tonsillitis
- sinitis
2) spread to adjacent tissue
- meningitis
- brain abscess
- middle ear infection
3) lower resp tract infection
- bronchitis
- pneumonia
4) spread to bloodstream
- bacteraemia

Question 8

What are the intrinsic sources of infection through the urogenital tract? Give examples

Answer 8

Bacteria landing here from the large intestine

• e.coli
• klebsiella
• enterobacter spp.
• candida/ yeast
• strep B

Question 9

What are extrinsic sources of bacteria affecting the urogenital tract?

Answer 9

1) Nonsocomial transmission by catheters
- E. Coli
- Klebsiella
2) sexually transmitted
- Neisseria gonorrhoea
- Chlamydia trachomatis
- Syphilis
- HIV/ HSV

Question 10

Skin is a portal of entry, how might pathogens enter through the skin?

Answer 10

• surgery/ wound
• skin disease (varicella, eczema)
• IVDA
• insect bites
• bites (human and animal)
• cannula

Question 11

Name some bacteria which enter through broken skin

Answer 11

1) bacteria originally found in the mouth
- staph aureus
- strep pyogenes
2) hospitals
- pseudomonas
- MRSA

Question 12

What are some of the consequences of infections via broken skin?

Answer 12

• superficial infection
• cellulitis
• abscess (pus filled pocket)
• fasciitis
• myositis (infection of muscle)
• gangrene/ necrosis (cell death under superficial layer)
• bacteraemia

Question 13

Name some bacteria that enter through the GI tract

Answer 13

E. Coli
Campylobacter jejuni
Shigella (dysentery) 
Vibrio cholerae 
Salmonella enterica
Salmonella typhi 
Listeria 
C. Difficile

Question 14

Name some viruses that enter through the GI tract

Answer 14

Hep A
Hep E
Norovirus

Question 15

Other than viruses and bacteria, what could have a pathogenic effect on the GI tract?

Answer 15

Toxins (enterotoxins, botulinum toxins)

Parasites

Question 16

What are the consequences of bacterial infections acquired through the GI tract

Answer 16

Diarrhoea
Vomiting
Dysentery (bloody stools)
Bacteraemia

Question 17

What are true pathogens

Answer 17

Bacteria which can cause disease in normal people e.g. Staph aureus

Question 18

What are opportunistic pathogens?

Answer 18

Pathogens which can only cause disease when they are given a chance (when immunocompromised) e.g. Staph epidermis

Question 19

Define the term pathogenicity

Answer 19

Ability to cause disease

Question 20

What are commensalism?

Answer 20

Bacteria which do not cause disease

Question 21

What are the two factors which affect pathogenicity?

Answer 21

Infectivity- ability to get into the host system and establish themselves

Virulence- features that enhance disease causation ( whodunnits enhance the symptoms)

Question 22

What are the factors involved in infectivity?

Answer 22

• transmission to host
• ability to colonise host
• ability to find unique niche
• ability to replicate
• immune evasion

Question 23

What are the four factors that affect virulence?

Answer 23

1) Toxins (pneumocystis forms pores in lungs)
2) Enzymes (hyaluronan lyase)
3) Interference with host cell function (superantigens from S.aureus interfere with T cells)
4) Complete immune evasion- S. aureus leukocidins= neutrophil death

Question 24

Define the term infectious dose

Answer 24

The number of bacteria required to initiate an infection

Question 25

What can affect the infectious dose?

Answer 25

Route of transmission (stomach acid)
Ability to colonise host
Tropism and motility- cholera have flagella
Replication speed
Immune evasion at site (TB survives inside macrophages)

Question 26

Describe the pathogenicity of vibrio cholera

Answer 26

• massive infective dose
• flagella to penetrate mucus
• makes 2 component toxins (A+B)
• binds to gut
• triggers cAMP
• Cl- efflux
• Na+ and H20 follow
• diarrhoea

Question 27

Which disease originates from the GI tract, moves down to the urogenital tract and is passed onto neonates?

Answer 27

Strep B