Community Acquired Bacterial Infections

Question 1

Define virulence factor.

Answer 1

Molecules produced by pathogens that contribute to the pathogenicity of the organism

Question 2

List some common bacterial virulence factors and include their function.

Answer 2

Flagella – movement and attachment

Pili – adherence factors

Capsule – protects against phagocytosis

Endospores – metabolically dormant forms of bacteria – they are heat, cold, desiccation and chemical resistant

Biofilms – organised aggregates of bacteria embedded in a polysaccharide matrix – antibiotic resistant

Question 3

Give examples of bacteria that can form possess biofilms

Answer 3

Biofilms
Pseudomonas aeruginosa
Staphylococcus epidermidis

Question 4

What are exotoxins?

Answer 4

A toxin released by a living bacterial cell into its surrounding

Question 5

What are the five different types of exotoxin? Briefly describe what they do

Answer 5

Neurotoxins - act on nerves or motor endplate to cause paralysis

Enterotoxins - act on the GI tract to cause diarrhea and vomiting

Pyrogenic exotoxins - stimulate release of cytokines to cause rash, fever and toxic shock

Tissue invasive toxins - allow bacteria to destroy and tunnel through tissue

Miscellaneous exotoxin - specific to becterium/function not well understood

Question 6

What is an endotoxin?

Answer 6

This is the lipid A part of lipopolysaccharide (LPS) that is found on the outer membrane of Gram-negative cells

Gram negative bacteria shed this all the time

NOTE: so ONLY Gram-negative cells can produce endotoxins

Question 7

Why can treating patients with Gram-negative infection sometimes worsen their condition?

Answer 7

Antibiotics can cause lysis of the bacteria meaning that the endotoxins are released into the circulation in large quantities

This can trigger an immune response that leads to SEPTIC SHOCK

Question 8

Define outbreak

Answer 8

A greater than normal or greater than expected number of individuals infected or diagnosed with a particular infection in a given time period, or a particular place, or both

Question 9

How can an outbreak be identified?

Answer 9

Surveillance

Good and timely reporting systems are necessary

Question 10

What type of bacterium is Legionella pneumophila and what is the route of infection?

Answer 10

Gram negative

It is transmitted through inhalation of contaminated aerosols and will infect and grow in alveolar macrophages NB human infection is the dead end

Question 11

Name 2 respiratory tract community acquired bacterial infections

Answer 11

Legionella pneumophilia gram-

Mycobacterium tuberculosis gram +

Question 12

What is the secretion system which is an important virulence factor for L. pneumophila?

Answer 12

Type IV secretion system

Question 13

What feature of Mycobacterium tuberculosis makes it more difficult to treat?

Answer 13

It has a mycolic acid outer membrane – this prevents normal antibiotics from getting into the cell

Incredibly slow growing

Question 14

State three bacterial sexually transmitted diseases including the species of bacteria that cause the diseases.

Answer 14

Chlamydia - Chlamydia trachomatis gram -

Syphilis –Treponema pallidum (dunno what gram)

Gonorrhoea –Neisseria gonorrhoeae gram -

Question 15

What is a major consequence of Chlamydia in the developing world?

Answer 15

Blindness (due to eye infection)

Question 16

How does Neisseria gonorrhoeae route of infection

Answer 16

urogenital:It interacts with non-ciliated epithelial cells in the urogenital tract

Question 17

What are the important virulence factors of Neisseria gonorrhoeae?

Answer 17

Pili

Antigenic variation escapes detection and clearance by the immune system

Question 18

Name 2 common GI bacterial infections?

Answer 18

Campylobacter jejuni
vibrio cholerae
Salmonella sp.
NOTE: Salmonella sp. can cause outbreaks whereas Campylobactertends to be sporadic cases

Question 19

What is the route of infection of Campylobacter and Salmonella?

Answer 19

food- Ingestion of undercooked poultry

Question 20

What are the important virulence factors of Vibrio cholerae?

Answer 20

Cholera toxin

Type IV fimbria

Question 21

Explain how cholera toxin works.

Answer 21

It has A and B subunits

A is the active toxin

B allows entry of the toxin into the epithelial cell

The A subunit activates adenylate cyclase, thus increasing the production of cAMP

The cAMP then binds to CFTR (cystic fibrosis transmembrane receptor) and causes Cl- efflux

Water follows the ion movement so you get massive movement of water into the lumen of the intestine

Question 22

What cells do listeria monocytogenes target?

Answer 22

They can enter non-phagocytic cells and cross tight barriers (e.g. BBB and maternal-foetal barrier)

Question 23

Name some bacterial vector-borne diseases and the becteria that cause them

Answer 23

Q fever (Coxiella burnetti; Gram –)

Plague (Yersinia pestis; Gram-)

Question 24

List some vaccine-preventable diseases.

Answer 24

1. haemophilus influenzae (not to be confused with influenza virus)
2. pertussis (bordetella pertussis)
3. tetanus (clostridium tetani)

Question 25

Give 2 examples of bacteria that produce neurotoxins

Answer 25

Tetanus or Botulinum toxins

Question 26

Give examples of bacteria that produce the 2 sub-groups of enterotoxins

Answer 26

1) Infectious diarrhea
i. e. Vibrio cholera, Escherichia coli, Shigella dysenteriae and Campylobacter jejuni

2) Food poisoning i.e. Bacillus cereus or Staphylcoccus aureus

Question 27

Give 2 examples of bacteria that produce pyrogenic exotoxins

Answer 27

Staphylcoccus aureus or Streptococcus pyogenes

Question 28

What are the 6 catagories of Communicable diseases in Europe?

Answer 28

1) Respiratory tract infections
2) Sexually transmitted infections, including HIV and blood-borne viruses
3) Food- and waterborne diseases and zoonoses
4) Emerging and vector-borne diseases
5) Vaccine-preventable diseases
6) Antimicrobial resistance and healthcare-associated infections

Question 29

Differentiate antimicrobial, antibacterial and antibiotic

Answer 29

antimicrobial- interferes with growth and reproduction
antibacterial- reduce/eliminates bacteria
antibiotic is a type of antimicrobial

Question 30

Explain why patients are at risk of HAI

Answer 30

1. Intervention- catheters, intubation etc
2. Dissemination - there are infected people in hospital and so will spread
3. Concentration

Question 31

List the common HAI bacteria

ESCAPE

Answer 31

Gram +ve:
Enterococcus faecium
Staph aureus 
C diff
gram -ve: 
Acinetobacter baumanii
Pseudomonas aeruginosa
enterobacteriaceae

Question 32

Give 2 enzymes involved in cleaving antibiotics leading to AB resistance

Answer 32

1. Extended spectrum beta lactamase (cleaves cephalosporins)- common in ecoli
2. Carbapenemase enzyme (cleaves carbapenems)
3. Altered target- methicillin normally binds to penicillin binding protein on MRSA but MRSA has evolved with PBP2A which binds to it weakly,