Lecture 19 - Opportunistic Infections

Question 1

Frequently encountered opportunistic pathogens
1)
2)
3)
4)
5)
6)
7)
8)
9)

Answer 1

1) E coli
2) Staph aureus
3) Klebsiella pneumoniae
4) Enterococcus
5) Pseudomonas aeruginosa
6) Enterobacter
7) Serratia
8) Proteus
9) Clostridium difficile

Question 2

Host factors predisposing to opportunistic infection (local)
1)
2)
3)
4)
5)

Answer 2

1) Anatomical defects
2) Surgical, other wounds
3) Burns
4) Catheterisation
5) Foreign bodies

Question 3

Host factors predisposing to opportunistic infection (systemic)
1)
2)
3)
4)
5)
6)
7)
8)
9)

Answer 3

1) Extremes of age
2) Leukopenia
3) Malignancy
4) Malnutrition
5) Diabetes
6) Liver disease
7) Certain infections
8) Antimicrobial treatment
9) Congenital immune defects

Question 4

Example of an anatomical defect leading to opportunistic infection

Answer 4

Bladder that won’t empty properly
Leads to stagnation of urine, infection

Bronchial obstruction from a malignancy, smoking

Question 5

Types of infection
1)
2)
3)
4)
5)
6)

Answer 5

1) Wound infection
2) UTI
3) Intra-abdominal infection
4) Pneumonia
5) Septicaemia
6) Meningitis (especially neonates)

Question 6

Leukopenia

Answer 6

No white cells

Question 7

Examples of diseases that immunosuppress

Answer 7

HIV

Acute stage of measles is very immunosuppressive

Question 8

Type of bacterium that Pseudomonas is

Answer 8

G- rod

Question 9

Pseudomonas spp
1)
2)
3)
4)
5)
6)
7)
8)

Answer 9

1) G- rod
2) Motile
3) Aerobes or facultative anaerobes
4) Non-fermenting
5) Non-sporing
6) Widespread
7) Low nutritional requirements
8) Pseudomonas aeruginosa produces green pigment

Question 10

How are Pseudomonas divided into species?

Answer 10

Biochemical tests

Question 11

How are P aeruginosa normally subtyped for epidemiological studies?

Answer 11

RFLP, MLST (multilocus sequence typing)

Question 12

Epidemiology of Pseudomonas
1)
2)
3)
4)
5)
6)

Answer 12

1) Widespread in nature, especially in moist environments
2) Transiently colonises skin, GIT, mucous membranes
3) Leading nosocomial pathogen
4) Mostly acquired from the environment
5) Spread in hospitals from hands, fomites
6) Intrinsically resistant to penicillins, readily acquires resistance from other bacteria

Question 13

Patients most at risk of P aeruginosa infection
1)
2)
3)
4)
5)
6)

Answer 13

1) Burns
2) Febrile neutropenia
3) Pneumonia
4) UTI
5) Sepsis
6) Major problem in CF patients

Question 14

Superficial P aeruginossa infections
1)
2)

Answer 14

1) Skin: wound infection, otitis externa

2) Eye: Keratitis, corneal ulcer

Question 15

Deep and systemic P aeruginosa infections
1)
2)

Answer 15

1) Pulmonary: nosocomial pneumonia, chronic infection in CF patients
2) Other: UTI, osteomyelitis, septicaemia, mostly in immunocompromised patients

Question 16

P aeruginosa properties in biofilms
1)
2)
3)
4)
5)
6)
7)

Answer 16

1) Non-motile
2) Mucoid phenotype - increased capsule
3) More adherent
4) Less invasive
5) Shorter LPS (no O antigen)
6) Slowed growth
7) Increased antimicrobial resistance

Question 17

P aeruginosa adhesion and invasion
1)
2)
3)
4)
5)
6)

Answer 17

1) Doesn’t invade intact skin unless in very large numbers
2) Adheres weakly to intact epithelium via flagella, lps, pili
3) Neuraminadase assists invasion
4) LPS core binds to CFTR
5) Once adherent, bacteria express biofilm
6) Flagella and LPS bind to TLRs, affect cytokines

Question 18

What aids the spread of Pseudomonas through the body?
1)
2)
3)
4)
5)

Answer 18

1) Reduced polymorphonucleosites
2) Flagella
3) Exoenzymes
4) Exotoxins
5) LPS-CFTR mediated invasion

Question 19

Exoenzymes secreted by Pseudomonas
1)
2)
3)
4)

Answer 19

1) Haemolyins
2) Proteases
3) Elastases
4) Phospholipases

Act on pulmonary tissues and surfactant

Question 20

Extoxins secreted by Pseudomonas
1)
2)

Answer 20

1) Exotoxin A

2) Exoenzyme S and U (ExoS, ExoU)

Question 21

Effects of CFTR-LPS mediated fusion

Answer 21

Aggravates corneal damage

Question 22

Agar used to culture Pseudomonas

Answer 22

Cetrimide agar

Question 23

What is cetrimide agar?

Answer 23

Used to culture P. aeruginosa
Contains cetrimide, a disinfectant
Kills other bacteria, doesn’t worry Pseudomonas

Question 24

Antimicrobial resistance conferred by biofilm formation

Answer 24

Phenotypic, not genotypic

Question 25

Why can Pseudomonas and Staph aureus grow in CF lungs?

Answer 25

Not inhibited by high salt content

Question 26

Bacteria that normally persist in CF lungs

Answer 26

Bacteria with reduced virulence

Question 27

Why can high salt or sugar inhibit bacterial growth?

Answer 27

Reduces available water content

Question 28

Most common bacteria in the lungs of young CF patients

Answer 28

Staph aureus and Pseudomonas aeruginosa

Question 29

Pseudomonas type III secreted proteins

Answer 29

1) Exoenzyme S
2) Exoenzyme T
3) Exoenzyme U
4) Exoenzyme Y

Question 30

Pseudomonas exoenzyme actions

Answer 30

Act on various host cell targets to interfere with phagocytosis, enhance cytokine produciton

Question 31

Exotoxin A function

Answer 31

Exactly the same as diphtheriatoxin
Interferes with chain-elongation in ribosomes
Phage-encoded

Question 32

How does exotoxin A function in exactly the same way as diphtheriatoxin, but doesn’t cause diphtheria?

Answer 32

Same A subunit, different B subunit (binds to different receptors)

Question 33

LasA, LasB

Answer 33

Proteases in Pseudomonas

Act together as elastases

Question 34

Effect of Pseudomonas phospholipases

Answer 34

Damages cell membranes, degrades surfactant