Opportunistic Infections

Question 1

List 9 commonly encountered opportunistic pathogens. Which of these may cause nosocomial epidemics?

Answer 1

E. coli
Staphylococcus aureus*
Klebsiella pneumoniae*
Enterococcus spp.*
Pseudomonas aeruginosa*
Enterobacter spp.*
Serratia spp.*
Proteus spp.
Clostridium difficile
*May cause nosocomial infections

Question 2

What host factors combat colonisation and penetration by microbes?

Answer 2

Physical and chemical barriers

Question 3

What host factors combat multiplication of microbes and tissue damage caused by microbes?

Answer 3

Inflammatory response and phagocytosis

Adaptive immune response

Question 4

How do microbial virulence and host resistance affect disease outcome?

Answer 4

If host resistance is reduced, pathogen does not need to be very virulent to cause overt infection (and vice versa)

Question 5

Give 5 examples of local host factors that may predispose to opportunistic infection

Answer 5

Anatomical defects
Surgical and other wounds
Burns
Catheterisation (bladder, IV)
Foreign bodies in general (e.g. suture)

Question 6

Why is it important to recognise opportunistic infections?

Answer 6

May be 1st sign that there is something wrong with the host (e.g. immunosuppression, obstruction, etc)

Question 7

What is the effect of foreign bodies on opportunistic infection?

Answer 7

Increases likelihood of infection (allows microbes to evade immunity)

Question 8

Give an example of a type of infection that is commonly opportunistic

Answer 8

UTIs (in females especially)

Question 9

What might pneumonia that does not respond to conventional treatment suggest?

Answer 9

Obstruction or lung disease (pre-disposing factor exists)

Question 10

List 9 systemic host factors that may predispose to opportunistic infection

Answer 10

Extremes of age
Leucopenia
Malignancy
Malnutrition
Diabetes
Liver disease
Certain infections
Treatment with antimicrobials
Primary (congenital) immunodeficiency

Question 11

What opportunistic infection does diabetes predispose to?

Answer 11

Candida albicans infection (candidiasis; often the 1st presentation of DM)

Question 12

Give 2 examples of an infection that predisposes to opportunistic infection

Answer 12

HIV

Measles (temporary severe immunocompromise)

Question 13

Give 2 examples of opportunistic infections associated with antimicrobial treatment

Answer 13

Clostridium difficile infection (pseudomembranous collitis)
Fungal infection (e.g. thrush following broad spectrum antibiotic for UTI)

Question 14

List 6 common presentations of opportunistic infections

Answer 14

Wound infection
UTI
intra-abdominal infection
Pneumonia
Septicaemia
Meningitis (especially in neonates)

Question 15

How are opportunistic infections diagnosed?

Answer 15

By culturing an appropriate specimen (e.g. wound swab, pus, urine, sputum, blood, CSF)

Question 16

What is the risk with taking antimicrobials in hospital?

Answer 16

Patient are susceptible to becoming colonised with resistant organisms

Question 17

How are opportunistic infections treated?

Answer 17

Depends on antibiotic susceptibility (nosocomial strains are often multi-resistant, although multi-resistant strains are now also seen in the community)
May need potent bactericidal agents (due to immunocompromise - may not have neccessary armoury to deal with live microorganisms)

Question 18

How can opportunistic infections best be prevented?

Answer 18

Aseptic technique (especially hand hygiene)

Question 19

What kind of bacteria is Pseudomonas?

Answer 19

Gram negative bacilli

Question 20

What is the metabolic classification of Pseudomonas?

Answer 20

Aerobes or facultative anaerobes

Question 21

Is Pseudomonas motile?

Answer 21

Yes

Question 22

Does Pseudomonas ferment?

Answer 22

No

Question 23

Does Pseudomonas form spores?

Answer 23

No

Question 24

What result does Pseudomonas produce on a catalase test?

Answer 24

Catalase positive

Question 25

What result does Pseudomonas produce on an oxidase test?

Answer 25

Oxidase positive

Question 26

Does Pseudomonas produce pigments?

Answer 26

Some do, including Ps. aeruginosa

Question 27

What is the name of the pigment produced by Ps. aeruginosa?

Answer 27

Pyocyanin (greenish pus)

Question 28

What are the nutritional requirements of Pseudomonas?

Answer 28

Low nutritional requirements (can survive almost anywhere but love moist environments)

Question 29

Where is Pseudomonas' favourite place to grow?

Answer 29

Moist environments

Question 30

How are Pseudomonas classified?

Answer 30

Divided into species based on biochemical tests

Question 31

How is Pseudomonas subtyped for epidemiological studies?

Answer 31

RFLP MLST (multilocus sequence typing) May use whole genome sequencing as cost comes down

Question 32

Colonisation with which organism is associated with a poor prognosis for CF?

Answer 32

Pseudomonas

Question 33

List 3 genera related to Pseudomonas. Which of these are opportunistic pathogens? Which species often colonise the RT of patients with CF and are intrinsically resistant to many commonly-used antibiotics?

Answer 33

``` Burkholderia capacia (opportunistic)* Stenotrophomonas maltophilia (opportunistic)* Burkholderia pseudomallei *Colonise CF patients (also Ps. aeruginosa) ```

Question 34

What is a saprophyte? Give an example

Answer 34

Organism that grows freely in the environment | E.g. Ps. aeruginosa

Question 35

What organism causes melioidosis, which can lead to pneumonia?

Answer 35

Burkholderia pseudomallei

Question 36

What is 1 reason Ps. aeruginosa (and related pathogens) are intrinsically resistant to many commonly-used antibiotics?

Answer 36

Due to chromosomal B-lactamase

Question 37

Does Ps. aeruginosa colonise normal healthy individuals?

Answer 37

Only transiently colonises skin, mucous membranes and GIT

Question 38

List 6 conditions associated with Ps. aeruginosa

Answer 38

``` CF Pneumonia UTI Sepsis Burns (more previously) Febrile neutropenia (more previously) ```

Question 39

How is Ps. aeruginosa spread in hospitals?

Answer 39

On hands and fomites

Question 40

How can Ps. aeruginosa be isolated in the lab?

Answer 40

Grown on cetrimide agar (disinfectant; kills all other organisms but Pseudomonas can grow)

Question 41

What kind of superficial infections can be caused by Ps. aeruginosa?

Answer 41

Skin (wound infection, otitis externa, folliculitis) | Eye (keratitis, corneal ulcer - can also invade and cause deep ulcer)

Question 42

What kind of deep and systemic infections can be caused by Ps. aeruginosa?

Answer 42

``` Pulmonary (nosocomial pneumonia, chronic infection in CF patients) UTI* Endocarditis* Osteomyelitis* Septicaemia* *In immunocompromised patients ```

Question 43

How does Ps. aeruginosa adhere to intact epithelium?

Answer 43

Weakly via flagella, pili, LPS | Capsule assists

Question 44

What is a risk factor for eye infection with Ps. aeruginosa?

Answer 44

Contact lens use (grows in fluid, forms biofilm, adheres to contact lens)

Question 45

How does Ps. aeruginosa invade?

Answer 45

Does not invade intact skin unless in very high numbers

Question 46

What part of Ps. aeruginosa binds to CFTR? What is the result of this?

Answer 46

LPS core | Prevents invasion in individuals with normal CFTR - adheres to CFTR and can be phagocytosed by macrophages

Question 47

What is the role of the capsule of Ps. aeruginosa?

Answer 47

Assists adherence and biofilm formation

Question 48

List 7 properties of Ps. aeruginosa in biofilms

Answer 48

``` Non-motile (no flagella) More capsule material (mucoid phenotype) More adherent Less invasive Shorter LPS (no O-Ag) Slowed growth Increased antibiotic resistance ```

Question 49

What is responsible for the change in the properties of Ps. aeruginosa when in a biofilm?

Answer 49

Activation of genes regulated by quorum sensing (also inactivation of some genes)

Question 50

What is quorum sensing?

Answer 50

Bacterial "cross-talk" which aids the formation of biofilms

Question 51

What are the stages of biofilm formation?

Answer 51

``` Bacteria adhere to an innate (or non-innate e.g. respiratory epithelium) surface Produce mucus material Form "mushroom-like" structure Change back into motile form Break out of mushroom structure Process repeats ```

Question 52

List 5 cellular aspects of Ps. aeruginosa that aid it spread through tissues and the body

Answer 52

``` Reduced PMNs Flagella Exoenzymes (act on pulmonary tissues and surfactant) Exotoxins LPS-CFTR-mediated invasion ```

Question 53

List 5 unique aspects of the Ps. aeruginosa infection in CF patients

Answer 53

Defect in CFTR causes abnormal ion transport, thickened mucus and impaired mucociliary function Pseudomonas (and Staph) are not being inhibited by high salt concentrations Bacteria in biofilms resist mechanical removal and are less visible to the innate immune system DNA secreted by bacteria and released from dying cells causes thickened mucus, trapping Ps. aeruginosa Bacterial variants which persist are those with reduced virulence

Question 54

What is the role of type III secreted proteins in Ps. aeruginosa pathogenesis?

Answer 54

Act on various host cell targets to interfere with phagocytosis and enhance cytokine production

Question 55

What is the role of exotoxin A in Ps. aeruginosa pathogeneis?

Answer 55

Blocks protein synthesis

Question 56

What is the role of LasA and LasB in Ps. aeruginosa pathogenesis?

Answer 56

Proteases that act together as elastase

Question 57

What is the role of phospholipase in Ps. aeruginosa pathogenesis?

Answer 57

Damages cell membranes, degrades surfactant