Opportunistic Infections

Question 1

What are the frequently encountered opportunistic pathogens?

Answer 1

E coli
Staph aureus
Klebsiella pneumoniae
Enterococcus spp
Pseudomonas aeruginosa
Enterobacter spp
Serratia spp
Proteus spp
C. difficile

Question 2

Which frequently encountered opportunistic pathogens cause nosocomial epidemics?

Answer 2

Staph aureus
Klebs pneumo
Enterococcus spp
Pseduomonas aeruginosa
Enterobacter spp
Serratia spp

Question 3

What local host factors contribute to opportunistic infection?

Answer 3

Anatomical defects
Surgical and other wounds
Burns
Catheterisation (bladder, IV)
foreign bodies (sutures etc.)

Question 4

Opportunistic infections are especially important to recognize because

Answer 4

They are a sign that something else is wrong with the patient - always ask WHY the patient has this infection

Question 5

T/F Sutures reduce the chance of infection

Answer 5

False; the presence of a foreign body including sutures increases the chance of infection

Question 6

Why do foreign bodies predispose to opportunistic infection?

Answer 6

They can provide a haven from the immune system for bacteria eg injecting medical students with S aureus and talc - the ability to hide in the talc made the S aureus more pathogenic

Question 7

T/F Burns are commonly associated with Pseudomonas infection

Answer 7

False; previously Pseudomonas infections were more common; now we see more Staph and other bacteria

Question 8

Catheters are a source of opportunistic infection because

Answer 8

they bypass normal host defenses

Question 9

What systemic host factors contribute to opportunistic infection?

Answer 9

Extremes of age
Leucopenia
Malignancy
Malnutrition
Diabetes
Liver disease
Certain infections (HIV, measles)
Tx with antimicrobials (C. diff)
1' congenital immunodeficiency

Question 10

Leucopenia as a predisposing factor for opportunistic infection is commonly seen in

Answer 10

Patients undergoing treatment for malignancy which itself is immunocompromising

Question 11

Candidiasis (Candida albicans infection) can be an indication of

Answer 11

Diabetes

Question 12

Someone who is treated with antimicrobials is susceptible to infection by

Answer 12

C difficile

Fungi (eg post UTI tx co-amoxyclav, then they get thrush)

Question 13

Why does antimicrobial treatment predispose to fungal infection eg candidiasis post UTI Tx?

Answer 13

It alters the normal microbiota that protects against fungal overgrowth

Question 14

Common types of opportunistic infections seen include

Answer 14

wound infection
UTI
intra-abdo infection
pneumonia
septicaemia/sepsis
meningitis (esp neonates)

Question 15

Why are exogenous sources of OI important to recognize?

Answer 15

something has gone wrong with infection control procedures

Question 16

Sources of OI pathogens can be __________ or __________

Answer 16

Endogenous - own microbiota OR own microbiota as acquired in hospital
Exogenous - other people

Question 17

Why are bactericidal agents required in some OIs?

Answer 17

If the patient is immunocompromised they not have the necessary immune response to deal with microbes that are alive but not growing (bacteriostatic) and can relapse

Question 18

What is used for epidemiological classification of Pseudomonas?

Answer 18

RFLP or multilocus sequence typing

Question 19

What makes Pseudomonas resistant to many ABs?

Answer 19

chromosomal encoded beta lactamase that degrades many penicillins (eg amoxycilin) and is not inhibited by clavulanic acid

Question 20

Psuedomonas colonises

Answer 20

skin, mucous membranes, gut

Question 21

T/F Pseudomonas colonization is permanent

Answer 21

False; transient colonization UNLESS they have CF or other disorder that allows permanent colonization

Question 22

Pseudomonas infections are mostly acquired

Answer 22

from the environment

Question 23

Pseudomonas is spread in hospital on

Answer 23

hands and fomites (inanimate objects)

Question 24

What is unique about Pseudomonas isolation techniques in the lab?

Answer 24

Weak disinfectant agents are used - centrimide agar - that stop other bacteria from growing ie acts as a selective media; allows pseudomonas to flourish

Question 25

What resistance mechanisms does Pseudomonas have?

Answer 25

intrinsic (chromosomal beta lactamase); AND readily acquires resistance from other bacteria via plasmids (clav-acid is effective against plasmid-acquired beta lactamases)

Question 26

Why did Pseudomonas develop resistance to carbenicillin and ticarcillin?

Answer 26

these ABs are not susceptible to the chromosomally-encoded beta lactamase BUT as pseudomonas acquires plasmid-encoded resistance it acquires beta lactamases that these drugs are susceptible to; therefore they need to be used in combination with clavulanic acid which inhibits plasmid-encoded beta lactamases

Question 27

Superficial infections of PA include

Answer 27

wound, otitis externa, folliculitis, keratitis, corneal ulcer, and deep eye infection

Question 28

Deep and systemic infections of PA include

Answer 28

nosocomial pneumonia, chronic pulm infection in CF patients, UTI, endocarditis, osteomyelitis, septicaemia

Question 29

How is PA in biofilm different?

Answer 29

non-motile
more capsule/hypermucoid
more adherent
less invasive
shorter LPS w/o O Ag
slowed growth
increased resistance to ABs

Question 30

Why do PA in biofilms have greater AB resistance?

Answer 30

slower growth and more capsule makes it harder for AB to penetrate

Question 31

What is the cause of the changes to PA observed in biofilms?

Answer 31

Changes in activation of genes that are regulated by quorum sensing

Question 32

What is quorum sensing?

Answer 32

Cross-talk between bacteria during biofilm formation that leads to the turning on and off of certain genes, causing different properties to be expressed by the bacteria

Question 33

Why do biofilms tend to persist?

Answer 33

They resist mechanical removal (less motile) and they are less visible to the innate immune system (short or no O Ag)