Opportunistic Infections Flashcards
List 9 commonly encountered opportunistic pathogens. Which of these may cause nosocomial epidemics?
E. coli Staphylococcus aureus* Klebsiella pneumoniae* Enterococcus spp.* Pseudomonas aeruginosa* Enterobacter spp.* Serratia spp.* Proteus spp. Clostridium difficile *May cause nosocomial infections
What host factors combat colonisation and penetration by microbes?
Physical and chemical barriers
What host factors combat multiplication of microbes and tissue damage caused by microbes?
Inflammatory response and phagocytosis
Adaptive immune response
How do microbial virulence and host resistance affect disease outcome?
If host resistance is reduced, pathogen does not need to be very virulent to cause overt infection (and vice versa)
Give 5 examples of local host factors that may predispose to opportunistic infection
Anatomical defects Surgical and other wounds Burns Catheterisation (bladder, IV) Foreign bodies in general (e.g. suture)
Why is it important to recognise opportunistic infections?
May be 1st sign that there is something wrong with the host (e.g. immunosuppression, obstruction, etc)
What is the effect of foreign bodies on opportunistic infection?
Increases likelihood of infection (allows microbes to evade immunity)
Give an example of a type of infection that is commonly opportunistic
UTIs (in females especially)
What might pneumonia that does not respond to conventional treatment suggest?
Obstruction or lung disease (pre-disposing factor exists)
List 9 systemic host factors that may predispose to opportunistic infection
Extremes of age Leucopenia Malignancy Malnutrition Diabetes Liver disease Certain infections Treatment with antimicrobials Primary (congenital) immunodeficiency
What opportunistic infection does diabetes predispose to?
Candida albicans infection (candidiasis; often the 1st presentation of DM)
Give 2 examples of an infection that predisposes to opportunistic infection
HIV
Measles (temporary severe immunocompromise)
Give 2 examples of opportunistic infections associated with antimicrobial treatment
Clostridium difficile infection (pseudomembranous collitis) Fungal infection (e.g. thrush following broad spectrum antibiotic for UTI)
List 6 common presentations of opportunistic infections
Wound infection UTI intra-abdominal infection Pneumonia Septicaemia Meningitis (especially in neonates)
How are opportunistic infections diagnosed?
By culturing an appropriate specimen (e.g. wound swab, pus, urine, sputum, blood, CSF)
What is the risk with taking antimicrobials in hospital?
Patient are susceptible to becoming colonised with resistant organisms
How are opportunistic infections treated?
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)
How can opportunistic infections best be prevented?
Aseptic technique (especially hand hygiene)
What kind of bacteria is Pseudomonas?
Gram negative bacilli
What is the metabolic classification of Pseudomonas?
Aerobes or facultative anaerobes
Is Pseudomonas motile?
Yes
Does Pseudomonas ferment?
No
Does Pseudomonas form spores?
No
What result does Pseudomonas produce on a catalase test?
Catalase positive
What result does Pseudomonas produce on an oxidase test?
Oxidase positive
Does Pseudomonas produce pigments?
Some do, including Ps. aeruginosa
What is the name of the pigment produced by Ps. aeruginosa?
Pyocyanin (greenish pus)
What are the nutritional requirements of Pseudomonas?
Low nutritional requirements (can survive almost anywhere but love moist environments)
Where is Pseudomonas’ favourite place to grow?
Moist environments
How are Pseudomonas classified?
Divided into species based on biochemical tests
How is Pseudomonas subtyped for epidemiological studies?
RFLP
MLST (multilocus sequence typing)
May use whole genome sequencing as cost comes down
Colonisation with which organism is associated with a poor prognosis for CF?
Pseudomonas
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?
Burkholderia capacia (opportunistic)* Stenotrophomonas maltophilia (opportunistic)* Burkholderia pseudomallei *Colonise CF patients (also Ps. aeruginosa)
What is a saprophyte? Give an example
Organism that grows freely in the environment
E.g. Ps. aeruginosa
What organism causes melioidosis, which can lead to pneumonia?
Burkholderia pseudomallei
What is 1 reason Ps. aeruginosa (and related pathogens) are intrinsically resistant to many commonly-used antibiotics?
Due to chromosomal B-lactamase
Does Ps. aeruginosa colonise normal healthy individuals?
Only transiently colonises skin, mucous membranes and GIT
List 6 conditions associated with Ps. aeruginosa
CF Pneumonia UTI Sepsis Burns (more previously) Febrile neutropenia (more previously)
How is Ps. aeruginosa spread in hospitals?
On hands and fomites
How can Ps. aeruginosa be isolated in the lab?
Grown on cetrimide agar (disinfectant; kills all other organisms but Pseudomonas can grow)
What kind of superficial infections can be caused by Ps. aeruginosa?
Skin (wound infection, otitis externa, folliculitis)
Eye (keratitis, corneal ulcer - can also invade and cause deep ulcer)
What kind of deep and systemic infections can be caused by Ps. aeruginosa?
Pulmonary (nosocomial pneumonia, chronic infection in CF patients) UTI* Endocarditis* Osteomyelitis* Septicaemia* *In immunocompromised patients
How does Ps. aeruginosa adhere to intact epithelium?
Weakly via flagella, pili, LPS
Capsule assists
What is a risk factor for eye infection with Ps. aeruginosa?
Contact lens use (grows in fluid, forms biofilm, adheres to contact lens)
How does Ps. aeruginosa invade?
Does not invade intact skin unless in very high numbers
What part of Ps. aeruginosa binds to CFTR? What is the result of this?
LPS core
Prevents invasion in individuals with normal CFTR - adheres to CFTR and can be phagocytosed by macrophages
What is the role of the capsule of Ps. aeruginosa?
Assists adherence and biofilm formation
List 7 properties of Ps. aeruginosa in biofilms
Non-motile (no flagella) More capsule material (mucoid phenotype) More adherent Less invasive Shorter LPS (no O-Ag) Slowed growth Increased antibiotic resistance
What is responsible for the change in the properties of Ps. aeruginosa when in a biofilm?
Activation of genes regulated by quorum sensing (also inactivation of some genes)
What is quorum sensing?
Bacterial “cross-talk” which aids the formation of biofilms
What are the stages of biofilm formation?
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
List 5 cellular aspects of Ps. aeruginosa that aid it spread through tissues and the body
Reduced PMNs Flagella Exoenzymes (act on pulmonary tissues and surfactant) Exotoxins LPS-CFTR-mediated invasion
List 5 unique aspects of the Ps. aeruginosa infection in CF patients
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
What is the role of type III secreted proteins in Ps. aeruginosa pathogenesis?
Act on various host cell targets to interfere with phagocytosis and enhance cytokine production
What is the role of exotoxin A in Ps. aeruginosa pathogeneis?
Blocks protein synthesis
What is the role of LasA and LasB in Ps. aeruginosa pathogenesis?
Proteases that act together as elastase
What is the role of phospholipase in Ps. aeruginosa pathogenesis?
Damages cell membranes, degrades surfactant
