How is infection diagnosed Flashcards
Factors to consider when you are suspicious of an infection
Source of infection
Factors increasing risk of sepsis
Indications of clinical concern
If they have informed support network at home
What must be recorded when we prescribe antibiotics?
- Note down the clinical indication (observations/symptoms/diagnosis)
- The drug prescribed
- Dosage
- Duration of treatment
- Drug allergies
- Current medication of patient
- Renal function of patient
What makes a sample relevant and of high quality?
- Appropriate colors for viral pots
- Eliminate/minimize contamination
- Clear instructions if patient is collecting sample
- Sample prior to antimicrobials if possible
- Clear labels
- Sufficient volume of sample at correct timeline
- Contact lab if uncertain of the tests or sample types
- Check sample collected well
What does a charcoal medium do when collecting samples?
Stops toxic metabolites attacking bacteria
What are sterile sites?
No bacteria e.g. joint fluid/blood
Who works in the processing labs?
- Medical technical officers
- Biomedical scientists
- Clinical microbiologists
- Look at unusual microorganisms, repeated specimens, special interest patients and offering advice
Which pathogens is microscopy good for?
Good for bacteria, fungi, protozoa and metazoa but not viruses
Why is microscopy beneficial?
Fast
Why is microscopy not beneficial?
Presumptive results
Easier when higher numbers
Not detected doesn’t mean not present
What is non-selective agar?
- Used for secondary culture
- Supports growth of wide range of organisms
What is non-selective agar used for?
Sterile sites
What is selective agar used for?
Non-sterile sites
When is Mannitol salt used?
- Mannitol salt agar used for Staphylococcus spp. Staphylococcus can tolerate high salt content
- Mannitol is fermented by S.aureus but not S.epidermis
Characteristics of selective and differential agar
- Non-sterile sites - skin/throat/faeces
- Looking for certain organism
- Often contain chemical indicator
What is latex agglutination?
Antibodies attached to blue beads. If bacteria present in sample, antigen bonds to antibody and the beads clump together, becoming blue
What is the diffusion test?
Pure culture spread onto non-selective agar. Add filter paper impregnated with antibiotics. Incubate and examine growth. If microorganism is sensitive to antibiotic, it can’t grow - forms ring
What is the diffusion test MIC?
Bacterial culture with different dilutions of antibiotics. Highest dilution which inhibits bacterial growth. Can be performed at the same time as confirmatory tests
Antimicrobial prescribing decision
- Continue
- Stop
- Change
- Switch IV to oral (or vice versa)
- Must be clearly documented in notes
- Review 24/48 hours
What is PCR used for?
Detecting viruses
What does PCR depend upon?
Genomic sequence being unique to the organism
Process of PCR
- Primers attach to unique sequence of DNA
- Amplification of DNA strand
- Increasing the temperature stops reaction
- Left with DNA of varying lengths
- We know the size of fragment that we are looking for
