D Flashcards
Def of Infectious Diseases
- Clinically evident diseases resulted from the presence of pathogenic microorganisms with the potential of transmission from a person to another.]
- Infectious Diseases are many but limited by our knowledge, facilities, & ignorance.
what are causes of Infectious Diseases?
- Bacterial.
- Viral.
- Fungal.
- Parasitic.
Samples will be subjected to:
- Phenotypic microbiological analyses.
- Immunological-serological analyses.
- Genotypic-Molecular biological analyses.
Types of samples
- Blood.
- Sputum.
- Urine.
- CSF.
- Stool.
- Pus.
Phases of diagnosis
Preanalytical phase of diagnosis
Importance of Sampling
(good sample = true result)
- The successful identification of microbe depends on sampling.
- The specimen is the beginning:
As all diagnostic information from the laboratory depends upon the knowledge by which specimens are chosen & the care with which they are collected & transported.
Proper selection of type of sample
Collect the appropriate type of specimen for diagnosis of the infectious disease.
what does the quality of the sample Depend on?
- Proper Selection
- Proper Collection
- Proper Transport
Proper collection of sample
Avoid harming the patient & causing discomfort
Site:
- Collected tom: site pathingen is most likely to be round.
Time:
- The acute stage is the best.
- Before antimicrobial therapy has begun.
Quanlity:
- Sufficient quantity.
proper transport of sample
- Specimens should be protected from heat & cold.
- Specimen transported promptly Within 2 hours.
- Use of transport media especially for anaerobic culture.
Def of Direct methods of diagnosis
- Detection of organisms, their structural components & their products.
Clinical specimens from various organs
- Circulatory System.
- (Skin- Abscess - Wound) Specimens.
- Eyes & Ears.
- Respiratory System.
- Central Nervous System.
- Urinary Tract.
- Genital Tract.
- Oral Cavity.
- Gastrointestinal Tract.
- Body Fluids.
Examples of Direct methods of diagnosis
- Macroscopic evaluation.
- Microscopy (Unstained & Stained).
- Culture & biochemical reactions.
- Detection of microbial antigens & products.
- Molecular identification of nucleic acids (PCR & DNA probe technology).
Def of InDirect methods of diagnosis
- Detection of antibodies against the microorganism in the patient’s serum.
Examples of InDirect methods of diagnosis
- Serologic method
Macroscopic examination of samples
Microscopic examination of samples
Def of Culture
The process of growing & propagating organisms in a media that is conducive for their growth.
Importance of Culture
It Reproduce the organism for use for additional testing
Types of Culture
Identification of bacteria
- Morphology.
- Growth requirements.
- Biochemistry.
- Enzymes.
- Antigens.
Rapid identification of bacteria
Automated bacterial identification & Antimicrobial susceptibility systems.
Example of Automated bacterial identification and antimicrobial susceptibility systems
VITEK system.
Principle of Automated bacterial identification and antimicrobial susceptibility systems
Time of results of Automated bacterial identification and antimicrobial susceptibility systems
Available within 6-8 hours.
Drawbacks of Culture of Pathogenic Microbes
Diagnosis of infection with slow-growing or non-culturable bacteria tends to rely on….
Direct: by molecular methods (PCR).
Indirect: by serodiagnosis (antibody detection).
Diagnostic Methods through time
Def of Direct Antigen detection
- Assays are available for rapid detection of
- Bacterial Antigens (surface antigen - soluble antigen).
- Or toxin in biological fluids e.g. (CSF - blood - urine).
When are Direct Antigen detection useful?
- Prior antibiotic therapy has been initiated & cultures are negative after 24 hours of incubation.
- Rapid results in critical ill patients e.g. meningitis.
Principle & Types of Direct Antigen detection
Def of Molecular biology Techniques
Molecular detection techniques for bacterial, viral and fungal DNA.
Importance of Molecular biology Techniques
Disadvantages of Molecular biology Techniques
Def of MULTIPLEX PCR
Simultaneous detection of dozens of targets from one patient sample
Characters of MULTIPLEX PCR
Def of Indirect tests (serodiagnosis & Immune status tests)
Tests for detection of specific antibody for infectious agents including (IgM - IgG - IgA).
What is diagnostic in Indirect tests (serodiagnosis & Immune status tests)?
Rising antibody titer (at least 4 folds) is diagnostic.
Time of sample collection in Indirect tests (serodiagnosis & Immune status tests)
Samples are withdrawn at acute & convalescent stages (within 14 days).
Techniques of Indirect tests (serodiagnosis & Immune status tests)
Advantages of Indirect tests (serodiagnosis & Immune status tests)
- Inexpensive.
- Easy to perform.
- Allows identification of:
- Acute infection → IgM.
- Past infection → IgG.
Disadvantages of Indirect tests (serodiagnosis & Immune status tests)
- Delayed response.
- False negative results during sero-conversion window.
- Time of infection not always clear.
Sampling for mycological examination
- Clean the site with alcohol 70%.
- Sterile scalpel is used for scrapping.
- Sterile scissor is used for trimming the nails.
- Scales are transferred in clean dark paper.
Inoculation of fungal infections
Sampling for viral examination
Time: Sample should be collected during the most active stage of the disease.
Transport:
* Samples as (urine - stool - sputum - CSF) are transported directly to the lab.
* Swaps from (throat - nose - vesicles - cervix) are transported in viral transport medium.
Biohazard label should be used for containers of …..
(HBV - HCV - HIV)
Methods of viral detection
Def of MIC (minimum inhibitory concentration
The lowest concentration of antimicrobials that will inhibit the growth of organisms.
importance of MIC (minimum inhibitory concentration
Confirm resistance of organisms to an antimicrobial agent.
Methods of MIC (minimum inhibitory concentration
Post-Analytical phase of diagnosis
- Reporting of:
- Identification.
- Antibiotic sensitivity.
- Treatment
Def of Rapid Detection Tests
Tests that give results in minutes to 1-2 hours.
Characters of Rapid Detection Tests
- Accurate.
- Simple to use.
- Low cost.
- Stable under extreme conditions.
- Little or no processing.
- Culturally acceptable “Give the same result of the culture”.
- Easy to interpret.
Revolution in Direct Detection of Infections
- Direct antigens.
- Direct antibody.
- Nucleic Acid (NA) based technology.
Check conclusion
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Check take home messages
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