Diagnostic BacT Flashcards
why are bacterial diagnostics needed?
Bacterial diagnostics are needed for rapid and accurate information on how to treat pathenogenic bacteria.
Why is it important to have an understanding of bacteriology?
The time lapse in which happens to do different diagnostic tests with bacteria can be detrimental to the patient. Therefore knowledge of clinical signs can be helpful in diagnosis.
How do diagnostic tests help the clinician?
They complement clinical judgement. Improve patient care. Enhance selection of antimicrobial therapy. Prevent transmission and Zoonosis. Prevent future infections.
What is the Role of the clinician?
Presumptive Dx based on Hx, symptoms, Direct exam of clinical samples.
List of DDx.
Select appropriate samples of determine tests, select lab.
Use appropriate collection and transport methods.
Prepare submission forms.
Provide adequate Hx, Signalment info to obtain significant info from the lab.
What are some issue would one be concerned about when choosing a laboratory?
QC- Quality Control
QA- Quality Assurance
TQM- Total Quality Managment
(attention to method reproducibility of tests, comparasion to consensus standards trouble shooting/ corrective action)
When choosing a diagnostic method, which two factors are of key importance?
Identification of the agent
Identification of the host immune response
Identification of the agent can be achieved by?
Direct detection of the agent (simple/ Differential staining, Fluorescent antibody staining)
Isolation and Identification
Direct detection of antigens, Toxins (immunology techniques such as ELISA)
Nucleic acid detection (PCR)
Identification of the host immune response is achieved by?
Antibodies (eg, Brucella infection)
Cell mediated immune response (TB)
An ideal diagnostic test has what in regards to sensitivity and specificity?
High for both!
Which relates to a true positive?
sensitivity, people with humiliating disease are very sensitive of the subject.
which relates to a true negative?
Specificity, people specifically do not have the disease.
what is the positive predictive value?
precentage of all positive test results that are true positives.
what is negative predictive value?
precentage of all negative test results that are true negatives.
What are the best ways to collect a specimen?
Collect from actual site of infection
Minimize contamination
Collect early in the stage of the Dz process
Use appropriate transportation
Collect before the initiation of antimicrobial therapy
If you decide to collect a specimen after starting antimicrobial therapy, how do you go about collecting the specimen?
Collect either before the next dose, or 48 hours after the last dose.
T/F one should not submit a swab, fluid, surgical masses removed to the labratory, rather one should submit the material.
True
For multiple tests one should submit what?
Multiple specimens from multiple lesions
T/F A single blood sample is sufficient for blood and fecal samples?
FALSE. Multiple samples should be submitted, esp fecal- to determine if normal flora or pathogen.
What are ways to transport Bacterial samples?
Swabs Leak proof sterile containers Syringe- MUST REMOVE NEEDLE Blood culture bottle for blood only! DONT PUT SHIT IN AN AIRTIGHT TUBE!!
what is the single most important and cost effective laboratory procedure?
Direct microscopic examination
What type of results can Direct microscopic examination provide?
Number of bacteria
Morphology of bacteria
Gram Properties
Host cellular response- presence of macro,neutro,etc.
What are some things that can be inferred from Direct Microscopic Examination?
Likelihood of infection
Likely pathogens
predominant organisms
What is a simple stain? what is the color?
Methylene blue…
What are common in house differential stains?
Grams, Acid Fast, Wright-Giemsa
Gram Positive species appear?
Purple
ex. Strep. pyogenes, Staph. aureus
Gram negative species appear?
Pink
ex. E. coli, Pasteurella multocida
What contributes to which stain will be accepted in the gram stain?
Peptidoglycan- thick- purple, thin- pink-counterstain
What are the properties of the Acid Fast (kinyon’s stain)?
Acid Fast positive- Pink
Acid Fast Negative- Blue
what accounts for the color of the acid fast stain results?
Mycolic acid
What is the sensitivity of direct staining blood?
blood must have 10^4-10^5 bacteria/ml of sample to see 2-3 organisms under 100x field.
What are some limitations to direct microscopic examination of bacteria?
Blood
CSF
Mycoplasma (no cell wall) Spirochetes (too small to be seen) neither stain
What is the preferred collection of urine to be submitted for laboratory analysis?
cytocentesis, catheterization can force bacteria in lower urethra into bladder.
How many bacteria must be present per ml to be evaluated by laboratory tests?
10^5/mL-
If a culture has to stay at the clinic overnight should it be frozen or refrigerated?
Refrigerated
For transudates and exudates what is important?
Anaerobic transport medium
For lavages or washes use a buffered solution
Saline can be too acidic- LRS better choice.
what is important about submitting a fecal sample for analysis?
2-3 grams
leak proof container- airtight will pop> gas build up!
Send multiple samples over time
What is an ideal regimen for submitting blood samples?
Several specimens over a period of time @ the onset of fever.
3-4 in first 1.5-3hrs.
When collecting tissues for laboratory analysis what is good protocol?
Portion of a tissue Multiple specimens COLLECT FIRST DURING NECROPSY Send in sealed leak proof containers Refrigerate if delivery is delayed
What type of interpretation can the laboratory provide to the clinician?
Normal flora Vs. Pathogen
Correlate clinical signs and organism
Quantify- Light, Moderate, Heavy.
How are False negative results obtained?
Possible tissue sampling Transport storage issues Antimicrobial therapy Fastidious organisms
What are the biosafety levels from highest to lowest?
BSL-4
BSL3
BSL2
BSL1
Which bacteria need specials Cultures?
Mycoplasma Salmonella Listeria Mycobacterium Campylobacter
what are methods of bacterial identification?
Biochemical Antigenic Phage typing Virulence typing Whole-cell Fatty Acid analysis Genetic Analysis Protein Analysis Enzyme isotyping
What is MALDI-TOF
Matrix Assisted Laser desorption Ionization- Time of Flight
mass spectrometry.
measures unique fingerprint of organism- highly abundant proteins
What is the limitation of PCR identification?
The clinician needs to know which organism they are looking for.
what are examples of Humoral Response tests?
Agglutination
Precipitation
ELISA
What are examples of Cell mediated immune response tests?
Tuberculin Reaction
Interferon gamma test
Immune tests can result in false positives, why?
Prior antigen exposure, vaccination, cross reactions.
Immune tests can result in false negatives, Why?
Anergy, immunosupression
