Chapter 6: Specimen Collection and Processing Flashcards
Identification mechanisms:
Cultures, microscopy, specialized tests
Basic Principles of Specimen Collection: Fundamentals
– Collect specimen in acute phase of infection (before antibiotics are administered)
– Select correct anatomic site
– Use proper technique (minimal contamination - especially with normal microbiota)
– Collect appropriate quantity
– Pack to maintain viability and prevent leakage
– Label specimen accurately – anatomic site, patient info, date
– Transport or store specimen promptly
– Notify lab in advance if unusual pathogens or bioterrorism agents are suspected
Why are swabs not recommended?
Quantity insufficient, contamination, drying
- cotton may be toxic to bacteria and dacron, rayon, calcium alginate
However, could be used for upper respiratory, external ear, eye, and genital tract
Lesions, wounds, abscesses collection:
– Need exact anatomic sites
– Collect from needle aspiration from advancing line
of infection, clean area to remove contaminants
– Aspirated material should be placed into a sterile
tube or transport vial.
Educating patients with thorough instructions:
– Should be instructed by appropriate medical personnel in verbal and written forms
– Attach printed instructions in multiple languages with pictures
Specimen Labeling:
– Name
– Date of birth
– ID number
– Room number
– Physician
– Culture site
– Date/time of collection
– Name/initials of colletor
Test Requisitions:
– Patient’s name
– Patient’s date of birth and gender
– Patient’s room number or location
– Physician’s name and address
– Specific anatomic site
– Date and time of specimen collection
– Diagnosis or relevant history
– Antimicrobial agents (if any that patient is receiving)
– Transcriptionist of orders
Safety for Those Handling Specimens:
– Transport specimens in leak-proof secondary containers
– Specimen and papers kept separate
– Specimens should not contain needles or
sharps
– Must handle specimens with proper personal protective equipment (PPE) and engineering controls (Appropriate biosafety Cabinet)
Preservation, Storage, and Transport:
– Transport w/n 30 minutes of collection, preferable w/n 2 hours
– Storage should be immediate. Some pathogens will be at room temp, refrigerated, or froze
Urine preservatives:
Boric acid, maintain colony cunts for 24 hours at room temp
Stool preservatives:
– Refrigerate for up to 2 hours, if longer use Cary-Blair transport media
– C. diff refrigerated for 48 hours or froze at -70 if longer
– Ova and parasite exams have special fixations
Use of anticoagulants for:
Used to prevent clotting of blood, bone marrow,
and synovial fluid.
SPS is most common, concentration should need exceed 0.025%
Heparin used for viral cultures and mycobacterium from blood.
Holding or transport media:
Contain substances that do not promote growth of the microorganisms but ensure preservation – swab collection systems
- Stuart’s transport medium
- Amie’s transport medium
- Some transport media contain charcoal to absorb the fatty acids given off by cotton swabs.
Direct inoculation – contamination more likely
– Blood to broth culture bottles
– Synovial and peritoneal fluid to culture bottles
– Neisseria gonorrhoeae specimens to JEMBEC system (commercial transport system)
– Additional specimen should also be provided for direct examination and Gram stain.
Category A:
capable of causing permanent disability or life-
threatening or fatal disease to an otherwise healthy
humans or animals
Category B:
not in a form generally capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals
Unacceptable Specimens/Specimen Rejection:
– Requisition information does not match specimen label
– Inappropriate transport container or leakages
– QNS – quantity not sufficient
– Transport time longer than 2 hours with no preservatives
– Specimen received in fixative/wrong preservatives
– Anaerobic culture for specimens in which anaerobes are indigenous
– Microbiology processing of a particular specimen results in questionable data
– Specimen is dried up.
– More than one specimen from same source on same day (exception: blood cultures)
– One swab submitted with multiple requests for various organisms
– Expectorated sputum gram stain reveals less than 25 white blood cells (WBCs), greater than10 epithelial cells per low power field, and mixed bacterial biota
During macroscopic observation, record ___
– Swab or aspirate
– Stool consistency (formed or liquid)
– Blood or mucus present
– Volume of specimen
– Fluid: clear or cloudy
– Help determine adequacy and any special tests needed
Direct Microscopic Observation:
– determine quality of specimen
– can give lab worker indication of infectious process involved
– rapid information, useful in initial treatment
Nonselective media:
– Support growth of most nonfastidious organisms
– Sheep blood agar (SBA) – standard medi
Differential media:
– Allows grouping of microbes based on demonstrated characteristics on the media
– Sheep blood agar (hemolysis), MacConkey agar (lactose fermentation)
Selective media:
Support growth of one type of organism but not another.
MacConkey Agar - enteric gram-negative bacilli
Columbia nalidixic acid agar - gram positive organisms
Enriched media:
Contain growth factors added to nonselective media to allow fastidious organisms to grow
- Chocolate agar
Enrichment broth:
– A liquid medium designed to encourage small numbers of particular organisms to grow
– Suppress other biota present
– Subculture to isolate particular organisms
- Lim broth (enhances group B streptococci)
Broth media - liquid:
Supplement to agar plates to detect small numbers of aerobes, anaerobes, and microaerophiles
- Thioglycolate broth (requirements for oxygen)
Incubation Conditions:
- Most cultures grow between 35° C and 37° C
- Oxygen conditions depend on organisms (aerobic, anaerobeic, capnophilic)
- Time required (most held for 24-72 hours)
Points to remember:
- Specimens must be appropriately selected, collected, and transported.
- Must prioritize the processing of specimens as they are received in the laboratory based on the critical nature of the infection and the potential for specimen deterioration.
- Suboptimal specimens provides misleading results.
Guidelines for specimen rejection must be followed - Macroscopic observation, microscopic observation,
appropriate culturing, and analysis are key to initial identification of microbes - Communicate accurate and timely results
