Additional notes on Bacte Lab

• Basic Principles of Specimen Collection

  • Maintain viability of organisms with minimal contamination
• Specimen Collection


  1. Collect the specimen in the acute phase of the infection and before antibiotics are administered

  2. Select the correct anatomic site for collection of the specimen

  3. Collect the specimen using the proper technique and supplies with minimal contamination from normal biota

  4. Collect the appropriate quantity of specimen

  5. Package the specimen in a container or transport medium designed to maintain the viability of the organisms and avoid hazards that result from leakage

  6. Label the specimen accurately with the specific anatomic site and the patient information—patient's name and a unique identification number, as well as date and time of collection

  7. Transport the specimen to the laboratory promptly or make provisions to store the specimen in an environment that will not degrade the suspected organism(s)

  8. Notify the laboratory in advance if unusual pathogens or agents of bioterrorism are suspected
• Transport Media


  Media that usually contain substances that do not promote multiplication of microorganisms but ensure their preservation and are available in swab collection systems
• Transport Media


  • Stuart or Amie transport medium
  • Transport systems containing charcoal to absorb fatty acids given off by the swab that can be detrimental to the survival of Neisseria gonorrhoeae and Bordetella pertussis
  • JEMBEC system for N. gonorrhoeae specimens containing selective agar and a carbon dioxide (CO2)-generating tablet
  • Nasopharyngeal swabs for the isolation of B. pertussis inoculated directly onto selective agar
• Specimen Priority Levels


  • Critical/Invasive (Amniotic fluid, blood, brain, cerebrospinal fluid, Heart valves, Pericardial fluid)
  • Unpreserved Body fluids (not listed for level 1), Bone Drainage from wounds, Feces, Sputum, Tissue
  • Quantitation Required (Catheter tip, Urine, Tissue for quantitation)
  • Preserved (Feces in preservative, Urine in preservative, Swabs in holding medium (aerobic and anaerobic))
• Nonselective media


  Support the growth of most nonfastidious microbes
• Selective media


  Support the growth of one type or group of microbes but not another
• Differential media


  Allow grouping of microbes based on different characteristics demonstrated on the medium
• Enriched media


  Contain growth enhancers that are added to nonselective agar to allow fastidious organisms to flourish
• Enrichment broth


  A liquid medium designed to encourage the growth of small numbers of a particular organism while suppressing other flora present
• Broth media


  Can be used as a supplement to agar plates to detect small numbers of most aerobes, anaerobes, and microaerophiles
• Isolation Techniques


  1. Inoculate specimens to agar plates using a general purpose isolation streak to yield a semi-quantitative estimate of growth

  2. Flame the loop in between plates to prevent carryover of a possible contaminant from one plate to another

  3. Use gamma-sterilized disposable loops to eliminate the step of flaming the loop between quadrants or between plates

  4. Inoculate urine specimens using a quantitative isolation
• Incubation Conditions


  • Temperature of 35° to 37°C
  • Aerobes grow in ambient air
  • Anaerobes cannot grow in the presence of oxygen and require an anaerobic atmosphere
  • Capnophiles require an increased concentration of CO2
  • Microaerophiles grow with reduced oxygen and increased CO2
• Most routine bacterial cultures are held for 48 to 72 hours. Cultures for anaerobes and broth cultures may be held for 5 to 7 days. Unusual organisms may require special medium or conditions beyond the routine.