Specimen Preparation

• Back-up broth medium


  Supplemental or enrichment broth
• Back-up broth medium


  • Fluid medium
  • For small numbers of organisms present
  • For anaerobes in aerobic cultures
  • For organisms that may be damaged by previous or concurrent antimicrobial therapy
• Back-up broth medium use

  1. Incubated for a certain period

  2. Then subcultured
• Common back-up broths


  • Thioglycollate (thio) broth
  • Brain-heart infusion broth (BHIB)
  • Tryptic soy broth (TSB)
  • Lim broth (used to enhance the group of beta streptococci)
• Lim broth


  Used to enhance the group of beta streptococci
• Specimen types


  • Swab
  • Tissue
  • Fluid
• Tissue specimen preparation


  1. Homogenization (grinding)

  2. Minced with sterile scissors and forceps into small pieces
• Fluid specimen preparation


  1. Concentration of large volumes of fluids (to increase the recovery of bacteria)

  2. Centrifugation (for fluid greater than 1 ml, inoculate media and prepare smears)

  3. Filtration (for thin fluid consistency to avoid filter clogging)
• Sterile body fluids


  • Peritoneal fluids
  • Pleural fluids
  • Continuous ambulatory peritoneal dialysis fluid [CAPD]
• Specimen decontamination


  For legionellae or mycobacteria
• Swab specimen preparation


  1. 1st swab inoculated to culture media and make a direct smear

  2. 2nd swab placed into 0.5 to 1.0ml of broth or saline and then vortexed to loosen material from the swab to produce an even suspension of organisms