Pouring LB Agar Plates

LB Media is a generic rich media suitable for growing many aerotolerant species of bacteria, including E. coli, Bacillus subtilius, Staphylococcus auerus or Staphylococcus epidermidis and different yeasts including Saccharomyces and Candida species. Many kinds of molds will also grow (Aspergillus or Penicillium, for instance). However, the presence of these organisms on your plate generally represents contamination, and the plate should be tossed! LB agar will not necessarily support the growth of more fastidious organisms such as Streptococci, and pH media and conditions are less than ideal for culturing species of Lactobacilli from yogurt.

Ingredients (per Liter):
Adjust as needed to make 500, 250 or 100mL of media.

  1. 10g Tryptone: Tryptic digest of proteins to release small peptides and amino acids that bacteria can use for food and/or protein synthesis.
  2. 5g Yeast Extract: Source of additional proteins, vitamins and minerals; some sugars present, necessary for growth.
  3. 10g NaCl (table salt)
  4. 15g agar
  5. 1L distilled water - note tap water may work if you don't have access to a source of distilled water. However, note that the pH of municipal water supplies can sometimes drop to as low as pH=6, and there may be contaminants of ions or other compounds that could potentially impact the growth of bacterial species of interest. For growth of the bacteria listed above, however, tap water should work; else try a local drug store for gallon/liter jugs of distilled water.
Additional equipment