Gram negative organisms cannot be differentiated at the genus level (such as E. coli, Klebsiella or Enterobacter) on the agar plates used in on-farm cultures. However, they can be identified as lactose negative or lactose positive by what color they ferment lactose in MacConkey agar. In this episode, Dr. Pamela Ruegg explains what this means and discusses treatment options for a gram negative infection. Hint: gram negative infections often resolve on their own. Therefore, it is not always necessary to treat with antibiotics. Remember, it is always advisable to consult your local veterinarian when making these decisions.