text: DNA–DNA hybridization (DDH) is used as a primary method to distinguish bacterial species as it is difficult to visually classify them accurately. This technique is not widely used on larger organisms where differences in species are easier to identify. In the late 1900s, strains were considered to belong to the same species if they had a DNA–DNA similarity value greater than 70% and their melting temperatures were within 5 °C of each other. In 2014, a threshold of 79% similarity has been suggested to separate bacterial subspecies. 
  DDH is a common technique for bacteria, but it is labor intensive, error-prone, and technically challenging. In 2004, a new DDH technique was described. This technique utilized microplates and colorimetrically labelled DNA to decrease the time needed and increase the amount of samples that can be processed. This new DDH technique became the standard for bacterial taxonomy.