Selection of Kanamycin-Resistant Gram-Negative Transformants: Isolates kan-resistant colonies (50 µg/mL) of E. coli and related enterics on a MacConkey base.

Lactose Fermentation Differentiation: Differentiates lactose fermenters (pink/red with 30 µg/mL neutral red) such as E. coli, Klebsiella, Enterobacter from non-fermenters (colorless) like Salmonella, Shigella, Pseudomonas.

Cloning and Plasmid Maintenance: Screens recombinant clones carrying kanamycin-resistance markers in E. coli while reporting lactose phenotype.

Conjugation/Transposon/Mating Selections: Selects kan-marked transconjugants among Enterobacteriaceae; bile salts #3 (0.15%) and crystal violet (1 µg/mL) suppress Gram-positives.

Counterselection in Mixed Cultures: Suppresses background flora lacking kan resistance while enriching target enterics; crystal violet and bile salts inhibit Gram-positives.

Colony Purity Checks: Verifies purity of kan-resistant strains and monitors lactose-fermentation stability across passages.

Environmental/Clinical Surveillance of Resistant Coliforms: Enumerates kan-resistant coliforms from complex samples with differential readout.

Isolation from Fecal or Enteric Samples: Recovers kan-resistant enteric bacteria where Gram-positives are inhibited and lactose metabolism is visualized.