Question

Draw the cells from Gram Stain yogurt slide. (Label organism, gram reaction, cell morphology, and cell arrangement)

Answer 1

The Gram stain of yoghurt slide contains bacterial smear of Lactobacillus species. Lactobacilli are rod-shaped, Gram-positive, fermentative organotrophs. They are usually straight, and often arranged in pairs or chains of varying length.

The Gram staining of bacterial smear of Lactobacillus sp is first air dried and stained with crystal violet or Gentian violet for 30 seconds. The bacteria Lactobacillus get stained (bluish purple). After that it is washed with water and stained with iodine (0.5% solution) which works as mordant. Consequently, a crystal violet iodine (CVI) complex is formed. Then it is followed by the treatment with alcohol, it is found that Lactobacillus retain the stain, so it is Gram-positive in nature.