Specimen and Slide Preparation

Specimen and Slide Preparation

Specimen Collection

  • The first step is specimen collection, where a sample of the microorganism to be studied is obtained from a source.
  • Methods of collection can vary based on the source, such as swabbing, scraping, aspiration, or biopsies.
  • It is crucial to ensure that the specimen is uncontaminated and represents the microorganism or microbial community accurately.

Sample Storage and Transport

  • After collection, specimens need to be properly stored and transported to prevent any changes in the microbial population.
  • The sample is often stored in sterile containers or transport media.
  • Ideally, specimens should be processed as soon as possible, within 2 hours of collection.


  • Staining is a crucial process in slide preparation where a dye is used to increase the contrast of the microorganisms, making them easier to see under a microscope.
  • Most commonly, the Gram stain is employed, which differentiates bacteria into Gram-positive (which retain the violet crystal stain) and Gram-negative (which do not retain the violet stain).
  • Further staining methods, such as Ziehl-Neelsen stain or Acid-fast stain, are used for specific types of bacteria.

Slide Preparation

  • There are two main types of slide preparation: wet mount and fixed smear.
  • Wet mounts are quick and easy to make, making them ideal for viewing live microorganisms and determining motility, but they dry out quickly and cannot be stained.
  • A fixed smear involves heat-fixing the specimen to the slide, which kills the cells but adheres them to the slide, allowing for staining and longer-term study.

Microscopic Examination

  • Once the slide is prepared and stained, it can be examined under a microscope.
  • Microscope binoculars should be properly adjusted to the user’s inter-pupillary distance, and the viewer should focus on the slide using the 10x objective, switching to the oil immersion lens (100x) for detailed viewing.
  • Cells can be measured, and the morphological characteristics, such as cell shape and arrangements, can be systematically observed and recorded.