Microbiology is the study of microbes i.e. the organisms which we can’t see with the naked eyes. Although many microorganisms are beneficial for the human use, some are pathogenic also which causes diseases. Clinical Microbiological Laboratory is concerned with finding of those infectious, pathogenic microbes.

Laminar flow hood, Incubator, Autoclave, Refrigerator, Bunsen Burner, Wire loop, Petri plates, Glass slides, Weighing balance, Media plates, Sensitivity disks, Staining rack, Microscope, Bio safety Cabinet, Centrifuge etc.

Some of the media used in the microbiology lab are :

  1. MacCONKEY AGAR : It is the selective and differential media used for the isolation of Gram-negative Bacteria. This media can be used for differentiating Lactose fermenting and Non-lactose fermenting bacteria.
  2. BLOOD AGAR : It is the enriched media for the growth of bacteria such as streptococci.
  3. CHOCOLATE AGAR : It is the lysed Blood Agar. The only difference in blood agar and chocolate agar is that in blood agar RBCs are lysed. This enriched media is suitable for the growth of bacteria that are unable to grow on Blood Agar.
  4. THIOSULFATE CITRATE BILE SALT AGAR (TCBS) : It is the selective as well as differential media for the growth of vibrio cholerae , a causative organism for cholera.

Gram staining is the process for differentiating Gram positive and Gram negative bacteria. When the whole procedure of gram stain is followed and the slide is observed under the microscope, Gram positive bacteria appear Violet in color and Gram negative bacteria appear Pink in color.
For the gram staining we need Glass slide, Normal Saline, Inoculating loop, Bunsen burner, Crystal Violet, Gram’s Iodine, Acetone, Safranine.


  1. The isolated colony of the microorganism is taken and in the drop of normal saline on the glass slide the colony is mixed with the help of inoculating loop to make a smear. The prepared smear is heat fixed.
  2. A staining rack is taken and on the smear, Crystal Violet is added. After 1 minute, the stain was removed by washing the slide in running water.
  3. After that, Gram’s Iodine is added on the smear as a decolorizing agent which is again washed after 1 minute under the running tap water.
  4. The next step is to add Acetone on the smear which is added in the hand to hand process.
  5. After the decolorisation is done, Safranine is added on the smear which is also washed after 1 minute.
  6. The glass slide is then air dried and observed under the microscope.

It was observed under the microscope that the Gram positive bacteria appear Violet in color due to Crystal Violet stain whereas Gram negative bacteria appear Pink in color due to safranine.

The tests analyzed in the microbiology section of the laboratory are basically the culture and sensitivities tests of urine, stool, sputum, pus swab etc.
The basic procedure of performing all the tests are :

  1. First of all, all the tests are performed inside the laminar flow hood.
  2. The samples collected from the patients and the media plates are kept inside the laminar flow.
  3. The inoculating wire loop is heat sterilized and with the help of it, the samples are cultured or streaked on the media plates.
  4. After inoculation, the cultured media plates are incubated for 24 hours (48 hours if necessary) for allowing the growth of bacteria.
  5. After the growth, staining is done or sensitivities are checked according to the requirement by the doctor.
  6. The report is prepared for the patient.