How would your plates appear if you incubated agar when they

How would your plates appear if you incubated agar when they were contaminated? What about if they weren\'t?

Solution

Ans. Incubating a contaminated plate shows microbial growth. Incubation of a sterile plate (no contamination, no inoculation) shows no microbial growth.

In case of an inoculated plate- the contaminated plate (contaminated with microbes other than those present in inoculum) show much rapid and outgrowth of many undesirable colonies. When not contaminated, the same inoculated plate shows less number of colonies and clearly separated (most often) colonies.

Sometimes it’s preferred to incubate inoculated plates as a control. The control plate serves the following purpose-

I. Since this plate is not inoculated, there shall be no microbial growth on the plate after incubation period. If so, absence of microbial growth on plate indicates that the all steps, from media preparation to inoculation chamber, follows aseptic techniques and are reliable and reproducible.

II. If an uninoculated plate show microbial growth, contamination has occurred at one or more steps. Moreover, the cultural techniques adopted need to be recalibrated thoroughly.