Question

which of the following methods could not be used to sterilize broth in a flask?

a. heating in an oven

b. autoclaving

c. boiling

d. tyndallization

Answer 1

Answer: option a - heating in an oven.

Explanation:

1). Autoclaving is the process of heating the substance at 121 degree celsius at 15 psi pressure in a closed vessel (autoclave). it is a form of steam sterilisation. It is the best method for sterilising broth, as it kills heat resistant bacteria as well as their spores. It is widely used in labs.

2). Although, boiling is not the best method for sterilization since it does not kill the spores of bacteria, but it may be used for common classroom usage when the broth does not have to be stored for long (1-2 days).

3). Tyndallization is a relatively old fashioned method of sterilization used generally when time is not a constraint, or for pressure-sensitive substances. In this method, the broth is heated to a boiling(or slightly lower) temperature and held for a longer time(about 15 min). The spores that survive, are allowed to germinate and subjected to the same heating process. this is done for three days until all heat resistant spores are sterilised.

4). Heating in an oven is not used for sterilisation as this method is unable to kill spores of bacteria although the vegetative microbes may be killed. This form of dry heating is only effective for sterilisation of glassware, but not suitable for broth contained in a flask.