Explain the Glass Test Tubes - Food Microbiology

Sterile glass tubes are used for culturing microorganisms in liquid or solid media. Sterility in tubes is maintained by using cotton plugs developed by Schroeder & Von Dusch or by heat resistant plastic and metal caps. (a). Metal caps have the advantage over the cotton plugs as: (i) these save labour, and (ii) slip on and off the test tubes easily.

Solid media in test tubes can be used to make agar slants or deep tubes (b). Agar slants are prepared by allowing liquefied solid media to harden in the slanted position. These provide more surface area for culturing than deep tubes and are used for maintaining the pure microbial cultures. Agar slants have an advantage over the petri plate as: (i) it is easy to store and transport, and (ii) less readily contaminated. Agar deep tubes are prepared by allowing liquified solid media to harden in the upright position (b). These are used to (i) study the gaseous requirement of microorganism, or (ii) preparing agar plates after liquefecation.