Detection Of Bacteria In Spoiled Tinned Food

Generally food is spoiled due to four important reasons. During packing, (i) the poor knowledge to the packer, (ii) mishandling the raw materials before packing resulting high level of contamination, (iii) failure of proper equipment functioning, and (iv) defects in containers spoiled the tinned food. While opening such food containers, a bad smell and acidic taste indicate the food spoilage. Such spoiled food imparts acid and gas production. Sometimes, the tin or the packed item may start swelling due to gas (CO₂, H₂ but not H₂S) formation by anaerobic thermophilic microorganisms. In many cases, the food contents become blackened due to H₂S reaction with iron content of the container material. Common food spoilage occurs due to both aerobic and anaerobic endospore formers of bacilli and clostridia as well as non-spore forming bacteria.

Requirements

• Food materials to be tasted
• Gram’s stain
• Endospore stain.

Procedure

1. Collect such food items from any shop, home, etc. and bring it to the laboratory.
2. Transfer a small amount in pre-sterilised beaker through the opening.
3. Prepare Gram-stained and endospore-stained slides from the sample (liquid/semisolid)
4. Examine these slides in a bright field oil immersion.

Result

The presence of spore and cells of Gram-stained bacteria indicates the bacteriological food spoilage. The tinned food can also be made spoiled by artificial inoculation with Clostridium thermosaccharolyticum, Clostridium sporogenes, Bacillus coagulans, Bacillus stearothermophilus or E.coli.

Reference:

Dr. R. C. Dubey – Practical Microbiology