Final answer:
The contamination in the forgotten soup container in the refrigerator is probably caused by bacteria, which are common culprits of foodborne illnesses.
Step-by-step explanation:
The contamination of a soup container that was forgotten in the refrigerator is likely caused by microorganisms such as bacteria, which are commonly responsible for foodborne illnesses. These illnesses are colloquially known as 'food poisoning' and can result from the consumption of food contaminated with pathogenic bacteria, viruses, fungi, or parasites. Given the suitable conditions for bacterial growth in food left in the fridge, bacteria are probably the contaminants in this scenario.
Outbreaks of bacterial infection related to food consumption are quite common. Microorganisms like Salmonella, Escherichia coli (E. coli), Listeria monocytogenes, and Campylobacter jejuni are some of the bacteria that lead to these illnesses and can be found in a variety of contaminated foods.