This is a superbug

The correct option is bacteria.

The term "superbug" is a colloquial and widely used term in medicine and biology to describe strains of bacteria, viruses, parasites, or fungi that have developed resistance to most of the antibiotics and other medications commonly used to treat the infections they cause.
However, in everyday language and primary scientific contexts, it most commonly and specifically refers to antibiotic-resistant bacteria (such as Methicillin-resistant Staphylococcus aureus, or MRSA). Therefore, among the choices provided (virus, transgenic plant, worms, bacteria), "bacteria" is the most accurate and appropriate classification for a superbug.