What characteristic defines bacterial cells?

Bacterial cells are characterized by their lack of a membrane-bound nucleus, which distinguishes them from eukaryotic cells that do contain nuclei. Instead, the genetic material in bacteria is found in a region called the nucleoid, and the cells generally have a simpler structure. One common feature of many bacteria is the presence of a slime capsule, which can provide protection against desiccation and certain immune responses, and can help bacteria adhere to surfaces, forming biofilms.

This characteristic of having a slime capsule is prevalent among various bacteria but is not universal. The other statements regarding the presence of a nucleus, multicellularity, and membrane-bound organelles pertain to eukaryotic cells. Eukaryotes are complex cells that possess a nucleus and other organelles such as mitochondria and endoplasmic reticulum, whereas bacteria (prokaryotes) do not have these features. Therefore, having a slime capsule indeed highlights a distinct characteristic that can be observed in some bacterial cells.