bacterium
n. (pl.
bacteria) a unicellular, prokaryotic microorganism, that is, an organism whose chromosome is not contained in a nuclear envelope. Bacteria are considered to represent an earlier stage in the evolution of life than eukaryotes (organisms whose chromosomes are contained in nuclear envelopes, i.e., all organisms except bacteria). In humans, many bacteria cause disease (e.g., tetanus, syphilis, tuberculosis), whereas others are beneficial (e.g., preventing the growth of harmful microbes in the large intestine and enhancing the immune response). —bacterial
adj.