Notes Bacteria are small, single cells and are the only ones characterized by prokaryotic organization. Too tiny to see with the naked eye, a bacterial cell is usually one of three basic shapes; bacillus, a rod shaped cell; coccus, a spherical cell; or spirillum, a spiral cell. A few kinds of bacteria aggregate into stalked structures or filaments. A bacterium's plasma membrane is encased within a cell wall. Members of the kingdom Eubacteria have a …
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…from bacteria, a fungi that is used as a drug to fight pathogenic microorganisms. Antibiotics work by interfering with the microorganism's cellular processes. In most cases, this includes preventing cell wall formation, breaking up cell membranes, or disrupting chemical processes. Because these processes do not occur in viruses, antibiotics cannot be used for fighting viral diseases. Since penicillin's discovery, other antibiotics such as tetracycline, streptomycin, and ampicillin have been discovered in nature or produced chemically.