Multiple choice Which of the following is the largest bacterium in the world? Bdellovibrio Thiomargarita namibiensis Helicobacter pylori Epulospiscum fishelsoni Reveal answer Fill a bubble to check yourself B Correct answer Explanation Thiomargarita namibiensis means sulphur pearl of Namibia. It is the largest bacterium in the world. It is visible to the naked eye as a speck of size 3 - 4 mm.