Microbiology emerged from Pasteur and Koch's bacterial research in late 1800s. Bacteria are prokaryotic single-celled organisms without membrane-bound nucleus. Woese's 1977 discovery divided bacteria into eubacteria, archaea, and eukarya. Bacteria range in width from 0.5 to 5 micrometres and can be shaped like spheres. Archaea lack peptidoglycan in cell walls and can survive extreme environments
Symbiotic bacteria live in relationships with other organisms or each other. Endosymbionts live inside other organisms, explaining eukaryotic evolution. Ectosymbiosis occurs when one organism lives on another's surface
Foodborne illness results from contamination by bacteria, viruses, parasites, or toxins. Symptoms include vomiting, fever, aches, and diarrhea. Incubation period ranges from hours to days depending on pathogen. Bacteria multiply rapidly between 40-140°F (4-60°C)
Unicellular organisms consist of a single cell, unlike multicellular ones. Most prokaryotes are unicellular, including bacteria and archaea. Unicellular organisms are thought to be the oldest form of life. Early protocells emerged 3.5-4.1 billion years ago
Fewer than a hundred pathogenic bacteria exist in humans. Most bacteria are harmless commensals or saprophytes. Pathogenic bacteria can overcome normal body defenses
Pathogens are tiny organisms that cause diseases in the body. Main types include bacteria, viruses, fungi, and protozoa. Not all pathogens are harmful, some help the body