- published: 22 Apr 2012
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A pathogen (Greek: πάθος pathos, "suffering, passion" and γενής genēs (-gen) "producer of") or infectious agent — in colloquial terms, a germ — is a microorganism such as a virus, bacterium, prion, or fungus, that causes disease in its animal or plant host. There are several substrates including pathways wherein pathogens can invade a host; the principal pathways have different episodic time frames, but soil contamination has the longest or most persistent potential for harboring a pathogen.
Not all pathogens are negative. In entomology, pathogens are one of the "Three P's" (predators, pathogens, and parasitoids) that serve as natural or introduced biological controls to suppress arthropod pest populations.
Pathogenic viruses are mainly those of the families of: Adenoviridae, bacteria Picornaviridae, Herpesviridae, Hepadnaviridae, Flaviviridae, Retroviridae, Orthomyxoviridae, Paramyxoviridae, Papovaviridae, Polyomavirus, Rhabdoviridae, Togaviridae. Viruses typically range between 20-300 nanometers in length.
Stanley Falkow, PhD, (born 1934 in Albany, New York) is microbiologist and a professor of microbiology and immunology at Stanford University School of Medicine. He is sometimes referred to as the father of molecular microbial pathogenesis, which is the study of how infectious microbes and host cells interact to cause disease at the molecular level. He formulated molecular Koch's postulates, which have guided the study of the microbial determinants of infectious diseases since the late 1980s. It was while she was at Walter Reed visiting his mentor Lou Baron, that Falkow met Esther Lederberg, one of the leading researchers elucidating the relationship between plasmids and antibiotic resistance. (He would later become her Department Chairman at Stanford in 1981.)
Falkow received his B.S. degree from the University of Maine, graduating cum laude, and went on to earn his Ph.D. from Brown University. Following the completion of his graduate studies, Dr. Falkow went on to become a staff member at the Walter Reed Army Institute of Research (WRAIR) in the Department of Bacterial Immunology where he was eventually named the assistant chief of the department. Dr. Falkow's early work in the 1960s focused on the genetic mechanisms that enable populations of bacteria to become resistant to antibiotics. He demonstrated that organisms, such as shigella, can possess gene fragments called plasmids that exist apart from the bacterial chromosome and that they carry specialized information for survival. Under selective pressure from antibiotics, one species of bacteria can pass its plasmids to another unidirectionally rather than by mating, thereby preserving its own specialized survival genes.