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Virulence: The degree of pathogenicity within a group or species of microorganisms or viruses as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenic capacity of an organism is determined by its Virulence factors.

Lysogenic Cycle of Bacteriophages

JoVE 10824

In contrast to the lytic cycle, phages infecting bacteria via the lysogenic cycle do not immediately kill their host cell. Instead, they combine their genome with the host genome, allowing the bacteria to replicate the phage DNA along with the bacterial genome. The incorporated copy of the phage genome is called the prophage. Some prophages can re-activate and enter the lytic cycle. This often occurs in response to a perturbation, such as DNA damage, but can also transpire in the absence of external cues. In some cases, the genes encoded by prophages can alter the phenotype of the infected bacterium, a process known as lysogenic conversion. Some phages encode proteins or toxins called virulence factors that can facilitate bacterial infections. Through lysogenic conversion, normally non-pathogenic bacteria can become highly virulent via infection by a phage carrying virulence factors. For example, such phages are largely responsible for the pathogenicity of the bacterial species that cause botulism (Clostridium botulinum), diphtheria (Corynebacterium diphtheriae), and cholera (Vibrio cholerae). Without lysogenic conversion, these bacteria do not usually cause disease. A particularly well-studied example of lysogenic conversion is that of the Escherichia coli strain O157:H7. Several massive food recalls have stemmed

 Core: Biology

Compound Administration I

JoVE 10198

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN


As many research protocols require that a substance be injected into an animal, the route of delivery and the amount of the substance must be accurately determined. There are several routes of administration available in the mouse and rat. …

 Lab Animal Research

Introducing Experimental Agents into the Mouse

JoVE 5161

Many investigations performed in mice (Mus musculus) require the administration of an experimental agent to the animal. For example, it may be of interest to test the efficacy of a specific therapy, to induce a pathologic condition, or to administer anesthesia or palliative care. In order to ensure safe and efficient delivery, it is important to consider a variety of factors prior to…

 Biology II
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