Bacterial Pathogenicity Flashcards
what is a pathogen
a microorganism that is able to cause disease in a plant, animal or insect.
what is pathogenicity
Pathogenicity is the ability to produce disease in a host organism. Microbes express their pathogenicity by means of their virulence, a term which refers to the degree of pathogenicity of the microbe
what are determinants of virulence
the determinants of virulence of a pathogen are any of its genetic or biochemical or structural features that enable it to produce disease in a host.
discuss relationship between host and pathogen
The relationship between a host and a pathogen is dynamic, since each modifies the activities and functions of the other. The outcome of such a relationship depends on the virulence of the pathogen and the relative degree of resistance or susceptibility of the host, due mainly to the effectiveness of the host defense mechanisms.
Two broad qualities of pathogenic bacteria underlie the means by which they cause disease: what are they
invasiveness and toxogenesis
what is invasiveness
Invasiveness is the ability to invade tissues. It encompasses mechanisms for colonization (adherence and initial multiplication), production of extracellular substances which facilitate invasion (invasins) and ability to bypass or overcome host defense mechanisms
what is toxogenesis
Toxigenesis is the ability to produce toxins. Bacteria may produce two types of toxins called exotoxins and endotoxins. Exotoxins are released from bacterial cells and may act at tissue sites removed from the site of bacterial growth. Endotoxins are cell-associated substance
what are Koch’s Postulates
- the microorganism or other pathogen must be present in all cases of the disease
- the pathogen can be isolated from the diseased host and grown in pure culture
- the pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal
- the pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen
describe adhesion
adhesion is where bacterial proteins and carbohydrates bind to host structure to promote bacterial adherence. pathogens have developed multiple strategies for attachment which span into 3 categories
1. Transient association with mucus
2. Weak association with host carbohydrates
3. Strong association with host surface proteins.
adhesion of bacteria to the host surface is a key element in the formation of biofilms
bacterial adherence or attachment to a eucaryotic cell or tissue surface requires the participation of two factors: a receptor and a ligand.
The mechanisms for adherence may involve two steps:
1. nonspecific adherence: reversible attachment of the bacterium to the eucaryotic surface -nonspecific attractive forces which allow approach of the bacterium to the eucaryotic cell surface
2. specific adherence: irreversible permanent attachment of the microorganism to the surface - involves permanent formation of many specific lock-and-key bonds between complementary molecules on each cell surface
describe invasion
The invasion of a host by a pathogen may be aided by the production of bacterial extracellular substances which act against the host by breaking down primary or secondary defenses of the body. Medical microbiologists refer to these substances as invasins. Most invasins are proteins (enzymes) that act locally to damage host cells and/or have the immediate effect of facilitating the growth and spread of the pathogen. The damage to the host as a result of this invasive activity may become part of the pathology of an infectious disease.
describe dispersal
“Spreading Factors” is a descriptive term for a family of bacterial enzymes that affect the physical properties of tissue matrices and intercellular spaces, thereby promoting the spread of the pathogen.
what are virulence factors
Virulence factors are molecules produced by pathogenic bacteria, viruses, fungi, and protozoa that add to their effectiveness and enable them to achieve the following:
- colonization of a niche in the host (this includes attachment to cells)
- immunoevasion, evasion of the host’s immune response
- immunosuppression, inhibition of the host’s immune response
- entry into and exit out of cells (if the pathogen is an intracellular one)
- obtain nutrition from the host
describe basic principles of innate immunity
The innate immune system is the first line of defense that consists of a group of cellular and humoral factors. The cellular component of innate immunity includes NK T cells, mast cells, eosinophils, basophils, macrophages, neutrophils and dendritic cells (DCs), while the humoral factors primarily include cytokines and complement. The major functions of the innate immune system include recruiting immune cells into sites of infection, activation of complement, identification of foreign substances and preparation and activation of the adaptive immune systems. Innate responses are immediate, maximal and antigen independent. In the absence of stimulation, nonactivated innate cells are well known to maintain tolerance and prevent inappropriate immune activation.
