Differentiate between colonization infection and disease Chapter 11 Disease is defined as any deviation from health Infectious disease is the disruption of a tissue or organ caused by microbes or their products The pattern of the host parasite relationship can be viewed as a series of stages that begins with contact progresses to infection and ends in disease Because of numerous factors relating to host resistance and degree of pathogenicity not all contacts lead to colonization not all colonization lead to infection and not all infections lead to disease In fact contamination without colonization and colonization without disease are the rules Enumerate the sites where normal biota is found in humans The large and mixed collection of microbes adapted to the body has been variously called the normal resident biota or indigenous biota though some microbiologists prefer to use the term normal flora The normal residents include an array of bacteria fungi protozoa and to a certain extent viruses and arthropods Most normal healthy body surfaces such as the skin large intestine outer openings of the urogenital tract and oral cavity provide numerous habitats for a virtual garden of microorganisms Discuss how the Human Microbiome Project will change our understanding of normal biota Since it has become known that there are more unknown than known species that populate the human body an effort is now underway to utilize metagenomics to identify the microbial profile inside and on humans The Human Microbiome Project began in 2007 o The aim of this project is to collect genetic sequences in the gut respiratory tract skin and so on to determine which microbes are there even when they can t be grown in the laboratory o A secondary aim is to determine what role these normal biota play in health and o When the project is completed the information that we know now will be very disease different Point out how microbial antagonism can be helpful to the human host The human body offers a seemingly endless variety of environmental niches with wide variations in temperature pH nutrients and oxygen tension occurring from one area to another o Because the body provides such a range of habitats it should not be surprising that the body supports a wide range of microbes o Most areas of the body in contact with the outside environment harbor resident microorganisms while internal organs and tissue along with the fluids they contain are generally microbe free The vast majority of microbes that come in contact with the body are removed or destroyed by the host s defenses long before they are able to colonize a particular area Of those microbes able to establish an ongoing presence an even smaller number are able to remain without attracting the unwanted attention of the body s defenses o This last group of organisms has evolved along with its human hosts to produce a complex relationship in which its effects are generally not damaging to the host Normal biota are generally either in a commensal or a mutualistic association with their hosts o Although generally stable the biota can fluctuate to a limited extend with general health age variations in diet hygiene hormones and drug therapy The generally antagonistic effect good microbes have against intruder microorganisms is called microbial antagonism Normal biota exist in a steady established relationship with the host and are unlikely to be displaced by incoming microbes This antagonistic protection is partly the result of a limited number of attachment sites in the host site all of which are stably occupied by normal biota o Antagonism is also augmented by the chemical or physiological environment created by the resident biota which is hostile to most other microbes Characterizing the normal biota as beneficial or at worst commensal to the host presupposed that the host is in hoof health With a fully functioning immune system and that the biota is present only in its natural microhabitat within the body Hosts with compromised immune systems could very easily experience disease caused by their previously normal biota Factors that weaken host defenses and increase susceptibility to infection include the following o Old age and extreme youth infancy prematurity o Genetic defects in immunity and acquired defects in immunity AIDS o Surgery and organ transplants o Underlying disease cancer liver malfunction diabetes o Chemotherapy immunosuppressive drugs o Physical and mental stress o Pregnancy o Other infections Differentiate between pathogenicity and virulence A microbe whose relationship with its host is parasitic and results in infection and disease is termed a pathogen The type and severity of infection depend both on the pathogenicity and the condition of the host Pathogenicity is a broad concept that describes and organism s potential to cause disease and is used to divide pathogenic microbes into one of two groups o True pathogens primary pathogens are capable of causing disease in healthy persons with normal immune defenses They are generally associated with a specific recognizable disease which may vary in severity from mild colds to severe malarial to fatal rabies Examples of true pathogens include the influenza virus plague bacillus and malarial protozoan o Opportunistic pathogens cause disease when the host s defenses are compromised or when they become established in a part of the body that is not natural to them Opportunists are not considered pathogenic to a normal healthy person and unlike primary pathogens do not generally possess well developed virulence properties Examples of opportunistic pathogens include Pseudomonas species and Candida albicans The relative severity of the disease caused by a particular microorganism depends on the virulence of the microbe Although the terms pathogenicity and virulence are used interchangeably virulence is the accurate term for describing the degree of pathogenicity The virulence of a microbe is determined by its ability to o Establish itself in the host o Cause damage To establish themselves in a host microbes must enter the host attach firmly to host tissues and survive the host defenses To cause damage microbes produce toxins or induce a host response that is actually injurious to the host Any characteristic or structure of the microbe that contributes to the preceding activities is called a virulence factor o Virulence can be due to single or multiple factors In some microbes the causes of virulence