Micro Chapter 12.docx - CHAPTER 12 INFECTION AND DISEASE Symbiosis Describes a close relationship between two different types of organisms in a

Micro Chapter 12.docx - CHAPTER 12 INFECTION AND DISEASE...

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CHAPTER 12 INFECTION AND DISEASE Symbiosis Describes a close relationship between two different types of organisms in a community Symbiosis can be classified as mutualism, commensalism, parasitism, or amensalism Mutualism - Both members benefit from the interaction - In humans, Escherichia coli releases vitamins during the breakdown of nutrients that are not digestible by the human gastrointestinal (GI) tract but necessary for the survival of the bacteria. The vitamins released by E. coli can easily be absorbed by the intestinal epithelium of the human large intestine . Symbiosis (Cont (. Commensalism - One organism benefits, and the other is neither harmed nor helped - E.g. saprophytic mycobacteria that inhabit the ear and external genitals, living on secretions and removed cells Parasitism - One organism benefits while the other is harmed slightly or may be killed - Pathogen: A parasite that causes disease Amensalism - One organism can hamper or prevent the growth/survival of another without being affected by the other organism - Penicillium,a mold that secretes penicillin, a chemical capable of killing a wide range of bacteria . Normal Flora ( Microbiota ( Newborns first contact to microbes—birth canal- Lactobacilli residing in the
mother s vagina becomes the predominant organisms in the the newborn ’s intestine Followed by breathing Followed by feeding Throughout life microbes will establish residency in mucous membranes open to the environment Normal Flora (Cont (. Resident flora - Remain part of the normal flora throughout life of a person e.g. Staphylococcus epidermidis(skin ( Transient flora - Found in the same locations as a resident microbe - Only remain for a few hours, days, or months before they vanish Opportunistic Pathogens Pathogen —a microorganism that is capable of causing disease Balance between normal flora and human host is maintained When balance is interrupted—microbes of the normal flora can become opportunistic pathogens These organisms do not cause disease in their normal habitat in a healthy person Opportunistic Pathogens (Cont (. Compromised immune system Changes in the normal flora - Normal flora is usually protective - Competition no longer exists Entrance of the normal flora into areas of the body where it is not present under normal conditions Stages of Infection
Contamination - Presence of microbes in or on the body Infection - The microorganism has to gain entry into the host and its tissue - An infection does not necessarily cause disease Portals of Entry Sites where pathogens enter the body Source of infection can be exogenous or endogenous Exogenous —from outside the body Endogenous —organism is already in the body (e.g., normal flora ( Portals are generally the same areas that support normal flora Majority of pathogens have their preferred portal of entry If pathogen enters the wrong portal, infection will not occur Some infectious agents enter via more than one portal Portals of Entry Skin - Thick layer of keratinized dead cells -

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