Microorganism Colonization Of Host Surfaces

THE HOST'S PERSPECTIVE

Once a microbe and the human host are brought into contact, the outcome of the encounter depends on what happens during each step of interaction (see Figure 3-1), beginning with colonization. The human host's role in microbial colonization, defined as the persistent survival of microorganisms on a surface of the human body, is dictated by the defenses that protect vital internal tissues and organs against microbial invasion. The first defenses are the external and internal body surfaces that are in relatively direct contact with the external environment and as such are the body areas with which microorganisms will initially assodate. These surfaces include:

  • Skin (induding conjunctival epithelium covering the eye)
  • Mucous membranes that line the mouth or oral cavity, the respiratory tract, the gastrointestinal tract, and the genitourinary tract

Because body surfaces are always present and they protect against all microorganisms, skin and mucous membranes are considered constant and nonspedfic protection mechanisms. As is discussed in this text, other protective mechanisms are produced only in response to the presence of microbial agents (Le., indudble defenses) and some are specifically directed to particular microorganisms (i.ev specific defenses).

Skin and Skin Structures

Skin serves as a physical and chemical barrier to microorganisms; its protective charaderistics are summarized in Box 3-1 and Figure 3-3. The acellular, outermost layer of skin and tightly packed cellular layers underneath provide an impenetrable physical barrier to all microorganisms, unless damaged. Additionally, these layers continuously shed, thus dislodging bacteria that have attached to the outer layers. The skin is also a dry and cool environment that contrasts with the warm

Epidermis

Dermis

Subcutaneous tissue

Deeper tissues and internal organs

Figure 3-3 Skin and skin structures.

Epidermis

Dermis

Subcutaneous tissue

Deeper tissues and internal organs

BOX 3-1 Protective Characteristics of the Skin and Skin Structures

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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