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nester19 - Important Point Basically every surface(except...

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1 Chapter 19: Host-Microbe Interactions Important Point: Host-Microbe Interactions “Relatively few microbes are able to inflict any noticeable damage, invading tissues or producing toxic substances,” which is fortunate considering that microbial cells living on the human body, our Normal Flora, outnumber our own cells. “Those minority of microorganisms that can cause us harm we call Pathogens.” To immunocompromised individuals the subset of microbes that are potentially pathogenic is larger than for those whose defenses are fully intact. Host compromised or not, pathogens “have distinct patterns of interaction with the host that enable them to have the upper hand in the relationship and elude at least some of the body’s defenses.” “This chapter will explore some of the ways in which microbes colonize the human host, living either as members of the normal flora in harmony with the host or subverting the host defences and causing disease.” Normal Flora Normal flora are helpful to us for a number of reasons including supplying nutrients, priming our adaptive immunity, and protecting us from pathogens. Normal flora may be differentiated in terms of the duration of their residence in/on our bodies. Resident Flora persists with us for relatively long times, often colonizing us early in life and persisting until death (plus passing on from parent to offspring). Transient Flora, on the other hand, persists for only relatively short periods. Among transient flora are those organisms that come into contact with us but never successfully colonize. One reason for this transience is that resident flora already occupy niches (space, food) that consequently are denied to transients. Normal Flora Locations & Species Note that much of those locations not mentioned are sterile in healthy individuals. Basically every surface (except deep lungs and, perhaps, the stomach). Antibiotic-Associated Superinfection Among those flora denied residence by normal flora are potential pathogens. Thus normal flora can play a protective role by preventing pathogen colonization. Circumstances where normal flora are disrupted, such as following antibiotic treatment, therefore can result in disease (a superinfection). One common superinfection is the overgrowth of the yeast Candida albicans following the antibiotic- mediate destruction of vaginal Lactobacilli.
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