NURS 2550H Chapter Notes - Chapter 1: Mycobacterium Tuberculosis, Phagocytosis, Hair Follicle
26 Jun 2018
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Week 1 Readings (sept. 11th) NURS 2550
Chapter 12- Infection and Disease
Symbiosis: describes a close relationship between 2 different types of organisms in a
community.
oMutualism: a relationship between 2 organisms in which both members benefit
from the interaction i.e. in the large intestine Escherichia coli releases vitamins
during the breakdown of nutrients that are not digestible by the human GI tract
but necessary for the survival of the bacteria.
oCommensalism: one of the organisms benefits and the other is neither harmed
nor helped. Many microorganisms in the normal flora of the human skin and
mucous membranes are commensals.
oParasitism: one organism benefits and the other is harmed, either slightly or to
such an extreme that the host will be killed. A parasite that can cause disease is
called a pathogen.
oAmensalism: one organism can hamper or prevent the growth and/or survival of
another, without being positively or negatively affected by the other organism
i.e penicillin.
Normal flora (microbiota):
oA newborn’s first contact with microorganisms occurs while travelling through
the birth canal. Next exposure with the beginning of breathing and is soon
followed by feeding.
oStarting at birth the human body enters a state of dynamic equilibrium with
microorganisms.
oThe microbes that establish themselves on the skin and mucous membranes
usually do not cause disease and constitute the normal flora of the human body.
Resident flora: remains part of the normal flora throughout the life of a
person.
Transient flora: can be found in the same locations as the resident flora
but remains in the body for only a few hours, days or months before it
vanishes. These organisms cannot survive for reasons such as
competition with other microorganisms for nutrients, elimination by the
host’s immune system or chemical and physical changes in the body of
the host.
*Probiotics: yogurt as medicine? (p.236)
Opportunistic pathogens: does not cause disease in its normal habitat in a healthy
person, but can cause infection under conditions of immune suppression, changes in the
normal flora, or when a member of the normal flora gains access into an area of the
body it normally does not habitat. (p.237)
STAGES OF INFECTION
Contamination: refers to the presence of microbes in or on the body, or on objects.
Contamination can reach the body in food or drink, by air, or by fomites (objects or
materials that are likely to carry infection, such as clothes, utensils, and furniture), or
they can be introduced by wounds, insect bites and sex.
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Week 1 Readings (sept. 11th) NURS 2550
oSome microbes remain at the site at which they first came in contact with the
body; they do not cause harm and become part of the normal flora or a transient
flora. To initiate an infection the microorganism must gain entry into the host
and its tissues.
Infection: refers to the presence and growth of a microorganism in the body with the
exception of organisms in/on the normal flora. Notably, an infection may or may not
cause disease.
Portal of entry: the site where a pathogen enters the body i.e. skin, mucous
membranes, the placenta, or the so-called parenteral route (administered or occurring
elsewhere in the body than the mouth and alimentary canal).
oThe source of the infectious agent can be exogenous, from outside the body, or
endogenous, in which case the organisms is already in the body such as in the
normal flora.
oi.e. influenza virus uses the respiratory mucosa as its portal of entry, where it
may successfully infect its host, but when limited to contact with the skin only,
the influenza virus will not cause infection.
*Some infectious agents can enter via more than one portal of entry.
oSkin: the outermost layer of the epidermis, the top layer of the skin, consists of a
thick layer of keratinized dead cells that provides the first line of defence against
microbial invasion. Some pathogens do however enter through hair follicle and
sweat gland openings in the skin. Damage to the skin can cause infection.
oMucous membranes: The GI tract serves as the portal of entry for pathogens
present in food, liquid and other ingested substances. Microorganisms that can
survive in the GI tract are adapted to the action of digestive enzymes and
environments that undergo drastic pH changes. The respiratory tract is the most
frequent used portal of entry. The urogenital tract is a portal of entry for
pathogens that are generally contracted by sexual contact. Close proximity of the
anus to the female urethra also causes increased risk for UTIs.
oPlacenta: usually an effective barrier against microorganisms that may be
present in the maternal circulation. Some microbes can pass this barrier and
infect the fetus. (p.239)
oParenteral route: in this manner, pathogens are introduced directly into the
subcutaneous tissue, as happens with punctures by a nail, thorn, or
contaminated needles.
Virulence and pathogenicity: after pathogens gained entry into the body they must
undergo adhesion and several other steps to be able to multiply and cause an infection
and possible disease.
oVirulence: refers to the degree of pathogenicity of a microbe.
oAdhesion: the 1st and most crucial step in infection, because without adhesion to
the host cells or tissue, the microbes will be removed by ciliary motion, sneezing,
coughing, swallowing, urine flow, flow of tears, or intestinal peristalsis.
Nonspecific and specific adhesion
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