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Chapter 7.
NORMAL FLORA
Tiana Milanda
Normal Flora
• Microorganisms that colonize a host
without causing disease
• Two types of normal flora exist :
– resident flora are microorganisms that
inhabit sites on the body for extended
periods
– transient flora are microorganisms that
are temporary
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RESIDENT FLORA
• Do NOT produce disease under normal conditions
• Includes bacteria, fungi, protozoa, viruses and arthropods in the most areas of the body in contact with the outside environment
• Large intestine has the highest numbers of bacteria
• Internal organs, tissues & fluids are microbe-free
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TRANSIENT FLORA
• Cling to the skin surface, but does not ordinarily grow on it.
• It is acquired by routine contact, and it varies markedly from person to person and over time.
• May be present for several days, weeks, or months, and then disappear.
• It is greatly influenced by the hygiene of the person.
• May or may not cause disease.
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RELATIONSHIP BETWEEN NORMAL
FLORA AND HOST
• Mutualism
• Commensalism
• Parasitism
Mutualism
• in this type of relationship, both
partners benefit
– E. coli synthesizes vitamin K in the
intestine
– in exchange the large intestine provides
nutrients necessary for survival of the
microorganisms
E. coli
Commensalism
• one organism is benefited and the other
is unaffected by this type of relationship
– many of the microorganisms that make up
our normal flora inhabit places like the eyes,
ears, and external genitalia
• these bacteria live on secretions and sloughed off
cells
• they bring no benefit to the host and yet the
microorganisms benefit greatly from the
environment they inhabit
Parasitism
• one organism benefits at the expense of the other
– all pathogens are parasites
• TRUE PATHOGENS – capable of causing disease in
healthy persons with normal immune defenses
– Influenza virus, plague bacillus, malarial
protozoan
parasitic microorganisms
Normal Flora
• the presence of normal flora
– cover potential adherence sites for invading
microorganisms
– consume the available nutrients
– produce compounds toxic to other
microorganisms
This is call microbial antagonism.
bacteria found on skin
Normal Flora
• when the balance between normal flora and pathogens
is upset, disease can result
– the normal bacterial microorganisms of the adult
human vagina maintain the pH at about 3.4 – 4.5
– the presence of this normal flora inhibits the
overgrowth of Candida albicans, yeast
– if the presence of the normal flora is eliminated by
antibiotics, or excessive douching, the pH of the
vagina becomes nearly neutral, creating an
environment very conducive to the growth of C.
albicans
C. albicans
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OPPORTUNISTIC FLORA
• Are potentially pathogenic organisms that do not cause disease in their normal habitat in a healthy person
• Organisms that gain access through broken skin or mucous membranes can cause opportunistic infections
• If the host is already weakened or com-promised by infection.
• Pseudomonas sp & Candida albicans
Table 13.4
Normal flora established during birth process.
Once established, composition of flora is
dynamic :
• Changes result from physiological variation
within the host
• Each member of flora ecosystem is
influenced by presence and condition of
other members
Dynamic nature of normal flora
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FLORA of the SKIN
• Staphylococcus, Micrococcus, Coryne-bacterium, Mycobacterium, Yeast.
• Most live in the upper dead layers of the epidermis, glands, and follicles.
• Present in sebaceous glands and hair follicles Propionibacterium acnes
• Dependent on skin lipids for growth.
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FLORA of the SKIN
• Epidermis region normally unsuitable for growth due to periodic drying
• Breach of barrier can lead to disease
• Factors that influence flora: weather, age of host, personal hygiene
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BACTERIA of the EYE
• The conjunctiva, a continuation of the skin and a mucous membrane, contains basically the flora of the skin.
• Staphylococcus aureus and Staphylococcus epidermidis.
• Lacrimal fluid contains mucus, antibodies, and lysozyme, an enzyme that destroys bacteria.
Flora of Oral Cavity
• Before teeth appear: streptococci and lactobacilli
• Teeth: change in microflora
• Streptococcus, Neisseria, Staphyloccoccus, Lactobaccillus, Actinomyces, Bacteroides.
• Saliva: lysozymes
• Food particles contributes to microbial growth
• Saliva creates a thin organic film of acidic glycoproteins which serves as a firm attachment site for microbes (anaerobic)
• Extensive attachment: dental plaque
• Resident microbes begin to release high concentrations of organic acids that decalcify enamel resulting in dental caries& gingivitis
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FLORA of the GASTROINTESTINAL
TRACT
• Stomach, small intestine
and large intestine
• Stomach fluids are highly
acidic and act as a
protective barrier
• Helicobacter pylori
normally colonizes
stomach wall but can
cause ulcers in
susceptible individuals
Flora of Gastrointestinal Tract
• Large intestine: cecum and colon
• Colon has a large number of
microbes exp. E.coli
• Obligate anaerobes predominate:
Clostridium, Bacteroides and
Enterococcus faecalis
• Intestinal flora carry out essential
metabolic reactions, exp. vitamin
B12 and K
• Antibiotic therapy can sometimes
lead to destruction of normal
microflora and lead to
opportunistic infections and disease
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FLORA of the UPPER
RESPIRATORY SYSTEM
• Enter upper respiratory tract
(nasopharynx, oral cavity and
throat) during respiration
• Trapped in nasal passage and
expelled with nasal
secretions
• Oral Streptococci,
Staphylococcus aureus,
Staphylococcus epidermidis,
Neisseria sp., and
Haemophilus.
• Most microbes are inhaled,
the filtered out, destroyed,
or expelled.
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FLORA of the LOWER
RESPIRATORY SYSTEM
• Lower respiratory tract
(lungs, bronchi and
trachea))
• Usually no permanent
residents are present.
Flora of Urogenital Tract
• In males and females bladder is sterile
• Epithelial cells lining the urethra tend to be colonized by gram-negative microbes
• Normal flora can multiply due to changes such as pH and cause disease
• Flora changes in female from childhood-adulthood–menopause (alkaline-acidic)
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FLORA of the URINARY SYSTEM
• Staphylococcus, Streptococcus, and coliforms.
• In females, flora exists only in the first portion of urethra, the remainder of the tract is sterile.
• In males, the entire reproductive and urinary tract is sterile except for a short portion of the
anterior urethra.
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FLORA of the REPRODUCTIVE
SYSTEM
• In females and males,
flora occupies the external
genitalia.
• Internal reproductive
structures normally remain
sterile.
• Lactobacillus,
Streptococcus,
Corynebacterium,
Mycobacterium.
• Candida albicans