Transcript Normal Flora What’s growing on us? Normal flora (mostly bacteria)  In the past Medical Microbiology was largely focused on   those organisms that.

Normal Flora
What’s growing on us?
Normal flora (mostly bacteria)
 In the past Medical Microbiology was largely focused on
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those organisms that were frankly pathogenic.
It is now known that those microorganisms that normally
colonize the human host without disease production can
play an important role in the disease process.
Many of those once considered to be innocuous
members of the normal flora are now known to be
potentially pathogenic under certain circumstances (what
circumstances?). Therefore, it’s important to acquire
knowledge about our normal flora because:
Normal Flora
 An understanding of the different normal flora
(NF) found at specific body locations provides
greater insight into the possible infections that
might result from injury to those body sites.
 A knowledge of the native organisms in the
infected part of the body gives the clinician
perspective on the possible source and/or
significance of microorganisms isolated from
the site of infection.
Normal Flora
 Before a discussion of adult NF begins, a
discussion of how or when NF is acquired is
essential.
 A healthy fetus, in utero, is essentially free of
microorganisms.
 The infant is exposed to NF from the mom’s vaginal
tract during the delivery process and to
microorganisms in the environment almost
immediately thereafter.
Normal Flora
 Within a few hours, the oral and
nasopharyngeal flora of the neonate are
established.
 Within one day the resident microflora of the
lower intestinal tract are established.
 Adult NF refers to microorganisms that
normally live on or in any part of the body
without causing disease. There are two
basic types of NF:
Normal Flora
 Resident organisms – these are organisms
that normally GROW on or in the indicated
body site. Their presence becomes fixed in
well defined distribution patterns.
 Transient organisms – These organisms are
only temporarily present on or in the indicated
body site. They usually don’t become firmly
entrenched, but simply die within a few hours.
Normal Flora
 NF of the skin
 The actual physiology of the skin varies from one part
of the body to another and the resident microflora
reflect these variations.
 The skin, itself, is not a very favorable environment
for the colonization of microorganisms.
 Therefore, there are few resident microorganisms, but
many transient microorganisms. Why is the
microenvironment hostile?:
Normal Flora
 The skin is subject to periodic drying. However, in
certain parts of the body (body folds or areas near
orifices), there is sufficient moisture to support the
growth of resident microorganisms
 Skin has a slightly acidic pH due to organic acids
produced by normal secretions from the sebaceous
and sweat glands and by Staphylococcus epidermidis
that normally resides there. This prevents the
colonization by many organisms.
 Sweat contains a high content of NaCl, thus
producing a hypertonic condition on the skin surface
that osmotically stresses many microorganisms.
Normal Flora
 The skin surface contains many inhibitory substances
that help control colonization, overgrowth, and
production of infectious disease by resident
microorganisms. Remember that colonization does
not necessarily mean infection and disease.
 Lysozyme – is produced by the sweat glands and acts to lyse
G+ organisms, including Staph. epidermidis
 Complex lipids – are metabolized by Propionobacterium
acnes to unsaturated fatty acids that have antimicrobial
activity. These produce a strong odor. Use of deodorants
that have antibacterial substances to inhibit the growth of
these G+ organisms may lead to the growth of a
preponderance of G- organisms and the subsequent
development of infection.
Normal Flora
 Most skin NF are found on the superficial
squamous epithelium colonizing dead cells
or closely associated with the sebaceous
and sweat glands. The secretions from
these glands provide the environmental
conditions and nutrients for the growth of:
Skin Normal Flora
Staph. epidermidis and Staph. aureus
Skin NF
Propionibacterium acnes – this is an
anaerobic G+ branching bacillus
Skin NF
 P. acnes is usually harmless, but has been associated
with acne vulgaris (acne), particularly during
adolescence when there is an overproduction of the
fluid secreted by the sebaceous glands (sebum).
 This provides the ideal environment for the growth of P.
acnes and substances produced by the organisms may
trigger an inflammatory response leading to the production
of acne.
 Tetracycline or accutane (prevents sebum secretions, but has
some severe side effects) may be used for treatment of
acne.
Skin NF
Diphtheroids (aerobic corynebacterium)
Skin NF
Streptococcus species
Skin NF
Clostridium perfringens
Skin NF
Candida albicans
Normal Flora
 Normal flora of the nose and nasopharynx (part
of the pharynx above the soft palate)
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Staph aureus*
Staph epidermidis
Diphtheroids
Streptococcus pneumoniae*
Haemophilus influenzae*
Neisseria meningitidis*
* may be causing disease if found in large numbers
(relative numbers are important)
Nose/nasopharynx NF
Neisseria meningitidis
Nose/nasopharynx NF
Haemophilus influenzae
Normal Flora
 Normal flora of the oral cavity and oropharynx
 Organisms found are those that are able to resist
mechanical removal by adhering to various surfaces
such as the gums and teeth.
 Those bacteria that can’t resist the mechanical flushing of
the oral cavity are swallowed and destroyed by the HCl in the
stomach.
 This is a comfortable environment for microorganisms
due to the availability of water and nutrients. The
most common NF in this area includes:
Normal oral flora
 viridans group Streptococcus species
 Strep. pyogenes*
 Diphtheroids
 Staph. epidermidis
 Staph. aureus*
 Neisseria meningitidis*
 Other Neisseria species
 Haemophilus influenzae*
 Other Haemophilus species
Normal oral flora
 Candida albicans*
 Actinomycetes sp.*
 Lactobacillus sp.
 Bacteroides sp.
 Fusobacterium sp.
 Enterobacteriaceae*
 * these organisms are probably causing infection if
they are the predominant organism found in this
area or they are found in large numbers.
Normal oral flora
Actinomycetes
Normal oral flora
Granules of Actinomycetes
Normal oral flora
Bacteroides sp.
Normal oral flora
Fusobacterium sp.
Normal oral flora
Fusobacterium nucleatum
Normal oral flora
Lactobacillus
Normal oral flora
E. coli (a member of the
Enterobacteriaceae)
Normal oral flora
Some of the Strep. species that adhere to the teeth
(sanguis, mutans, salivarious) contribute to the
formation of dental plaques and caries
Normal Flora
 Normal flora of the alimentary tract
 Because of the high acidic content of the stomach,
very few organisms are found there. They include:
 Candida sp.
 Lactobacilli
 A few Strep. sp. (mainly Enterococcus faecalis)
 The small intestine also has few microorganisms
because of the combined inhibitory effects of stomach
acid, bile, and pancreatic secretions. Normal flora
include:
Normal intestinal flora
 Enterococcus faecalis
 Lactobacilli
 Diphtheroids
 Candida sp.
 The large intestine has the largest microbial
population in the body. There are 1012
organisms excreted per gram of wet weight
feces.
 Over 300 different species of bacteria are
normally found in the large intestine
Normal intestinal flora
 The anaerobic/facultatively anaerobic ratio of
organisms is 300/1 and includes the following:
 Bacteroides sp.
 Fusobacterium sp.
 Lactobacillus
 Clostridium sp.
 Peptostreptococcus sp.
 Staph. sp.
 Enterococcus faecalis
Normal intestinal flora
 Other Strep. sp.
 Pseudomonas species
 Enterobacteriaceae
 Candida sp.
Normal intestinal flora
Pseudomonas species
Normal intestinal flora
Peptostreptococcus species
Normal intestinal flora
 Normal physiological processes move the
microorganisms through the colon so that a
normal adult excretes 3X 1013 microorganisms
daily.
 Under normal conditions the resident flora are
self-limiting. Competition( for example, colicin
produced by E. coli) and mutualism between
them and the host (E.coli produces vitamin K
and B for the host) maintains the status quo.
Normal intestinal flora
 Anything the disturbs the intestinal
environment (stress, altitude change,
starvation, diarrhea, antibiotics) can serve to
greatly alter the normal flora leading to
gastrointestinal disease such as yeast
infections and antibiotic associated
pseudomembraneous colitis.
Normal flora
 NF of the genitourinary tract
 NF of the urethra include:
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Staph. epidermidis
Enterococcus faecalis
Diphtheriods
Neisseria sp. (NOT N. gonorrhoeae)
Enterobacteriaceae
 NF of the vaginal tract – the microflora present on
this large, moist surface area changes with the
menstrual cycle. Organisms include:
Normal genitourinary flora
 Lactobacillus
 Bacteroides
 Enterococcus sp.
 Staph. epidermidis
 Diphtheroids
 Strep. agalactiae
 Clostridium perfringens
 Peptostreptococcus
 Enterobacteriaceae
 Candida albicans
Normal genitourinary flora
 NF of the external genitalia include:
 Strep. sp.
 Staph. sp.
 Diphtheroids
 Bacteroides
 Candida sp.