Normal Flora
Ibrahim Jamfaru
School of Medicine
UHAS
Humans as Habitats
• Bodies are great places to be!
• Warm, stable, lots of nutrients available, constant pH and osmotic pressure,
etc.
• Our bodies are not uniform environments, though
• Each region or organ differs: skin, GI tract, respiratory tract, etc. provide
different conditions
• Animals possess great defense mechanisms
• “Normal” doesn’t mean non-pathogenic; we sometimes have pathogens (S.
pyogenes, S. aureus, etc.) in low numbers in and on us
Humans as Habitats (cont.)
• Colonization (and infection) frequently begin at mucous membranes
•These are found throughout the body. Consist of single or multiple
layers of epithelial cells, tightly packed cells in direct contact with
the external environment.
Bacteria may associate
loosely or firmly
Breaches in the mucosal
barrier can result in
infection
(pathogenesis)by
opportunistic
pathogens
Normal Flora
• Definition
Normal flora is the mixture of
microorganisms (bacteria and fungi)
that are regularly found at any
anatomical site of human body.
Resident flora
Two broad categories
Transient flora
Normal Flora
Resident flora: This consist of relatively fixed types of
microorganisms regularly found at a given site of the body
at a given age. If this flora is disturbed due to extraneous
conditions it promptly re-establishes itself.
Transient flora: This consist of non-pathogenic or
potentially pathogenic microorganisms that inhabit a given
site of a body for a short duration.
Normal Flora
• Skin
• Eyes (i.e.Cunjunctiva)
• Nose (i.e. Respiratory tract)
•
GIT (mouth, stomach, SI, LI)
•
•
Ears
Urinogenital tract
Normal Flora
• Resident flora
• Acquired rapidly during &
after birth
Normal Flora
• Resident flora
• Reflects age of person
Normal Flora
Resident flora
Changes continuously through
out life
.
Normal Flora
• Resident flora
• Reflects nutrition of person
Normal Flora
• Resident flora
• Reflects genetics of person
Normal Flora
• Resident flora
• 90% is S. epidermidis; S.
aureus, may be in moist
areas
Normal Flora
Resident flora
Reflects environment of person
Normal Flora
• Resident flora
• Reflects sex of person
Normal Flora
Sterile tissues
In a healthy human, the
internal tissues such as:
• blood
• brain
• muscle
• cerbrospinal fluid (CSF)
- are normally free of
microorganisms.
Importance of The Normal
Flora (Advantages)
1. They constitute a protective host
defense mechanism by occupying
ecological niches.
Importance of The Normal Flora (Advantages) - Contn
They produce vitamin B and
vitamin K in intestine.
2.
Importance of The Normal Flora (Advantages)
3. The oral flora contribute to immunity
by inducing low levels of circulating
and secretory antibodies that may
cross react with pathogens.
Importance of The Normal Flora (Advantages)
4. The
oral bacteria flora exert microbial
antagonism against nonindigenous
species by production of inhibitory fatty
acids, peroxides, bacteriocins, etc.
Importance of The Normal Flora (Advantages)
5. The
normal flora may antagonize other
bacteria through the production of
substances which inhibit or kill
nonindigenous species.
Importance of The Normal Flora (Disadvantages)
1. They can cause disease in the
following:
a) When individuals become
immunocompromised or
debilitated.
b) When they change their usual
anatomic location.
Importance of The Normal Flora
2. The
oral flora of humans may harm their
host since some of these bacteria are
pathogens or opportunistic pathogens
Estimation of the Normal flora
• It has been calculated that the normal flora human
body about 1012 bacteria on the skin, 1010 in the
mouth, and 1014 in the gastrointestinal tract.
Normal Flora of the Skin
• The most important sites are:
1. Axilla (Cavity beneath Joint)
2. Groin
3. Areas between the toes
Normal Flora of the Skin
• The majority of skin microorganisms
are found in the most superficial layers
of the epidermis and the upper parts of
the hair follicles.
Normal flora of the skin
• Skin surface is unfavorable habitat.
Usually only populated by transient microbes
Exceptions are moister areas: scalp, face, ears,
underarms, genitourinary, palms, toes.
• Most resident skin microorganisms inhabit deeper
layers of the epidermis, sweat glands, and follicles.
• Most of the residents are Gram-positives, especially
Staphylococcus and Propionibacterium
Normal flora of the skin (cont.)
• Microorganisms are primarily associated with glands:
• 1) Eccrine glands
 Widely distributed
 Main glands for perspiration; secrete a hypotonic saline solution with a
variety of organic and inorganic substances
 Relatively devoid of microorganisms, probably due to salinity and low pH
• 2) Apocrine glands
 Restricted to underarms, genitals, etc.
 Don’t develop before puberty
 Apocrine sweat has higher pH than eccrine sweat
 Population numbers can be high
• 3) Sebacious glands -- associated with hair follicles
 Produce sebum, chief component of skin lipids
 These lipids have antibacterial activity, esp. against Gram-positive cocci.
Normal Flora of the Skin
• Important bacteria:
1. Staphylococcus epidermidis
2. Micrococcus sp.
3. Corynebacteria sp.
4. Mycobacterium smegmatis
Normal Flora of the Conjunctiva
1.
Staphylococcus epidermidis
2.
Corynebacterium sp.
3.
Propoinibacteriumacnes)
4.
Staphylococcus aureus
5.
Viridans streptococci
6.
Neisseria sp.
7.
Haemophilus influenzae
Pathogens which do infect the conjunctiva
• Neisseria gonorrhoeae
• Chlamydia trachomatis
Normal Flora of the Respiratory Tract
A) The nares (nostrils)
1.
2.
3.
4.
5.
6.
Staphylococcus epidermidis
Corynebacteria
Staphylococcus aureus
Neisseria sp.
Haemophilus sp
Streptococcus pneumoniae
Normal Flora of the Respiratory Tract
B)
The upper respiratory tract
(nasopharynx).
1.
Non-hemolytic streptococci
2.
Alpha-hemolytic streptococci
3.
Neisseria sp.
4.
Streptococcus pneumoniae
5.
Streptococcus pyogenes
6.
Haemophilus influenzae
7.
Neisseria meningitidis
Normal Flora of the Respiratory Tract
• C) The lower respiratory tract
(trachea, bronchi, and pulmonary
tissues):
• Usually sterile.
• The individual may become
susceptible to infection by pathogens
descending from the nasopharynx e.g.
• H. influenzae
• S. pneumoniae).
•Upper respiratory tract -Staphylococcus, Streptococcus,
diphtheroid bacilli, Gram-neg. cocci. Also
some pathogens
•Lower respiratory tract -essentially sterile
Normal Flora of the Human Oral Cavity
• Oral bacteria include:
1. Viridans streptococci
2. Lactobacilli
3. Staphylococci (S. aureus and S. epidermidis)
4. Corynebacterium sp.
5. Bacteroides sp.
6. Streptococcus sanguis (dental plaque)
7. Streptococcus mutans (dental plaque)
8. Actinomyces sp.
The Normal Flora of The Ears (i.e. external ear)
• The external ears contains a variety of
microorganisms. These include:
1. Staphylococcus epidermidis
2. Staphylococcus aureus
3. Corynebacterium sp
Normal flora of the Urinogenital Tract
a)
The anterior urethra
1. Staphylococcus epidermidis
2. Enterococcus faecalis
3. Alpha-hemolytic streptococci.
4. Some enteric bacteria (e.g. E. coli, Proteus sp.)
5. Corynebacteria sp.
6. Acinetobacter sp.
7. Mycoplasma sp.
8. Candida sp.
9. Mycobacterium smegmatis
Normal flora of the Urinogenital Tract
b)
The vagina
1. Corynebacterium sp.
2. Staphylococci, Gardenerella vaginalis
3. Nonpyogenic streptococci
4. Escherichia coli
5. Lactobacillus acidophilus
6. Flavobacterium sp.
7. Clostridium sp.
8. Viridans streptococci, Ureaplasma u.
9. Other Enterobacteria
Normal Flora of the Gastrointestinal Tract (GIT)
• In humans, the GIT flora are
influenced by:
1.
Age
2.
Diet
3.
Cultural conditions
4.
The use of antibiotics
Normal Flora of the Gastrointestinal Tract (GIT)
• At birth
• The entire intestinal tract is sterile, but
bacteria enter with the first feed. The initial
colonizing bacteria vary with the food
source of the infant.
Normal Flora of the Gastrointestinal Tract (GIT)
• In breast-fed
1. Bifidobacteria account for more than
90% of the total intestinal bacteria.
2. Enterobacteriaceae
3. Enterococci
4. Bacteroides
5. Staphylococci
6. Lactobacilli
7. Clostridia
Normal Flora of the Gastrointestinal Tract (GIT)
• In bottle-fed infants
• Bifidobacteria are not predominant.
When breast-fed infants are
switched to a diet of cow's milk or
solid food, bifidobacteria are
progressively joined by:
1. Enterics
2. Bacteroides
3. Enterococci
4. Lactobacilli
5. Clostridia
Normal Flora of the Gastrointestinal Tract (GIT)
In the upper GIT of adult humans
(stomach)
• mainly acid-tolerant lactobacilli
e.g. Helicobacter pylori
Stomach
•
pH of stomach is low, around 2
•
Acts as a microbiological barrier
•
Bacterial count of stomach contents is low, but
walls can be heavily colonized.
• Primarily Lactobacillus and Streptococcus
Normal Flora of the Gastrointestinal Tract (GIT)
• The proximal small
intestine
1. Lactobacilli
2. Enterococcus faecalis
3. Coliforms
4. Bacteroides
Normal flora of the GI tract (cont.)
• The upper portions of the small intestine are acidic and
resemble the stomach. The lower portions have increasing
numbers of bacteria, from 105 to 107 per gram.
• The large intestine has enormous numbers of bacteria,
1010 to 1011 cells/gram! Is essentially a fermentation vessel.
Bacterial-human relationships
• Normal flora
• Opportunistic infections
• Pathogenic infections
Normal flora - Risks
• Dental plaque ( A biofilm or mass of bact.)
• Dental caries: destruction of enamel, dentin or
cementum of teeth
• Periodontal disease
• Inflammatory bowel disease
Opportunistic flora
• Some normal flora become opportunistic pathogens
• (Staphylococcus aureus, Streptococcus mutans,
Enterococcus faecalis, Streptococcus pneumoniae,
Pseudomonas aeruginosa, etc.)
• Breach of skin/mucosal barrier: trauma, surgery, burns
• Bacterium at one site may be commensal, but might be
pathogenic at another site
Mouth flora
Opportunistic flora
• Growth of commensals may put patient at risk
• Broad-spectrum antibiotic therapy decreases total number of
bacterial in gut
• During repopulation, faster-growing aerobic Enterobacteriaceae over slowerreplicating anaerobes increases probability of gram-negative bacteremia
• Cross-reactive responses to host tissue: Superantigen
• Chronic, low-grade inflammation
Gastrointestinal flora
• Antibiotics overuse
• Antibiotic associated diarrhae
• C. dfficile -associated diarrhea
(CDAD)
• Pseudomembranous colitis
• toxic megacolon
The flora of the large intestine (colon)
1.
Enterococci
2. Clostridia
3. lactobacilli
4. Bacteroides
5. Bifidobacterium (Bifidobacterium bifidum)
6. Escherichia coli
7. Methanogenic bacteria
8. Viridans streptococci
9. Staphylococcus sp.
10. Proteus sp.
11. Candida albicans (Yeast)
12. Mycoplama sp.
Normal flora - Risks and Opportunistic
Clinical conditions that may be caused by members of the normal flora
Probiotics/Prebiotics
• Probiotic
• Oral administration of living organisms to promote health
• Mechanism speculative: competition with other bacteria;
stimulation of nonspecific immunity
• Species specific: adherence and growth (tropism)
• Prebiotic
• Non-digestible food that stimulates growth or activity of GI
microbiota, especially bifidobacteria and lactobacillus bacteria
(both of which are non inflammatory)
• Typically a carbohydrate: soluble fiber
THANKS
ASSIGNMENT
A 19-years-young man underwent dental treatment at a clinic. Four
weeks later, patient reported with low grade fever, myalgias and
fatigue. His temp is 100.2o C, spleen is palpable and systolic cardiac
murmur is heard in precordium. Suspecting infective endocarditis,
blood cultures were taken. Which organism is most likely to be
isolated?
1. Salmonella typhi
2. Shigella dysentriae
3. Mycobacterium tuberculosis
4. Viridans streptococcus
5. Vibrio cholerae