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1. Dr. Aditi Nayak

2. CONTENTS
 INTRODUCTION
 ORIGIN OF NORMAL FLORA
 RELATIONSHIPBETWEEN HUMANS AND NORMAL FLORA
 TYPES
 DISTRIBUTION IN SPECIFIC AREAS
 BENEFICIAL EFFECTS
 HARMFUL EFFECTS
 FACTORS INFLUENCINGNORMAL FLORA
 CONCLUSION

3. INTRODUCTION
 The mixture of microorganisms regularly found at any anatomical
site is referred to as the normal microbiota/ the indigenous
microbial population/ the microflora or the normal flora.
 Considered as gnotobiotic [Greek gnotos, known, and biota, the
flora and fauna of a region]
 The normal flora of humans consists of a few eukaryotic fungi and
protists, but bacteria are the most numerous and obvious microbial
components of the normal flora.
 Viruses as normal flora is doubtful. some may be considered such
as; Echoviruses.

4. Relationship between normal flora and host

5. NORMAL MICROBIOTA IN HOST
TWO GROUPS
1. RESIDENT Flora
2. TRANSIENT flora
RESIDENT FLORA
Acquired rapidly during & after birth
Reflects age, sex, nutrition, genetics, environment of a person
 Are a part of the normal microbiota throughout the life and
changes continuously through out life
More important
TRANSIENT FLORA
Non-pathogenic or potentially pathogenic microorganisms that inhabit the
skin or mucous membranes for hours, days, or weeks
Does not establish itself permanently on the surface
Little significance

7. ORIGIN OF NORMAL FLORA
Origin of normal flora starts with the event of,
 Breaking of the foetal membrane
 Movement of foetus through birth canal
 Contact of newborns with many people
 Feeding habit (bottle-fed/breast-fed)
 Eruption of teeth, weaning, and introduction
of the first solid food.

8. THE RESIDENT FLORA:HUMAN AS A HABITAT
Sites That Harbor a Normal Flora Sterile (Microbe-Free) Anatomical Sites and
Fluids
 Skin and its contiguous mucous
membranes
External ear canal
External eye (lids, conjuctiva)
Nose and Nasopharynx
Oropharynx
Upper respiratory tract
Gastrointestinal tract (mouth,
stomach, small intestine,
large intestine:colon)
Genitourinary tract
All Internal Tissues and Organs
 Heart and circulatory system
 Liver
 Kidneys and bladder
 Lungs
 Brain and spinal cord
 Muscles
 Bones
 Ovaries/testes
 Glands (pancreas, salivary, thyroid)
 Sinuses
 Middle and inner ear
 Internal eye
Fluids Within an Organ or Tissue
 Blood
 Urine in kidneys, ureters, bladder
 Cerebrospinal fluid

10. Propionibacterium
ACNES FOUND ON SKIN AND THE
CONJUNCTIVA.
NORMAL FLORA OF SKIN
Staphylococcus epidermidis
Propionibacterium acnes
Mycobacterium smegmatis
Corynebacterium
Micrococcus sp.
Pityrosporum ovale and P. orbiculare (yeasts)
SITES OF OCCURANCE
Scalp, moist skin folds, especially between the toes,
tend to harbor fungi, whereas lipophilic mycobacteria
and staphylococci are prominent in sebaceous
secretions of the axilla, groin, external genitalia etc.

11. NORMAL FLORA OF EYE (CONJUCTIVA)
1. Staphylococcus epidermidis
2. Corynebacterium sp.
3. Propoinibacterium
4. Staphylococcus aureus
5. Viridans streptococci
6. Neisseria sp.
7. Haemophilus influenzae

12. NORMAL FLORA OF
EXTERNAL EAR
 Staphylococcus sp.
 Corynebacterium
 Neisseria sp.
 Aspergillus,Alternaria,
Penicillium, Candida

13. NORMAL FLORA OF
RESPIRATORY TRACT
A) The nares (nostrils)
1. Staphylococcus epidermidis
2. Corynebacteria
3. Staphylococcus aureus
4. Neisseria sp.
5. Haemophilus sp.
6. Streptococcus pneumoniae

14. 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

15. 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).

16. NORMAL FLORA OF ORO-PHARYNX
 Staphylococcus aureus and S. epidermidis
 Alpha-hemolytic streptococci (S.oralis,
S. milleri, S. gordonii, S. salivarius)
 Diphtheroids; Branhamella catarrhalis; an
 Small gram-negative cocci related to
Neisseria meningitidis.
 Micrococcus
 Porphyromonas, Prevotella, and
Fusobacterium.

17. NORMAL FLORA OF ORAL CAVITY
 Initially the microbiota consists mostly of the
genera Streptococcus, Neisseria, Actinomyces,
Veillonella, and Lactobacillus. Some yeasts also are
present.
When the first teeth erupt, the anaerobes
(Porphyromonas, Prevotella, and Fusobacterium)
become dominant due to the anaerobic nature of the
space between the teeth and gums.
 As the teeth grow, Streptococcus parasanguis and
S. mutans attach to their enamel surfaces; S.
salivarius attaches to the buccal and gingival
epithelial surfaces and colonizes the saliva.
 The presence of these bacteria contributes to the
eventual formation of dental plaque, caries, gingivitis,
and periodontal disease.

18. NORMAL FLORA OF GASTRO-INTESTINAL
TRACT
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.

19. 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

20. 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

21. NORMAL FLORA OF STOMACH
 Stomach contents harbor only transient organisms,
the acidic pH providing an effective barrier.
 However, the gastric mucosa may be colonized by
acid-tolerant lactobacilli
E.g Helicobacter
 streptococci.
Figure 8. Helicobacter pylori. ASM

22. NORMAL FLORA OF SMALL
INTESTINE
 The duodenum (the first 25 cm of the small
intestine) contains few microorganisms .Of
the bacteria present, gram-positive cocci
and rods comprise most of the microbiota.
 Enterococcus faecalis, lactobacilli,
diphtheroids, and the yeast Candida
albicans are occasionally found in the
jejunum.
 In the distal portion of the small intestine
(ileum), as the pH becomes more alkaline ,
anaerobic gram-negative bacteria and
members of the family

23. NORMAL FLORA OF LARGE
INTESTINE
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.

24. Figure 27.9
Major bacteria present Organ
Esophagus
Stomach
Small
intestine
Large
intestine
pH 2
Secretion of acid (HCl)
Digestion of macromolecules
pH 4–5
Continued digestion
Absorption of monosaccharides,
amino acids, fatty acids, water
pH 7
Absorption of bile acids,
vitamin B12
Duodenum
Jejunum
Ileum
Colon
Anus
Esophagus
Lactobacilli
Enterococci
Prevotella
Streptococcus
Veillonella
Helicobacter
Proteobacteria
Bacteroidetes
Actinobacteria
Fusobacteria
Bacteroides
Bifidobacterium
Clostridium
Enterobacteria
Enterococcus
Escherichia
Eubacterium
Klebsiella
Lactobacillus
Methanobrevibacter
(Archaea)
Peptococcus
Peptostreptococcus
Proteus
Ruminococcus
Staphylococcus
Streptococcus
Major physiological
processes
© 2012 Pearson Education, Inc.

25. Normal flora of the Urogenital
Tract
a)The anterior urethra
1. Staphylococcus epidermidis
2. Enterococcus faecalis
3.Alpha-hemolytic streptococci.
4.Some enteric bacteri
(e.g. E. coli, Proteus sp.)
5. Corynebacteria sp.
6. Acinetobacter sp.
7. Mycoplasma sp.
8. Candida sp.
9. Mycobacterium smegmatis

26. b) The vagina
1. Corynebacterium sp.
2. Staphylococci
3. Nonpyogenic streptococci
4. Escherichia coli
5. Lactobacillus acidophilus
6. Flavobacterium sp.
7. Clostridium sp.
8. Viridans streptococci
9. Other Enterobacteria
Lactobacillus species, in association
with a vaginal epithelial cell.

28. BENEFICIAL EFFECTS OF
NORMAL FLORA
 1. The normal flora synthesize and excrete vitamins in excess of their own needs,
which can be absorbed as nutrients by their host. For example, in humans, enteric
bacteria secrete Vitamin K and Vitamin B12, and lactic acid bacteria produce certain B-
vitamins. Germ-free animals may be deficient in Vitamin K to the extent that it is
necessary to supplement their diets.
 2. The normal flora prevent colonization by pathogens by competing for attachment
sites or for essential nutrients. This is thought to be their most important beneficial
effect, which has been demonstrated in the oral cavity, the intestine, the skin, and the
vaginal epithelium.
 3. The normal flora may antagonize other bacteria through the production of
substances which inhibit or kill nonindigenous species. The intestinal bacteria produce a
variety of substances ranging from relatively nonspecific fatty acids and peroxides to
highly specific bacteriocins, which inhibit or kill other bacteria.
 4. The normal flora stimulate the development of certain tissues, i.e., the caecum
and certain lymphatic tissues (Peyer's patches) in the GI tract.
 5. The normal flora stimulate the production of natural antibodies Since the normal
flora behave as antigens in an animal, they induce an immunological response, in
particular, an antibody-mediated immune (AMI) response. Low levels of antibodies
produced against components of the normal flora are known to cross react with certain
related pathogens, and thereby prevent infection or invasion. Antibodies produced

29. HARMFUL EFFECTS OF NORMAL
FLORA
 1. Bacterial synergism between a member of the normal flora and a potential pathogen. This
means that one organism is helping another to grow or survive. There are examples of a
member of the normal flora supplying a vitamin or some other growth factor that a pathogen
needs in order to grow. This is called cross-feeding between microbes. Another example of
synergism occurs during treatment of "staph-protected infections" when a penicillin-resistant
staphylococcus that is a component of the normal flora shares its drug resistance with
pathogens that are otherwise susceptible to the drug.
 3. Induction of a low grade toxemia Minute amounts of bacterial toxins (e.g. endotoxin) may
be found in the circulation. Of course, it is these small amounts of bacterial antigen that
stimulate the formation of natural antibodies.
 4. The normal flora may be agents of disease. Members of the normal flora may cause
endogenous disease if they reach a site or tissue where they cannot be restricted or tolerated
by the host defenses. Many of the normal flora are potential pathogens, and if they gain access
to a compromised tissue from which they can invade, disease may result.
 Transfer to susceptible hosts Some pathogens of humans that are members of the normal
flora may also rely on their host for transfer to other individuals where they can produce
disease. This includes the pathogens that colonize the upper respiratory tract such as Neisseria
meningitidis, Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus,
and potential pathogens such as E. coli, Salmonella or Clostridium in the gastrointestinal tract.
 Dental plaque, dental caries, gingivitis and periodontal disease result from actions initiated
and carried out by the normal bacterial flora.
 Some of the bacteria in the colon (e.g. Bacteroides) have been shown to produce metabolites

30. FACTORS INFLUENCING NORMAL
FLORA
 If the intestinal environment is disturbed, the normal
microbiota may change greatly.
 Disruptive factors include stress, altitude changes,
starvation, parasitic organisms, diarrhea, and use of
antibiotics or probiotics .
 hange in diet , change in environment also influence
disturbance in normal microbiota

31. Bringing it All Together
Several common themes can be extracted and summarized as,
 Bacteria perform physiological, nutritional and protective functions in the human body.
 Maintaining a balance is crucial. Normal flora consists of communities of bacteria that
function as microbial ecosystems. If these ecosystems are disrupted the consequences
can be unpredictable.
 It is thought that less that less than 1% of bacteria will grow on standard laboratory media.
That means that we have yet to explore greater than 99% the microbial world.
 Today, new technologies such as the polymerase chain reaction (PCR), high-throughput
DNA sequencing and DNA microarrays are starting to provide glimpses into these microbial
ecosystems.
 Researchers have suggested that it is now time to embark on a “second human genome
project “ where the genomic sequences of the microbes making up our normal flora are
determined. Advancing our understanding of normal flora will provide us with
fundamental information about who we are.

32. REFERENCE
 Microbiology (5th Edition)
- Lansing M. Prescott
 Foundations in Microbiology(4th Edition)
-Kathleen Park Talaro ,Arthur Talaro

33. THANK YOU