Normal flora refers to the diverse microorganisms that reside in various body sites, playing significant roles in health by preventing pathogen colonization and contributing to nutrition. The document outlines the normal flora of different body regions, including skin, respiratory tract, intestinal tract, and genitourinary tract, highlighting the balance between beneficial and potentially harmful organisms. Additionally, it discusses the implications of carrier states and colonization in relation to infections and disease.

1. Normal flora

2. Normal flora
Commensals / Human microbiome
Normal flora are various bacteria &
fungi that are permanent residents of
certain body sites, the skin, oropharynx,
colon & vagina
Viruses & parasites are usually not
considered members of the normal flora

3. Normal flora
Members of the normal flora vary in both number & kind from site to
site
Although the normal flora extensively populates many areas of the body,
the internal organs usually are sterile
The central nervous system, blood,
lower bronchi and alveoli, liver,
spleen, kidneys, & bladder
are free of all but the
occasional transient organism

4. Normal flora
 Normal flora VS Carrier State
The term carrier implies that an individual harbors a potential pathogen
and therefore can be a source of infection for others
An asymptomatic infection or continuing to carry the organism
after recovering from disease, and may shed it for a long period
 Normal flora VS Colonization with a new organism
Colonization: The acquisition of a new organism
After the new organism colonizes (i.e., attaches and grows, usually on a
mucosal membrane), it may cause infectious disease, or it may be
eliminated by our host defenses

5. Normal flora
Significance
Play role both in: Maintenance of health & in the causation of disease
1. Non-pathogens in their usual anatomic location
2. Protective Host- Defence mechanism - Colonization resistance
(Pseudomembranous colitis)
3. Nutritional function
The intestinal bacteria produce
several B vitamins and vitamin K

6. Normal flora

7. Normal flora

8. NORMAL FLORA
of
THE SKIN

9. NORMAL FLORA OF THE SKIN
Staphylococcus epidermidis
Predominant organism
Located superficially in the stratum
corneum, but some are found in the
hair follicles
Non-pathogenic on the skin
Can cause disease when it reaches certain sites,
such as artificial heart valves and prosthetic joints
There are about 103
–104
organisms/cm2
of skin

10. NORMAL FLORA OF THE SKIN
Anaerobic organisms, such as
Propioni bacterium and
Peptococcus
Are situated in the deeper follicles in
the dermis,
where the oxygen tension is low

11. NORMAL FLORA OF THE SKIN
The yeast Candida albicans is also a member of the normal flora
of the skin
It can enter a person’s bloodstream when needles pierce the skin
(e.g., in patients with intravenous catheters or in those who use
intravenous drugs)
It is an important cause of systemic infections in patients with
reduced cell-mediated immunity

12. NORMAL FLORA OF
THE RESPIRATORY TRACT
A wide spectrum of organisms colonize the nose, throat, and mouth
The lower bronchi and alveoli typically contain few, if any, organism
The nose is colonized by a variety of streptococcal and staphylococcal
species, the most significant of which is the pathogen S. aureus
The throat contains a mixture of viridans streptococci, Neisseria species,
and S. epidermidis
These nonpathogens occupy attachment sites on the pharyngeal mucosa
and inhibit the growth of the pathogens Streptococcus pyogenes,
Neisseria meningitis, and S. aureus, respectively

13. NORMAL FLORA OF THE RESPIRATORY TRACT
In the mouth, viridans streptococci make up about half of the bacteria
Streptococcus mutans
Plaque Formation
(1010
/g) in dental plaque, the precursor of caries
S. Sanguinis
The leading cause of subacute bacterial endocarditis
These organisms can enter the bloodstream at the
time of dental surgery and attach to damaged heart valves

14. NORMAL FLORA OF THE RESPIRATORY TRACT
Eikenella corrodens (normal oral flora)
Skin and soft tissue infections associated with human bites &
“clenched-fist” injuries
Bacteroides, Prevotella, Fusobacterium, Clostridium &
Peptostreptococcus (Anaerobes)
Found in the gingival crevices
If aspirated, these organisms can cause lung abscesses
(debilitated patients with poor dental hygiene)
Actinomyces israelii
Commensals of gingival crevices
Cause abscesses of the jaw, lungs, or abdomen

15. NORMAL FLORA OF THE
INTESTINAL TRACT
The stomach of fasting people
contains few organisms, primarily
because of its low pH
The small intestine usually
contains small numbers of
streptococci, lactobacilli, and
yeasts, particularly C. albicans

16. NORMAL FLORA OF THE INTESTINAL TRACT
The colon is the major location of bacteria in the body
20% of the feces consists of bacteria, approximately 1011
organisms/g

17. NORMAL FLORA OF THE INTESTINAL TRACT
 90% of the fecal flora are anaerobes … B. fragilis
 The most abundant facultative bacteria are the coliforms … E. coli

18. NORMAL FLORA OF THE INTESTINAL TRACT
Significant role in extraintestinal disease
 E. coli is the leading cause of urinary tract infections
 B.fragilis is an important cause of peritonitis associated with
perforation of the intestinal wall following trauma, appendicitis, or
diverticulitis
 Fusobacterium and Peptostreptococcus, and other important
facultative bacteria include Enterococcus faecalis, which causes
urinary tract infections and endocarditis
 P. aeruginosa 10% of normal stools
various infections, in hospitalized patients with decreased host defenses

19. NORMAL FLORA OF THE GENITOURINARY TRACT
Lactobacillus species
 The primary vaginal flora of adult
Produce Acid
Low pH
 Before puberty & after menopause low estrogen levels
lactobacilli are rare, the vaginal pH is high
 Suppression by antibiotics overgrowth of C. albicans .. Candida vaginitis
S. aureus
In 5% of women normal population, the vagina is colonized by S. aureus,
which predisposes them to toxic shock syndrome

20. NORMAL FLORA OF THE GENITOURINARY TRACT
Viginal colonization by members of fecal flora
Patients with recurrent UTI harbor organisms such as E. coli &
Enterobacter
Initial Colonization of Newborn
 About 15% - 20% of women of childbearing age carry Group B
streptococci in the vagina
 This organism is an important cause of sepsis and meningitis in
newborns and is acquired during passage through the birth canal

21. NORMAL FLORA OF THE GENITOURINARY TRACT
Urethral Colonization
During passage through the outermost portions of the urethra, urine
often becomes contaminated with S. epidermidis, coliforms,
diphtheroids, and nonhemolytic streptococci
The area around the urethra of women and uncircumcised men contains
secretions that carry Mycobacterium smegmatis, an acid-fast organism
The skin surrounding the genitourinary tract is the site of
S.saprophyticus, a cause of urinary tract infections in women