2. Normal Microbial Flora
• Population of micro-organisms that inhabit in
healthy normal person
• Normal microbiota describe the various
microorganisms that are permanent residents of
certain body sites
3. • Normal flora vary in both number and kind from
one site to another
• The internal organs such as CNS, blood, liver,
spleen, Kidneys and bladder are free of organisms
4. Types of skin Microbial flora
There are two groups of normal flora:
• Resident normal flora
• Transient normal flora
5. Resident normal floras
• The resident flora consists of relatively fixed types of
microorganisms
• regularly found in a given area at a given age
• if disturbed, it promptly reestablishes itself
6. Transient normal floras
• non-pathogenic or potentially pathogenic
microorganisms that inhabit the skin and mucus
membrane for a short period of time like hours,
days and weeks
• It is derived from the environment does not
produce disease & does not establish itself
permanently on the surface
• If the resident flora is disturbed, transient micro-
organisms may colonize, proliferate and produce
disease
7. Normal flora can cause disease when:
• the defense mechanisms of the body is
breached
or
• when the micro-organism is placed in the
abnormal body site
8. The role of Normal Flora
Synthesis of vitamin K in the gastrointestinal tract
Absorption of nutrients & breakdown of products
Prevent colonization by pathogenic micro-organisms and
possible disease through bacterial interference:
a. Competition for nutrition with pathogenic bacteria
b. Competition for binding sites with pathogenic bacteria
Members of the normal flora may produce disease under
certain circumstances
9. Normal flora of the Skin
The skin is rich in resident bacterial flora, like:
• Coagulase negative Staphylococci (S.epidermidis)
• Diphtheroids
• Propionibacterium acne
• Peptostreptococci
• Alpha-hemolytic streptococci and non-hemolytic streptococci
• Staphylococcus aureus
• Non-pathogenic Neisseria sp.
10. • Factors that eliminate nonresident
microorganisms from the skin:
1) Low pH
2) Lysozyme
3) Fatty acids in sebaceous secretions
11. Normal Flora of the Ear
• It is an extension of skin normal flora and often
profusely colonized
• Staphylococcus epidermidis
• Diphtheroids
• Alpha-hemolytic Streptococci
• non-hemolyic Streptococci
• Less frequently found are Bacillus spp.
12. Normal Flora of Respiratory Tract
• The upper respiratory tract is heavily colonized by normal flora
• Lower respiratory tract (trachea, bronchi, bronchioles and alveoli) do not
have a normal microbiota (it is sterile) as they removed by:
The continuous stream of mucus generated by the ciliated epithelial cells
Phagocytic action of alveolar macrophages
Lysozyme, which is present in nasal mucus has bactericidal effect
16. Normal Flora of the Mouth
• The normal flora of the oral cavity contains bacteria able to resist
mechanical removal by adhering to surface like the gum and teeth
• Sterile at birth, after 4-12 hrs contaminated from birth canal with
viridans Streptococci (as resident flora)
• Non-pathogenic Neisseria spp. (N. mucosa and N. lactamica)
• Diphtheroids
• Anaerobes like Fusobacterium spp
• Spirochetes
• Actinomyces
• Streptococci
17. Normal Flora of the Intestinal Tract
• At birth is sterile.
• Newborns (in intensive care): the intestine colonized by
Enterobacteriaceae (Klebsiella, Citrobacter, Enterobacter)
• infants:
- The initial residents of the colon of infants are members of the
Bifidobacteria
- Large number of Lactobacilli
• In formula-fed infants:
In formula-fed infants, Lactobacillus spp. predominate
18. Small intestine
• Lactobacilli
• Diphtheroids
are occasionally found in the jejunum.
• In the distal part of the small intestine (ileum), the
microbiota begin to take the characteristics of the
colon microbiota
• In the jejunum and ileum there are about 105–108
bacteria/ gm of the contents.
19. • In ileum the pH becomes more alkaline
• As a result anaerobic G-ve bacteria and members of
the family Enterobacteriaceae become established
• The population size in the cecum and transverse
colon is about 108–1010 bacteria/gm
• In sigmoid colon and rectum, there are about 1011
bacteria/gm of contents, constituting 10–30% of the
faecal mass
20.
21. Large intestine
• The colon has the largest microbial population in the body
• Microscopic count of faeces approach 1012 organisms/gm weight
anaerobes (96-99% of resident flora):
- Fusobacterium spp.
- Bifidobacterium
- clostridia (C.dificile in small amount)
- anaerobic G+ve cocci (Peptostreptococcus)
facultative aerobes includes:
- Coliform
- Enterococci
- small No. of Pseudomonas, lactobacilli, Proteus .
22. Normal Flora of the Genitourinary Tract
The upper genitourinary tract (kidney, ureters, and
urinary bladder) is usually sterile
Few bacteria are usually present in the distal part of the
urethra such as :
• Staphylococcus epidermidis
• Corynebacterium spp.
