The document discusses the normal microbial flora that inhabit healthy humans. It describes the different microorganisms typically found colonizing various body sites like the skin, respiratory tract, gastrointestinal tract, and genitourinary tract. The flora varies between sites and helps protect against pathogens by competing for resources and binding sites. While important for health, the normal flora can sometimes cause disease if defenses are compromised or microbes reach abnormal body sites. Key resident skin bacteria include Staphylococcus epidermidis and propionibacteria. The mouth harbors streptococci and actinomyces. The GI tract contains large numbers of lactobacilli and bifidobacteria in the small intestine and numerous anaerobes

1. HUMAN MICROBIAL FLORA
Assi. Lec.
Samira fattah
College of Health Sciences – Medica Microbiology Dept.

2. Normal Microbial Flora
• It denotes the population of micro-organisms that
inhabit the skin and mucus membrane of healthy
normal person.
• It is the term used to 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.
Although, the normal flora extensively populate many
areas of the body, the internal organs such as CNS,
blood, liver, spleen, Kidneys and bladder are free of all
but the occasional transient organism.

4. Types of skin Microbial flora
• There are two groups of normal flora:
1. Resident normal flora
2. 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
are 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.

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.

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 eliminating nonresident
microorganisms from the skin:
1) Low pH.
2) Lysozyme.
3) Fatty acids in sebaceous secretions.

11. Important factors to keep
skin microbiota under control
 Skin has a slightly acidic pH (4-6) due to organic acids
produced by staphylococci and secretions from skin oil and
sweat glands. The acidic pH discourages colonization of many
bacteria.
 Lack of moisture drives many resident microbiota into a
dormant state. However in certain parts of the body (scalp,
ears and axillary areas) moisture is sufficiently high to support
a resident microbiota.

12. Important factors to keep
skin microbiota under control
• Sweat of some parts of the skin contains a high concentration
of salt (sodium chloride). This makes the skin surface hyper-
osmotic which stresses most microorganisms.
• Lysozyme from sweat glands on the skin are bacterial inhibitory
substances. They help control of colonization, overgrowth and
infection from resident microorgsnisms.

13. How skin microbiota keep their
population
• Neither profuse sweating nor washing and bathing
can eliminate or significantly modify the normal
resident flora.
• The number of superficial microorganisms may be
diminished by daily scrubbing with soap containing
hexachlorophene or other disinfectants, but the flora
is rapidly replenished again .

14. Normal Flora of Respiratory Tract
• The upper respiratory tract is heavily colonized by normal flora.
• but the lower respiratory tract. (trachea, bronchi, bronchioles and
alveoli) do not have a normal microbiota (it is sterile) as they removed
by:
1. The continuous stream of mucus generated by the ciliated epithelial cells.
2. Phagocytic action of alveolar macrophages.
3. Lysozyme, which is present in nasal mucus has bactericidal effect

15. Respiratory Tract

16. Nose:
The flora of the Nose consists of:
• Staphylococcus aureus
• Staph.epidermidis
• Streptococci (Streptococcus pneumonia)
• Corynebacteria.
• Non pathogenic Neisseria
• Haemophilus sp.

17. Nasopharynx
• Some Neisseria species
• α-hemolytic Streptococci(S. pneumonia)
• Staphylococcus epidermidis
• Staphylococcus aureus
• Haemophilus infuanza
• Diphtheroids
• Branhamella catarrhalis

18. 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.
Those that can not attach are removed by the
mechanical flushing from the oral cavity to the
stomach where they are destroyed by
hydrochloric acid

19. • sterile at birth
• after 4-12 hrs contaminated from birth canal with viridans Streptococci
(as resident flora remain so far life).
• Non-pathogenic Neisseria spp.like N. mucosa and N. lactamica
• Diphtheroids
• Anaerobes like Prevotella spp., Fusobacterium spp.
• Spirochetes
• Actinomyces
• Streptococci
• Veillonella(anaerobic G-ve cocci)
• (When teeth erupt) Rothia spp.(G+, pleomorphic aerobes).

20. Normal Flora of the Intestinal Tract
• At birth is sterile.
• Newborns (in intensive care): the intestine colonized by
Enterobacteriaceae (Klebsiella, Citrobacter, Enterobacter).
• Breast-feed children:
- The initial residents of the colon of breast-fed infants are members
of the G+ve Bifidobacterium genus (G+, nonmotile, anaerobic
bacteria produce acid from carbohydrates & tolerate pH 5.)
because human milk contains a disaccharide amino sugar that
Bifidibacterium spp. require as a growth factor.
- Large No. of lactobacilli, lactic acid streptococci.

21. • In formula-fed infants:
In formula-fed infants, Lactobacillus spp. predominate
because formula lacks the required growth factor.
• With the ingestion of solid food, these initial colonizers of
the colon are eventually displaced by a typical G-ve
microbiota.

22. Normal adult:
• Esophagus:
• In the normal adult, the esophagus contains microorganisms
arriving with saliva and food.
• Stomach:
acidity keeps the No. of microorganisms at minimum (103–105/g of
contents) unless obstruction at the pylorus favours the proliferation
of gram-positive cocci and bacilli.

23. Many microorganisms are washed from the mouth
into the stomach. Owing to the very acidic pH (2-3)
of the gastric contents, most m.o. are killed.
These are mainly:
Streptococcus
Staphylococcus
Lactobacillus
Peptostreptococcus.

24. Some characteristics of stomach microbial flora
A/ Some bacteria may survive if they rapidly pass through the stomach
or if those ingested with food are particularly resistant to gastric pH.
B/ Normally the number of m.o. increase after a meal but quickly falls
as the acidic pH takes its role.
C/ Changes in the gastric microbiota also occur if there is an increase in
gastric pH following intestinal obstruction, which permits a reflux of
alkaline duodenal secretions into the stomach.

25. 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.

26. • It is within the ileum that 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 and in the
sigmoid colon and rectum, there are about 1011
bacteria/gm of contents, constituting 10–30% of the
faecal mass.

28. Large intestine
The colon has the largest microbial population in the body.
Microscopic count of faeces approach 1012 organisms/gm wet
weight.
Over 300 species have been isolated from the human faeces. The
colon can be viewed as a large fermentation vessel, and
microbiota consists primarily of anaerobic, G-ve, non-sporing
rods.

29. Large intestine
- anaerobes (96-99% of resident flora):
- Fusobacterium spp.
- Bifidobacterium
- clostridia (C.dificile in small amount)
- anaerobic G+ cocci (Peptostreptococcus)
- facultative aerobes (1-4%) includes:
G- coliform
enterococci
small No. of Pseudomonas, lactobacilli, Proteus .

30. Normal Flora of the Genitourinary Tract
• The upper genitourinary tract (kidney, ureters,
and urinary bladder) is usually free of m.o. In
both the male and female
• a few bacteria such as :
Staphylococcus epidermidis
Enterococcus faecalis
Corynebacterium spp.
are usually present in the distal part of the urethra.

31. Genitourinary Tract

32. Female
For anatomical reasons the female genital tract is much
more heavily colonized than that of the male and has a
complex microbiota that constantly changes with
maturation. The major m.o. are the acid-tolerant
lactobacilli, primarily Lactobacillus acidophilus.
Vulva
- Staphylococcus epidermidis
- Diphtheroids
- Coliforms

33. Vagina
• Soon after birth:
aerobic lactobacilli appear & persist as long as pH acid for several weeks,
when pH become neutral (until puberty) → mixed flora of cocci & bacilli.
• At puberty:
Aerobic & anaerobic lactobacilli (maintenance of acidic pH by production
of acid from carbohydrates; glycogen) → preventing the establishment of
harmful microorganisms in the vagina.
If lactobacilli suppressed (by drugs) → increase No. Of other bacteria &
yeasts cause irritation & inflammation.

34. • After menopause:
Lactobacilli again increase with a mixed flora :
- Peptostreptococci
- clostridia
- Prevotella
- Gardnerella vaginalis
- Ureaplasma urealyticum
- sometimes lesteria or E.coli or coliform).

35. Normal Flora of the Eye
Bacteria found on conjunctiva of the eye are:
• Diphtheroids (Corynebacterium xerosis)
• Staphylococcus epidermidis
• Staphylococcus aureus
• Commensal Neisseria
• Streptococcus pneumonia

36. Normal Flora of the Ear
• It is an extension of skin normal flora and often
profusely colonized.
• Staphylococcus epidermidis
• Diphtheroids
• Alpha-hemolytic and non-hemolyic Streptococci
• Less frequently found are Bacillus and Neisseria
species.

37. The role of Normal Flora
1) Synthesis of vitamin K in the gastrointestinal tract.
2) Absorption of nutrients & breakdown of products.
3) 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.

38. 4) Members of the normal flora may produce disease under
certain circumstances. For example, streptococci group are the
most common resident organisms of the upper respiratory tract.
They cause disease If large numbers of them are introduced into
the bloodstream (eg, following tooth extraction)
5) Microbial flora educate or train human immune system.