NORMAL MICROBIAL FLORA
DR NAZIA KHAN
ASSISTANT PROFESSOR
COLLEGE OF MEDICINE
• Human beings carry a lot of microorganisms both on
and in their body.
• A knowledge of normal microbial flora is important
to an understanding of the interaction of human
beings and their pathogen laden environment.
BENEFICIAL FUNCTIONS OF NORMAL
FLORA
1. Prevent colonization by pathogens
2. Produce antimicrobial substances
3. In newborn it is a powerful stimulus for the
development of the immune system
4. Microflora of intestine synthesize vitamin k
and several B vitamins
5. Normal flora may produce endotoxins
Harmful effects of normal flora
1. When organisms are displaced from their normal site
in the body to an abnormal site
2. When potential pathogens gain a competitive
advantage due to diminished populations of harmless
competitors example: by use of antibiotic therapy
3. When some harmless substances like ingested food
are converted into carcinogenic derivatives by
bacteria in the colon
4. Immunocompromised individuals
5. Drug resistance
6. Confusion in diagnosis
NORMAL FLORA OF THE SKIN
• The human skin is constantly bombarded by
organisms present in the environment .
• It is also contaminated by one’s own secretions
and excretions depending on individual’s personal
hygiene .
• Examples: Staphylococcus
Diphtheroids
E.coli
candida
NORMAL FLORA OF THE CONJUCTIVA
• It is relatively free from organisms due to the
flushing action of tears.
• Examples: Diphtheroids
Staphylococcus
NORMAL FLORA OF THE NOSE,
NASOPHARYNX AND ACESSORY SINUSES
• In the nose: Corynebateria
Staphylococcus
• The nasopharynx of infant is sterile at birth
• But acquires the common commensal flora
and pathogenic flora carried form the mother
and hospital staff
• Examples: Peudomonas
E.coli
NORMAL FLORA OF THE MOUTH AND
UPPER RESPIRATORY TRACT
• Mouth contains many organisms like
Examples: Micrococci
coliforms
Corynebacterium
Fusiform bacilli
Candida
• The mouth of the infant is not sterile at birth
NORMAL FLORA OF THE INTESTINAL
TRACT
• In 80-90 % newborn infants,the meconium is
sterile but in 10-20% a few orrganisms probably
acquired through labour may be present.
• In all cases,within 4-24 hours of birth an intestinal
flora is established
• In bresstfed children the intestine contains
lactobacillus while bottle fed babies have
enterococci, colon bacilli and stahpylococci
• With the change of food in adult person, flora
changes
• The umber of bacteria increases beyond
duodenum to the colon
• In adult duodenum there are 103 -106 bacteria
per gram
• In duodenum and upper ileum, lactobacili and
enterococci are present
• in adult normal colon,the resident bacterial
flora are mostly anaerobes
NORMAL FLORA OF THE
GENITOURINARY TRACT
• Examples: Mycobacterium smegmatitis
• In males: lactobacilli,
• Female urethra amy be sterile or may have gram
positive cocci
• The vulva of newborn child is sterile but after 24
hours it acquires many flora
• The nature of the flora of the vagina depends on
the Ph of its secretions and its enzymes
• The normal vaginal flora often includes:
anaerobic cocci, and bacilli, listeria,etc.
BACTERIA IN THE BLOOD AND TISSUES
• Blood is sterile
• The commensals from the normal flora of the
mouth,nasopharynx and intestinal tract may
get into the blood and tissues but they are
usually quickly eliminated by the normal
defence mechanisms
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‫الجمعة‪ 26 ،‬رمضان‪1437 ،‬‬
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THANK YOU
1.
Self assessment
The greatest number and variety of indigenous microflora of the human
body live in or on the:
• a. colon.
• b. genitourinary tract.
• c. mouth.
• d. skin.
2 . Which of the following sites of the human body does not have indigenous
microflora?
• a. bloodstream
• b. colon
• c. distal urethra
• d. vagina
3 . Which of the following would be present in highest numbers in the
indigenous microflora of the skin?
• a. C. albicans
• b. coagulase-negative staphylococci
• c. Enterococcus spp.
• d. E. coli
4. The indigenous microflora of the external ear canal is most like the indigenous
microflora of the:
• a. colon.
• b. mouth.
• c. skin.
• d. distal urethra.
5. Microorganisms are used in which of the following industries?
• a. antibiotic
• b. chemical
• c. food, beer, and wine
• d. all of the above
6. The term that best describes a symbiotic relationship in which two different
microorganisms occupy the same ecologic niche, but have absolutely no
• effect on each other is:
• a. commensalism.
• b. mutualism.
• c. neutralism.
• d. parasitism