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Module: BIOM - 1009

Lecturer: Dr Peña-Fernández

Date: 1/11/16

Normal Microflora of the Human Body
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Humans are exposed to many species of microorganisms during the birth process
 The microorganisms then colonise the new-born baby
 The skin is readily colonised by many species
 The mucous membranes of the oral cavity and GI tract are colonised as the child is fed
and exposed to the mother’s body
 These microflorae can provide benefits to the host and so, a symbiotic relationship is
formed between the humans and the benign microorganisms
 For example, humans get most of their vitamin K from bacteria in the GI tract
 The normal microflora of the body can vary highly between individuals

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There are many areas in the body that support the growth of microorganisms:
 Skin
 Such as Staphylococcus & Micrococcus
 Mouth & oral cavity
 Such as Streptococcus & Lactobacillus
 Respiratory tract
 Such as Streptococcus & Staphylococcus
 GI tract
 Such as Escherichia & Klebsiella
 Urogenital tract
 Such as Proteus & Candida

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There are also a number of locations that microbes should not be found:
 Organs
 Blood
 Lymph
 Nervous system

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Human skin
 The skin spans 2m2 and varies in its chemical composition and moisture content
 It is generally dry and acidic
 Therefore, it doesn’t support the growth of most microorganisms
 Most areas (e
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sweat glands) readily support the growth of Gram-positive bacteria and other
normal flora
 Within the ‘skin’ there are distinct microenvironments:
 Moist areas
 Nostrils, armpits and umbilicus
 Dry areas
 Forearms and palms of hands
 Sebaceous areas
 Side of nose, back of scalp, upper chest and back
 There are two types of skin microflora:
 Transient
 These continuously inoculate the skin and cannot multiply
 E
...
E
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g
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 AIDS patients and other immunocompromised individuals can get other infections
such as Candida

o

Oral cavity
 The oral cavity acts as a complex, heterogenous microbial habitat
 Saliva in the oral cavity contains antimicrobial enzymes such as lysozyme and lactoperoxidase
 High concentrations of nutrients near the mouth surface however promote the
growth of bacteria
 Dental plaque is the result of the extensive growth of microorganisms, especially Streptococci
 As the plaque develops, anaerobic bacteria begin to grow, these produce high amounts
of acid that result in the decalcification of the tooth
 Streptococcus sobrinus and Streptococcus mutans are both lactic acid bacteria
 Diets high in sugar encourages lactic acid bacteria to ferment and produce lactic acid
 Sucrose is common in developed countries and so 80-90% of people are
colonised by S
...
coli)
 The vagina of the adult female is weakly acidic (pH<5) and contains a lot of glycogen
 Lactobacillus acidophilus, a resident organism in the vagina, ferments glycogen producing lactic
acid which produces a protective environment
 This changes before, during and after puberty as well as after menopause



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