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Microflora of the human bodyMicroflora of the human body
bacteria and immunity systembacteria and immunity system
Zuzana Čermáková, D.V.M., Ph.D.
Institute of clinical microbiology
Tel. 606 718 562, 495 833 540,
E-mail: [email protected]
Importance in human healthImportance in human healthHuman digestionMicroorganisms can form an endosymbiotic relationship with other, larger organisms. For example, the bacteria that live within the human digestive system contribute to gut immunity (immunoglobulins A class above all), synthesise vitamins such as folic acid and biotin, vitamine B complex and ferment complex indigestible carbohydrates.Microorganisms are on the skin, in the mouth, in the upper respiratory tract....... = and forms normal microflora of human body – prevention of pathogens
Human floraHuman flora The human flora are the microorganisms that constantly inhabit the human body• They include bacteria, fungi and archea.• Some of these organisms are known to perform tasks that are useful for the human host, while the majority have no known beneficial or harmful effect
•Those that are expected to be present, and that under normal circumstances do not cause disease, are termed normal flora, or microbiota.
It is estimated that 500 to 1000 species of bacteria live in the human body
Though normal flora are found on all surfaces exposed to the environment (on the skin and eyes, in the mouth, nose, small intestine), the vast majority of bacteria live in the large intestine
Many of the bacteria in the digestive tract, Many of the bacteria in the digestive tract, collectively referred to as gut flora, are able to break collectively referred to as gut flora, are able to break down certain nutrients such as carbohydratesdown certain nutrients such as carbohydrates
The majority of these commensal bacteria are anaerobes, meaning they survive in an environment with no oxygen (GIT).
Bacteria of the normal flora can act as opportunistic pathogens at times of lowered immunity
Escherichia coli is a bacterium that lives in the colon; it is an extensively studied model organism model organism and probably the best understood bacterium of all
Certain mutated strains of these gut bacteria do cause disease; an example is E.coli O157:H7
Normal flora
is the mixture of organisms regularly found at any anatomical site (skin, GIT, vagine…)
Composition of normal flora depends upon many various factors: - genetics, age, sex, stress, nutrition, diet…
Mutualistic relationship: The normal flora derives from the host a supply of nutrients, a stable environment, constant temperature, protection and transport. The host obtains from the normal
…flora certain nutritional benefits, stimulation of the nutritional benefits, stimulation of the immune system, and colonization strategies that immune system, and colonization strategies that exclude potential pathogens at the siteexclude potential pathogens at the site.
• members of the normal flora are normaly adapted to their host /tissues/, most probably by biochimical interactions between bacterial surface components (ligands or adhesins) and host cell molecular receptors
• The explanations for why the normal bacterial flora are located at paticular anatomical sites are practically three:
1) Tissue tropism – one explanation of tissue tropism is that the host provides an essential growth factor needed by the bacterium, on the oposite site the host produses in other organs stomach acids, bile salts, lysozym….and this sites are not favourable for live organisms…
2) Many of the normal flora are able to specifically colonize a particular tissue or surface using their own surface components like capsules, fimbriae, cell wall components, as specific ligands for attachment to specific receptors located at the colonization sites
3) Some of the indigenous bacteria are able to construct bacterial biofilms on a tissue surface
- Many biofilms are a mixture of microbes, although one member is responsible for maintaining the biofilm and may predominate
The composition of the normal floraThe composition of the normal flora• It has been calculated that the normal human is
host to about 1012 bacteria on the skin, 1010 in the mouth and 1014 in the gastrointestinal tract
1. Normal flora of the skin
An adult person is covered approximately with 2 square meters fo skin
The density and composition of the normal flora of the skin vary with anatomical locale
Ex. the high moisture of content of the axilla…..is good place for „cultivation“ of bacteria and fungi
(relatively high density of bacterial cells)
…but at most other sites the bacterial population is fairly low – generally cells, generally 100 – 1000 per square cm• the majority of skin microorganisms are found in the majority of skin microorganisms are found in the most superficial layers of the epidermis and the upper most superficial layers of the epidermis and the upper parts of the hair folliclesparts of the hair follicles•Staphylococcus epidermidis, Micrococcus spp., nonpathogenic corynebacteria• their are generally nonpathogenic – commensals, or mutualists (in immunocompetent personsin immunocompetent persons)• Skin bacteria or their metabolites may protect against colonization by dermatophytic fungi or pathogenic bacteria
• sometimes potentially pathogenic Staphylococcus aureus is found on the face and hands, particularly in individuals who are nasal carriers
2.2. Normal flora of the respiratory tractNormal flora of the respiratory tract• The nares (nostrils) are always heavily colonized,
predominantly with Staphylococcus epidemidis and corynebacteria (about 20% of the general corynebacteria (about 20% of the general population) with population) with Staphylococcus aureusStaphylococcus aureus (also (also MRSA carriers),MRSA carriers),
• Sinuses (healthy) – are sterile (in normal conditions)
1. The upper respiratory tract (nasopharynx) – predominantly non-hemolytic and alphahemolytic streptococci and Neisseria species and sometimes pathogens such as Str.pneumoniae, Haemophilus influenzae, Neiseria meningitidis.
2. Lower respiratory tract (trachea, bronchi, pulmonary tissues) – are uppon the normal conditions free of microorganisms – mainly because of the efficient cleansing action of the ciliated epithelium which covers respiratory tract
Any bacteria reaching the lower respiratory tract are removed by the action of this epithelia and also by coughing, sneezing, swallowing, etc…
3. Normal flora of the Human Oral CavityStreptococci, lactobacilli, staphylococci and corynebacteria (aerobic, microaerophiles) and anaerobes ( bacteroides
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The mouth presents of different ecological situations with age, and this corresponds with changes in the composition of the normal flora (good example of importance of bacteria for immunity system):
• At birth the oral cavity is composed of the soft tissues (lips, cheeks, tongue, palate…) which are kept moist by the secretions of the salivary glands
• at birth the oral cavity is sterile but rapidly becomes colonized from the environment, particularly from the mother in the first feeding and then in other contact with mother – hands, lips…..• Streptococcus salivarius is dominant – 98% of the total oral flora until appearance of the teeth (6-9 months in humans)• S. mutans, S. sanguis…..• In contact with healthy adults young children are colonized with other bacteria – Staphylococcus epidermidis, Escherichia coli, nonpathogenic corynebacteria and immunity system starts „the training“ • Immunity system develops in children organism to 5 years of age
4. Normal flora of conjunctiva• a variety of bacteria may be cultivated from the normal conjunctiva but the number of organisms is usually small (S.epidermidis, nonpathogenic corynebacteria, Propionibacterium acnes) are dominant• S.aureus, streptococcus spp., Haemophilus spp., Neisseria spp. are occasionally found• The conjunctiva is kept moist (tears = lachrymal secretion with lysozyme) • Pathogens usually are: Chlamydia trachomatis, S.aureus, Neisseria gonnorhoae, streptococci, enterococci….
5. Normal flora of the Urogenital Tract• Urine is normally sterile • Lower parts of urethra may be colonized with a Lower parts of urethra may be colonized with a small density of nonpathogenic small density of nonpathogenic S.epidermidis, S.epidermidis, streptococcus spp. – alfa-hemolytic, enterococci, streptococcus spp. – alfa-hemolytic, enterococci, corynebacteriacorynebacteria• pathogenic bacteria – in urogenital system which can cause infection and inflammation may be:
Gramnegative rods (Proteus spp., E.coli), Streptococcus B group (agalactiae), enterococci….• about 80-90% infections of the urinary tract - woman – short distance from anus – source of bacteria
6. The vagineNormaly is colonized corynebacteria, nonpathogenic streptococci, staphylococci – nonpathogenic, small number of yeasts – Candida albicans and very important is Lactobacillus acidophilus (named Lactobacillus acidophilus (named Döderlein´s bacillus)Döderlein´s bacillus) – lower pH !!! – prevention against pathogenic flora (and also Trichomonas vaginalis)
Pathogens: Neisseria gonorrhoae, Str. agalactiae, gram-negative rods – E.coli, Proteus spp., yeasts,
7. Normal flora of the gastrointestinal tract (GIT)• E. coli, other gram-negative rods – nonpathogenic (Klebsiella spp., Proteus spp.,), Enterococcus, other streptococci, anaerobic bacteria – Clostridia, Bacillus spp., Bacteroides……
And many nonpathogenic protozoa, yeasts
Ex. Pathogens: Ex. Pathogens: Salmonella spp., Shigella spp., Salmonella spp., Shigella spp., pathogenic pathogenic E.coli, Helicobacter pylori, Campylobacter E.coli, Helicobacter pylori, Campylobacter jejunii…rotaviruses….jejunii…rotaviruses….parasites: parasites: Entamoeba Entamoeba histolytica histolytica (protozoon), wormes ……(protozoon), wormes ……
Benefits of the normal intestinal human flora
• synthesis and excretions of vitamins (B group), vitamin K (E.coli)
• prevent colonization by pathogens by competing for attachment sites or for essential nutrients
• the normal flora also produces substances which inhibit or kill nonindigenous species (pathogens)
•The normal flora in general stimulates the development of certain lymphatic tissues – parts of immunity system in GIT
• The normal flora – in general – stimulate the production of cross-reactive antibodies.
• It is known that the normal flora induce immunological responses • very low level usually non-specific antibodies (cross-reactive) react with certain related pathogens and can prevent infection or invasion
• „„training“ of the immunity system by contact training“ of the immunity system by contact with normal flora is very important and it is with normal flora is very important and it is condition for normla surviving of condition for normla surviving of macroorganisms (animals, human) in the macroorganisms (animals, human) in the normal environment normal environment
