Microflora of the human body bacteria and immunity systemZuzana Čermáková, D.V.M., Ph.D. Institute of clinical microbiology Tel. 606 718 562, 495 833 540, E-mail: email@example.com
Importance in human healthHuman digestionMicroorganisms can form an endosymbioticrelationship with other, larger organisms. Forexample, the bacteria that live within the humandigestive system contribute to gut immunity(immunoglobulins A class above all), synthesisevitamins such as folic acid and biotin, vitamine Bcomplex and ferment complex indigestiblecarbohydrates.Microorganisms are on the skin, in the mouth, in theupper respiratory tract....... = and forms normalmicroflora of human body – prevention of pathogens
Human floraThe human flora are the microorganisms thatconstantly inhabit the human body• They include bacteria, fungi and archea.• Some of these organisms are known to performtasks that are useful for the human host, while themajority have no known beneficial or harmful effect•Those that are expected to be present, and thatunder normal circumstances do not cause disease,are termed normal flora, or microbiota.
It is estimated that 500 to 1000 species of bacteriaive in the human body Though normal flora are found on all surfacesexposed to the environment (on the skin and eyes, in he mouth, nose, small intestine), the vast majority ofbacteria live in the large intestine Many of the bacteria in the digestive tract,collectively referred to as gut flora, are able to breakdown certain nutrients such as carbohydrates
The majority of these commensal bacteria areanaerobes, meaning they survive in an environmentwith no oxygen (GIT). Bacteria of the normal flora can act as opportunisticpathogens at times of lowered immunity Escherichia coli is a bacterium that lives in thecolon; it is an extensively studied model organismmodel organism and probably the best understoodbacterium of all Certain mutated strains of these gut bacteria docause 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 mmune system, and colonization strategies thatexclude potential pathogens at the site. site members of the normal flora are normaly adapted toheir host /tissues/, most probably by biochimicalnteractions between bacterial surface componentsligands or adhesins) and host cell moleculareceptors The explanations for why the normal bacterial floraare located at paticular anatomical sites arepractically three:
Tissue tropism – one explanation of tissuetropism is that the host provides an essentialgrowth factor needed by the bacterium, on theoposite site the host produses in other organsstomach acids, bile salts, lysozym….and thissites are not favourable for live organisms…Many of the normal flora are able to specificallycolonize a particular tissue or surface using theirown surface components like capsules, fimbriae,cell wall components, as specific ligands forattachment to specific receptors located at thecolonization sites
3) Some of the indigenous bacteria are able toconstruct bacterial biofilms on a tissue surface Many biofilms are a mixture of microbes, althoughone member is responsible for maintaining thebiofilm and may predominate
The 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 Normal flora of the skinAn adult person is covered approximately with 2 square meters fo skinThe density and composition of the normal flora of the skin vary with anatomical localeEx. 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 airly low – generally cells, generally 100 – 1000 persquare cm the majority of skin microorganisms are found in themost superficial layers of the epidermis and the upperparts of the hair follicles Staphylococcus epidermidis, Micrococcus spp.,nonpathogenic corynebacteria their are generally nonpathogenic – commensals, ormutualists (in immunocompetent persons) persons Skin bacteria or their metabolites may protectagainst colonization by dermatophytic fungi orpathogenic bacteria
sometimes potentially pathogenic Staphylococcus aureus is found on the face and hands, particularly in individuals who are nasal carriers3. Normal flora of the respiratory tract The nares (nostrils) are always heavily colonized, predominantly with Staphylococcus epidemidis and corynebacteria (about 20% of the general population) with Staphylococcus aureus (also MRSA carriers), Sinuses (healthy) – are sterile (in normal conditions)
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. 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 tractAny 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 andcorynebacteria (aerobic, microaerophiles) andanaerobes ( bacteroides **********The mouth presents of different ecological situationswith age, and this corresponds with changes in thecomposition of the normal flora (good example of mportance of bacteria for immunity system): At birth the oral cavity is composed of the softissues (lips, cheeks, tongue, palate…) which are keptmoist by the secretions of the salivary glands
• at birth the oral cavity is sterile but rapidlybecomes colonized from the environment,particularly from the mother in the first feeding andthen in other contact with mother – hands, lips…..• Streptococcus salivarius is dominant – 98% of thetotal oral flora until appearance of the teeth (6-9months in humans)• S. mutans, S. sanguis…..• In contact with healthy adults young children arecolonized with other bacteria – Staphylococcusepidermidis, Escherichia coli, nonpathogeniccorynebacteria and immunity system starts „thetraining“• Immunity system develops in children organism to5 years of age
4. Normal flora of conjunctiva a variety of bacteria may be cultivated from thenormal conjunctiva but the number of organisms isusually small (S.epidermidis, nonpathogeniccorynebacteria, Propionibacterium acnes) aredominant S.aureus, streptococcus spp., Haemophilus spp.,Neisseria spp. are occasionally found The conjunctiva is kept moist (tears = lachrymalsecretion 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 asmall density of nonpathogenic S.epidermidis,streptococcus spp. – alfa-hemolytic, enterococci,corynebacteria pathogenic bacteria – in urogenital system whichcan 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 ofbacteria
6. The vagineNormaly is colonized corynebacteria, nonpathogenicstreptococci, staphylococci – nonpathogenic, smallnumber of yeasts – Candida albicans and very mportant is Lactobacillus acidophilus (namedDöderlein´s bacillus) – lower pH !!! – preventionagainst pathogenic flora (and also Trichomonasvaginalis)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, otherstreptococci, anaerobic bacteria – Clostridia, Bacillusspp., Bacteroides……And many nonpathogenic protozoa, yeastsEx. Pathogens: Salmonella spp., Shigella spp.,pathogenic E.coli, Helicobacter pylori, Campylobacterejunii…rotaviruses….parasites: Entamoebahistolytica (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 or attachment sites or for essential nutrients the normal flora also produces substances which nhibit or kill nonindigenous species (pathogens) The normal flora in general stimulates thedevelopment of certain lymphatic tissues – parts of mmunity system in GIT The normal flora – in general – stimulate theproduction of cross-reactive antibodies.
It is known that the normal flora induce mmunological responses very low level usually non-specific antibodies cross-reactive) react with certain related pathogensand can prevent infection or invasion „training“ of the immunity system by contactwith normal flora is very important and it iscondition for normla surviving ofmacroorganisms (animals, human) in thenormal environment