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internet Review of Todar"s virtual Textbook of Bacteriology. "The Good, the Bad, and also the Deadly" sign words: bacteriology, bacteria, microbiology, microbe, normal flora, aboriginal bacteria, E. Coli, Staphylococcus, Streptococcus, Enterococcus, Lactobacillus, Bifidobacterium, corynebacteria, clostridium, neisseria, bacteroides, Haemophilus, biofilm, dentist plaque, dental caries, periodontal disease.
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The typical Bacterial Flora of human beings (page 3)(This chapter has 5 pages)© Kenneth Todar, PhDTheComposition that the typical Flora The common flora of humans are exceedingly complex and consistofmorethan 200 species of bacteria. The makeup of the regular flora might beinfluenced by miscellaneous factors, including genetics, age, sex, stress,nutritionanddiet the the individual. 3 developmental transforms in humans, weaning,the eruption the the teeth, and also the onset and also cessationof ovarian functions, invariably impact the ingredient of the normalflorain the minister tract, the oral cavity, and also the vagina, respectively.However, within the boundaries of these fluctuations, the bacter floraofhumans is sufficiently continuous to a give general summary of thesituation.

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A human very first becomes colonized by a common flora at the moment ofbirth and passage v the birth canal. In utero, the fetusis sterile, yet when the mother"s water breaks and also the birth processbegins, therefore does emigration of the body surfaces. Managing andfeeding that the infant after birth leader to establishment of astable normal flora ~ above the skin, dental cavity and intestinal street inabout 48hours.

It has been calculated the a human being adult houses around 1012bacteria on the skin, 1010 in the mouth, and also 1014in the gastrointestinal tract. The last number is much in overabundance ofthenumber that eucaryotic cell in every the tissues and also organs i m sorry comprisea human.The predominant bacteria ~ above the surfaces of thehuman human body are detailed in Table 3. Informal names recognize the bacteriain this table.Formal taxonomic surname of organisms are provided in Table 1.Table3.Predominant bacteria at various anatomical locations in adults. AnatomicalLocation
Predominantbacteria
Skin staphylococciand corynebacteria
Conjunctiva sparse,Gram-positive cocci andGram-negative rods
Oral cavity
teeth streptococci,lactobacilli
mucous membrane streptococci andlacticacid bacteria
Upperrespiratory street
nares (nasal membranes) staphylococciand corynebacteria
pharynx (throat) streptococci,neisseria,Gram-negative rods and also cocci
Lowerrespiratory street none
Gastrointestinaltract
stomach Helicobacterpylori (up come 50%)
small intestine lactics,enterics, enterococci,bifidobacteria
colon bacteroides,lactics, enterics,enterococci, clostridia, methanogens
Urogenital tract
anterior urethra sparse,staphylococci,corynebacteria,enterics
vagina lactic acidbacteria duringchild-bearing years; otherwise blended

Normal Flora the the Skin Theadulthuman is spanned with around 2 square meter of skin. Thedensityand ingredient of the common flora the the skin varies with anatomicallocale.The high moisture contents of the axilla, groin, and areas between thetoessupports the activity and expansion of fairly high densities ofbacterialcells, yet the thickness of bacterial populations at most other website isfairly low, usually in 100s or 1000s every square cm. Most bacteria onthe skin room sequestered in sweat glands.

The skin microbes uncovered in the mostsuperficiallayers of the epidermis and also the upper components of the hair follicles areGram-positive cocci (Staphylococcus epidermidis and Micrococcussp.) and corynebacteria such together Propionibacteriumsp. These are normally nonpathogenic andconsideredto it is in commensal, back mutualistic and also parasitic roles have beenassignedto them. For example, staphylococci and also propionibacteria produce fattyacids that inhibit the development of fungi and also yeast ~ above theskin. But, ifPropionibacterium acnes, anormal inhabitant of the skin, becomestrapped in hair follicle, the may flourish rapidly and also cause inflammationandacne.

Sometimes potentially pathogenic Staphylococcus aureus isfound on the face and also hands in people who room nasalcarriers. This is due to the fact that the face and hands are likely to becomeinoculated with the bacteria ~ above the sleep membranes. Such individualsmay autoinoculate themselves with the microorganism or spread it come otherindividuals or foods.Normal Flora the theConjunctivaA range of bacteria might be grew from the normal conjunctiva,butthe number of organisms is typically small. Staphylococcus epidermidisand details coryneforms (Propionibacteriumacnes) space dominant. Staphylococcusaureus, some streptococci, Haemophilus sp. And Neisseriasp. Are sometimes found. The conjunctiva is preserved moist and healthybythe consistent secretions from the lachrymal glands. Blinking wipes theconjunctiva every couple of seconds mechanically washing away international objectsincluding bacteria. Lachrymal secretions (tears) likewise containbactericidalsubstances consisting of lysozyme. Over there is little or no opportunity formicroorganismsto colonize the conjunctiva without distinct mechanisms to attach to theepithelial surfaces and some capability to withstand assault by lysozyme.Pathogenswhich execute infect the conjunctiva (e.g. Neisseria gonorrhoeae andChlamydiatrachomatis) room thought to have the ability to specifically connect to theconjunctivalepithelium. Newborn babies may be particularly prone come bacterialattachment. Due to the fact that Chlamydiaand Neisseria could bepresent top top the cervical and also vaginal epithelium of one infected mother,silver nitrate or one antibiotic might be put into the newborn"s eye toavoid infection after passage with the birth canal.

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Figure4. Coloniesof Propionibacteriumacnes,found on skin and also the conjunctiva.

Normal Flora that the RespiratoryTractA big number of bacterial species colonize the top respiratorytract(nasopharynx). The nares (nostrils) are constantly heavily colonized,predominantly v Staphylococcusepidermidis and corynebacteria, and often (in about 20% that thegeneralpopulation) through Staphylococcus aureus, this gift the maincarriersite the this essential pathogen. The healthy sinuses, in contrast aresterile. The pharynx (throat) is normally conquered bystreptococci and also various Gram-negative cocci. Periodically pathogens suchas Streptococcuspneumoniae, Streptococcus pyogenes, Haemophilus influenzae and Neisseriameningitidis colonize the pharynx.

The reduced respiratory tract(trachea,bronchi,and pulmonary tissues) is virtually cost-free of microorganisms,mainly because of the reliable cleansing action of the ciliatedepitheliumwhich present the tract. Any kind of bacteria reaching the lower respiratorytractare swept upward through the activity of the mucociliary blanket that linesthebronchi, to be gotten rid of subsequently by coughing, sneezing, swallowing,etc. If the respiratory tract epithelium i do not care damaged, together inbronchitisor famous pneumonia, the separation, personal, instance may come to be susceptible to infectionby pathogens such as H. Influenzae orS.pneumoniae descending from the nasopharynx.

Normal Flora that the UrogenitalTractUrine is generally sterile, and also since the urinary tract is purged withurine every couple of hours, microbe have troubles gaining access andbecoming established. The flora that the anterior urethra, together indicatedprincipallyby urine cultures, argues that the area my be populated by arelativelyconsistent common flora consists of Staphylococcus epidermidis,Enterococcusfaecalis and also some alpha-hemolytic streptococci. Your numbers arenotplentiful, however. In addition, part enteric bacteria (e.g. E.coli, Proteus)and corynebacteria, i m sorry are most likely contaminants indigenous the skin,vulvaor rectum, may occasionally be discovered at the anterior urethra.

The vagina becomes conquered soon after birth v corynebacteria,staphylococci, streptococci, E. Coli, and also a lactic acidbacteriumhistoricallynamed "Doderlein"s bacillus" (Lactobacillus acidophilus). Duringreproductive life, native puberty to menopause, the vaginal epitheliumcontainsglycogen due to the plot of turn estrogens. Doderlein"sbacilluspredominates, gift able to metabolize the glycogen come lactic acid. Thelactic acid and other products of line inhibit emigration byallexcept this lactobacillus and a select variety of lactic acidbacteria.The resulting short pH of the vaginal epithelium prevents establishmentbymost various other bacteria and the potentially-pathogenic yeast, Candidaalbicans.Thisis a striking instance of the protective result of the regular bacterialflora because that their person host.

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Figure5. A Lactobacillus species,possiblyDoderlein"s bacillus, in associationwith a vaginal epithelial cell.

Normal Flora that the OralCavityThe existence of nutrients, epithelial debris, and also secretions renders themouth a favorable habitat for a an excellent variety that bacteria. Oralbacteriainclude streptococci, lactobacilli, staphylococci and also corynebacteria,witha good number that anaerobes, specifically bacteroides.

The mouth gift a sequence of various ecological situationswithage, and this synchronizes with transforms in the composition of the normalflora. In ~ birth, the dental cavity is composed specifically of the soft tissuesof the lips, cheeks, tongue and also palate, i m sorry are preserved moist by thesecretionsof the salivary glands. At bear the oral cavity is sterile however rapidlybecomes conquered from the environment, an especially from the mom inthe first feeding. Streptococcus salivarius is leading andmaymake up 98% the the total oral flora until the figure of the teeth(6- 9 month in humans). The eruption the the teeth during the very first yearleads to emigration by S. Mutans and also S. Sanguis.Thesebacteria need a nondesquamating (nonepithelial) surface ar in bespeak tocolonize. They will certainly persist as lengthy as this remain. Various other strains ofstreptococciadhere strong to the gums and also cheeks yet not to the teeth. Thecreationof the gingival crevice area (supporting frameworks of the teeth)increasesthe habitat because that the variety of anaerobic varieties found. The complexityof the oral flora continues to boost with time, and also bacteroides andspirochetes colonize about puberty.

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Figure6. Variousstreptococci in a biofilm in the dental cavity.

The regular bacterial flora of the dental cavity clearly benefit fromtheir organize who gives nutrients and habitat. There might bebenefits, as well, to thehost. The regular flora occupy available colonization sites whichmakesit more challenging for other microorganisms (nonindigenous species) tobecomeestablished. Also, the dental flora contribute to organize nutrition throughthe synthetic of vitamins, and they add to immunity by inducinglow level of circulating and secretory antitoxin that might cross reactwith pathogens. Finally, the dental bacteria exert microbial antagonismagainstnonindigenous varieties by manufacturing of inhibitory substances together asfatty acids,peroxides and also bacteriocins.

On the various other hand, the oral flora room the usual cause of variousoral diseasesin humans, consisting of abscesses, dentist caries, gingivitis, andperiodontal disease. If oral bacteria can get entrance intodeeper tissues, they may cause abscesses of alveolar bone, lung,brain, or the extremities. Together infections commonly contain mixtures ofbacteriawith Bacteroides melaninogenicus regularly playing a leading role.If oral streptococci room introduced into wounds created by dentalmanipulation or treatment,they might adhere to love valves andinitiatesubacute bacterial endocarditis.

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Figure7. Coloniesof E. Coli cultivation on EMB agar.

NormalFlora the theGastrointestinal tract The bacter flora of the cradle (GI) tract of animalshas been studied moreextensively than that of any kind of other site. The composition differsbetweenvarious pet species, and also within an pet species. In humans, thereare differences in the composition of the flora i m sorry are influenced byage, diet, social conditions, and the use of antibiotics. Thelattergreatly perturbs the composition of the minister flora.

In the top GI tract of adult humans, the esophagus has onlythebacteria swallowed with saliva and food. Since of the high acidity ofthe gastric juice, very few bacteria (mainly acid-tolerantlactobacilli)can be cultured from the regular stomach. However, at least halfthepopulation in the United says is conquered by a pathogenic bacterium,Helicobacterpylori. Since the 1980s, this bacterium has been well-known to bethe reason of gastric ulcers, and also it is most likely a cause of gastric andduodenal cancer together well. The Australian microbiologist, Barry Marshall,received the Nobel compensation in Physiology and Medicine in 2005, fordemonstrating the relationship between Helicobacter and gastriculcers.

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Figure8. Helicobacterpylori. ASM

The proximal small intestine has a relatively sparse Gram-positiveflora,consisting mostly of lactobacilli and Enterococcus faecalis.This region has about 105 - 107 bacteria every mloffluid. The distal component of the tiny intestine includes greater numbersof bacteria (108/ml) and extr species, includingcoliforms (E. Coli andrelatives)and Bacteroides, in addition to lactobacilli and also enterococci.

Theflora of the large intestine (colon) is qualitatively comparable to thatfoundin feces. Populaces of bacteria in the colon reach levels of 1011/mlfeces. Coliforms become more prominent, and enterococci, clostridia andlactobacilli have the right to be regularly found, however the predominant varieties areanaerobicBacteroidesand anaerobic lactic mountain bacteria in the genus Bifidobacterium(Bifidobacterium bifidum). These organisms may outnumber E.coliby 1,000:1 to 10,000:1. Sometimes, far-reaching numbers ofanaerobicmethanogens (up come 1010/gm) might reside in thecolonof humans. This is ours only direct association through archaea together normalflora. The range of incidence of specific bacteria in the largeintestineof people is shown in Table 4 below.

Table 4. Bacteria discovered in thelarge intestineof humans.
BACTERIUM RANGE that INCIDENCE
Bacteroidesfragilis 100
Bacteroidesmelaninogenicus 100
Bacteroidesoralis 100
Lactobacillus 20-60
Clostridiumperfringens 25-35
Clostridiumsepticum 5-25
Clostridiumtetani 1-35
Bifidobacteriumbifidum 30-70
Staphylococcusaureus 30-50
Enterococcusfaecalis 100
Escherichiacoli 100
Salmonellaenteritidis 3-7
Klebsiellasp. 40-80
Enterobactersp. 40-80
Proteusmirabilis 5-55
Pseudomonasaeruginosa 3-11
Peptostreptococcussp. ?common
Peptococcussp. ?common
At bear the entire intestinal street is sterile, yet bacteria enterwith the first feed. The early colonizing bacteria vary v the foodsource the the infant. In breast-fed infants, bifidobacteria account formore 보다 90% of the full intestinal bacteria. Enterobacteriaceaeand enterococci are consistently present, but in short proportions, whilebacteroides,staphylococci, lactobacilli and clostridia are nearly absent. Inbottle-fedinfants, bifidobacteria are not predominant. As soon as breast-fed infantsareswitched come a diet the cow"s milk or solid food, bifidobacteria areprogressivelyjoined by enterics, bacteroides, enterococci lactobacilli andclostridia.Apparently, human milk has a development factor that enriches forgrowthof bifidobacteria, and these bacteria play vital role inpreventingcolonization of the child intestinal tract by non aboriginal orpathogenicspecies.
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Figure9. Clostridiumdifficile. Gram stain. The development of "C. Diff" in the intestinaltract is normally held in check by various other members that the common flora.When antibiotics offered for other infections reason collateral damage tothe common intestinal flora, the clostridium may have the ability to "grow out"and create a serious diarrheal syndrome called pseudomembranouscolitis. This is an example of an "antibiotic induced diarrheal disease".The composition of the flora of the gastrointestinal street variesalongthe tract (at longitudinal levels) and throughout the street (at horizontallevels) where certain bacteria affix to the gastrointestinalepitheliumand others take place in the lumen. There is frequently a really closeassociationbetween particular bacteria in the minister ecosystem and specific guttissues or cells (evidence of tissue tropism and particular adherence).Gram-positive bacteria, such as the streptococci and lactobacilli, arethought come adhere come the cradle epithelium usingpolysaccharidecapsules or cell wall teichoic mountain to connect to certain receptors onthe epithelial cells. Gram-negative bacteria such together theentericsmay attach by way of specific fimbriae whichbindto glycoproteins on the epithelial cell surface.

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It is in the intestinal tract the we see the greatest result of thebacterial flora on your host. This is due to their huge mass andnumbers. Bacteria in the person GI tract have actually been shown to producevitamins and also may otherwise contributeto nutrition and also digestion. However their many important results are intheir capability to defend their hold from facility andinfection byalien microbes and also their ability to wake up the advance and theactivity that the immunological tissues.

On the other hand, some of the bacteria in the colon (e.g. Bacteroides) have been shown toproduce metabolites that space carcinogenic, and also there may be anincreased incidence that colon cancer linked with this bacteria.Alterations in the GI flora brought on by negative nutrition or perturbancewith antibiotics can cause shifts in populations and colonization bynonresidents the leads to gastrointestinal disease.chapter continuedPrevious Page© Kenneth Todar, Ph.D. All legal rights reserved. - www.londonchinatown.org