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net Review of Todar"s virtual Textbook of Bacteriology. "The Good, the Bad, and the Deadly" tag words: bacteriology, bacteria, microbiology, microbe, typical flora, aboriginal bacteria, E. Coli, Staphylococcus, Streptococcus, Enterococcus, Lactobacillus, Bifidobacterium, corynebacteria, clostridium, neisseria, bacteroides, Haemophilus, biofilm, dental plaque, dental caries, periodontal disease.
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The normal Bacterial Flora of people (page 3)(This chapter has 5 pages)© Kenneth Todar, PhDTheComposition of the common Flora The regular flora of humans are exceedingly complex and consistofmorethan 200 types of bacteria. The makeup of the normal flora may beinfluenced by various factors, consisting of genetics, age, sex, stress,nutritionanddiet the the individual. 3 developmental alters in humans, weaning,the eruption the the teeth, and the onset and cessationof ovarian functions, invariably affect the ingredient of the normalflorain the intestinal tract, the dental cavity, and the vagina, respectively.However, within the boundaries of this fluctuations, the bacterial floraofhumans is sufficiently continuous to a provide general description of thesituation.

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A human an initial becomes colonized by a regular flora at the minute ofbirth and also passage v the birth canal. In utero, the fetusis sterile, yet when the mother"s water breaks and the birth processbegins, for this reason does colonization of the body surfaces. Taking care of andfeeding the the infant after birth leader to establishment of astable normal flora on the skin, dental cavity and also intestinal street inabout 48hours.

It has actually been calculated that a human adult houses around 1012bacteria top top the skin, 1010 in the mouth, and 1014in the cradle tract. The latter number is much in overfill ofthenumber the eucaryotic cell in all the tissues and organs i beg your pardon comprisea human.The predominant bacteria ~ above the surface of thehuman human body are listed in Table 3. Informal names recognize the bacteriain this table.Formal taxonomic name of biology are given in Table 1.Table3.Predominant bacteria at miscellaneous anatomical places in adults. AnatomicalLocation
Predominantbacteria
Skin staphylococciand corynebacteria
Conjunctiva sparse,Gram-positive cocci andGram-negative rods
Oral cavity
teeth streptococci,lactobacilli
mucous membranes streptococci andlacticacid bacteria
Upperrespiratory tract
nares (nasal membranes) staphylococciand corynebacteria
pharynx (throat) streptococci,neisseria,Gram-negative rods and cocci
Lowerrespiratory tract none
Gastrointestinaltract
stomach Helicobacterpylori (up to 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 that the Skin Theadulthuman is spanned with around 2 square meter of skin. Thedensityand composition of the typical flora of the skin varies v anatomicallocale.The high moisture content of the axilla, groin, and also areas in between thetoessupports the activity and growth of reasonably high densities ofbacterialcells, yet the thickness of bacterial populations at many other website isfairly low, typically in 100s or 1000s every square cm. Many bacteria onthe skin are sequestered in sweat glands.

The skin microbes uncovered in the mostsuperficiallayers of the epidermis and the upper components of the hair follicles areGram-positive cocci (Staphylococcus epidermidis and Micrococcussp.) and corynebacteria such together Propionibacteriumsp. This are usually nonpathogenic andconsideredto it is in commensal, although mutualistic and also parasitic roles have actually beenassignedto them. Because that example, staphylococci and also propionibacteria develop fattyacids the inhibit the expansion of fungi and also yeast on theskin. But, ifPropionibacterium acnes, anormal inhabitant that the skin, becomestrapped in hair follicle, it may grow rapidly and cause inflammationandacne.

Sometimes possibly pathogenic Staphylococcus aureus isfound ~ above the face and hands in people who room nasalcarriers. This is due to the fact that the face and also hands are most likely to becomeinoculated through the bacteria top top the nasal membranes. Such individualsmay autoinoculate themselves through the pathogen or spread out it to otherindividuals or foods.Normal Flora of theConjunctivaA variety of bacteria might be grew from the common conjunctiva,butthe variety of organisms is generally small. Staphylococcus epidermidisand details coryneforms (Propionibacteriumacnes) space dominant. Staphylococcusaureus, some streptococci, Haemophilus sp. And Neisseriasp. Are occasionally found. The conjunctiva is kept moist and healthybythe consistent secretions indigenous the lachrymal glands. Blinking wipes theconjunctiva every few seconds mechanically washing away international objectsincluding bacteria. Lachrymal secretions (tears) also containbactericidalsubstances consisting of lysozyme. Over there is tiny or no possibility formicroorganismsto colonize the conjunctiva without distinct mechanisms to connect to theepithelial surfaces and some capability to withstand attack by lysozyme.Pathogenswhich do infect the conjunctiva (e.g. Neisseria gonorrhoeae andChlamydiatrachomatis) room thought to be able to specifically connect to theconjunctivalepithelium. Newborn infants may be particularly prone come bacterialattachment. Since Chlamydiaand Neisseria can bepresent on the cervical and also vaginal epithelium of one infected mother,silver nitrate or one antibiotic might be put into the newborn"s eye toavoid epidemic after passage v the bear canal.

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

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

The reduced respiratory tract(trachea,bronchi,and pulmonary tissues) is virtually totally free of microorganisms,mainly since of the efficient cleansing activity of the ciliatedepitheliumwhich currently the tract. Any kind of bacteria getting to the reduced respiratorytractare swept upward by the action of the mucociliary blanket the linesthebronchi, come be eliminated subsequently through coughing, sneezing, swallowing,etc. If the respiratory tract tract epithelium becomes damaged, together inbronchitisor famous pneumonia, the separation, personal, instance may end up being susceptible come infectionby pathogens such together H. Influenzae orS.pneumoniae descending indigenous the nasopharynx.

Normal Flora that the UrogenitalTractUrine is generally sterile, and since the urinary tract is purged withurine every couple of hours, microbe have troubles gaining accessibility andbecoming established. The flora that the anterior urethra, as indicatedprincipallyby to pee cultures, suggests that the area my be occupied by arelativelyconsistent regular 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 more than likely contaminants from the skin,vulvaor rectum, might occasionally be found at the anterior urethra.

The vagina becomes colonized soon after ~ birth through corynebacteria,staphylococci, streptococci, E. Coli, and also a lactic acidbacteriumhistoricallynamed "Doderlein"s bacillus" (Lactobacillus acidophilus). Duringreproductive life, indigenous puberty come menopause, the vaginal epitheliumcontainsglycogen as result of the plot of turn around estrogens. Doderlein"sbacilluspredominates, being able come metabolize the glycogen come lactic acid. Thelactic acid and other assets of line inhibit colonization byallexcept this lactobacillus and a select variety of lactic acidbacteria.The resulting short pH the the vaginal epithelium prevents establishmentbymost various other bacteria as well as the potentially-pathogenic yeast, Candidaalbicans.Thisis a striking example of the protective effect of the normal bacterialflora for their human being host.

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

Normal Flora of the OralCavityThe existence of nutrients, epithelial debris, and secretions renders themouth a favorable habitat because that a great variety that bacteria. Oralbacteriainclude streptococci, lactobacilli, staphylococci and corynebacteria,witha good number that anaerobes, especially bacteroides.

The mouth gift a sequence of various ecological situationswithage, and also this synchronizes with alters in the composition of the normalflora. At birth, the dental cavity is composed solely of the soft tissuesof the lips, cheeks, tongue and palate, which are retained moist through thesecretionsof the salient glands. At birth the dental cavity is sterile yet rapidlybecomes conquered from the environment, specifically from the mother inthe first feeding. Streptococcus salivarius is dominant andmaymake increase 98% the the full oral flora until the figure of the teeth(6- 9 month in humans). The eruption of the teeth during the very first yearleads to emigration by S. Mutans and S. Sanguis.Thesebacteria require a nondesquamating (nonepithelial) surface ar in bespeak tocolonize. They will certainly persist as long as this remain. Various other strains ofstreptococciadhere strong to the gums and cheeks but not come the teeth. Thecreationof the gingival crevice area (supporting frameworks of the teeth)increasesthe habitat for the variety of anaerobic types found. The complexityof the dental flora proceeds to rise with time, and bacteroides andspirochetes colonize about puberty.

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Figure6. Variousstreptococci in a biofilm in the oral cavity.

The regular bacterial flora that the oral cavity clearly benefit fromtheir hold who offers nutrients and also habitat. There might bebenefits, together well, come thehost. The typical flora occupy obtainable colonization sites whichmakesit more daunting for other microorganisms (nonindigenous species) tobecomeestablished. Also, the dental flora contribute to hold nutrition throughthe synthesis of vitamins, and also they contribute to immunity by inducinglow level of circulating and secretory antitoxin that might cross reactwith pathogens. Finally, the oral bacteria exert microbial antagonismagainstnonindigenous species by manufacturing of inhibitory substances such asfatty acids,peroxides and also bacteriocins.

On the other hand, the dental flora space the usual cause of variousoral diseasesin humans, including abscesses, dental caries, gingivitis, andperiodontal disease. If dental bacteria can acquire entrance intodeeper tissues, they may cause abscesses the alveolar bone, lung,brain, or the extremities. Together infections commonly contain mixture ofbacteriawith Bacteroides melaninogenicus frequently playing a dominant role.If oral streptococci space introduced right into wounds created by dentalmanipulation or treatment,they may adhere to heart valves andinitiatesubacute bacterial endocarditis.

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Figure7. Coloniesof E. Coli cultivation on EMB agar.

NormalFlora that theGastrointestinal street The bacterial flora of the cradle (GI) tract of animalshas been studied moreextensively than that of any type of other site. The composition differsbetweenvarious animal species, and within an animal species. In humans, thereare differences in the composition of the flora i beg your pardon are influenced byage, diet, cultural conditions, and the use of antibiotics. Thelattergreatly perturbs the ingredient of the minister flora.

In the upper GI tract of adult humans, the esophagus contains onlythebacteria swallowed v saliva and also food. Since of the high acidity ofthe gastric juice, very few bacteria (mainly acid-tolerantlactobacilli)can it is in cultured from the normal stomach. However, at least halfthepopulation in the United says is conquered by a pathogenic bacterium,Helicobacterpylori. Because the 1980s, this bacterium has been recognized to bethe reason of gastric ulcers, and it is more than 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 actually a relatively sparse Gram-positiveflora,consisting largely of lactobacilli and also Enterococcus faecalis.This region has around 105 - 107 bacteria per mloffluid. The distal part of the small intestine contains greater numbersof bacteria (108/ml) and additional species, includingcoliforms (E. Coli andrelatives)and Bacteroides, in addition to lactobacilli and also enterococci.

Theflora the the huge intestine (colon) is qualitatively comparable to thatfoundin feces. Populaces of bacteria in the colon reach levels of 1011/mlfeces. Coliforms become an ext prominent, and enterococci, clostridia andlactobacilli deserve to be consistently found, yet the predominant varieties areanaerobicBacteroidesand anaerobic lactic acid bacteria in the genus Bifidobacterium(Bifidobacterium bifidum). These organisms may outnumber E.coliby 1,000:1 come 10,000:1. Sometimes, far-ranging numbers ofanaerobicmethanogens (up come 1010/gm) might reside in thecolonof humans. This is our only direct association v archaea as normalflora. The selection of incidence of certain bacteria in the largeintestineof people is presented in Table 4 below.

Table 4. Bacteria uncovered in thelarge intestineof humans.
BACTERIUM RANGE of 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 birth the whole intestinal street is sterile, however bacteria enterwith the very first feed. The initial colonizing bacteria vary v the foodsource that the infant. In breast-fed infants, bifidobacteria account formore 보다 90% the the total intestinal bacteria. Enterobacteriaceaeand enterococci are frequently present, however in short proportions, whilebacteroides,staphylococci, lactobacilli and clostridia are nearly absent. Inbottle-fedinfants, bifidobacteria room not predominant. Once breast-fed infantsareswitched to a diet the cow"s milk or hard food, bifidobacteria areprogressivelyjoined through enterics, bacteroides, enterococci lactobacilli andclostridia.Apparently, human being milk contains a expansion factor the enriches forgrowthof bifidobacteria, and these bacteria play critical role inpreventingcolonization that the infant intestinal tract by non indigenous orpathogenicspecies.
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Figure9. Clostridiumdifficile. Gram stain. The development of "C. Diff" in the intestinaltract is generally held in check by other members that the regular flora.When antibiotics provided for other infections cause collateral damage tothe common intestinal flora, the clostridium may be able to "grow out"and develop a major diarrheal syndrome called pseudomembranouscolitis. This is an instance of an "antibiotic induced diarrheal disease".The ingredient of the flora that the gastrointestinal tract variesalongthe street (at longitudinal levels) and across the tract (at horizontallevels) where certain bacteria attach to the gastrointestinalepitheliumand others occur in the lumen. There is commonly a an extremely closeassociationbetween particular bacteria in the minister ecosystem and certain guttissues or cells (evidence of organization tropism and specific adherence).Gram-positive bacteria, such together the streptococci and lactobacilli, arethought come adhere come the gastrointestinal epithelium usingpolysaccharidecapsules or cell wall teichoic acids to attach to particular receptors onthe epithelial cells. Gram-negative bacteria such together theentericsmay attach by way of specific fimbriae whichbindto glycoproteins top top the epithelial cell surface.

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It is in the minister tract the we view the greatest impact of thebacterial flora on your host. This is because of their large mass andnumbers. Bacteria in the person GI tract have actually been displayed to producevitamins and also may otherwise contributeto nutrition and also digestion. However their most important results are intheir capacity to safeguard their host from facility andinfection byalien microbes and their capacity to wake up the breakthrough and theactivity the the immunological tissues.

On the various other hand, several of the bacteria in the colon (e.g. Bacteroides) have been presented toproduce metabolites that room carcinogenic, and also there may be anincreased incidence of colon cancer associated with this bacteria.Alterations in the GI flora brought on by bad nutrition or perturbancewith antibiotics can reason shifts in populations and colonization bynonresidents that leads to cradle disease.chapter continuedPrevious Page© Kenneth Todar, Ph.D. All legal rights reserved. - www.derekwadsworth.com