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In e disciplina y Resea ch in Li e Sciences: A Pa h Towa ds Sus ainabili y (Vol. 3) - Jay a dhan V. Balkhande & Jalande
Vaghma e (Eds.)
ISBN: 978-93-95369-86-2 (pape back) 978-93-95369-58-9 (elec onic) | © 2025 Ad en Publishing.
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CHAPTER 8
Roles o No mal Mic o lo a in Human Heal h
Dhanpal B. Cha an
Depa men o Mic obiology, ACS College Gangakhed 431514 Maha ash a, India
Co esponding au ho Email: [email p o ec ed]
Recei ed: 11 No embe 2025; Accep ed: 21 No embe 2025; A ailable online: 27 No embe 2025
In oduc ion
E e y o ganism p o ec s i sel om in ading pa hogens. Ou en i onmen is su ounded by
millions o lo a, his lo a wo ks as p o ec i e as well as ha m ul e ec on he hos . Mic o lo a
consis s o bac e ia, ungi and some ex en o p o ozoa, bu i uses a e no gene ally conside ed as
no mal lo a. Recen s udies on human and animal sugges ed ha mic o lo a in luences human
ana omy, physiology, li e span and dea h o indi idual also. Some mic o lo a in human ood ca y
ou e men a ion and p oduce e men p oduc which main ained he no mal heal h o human,
hence e men ood is he elixi o human. Flo a boos s he de ence sys em. Immune sys em o
human is well s udied. Immunology is b anch o science, which deals wi h s udy o immune sys em
o an o ganism, OR i is he s a e o p o ec ion om an in ading pa hogens. When pa hogen
Dhanpal B. Cha an
In e disciplina y Resea ch in Li e Sciences: A Pa h Towa ds Sus ainabili y (Vol. 3) - Jay a dhan V. Balkhande & Jalande
Vaghma e (Eds.) ISBN: 978-93-95369-86-2 (pape back) 978-93-95369-58-9 (elec onic) | © 2025 Ad en Publishing.
80
o e come he immune sys em hen hey causes in ec ion and p oduce disease. Human body
composed o abou 1×10
13 cells and a same ime Human body ca ies abou 1×10
14 mic oo ganisms
in and on he body. Be o e bi h baby is ee om mic obes in he womb o mo he , when baby
bo n la ge numbe o en i onmen al lo a deposi ed on he body. Some mic obes ac as no mal
mic o lo a and o he ac as ha m ul lo a. A he age o six mon h baby s a s o de elop i s own
immune sys em.
No mal mic o lo a p o ec s om pa hogenic mic oo ganism. Fo example skin mic o lo a
c ea e acidic en i onmen which p e en g ow h o pa hogenic mic oo ganism on he skin. Some
mic oo ganism symbio ically associa ed wi h he hos and help in g ow h. Fo example Esche ichia
coli syn hesize i amin B -12 and i amin K, ibo la in, hiamin in he colon o human, hese
i amins canno syn hesize by humans. Some lo a in in es inal ac ca ies ou e men a ion and
p oduce ace ic and bu y ic acid which inhibi salmonella species in gu . Lac obacilli in eginal ca i y
e men he glycogen and p oduce he lac ic acid which main ains he acidic pH and p e en s he
g ow h o many pa hogens in u ogeni al ac . No mally lo a kep hei numbe up o 10 6 / gm. o
solid ma e in gu ; i his numbe exceed o dec ease i emendously in luence he heal h, his
numbe in luence by ood and an ibio ics. Some s udies showed ha an ibio ics educes he lo a
and allow some pa hogen o induces se e al diseases like diabe es, heuma oid a h i is, muscula
dys ophy, mul iple scle osis obesi y ib omyalgia and so on. O e all human heal h is depending on
he lo a o body. Eme ging he apy e ol es uses o lo a wi h success ul s o ies. Recen ly ecal
ansplan was success ully ea ed se e al diseases in human.
1. No mal Mic o lo a o Human Body
No mal mic o lo a (mic o bio a) means he mic oo ganism p esen in and on he human body.
Be o e bi h baby is ee om mic obial lo a. A he ime o bi h baby acqui es mic obial lo a
om mo he and also om he su ounding en i onmen . No mal mic o lo a help human o
su i e in he cons an ly changing en i onmen . The e a e mo e han 10 imes mic obes esiding
on human body han he o al numbe o he body cell. Mic oo ganisms in e ac wi h human
h ough di e en associa ions like symbiosis, mu ualism, commensalism and pa asi ism. Two kinds
o mic o lo a can be de ec ed 1) Residen mic o lo a 2) T ansien mic o lo a.
Residen mic o lo a : Always p esen in he si es such as mou h, skin, mucus memb ane eginal
opening and in es inal ac .
T ansien mic o lo a : They p esen in ce ain d y loca ion whe e esiden mic o lo a is ound e en
pa hogen can be ansien mic o lo a.
Roles o No mal Mic o lo a in Human Heal h
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Some common mic o lo a can become pa hogen when hos immune sys em weaken o
p olonged use o an ibio ics and immunosupp essi e d ugs. Physical and men al s ess also
weakens he immune sys em. When No mal mic o lo a became pa hogen hen hey a e called as
oppo unis ic pa hogen and hey cause oppo unis ic in ec ion.
Bac e ia, ungi and some p o ozoa a e conside ed as no mal mic o lo a bu i uses a e no ,
howe e some i uses a e able o eside in he human body wi hou p oducing disease symp oms
unless he e is changing in he immune s a us o ha hos . Fo example he i us such as he pes
simplex, Es ein- ba , Cy omegeli i uses eside in hos o longe ime and induce hei e ec when
immune sys em al e ed
1.1 No mal mic o lo a o he skin
The whole skin o he adul human possesses abou 2 m
2 o he skin. The chemical composi ion and
mois u e con ains is depends on he si e o skin. Fo example eginal skin possesses di e en
physical and chemical composi ion and P H and skin o a mpi has di e en physical and chemical
composi ions. Skin su ace is no a sui able o mic obial g ow h because i is acidic and pe iodically
d y. Mos skin no mal mic o lo a is dependen s on he sec e ions o he skin glands. Skin is acid in
na u e and p oduce nu ien s like u ea, amino acid, sal , lac ic acid and lipids. Skin mic o lo a
consis s o bac e ia, ungi and yeas , among hese bac e ia a e conside ed as a majo lo a o he
skin. Skin mic o lo a changes acco ding o age and en i onmen al condi ions. O e all 180 species
o bac e ia and se e al species o ungi a e epo ed om human skin. The mos common and s able
esiden mic oo ganism on he skin a e G am posi i e bac e ia like S ep ococcus, S aphylococcus
and a ious species o Co ynebac e ium, P opiobac e ium eco ded on he skin. These ou gene a
accoun one hal o all species ound on he skin. G am nega i e mic o lo a such as Acine obac e
and E. coli is also epo ed on human skin. Nea abou 5 species (C.albicans, Saccha omyces
ce i iase, Pi y ospo umo ale and Malassezia) o ungi a e epo ed on human skin among hese
Malassezia spp ungus is he mos common ungi on skin. Malassezia u u g ows on skin as
dand u . An ibio ics like ke oconazole o ziny i hione o seleniumsulphide con aining shampoo
con ol he g ow h o his ungus.
The skin esiden mic o lo a emain mo e o less cons an , a ious en i onmen al
condi ion and hos en i onmen such as wea he , age and pe sonal hygiene changes he no mal
mic o lo a o he skin.
Dhanpal B. Cha an
In e disciplina y Resea ch in Li e Sciences: A Pa h Towa ds Sus ainabili y (Vol. 3) - Jay a dhan V. Balkhande & Jalande
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1.2 No mal mic o lo a o he o al ca i y
O al ca i y o human is ull o nu ien s; sali a con ains wa e , amino acids, p o eins, lipids,
ca bohyd a es and ino ganic compounds, which suppo he mic obial g ow h. When baby bo n
hey ha bou s’ many mic obial lo a in hei o al ca i y om he eginal ca i y o he mo he . O al
ca i y con ains mos ae o ole en anae obes such as S ep ococci, Lac obacillus, Ace omyce es,
Neisse ia,Veilone and yeas .e c. Acidic glycop o ein o he sali a o m a hin o ganic ilm o he
suppo s he excessi e g ow h o S. sanguis, S sob inus, S. mu an, S. mi is and causes he plaque.
S ep ococcus mu an p oduce glucan, a s icky polyme o glucose ha allows mic obes o bind wi h
ee h su ace and causes ee h disease. F uc ose is e men ed by s ep ococcus and p oduce lac ic
acid which dissol e he enamel o ee h and cause ee h decay. The no mal lo a o human gum
(gingi a) a e S ep ococcus sanguis a acul a i e o ganism, he gum disease caused by
p ophy omonas,,bac e oids, usobac e ium, selenomonas.
Flagella ed T ichomonas enax may occu in gum ma gins and in plaques and ca i ies o
he ee h, i s p esence is usually associa ed wi h poo o al hygiene.
1.3 No mal mic o lo a o gas oin es inal
Human gas oin es inal ac is s a s oesophagus o la ge in es inal ac . The in es inal ac is a
e men a ion essel. The mic o lo a o human in es inal ac is esponsible o good heal h;
mic o lo a o gas oin es inal ac abso bs nu ien and p oduce i amin B12 and K, hiamine and
bio in. Gu mic o lo a main ain he diges ion abili y o human. S e oid p oduced in li e and
eleased in o in es ine om gall bladde as bile a e modi ied and ac i a ed s e oid compound a e
he abso bed om he gu . Wi hou gu mic o lo a i is no possible o su i e. I has been
es ima ed ha abou 10
10 o 1011 mic obial cell/ml o s omach con ain is epo ed.
S omach con ains G am posi i e P o eobac e ia, Ac inobac e ia, usonac e ia, helicobac e
pylo i. Small in es ine is he e y la ge and ha e possess huge numbe o mic oo ganisms,
lac obacillus, co nebac e ium, yeas Candida albicans, Bac e iods B. agilis, B. melaninogenicus, B.
o alis, usobac e ium, Esche ichia coli a e epo ed. G am posi i e species such as Bi idobac e ium
(baby eeding on mo he milk ha e Bi idobac e ium in hei gu whe e as baby eeding on bo le has
lac obacillus in hei gu ), Eubac e ium, lac obacillus. Clos idium pe e inges majo causa i e agen
o gas gang ene is also epo ed in colon. Pe son who consume mea whose gu lo a con ain la ge
numbe o Bac e oids and less numbe o lac obacillus and coli o ms
La ge in es ine is like e men a ion essel and mic obes u ilize he undiges ed ood and
p oduces gases. I has been es ima ed ha he 25% o s ool sample is composed o mic oo ganisms.
Roles o No mal Mic o lo a in Human Heal h
In e disciplina y Resea ch in Li e Sciences: A Pa h Towa ds Sus ainabili y (Vol. 3) - Jay a dhan V. Balkhande & Jalande
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Nea abou 300 species o mic obes isola ed om human eces. Mic o lo a p esen in la ge in es ine
a e belong o E.coli, p o ease,klebsiella,En e obac e ,candida albicans, p o ozoa like ichomonas
hominisinhabi an so he cecum, en amobeaendlimax a e commensal o he colon. En amoeba
his oly ica is commensal o gu bu i causes he disease amebic dysen e y. Gu mic o lo a a ec ed
when he an ibio ics used o ea he disease and gu mic o lo a can be killed and pa ien may ace
p oblem o diahho ea, o no malize he gu lo a heal h p o essional sugges p obio ics (con aining
gu common mic o lo a).
1.4 Veginal mic o lo a
Veginal ca i y is open ca i y and impo an sys em o ep oduc ion. Veginal ca i y in young
women composed o heal h mic obes in i and men a ion he heal h o young woen, mic o lo a o
heal hy eginal ca i y consis o complex mix u e o ae obic Lac obacillus species, including L.
acidophilus, L. jensenii, and L. hamnosus L. acidophilus, L. c ispa us, L. jensenii and yeas . These
mic obes u ilise glycogen and p oduce acid and hyd ogen pe oxide and p e en bio ilm o ma ion
and also es ic s hei eplica ion. Lac ic acid inhibi s his one deace ylases enzyme he eby
enhancing gene ansc ip ion and DNA es o a ion p ocesses. The p esence o hese po en ial
pa hogens is p ima ily linked o aginal in ec ions such as non-speci ic bac e ial agini is, Neisse ia
gono hea, and o he sexually ansmi ed diseases like gono hea, syphilis, and aginal h ush.
Resea ch s udy demons a ed ha a ia ion in lo a depend on (1) age (childhood – adolescence –
young adul hood – elde ly), (2) he egula mens ual cycle, (3) sexual in e cou se, (4) pe sonal
hygiene, (5) ashion- ela ed habi s, and (6) he use o in a aginal mic obicides o spe micides like
nonoxynol-4. In ela ion o he a o emen ioned dynamics o aginal mic o lo a p esence, esea ch
s udy con i med ha mos heal hy women expe ience sho - e m luc ua ions in aginal mic o lo a
composi ion which depend on en i onmen condi ion. Abou 22 –26% o heal hy women possess
lac obacilli as a p edominan lo a. Pe sonal beha iou s, ho monal changes, s ess and o he
ex e nal ac o s may in luence he dynamic na u e o aginal mic o lo a. The e olu ion o no mal
lo a is a li elong con inuous p ocess ha s a s immedia ely a e he bi h. I is belie ed ha
coloniza ion s a s du ing he pa u i ion p ocess. Veginal mic o lo a .
2. Fac o s ha Con ibu e o he Exis ence o No mal Mic o lo a
a) Biological Age
Age is an impo an ac o , wi h inc easing age physiological changes occu and ho monal
p oduc ion a e is also changes in di e en age and he skin mic o lo a epo ed in di e en age
g oups. Physiology is also changes wi h he age. S udy o Ma ei e .al epo ed ha , inc easing
Dhanpal B. Cha an
In e disciplina y Resea ch in Li e Sciences: A Pa h Towa ds Sus ainabili y (Vol. 3) - Jay a dhan V. Balkhande & Jalande
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biological age in communi y-dwelling adul s is associa ed wi h gas oin es inal dysbiosis. Mic obial
di e si y o he skin ends o inc eases wi h age, in addi ion o his age is also ela ed wi h he
al e a ion in he numbe o mic o lo a. The al e a ion in numbe o mic o lo a is s ill no known,
whe he hey g ow slowly (g adual) o suddenly as (p og essi e). The abili y o de ine hese
de ici s in popula ions o di e en ages may help o de e mine a ch onological age h eshold a
which de ici s occu and subsequen ly iden i y inno a i e die a y s a egies o ac i e and heal hy
ageing o he people. The di e si y o mic o lo a o inc eases wi h age inc ease wi h. The inc ease in
di e si y du ing he i s eigh yea s o li e is associa ed wi h a educed dominance o he
lac obacillus sp.
b) Geog aphy
Geog aphical condi ion also impac on he mic o lo a o he human body. Se e al s udies epo
di e ences in no mal mic o lo a depending upon geog aphical condi ion; esea ch s udy epo ed
by Benno e al. among Japnies people. In his s udy he selec ed u ban s. u al egions. On he
whole, he di e si y and coun s o aecal ma e mic o lo a we e ound o simila . U ban people
ha e signi ican ly less Bi idobac e ium adolescen is bu signi ican ly mo e numbe o bacilli,
clos idium species. As compa ed o hose who li e in u al a ea. These di e ences in gu mic o lo a
migh be due o di e ence in he die s (high ibe ) in he u al popula ion. Recen esea ch da a
ha e cla i ied c i ical sepa a ion in he mic o lo a composi ion be ween heal hy pe sons om
di e en aces and e hnici ies. Scien i ic communi y belie ed ha geog aphical di e ences in he
composi ion and di e si y o no mal mic o lo a epo ed in ce ain popula ions a e ac ually no o
gene ic o igin, bu due o he a ia ion in die composi ion. The mic o lo a o he gu a ies
acco ding o he milieu in e io s o he body.
c) Nu ien
In Indian my hological ale in Ma a hi “ Ana a i and ana ma i ” i.e. ( ood can sa e and ood can
kill). Read mee , see ood and ood ich wi h a s allow ead mee ea e bac e ia and p oduce he
ime hylamine oxide (TMAO) which leads o cause hea a ack human la ge in es ine is one o he
mos densely packed mic obial ecosys em on ou plana e wi h 1012 cell/gm. o aecal ma e . Food
na u ally also associa ed many lo as in i , eeding baby has bi idobac e ium i hei gu and human
milk selec i ely allow his bac e ia o g ow. Milk p oduc s a e good o heal h because hey es o e
he good bac e ia in he gu . The quan i y and quali y o ood also impac on he mic o lo a o he
gu . One s udy epo ed ha daily die a y up ake o calcium ends o p ecipi a e and induce
cy o oxic compound such as bile acids which educed cy olysis, a condi ion o changes elici ed by
inulin and galac o -oligosaccha ide consump ion. A die supplemen ed wi h calcium in an animal
Roles o No mal Mic o lo a in Human Heal h
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s udy ( a s) showed he educ ion inhabi a ion o Salmonella en e i idis in gu , some s udies also
con i med ha bo le eed babies ha e a mo e sophis ica ed such as Bi idobac e ium spp.,
Bac e oides, S ep ococcus and Clos idium spp, e en hough he di e ence be ween b eas - ed and
o mula- ed in an s is no eally signi ican . The oles o no mal in in es ine can be summa ized as
below: (1) Diges ing en e ic me abolic subs a es, (2) Resis ing coloniza ion by o eign non -sel
mic o lo a, (3) Assembling i amins, (4) De eloping a achmen si es, (5) Facili a ing he immune
sys em, p oducing exogenous enzymes, ( acili a ing in aluminal ansi ) (6) Ad ancing and u ning
o e speci ic in es inal cells. F uc o-oligosaccha ides (FOS), a speci ic suga con ained in ui like
bananas o plan s, e.g., esh onions, a ichokes, and aspa agus, a e e men ed la gely by he bac e ia
Bi idobac e ium species, and his u ns ou o be in e ela ed and in luence each o he . One s udy
epo ed ha daily consump ion o 20 g am (FOS) enhance he g ow h o bi idobac e ium and
casus abdominal discom o . Consump ion o di e en kinds o ib e changes he le els o
Bi idobac e ia, Lac obacillus spp, and also ungi lo a. Se e al e men able ibe s may acili a e he
expansion o no mal lo a, yielding sho -chain a y acids, p opionic acid and ace a e and
educed colonic p H, and inhibi he g ow h o ce ain bac e ia, such as C di icile . Polyphenols
p esen in ea when gi en o pigs inc eased Lac obacillus and educed le els o Bac e oides.
d) In ec ion
No mal mic o lo a does no allow exo ic lo a o g ow on he hos body. Pa asi es en e o he hos
body h ough se e al oo s like o al aecal, nasal ca i y, wounded skin e c. When hey en e he
body h ough he o al- aecal oo and in e ac wi h he commensal lo a o he gu and may causing
abdominal discom o like dia hoea. In ec ion ou numbe s he pa hogen as compa ed wi h he
no mal lo a and damage heal h o hos . Some in ec ion adds he pa hogen o hos body
pe manen ly o example salmonella sp and he pes simplex i uses . In ec ion also added many
asymp oma ic in es inal pa asi ic in ec ions. No mal mic o lo a may inc ease esis ance o pa asi ic
in ec ions a mucosal si es ia changes in he composi ion o in es inal bac e ia, and i may also al e
sys emic immuni y o hese pa asi es.
e) S ess
S ess is a e y common p oblem in he mode n e a. Due o Mo den li e s yle and g eed o become
each leads o s ess. Du ing he s ess ho mones like ad aline and co isol inc eases and he b ain
gu communica ion is dis u bed. This leads o uncon olled ea ing, which educes he good
bac e ia. Uncon olled au onomic al e a ions elici se ies o episode ha can make he wo se
condi ion. As a esul , gu lo a libe a e mo e end-p oduc such as, oxins, me aboli es, and e en
neu o ho mones ha changes he ood and mood habi s. Those people who li ing in anxie y educe
Dhanpal B. Cha an
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mic o lo a can ea wi h no mal lo a bu he con inuous s ess educes he supplemen a y
p obio ic lo a also.
) An ibio ics
Use an ibio ic o ea in ec ious diseases was ini ia ed du ing he wo ld wa second. A he
beginning penicillin was used as magic d ug, la e many an ibio ic was desc ied o ea in ec ious
disease, excessi e use o an ibio ics in luences he mic o lo a o hum. An an ibio ic dec eases he
di e si y o lo a. Long e m exposu e o an ibio ics c ea es dysbiosis in he hos body. An ibio ics
can wo k as a selec i e agen and can o p oduce he an ibio ic esis ance mic o lo a o ans e
an ibio ic esis ance gene o nea by species he an ibio ic ia gene ans e mechanism. Excessi e
use o an ibio ics can leads o he ou g ow h o common lo a o gu C. di icile which cause
dia hoea. Deple ion o he no mal mic o lo a may lead o educed coloniza ion esis ance wi h
subsequen o e g ow h o p e-exis ing, ins inc i ely insensi i e mic oo ganisms, like yeas s and
New coloniza ion by esis an po en ial pa hogens may also occu and may sp ead wi hin he body
o o o he pa ien s and cause a al in ec ions.
3. Re e ences
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Roles o No mal Mic o lo a in Human Heal h
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