2. Normal Body Flora

8/7/2019 2. Normal Body Flora

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Normal Body Flora

Other terms we use:

y Normal body biotay Normal body microbiotay Normal body microflora

Flora: The plant life characteristic ofa special location. Can be macroflora or microflora.

Microbiota: The combined microflora and microfauna characteristic ofa special location.

NORMAL FLORA = NORMAL BIOTA

Healthy human beings (animals) develop intimate and complex relationships with microorganisms

(usually BACTERIA & FUNGI) which reside ONor WITHIN (IN) CERTAIN SITES ofour bodies

- Some permanently- Others just temporarily

Those that live on/in us STABLY (i.e in symbiotic equilibrium) are calledNORMAL BODY FLORA/BIOTA.

Their numbers: Simply ENORMOUS!!!

It is estimated that they are 10x the total number ofour own cells!!!

Symbiotic Equilibrium (or LIVING IN SMYBIOSIS)

Symbiosis: Living together / close association ofTWO DISSIMILAR organisms (each one a symbiont).

One lives on/in the other (host).

3 Kinds:

1. Commensalism: One party gained, the other neither harmed nor benefit from theassociation

2. Mutualism: Both gain from association and are unable to survive without it3. Parasitism: One party adversely affects the other and the parasite cannot live without the

host.

Most microbial parasites are called pathogens. The term parasite is usually reservedfor protozoa,

worms or insects.

So normal flora/microbiota:

Are they commensals? Or Mutualists? Or even Parasites?

That depends!!!

- Mostly = Commensals- Taken collectively = Mutualists- Occasionally under certain circumstances may cause opportunistic infections


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RESIDENT BIOTA/FLORA

y Newborn- Initially anyorganisms that happen to land in a particular site- Week 2: all babies have similar population ofmicrobes!y These are called RESIDENT BIOTA/FLORAy Each site/body surface has its own characteristic biotay Combination/SIZE may vary a little, but the resident biota ofa site is characteristic ofthe site,

and PERMANENT.

y For one reason or another,occasionallyother species landon a particular site. BUT MOSTnot equipped to stay permanently. These are TRANSIENT BIOTA

- E.g: Skin biota reduced by washing antiseptics but cannot be eliminated!- On the other hand, Transient biota CAN be eliminated.y Hospitals: Most staffexposed to and thus harbor transient biota (including pathogens!) but

NOT affected by them. They can transfer these to their patients

= HOSPITAL/NOSOCOMIAL INFECTIONS!!

Prevention -> Good habit ofhand washing

OPPORTUNISTS

y Opportunity arises usually when there is:- A breakdown in the hosts immune system- Use ofbroad-spectrum antimicrobials- Implantation ofdevices (catheters, metal joints, etc)y A normal resident like Candida albicans can be opportunisticy A non-resident like Pseudomonas aeruginosa is opportunistic in such a circumstance too

CHANGING FLORA/BIOTA:

y Resident biota relatively stable, but DO change over timeE.g: Normal flora oftoothless newborns slightlydifferent from those with teeth

- Surface ofteeth: Streptococcal spp.

- Crevices: Anaerobes (Fusobacterium spp and Bacteroides spp)

y In intestines of>90% ofbreast-fedonly babies:- Bifidobacterium is the ONLY bacterium isolated!- Bifidus factor in breast milk favours its growth (?)- Bacteria ferments milk sugar to acetic and lactic acids-

Low pH = incompatible for growth ofother bacteria- Therefore less illnesses like diarrheay Babies that are given formula milk or fed solidfoods

= Bifidobacterium is replaced by normal biota as in adults

y Vagina ofnewborn baby girl = Lactobacillus spp- Acidic (effect oftransplacentally-acquiredoestrogen)- After 2-3 weeks,oestrogen , vagina becomes alkaline- Leads to appearance of:


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i. Clostridium sppii. Fusobacterium sppiii. Bacteroides sppiv. Candida Albicans

- Occasional infection by E.coli from GIT-

During puberty, Oestrogen, vaginal cells produce glycogen.

- Lactobacilli spp flourishes again- Protects from infection during reproductive years- [Lactobacillus acidophilus Doderleins bacillus]- At menopause -> vagina becomes alkaline againy Therefore, these are called CHANGING FLORA/BIOTAy The symbiotic equilibrium when disturbed -> infectiony When normal flora from one anatomical site move to another site:

= endogenous infections

- Can be relatively trivial

- May be life threatening

STERILE AREAS OF HUMAN BODYSITES include:

y CNSy Circulationy Lower bronchiy Alveoliy Livery Spleeny Kidneysy Urinary Bladder

SKIN

Largest human organ (~15% total body weight)

Functions:

- Protect host- Regulate temperature

Microorganisms/Normal Biota:

y 10^4 per sq. cm ofdry skiny 90% can be removed through washingy Within 8 hours -> back to near normaly Majority commensalsy Produce pathogen inhibiting fatty acidsy S. Aureus

= 5-10% ofpeople healthy carriers


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y S. Epidermidis= Opportunist. Some strains are non-pathogenic

y Others: Weakly pathogenic opportunistsNASAL CAVITY/NASOPHARYNX

y Air that enters contains dust,debris & microorganismsy At birth sterile. 24 hours later teemed with microorganismsy Average = 10^4 microorganisms inhaleddailyy Most removed by local mucociliary systemy Patients with cystic fibrosis produce abnormally thick mucus. Cilia cannot move well

Result: Frequent infections

y Toxic substances in cigarette smoke mucociliary system weakened.Result: Frequent URTIs

y Biota :- densely colonized-

Several = similar to those on skin- S.Epidermidis in nasal cavities of>90% ofhumans

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2. Normal Body Flora