The document discusses the normal flora of the human body, including resident and transient flora. It notes that the largest population of normal flora bacteria is found in the colon, with over 400 identified species including Bacteroides fragilis as the most common. The document outlines both beneficial and harmful effects of normal flora, and discusses probiotics which can support normal flora when it is suppressed.

1. By
Dr. Sameer S Faujdar
Assistant Professor
Department of Medical Microbiology
M M Medical College & Hospital,
Solan (HP)

2. • 1. Resident flora and transient flora
• 2. Harmful effects of the normal flora
• 3. Beneficial effects of the normal flora
• 4. Probiotics

3. • Normal flora is the term used to describe the
various bacteria and fungi that are permanent
residents of certain body sites, especially the skin,
oropharynx, colon, and vagina.
• Viruses and parasites, which are the other major
groups of microorganisms, are usually not
considered members of the normal flora.
• Other names: commensals, human microbiome,
indigenous microbiota.
• The members of the normal flora vary in both
number and kind from one site to another.

4. • The skin and mucous membranes always harbor a
variety of microorganisms that can be arranged
into two groups:
1. Resident microbiota: It consists of relatively
fixed types of microorganisms regularly found in a
given area at a given age; if disturbed, it promptly
reestablishes itself for example E. coli in intestine.
2. Transient microbiota: It consists of
nonpathogenic or potentially pathogenic
microorganisms that inhabit the skin or mucous
membranes for hours, days, or weeks for example
MRSA in nose and skin, MDR GNBs such as
Klebsiella, E. coli, Pseudomonas, Acinetobacter in
respiratory tract.

5. • ln contrast to resident flora, they can be easily
eliminated from the body surface by following proper
hand hygiene and other infection control practices.

6. • Humans acquire the normal flora soon after the birth
and continue to harbour until death.
• It has been estimated that humans have approximately
1013cells in their body and about 1014 bacteria are
associated with them.
• The majority of bacteria are present in the large bowel,
which constitutes the normal flora.
• Overall, anaerobic bacteria dominates over aerobic
bacteria.
• GIT is the predominant site, where over 400 species of
different bacteria have been counted till date.
• The most common normal flora in humans is
Bacteroides fragilis; however among aerobes, it is
Escherichia coli; both are a part of intestinal flora.

7. • Normal flora depends upon various
factors:
1. Temperature
2. Moisture
3. pH
4. Environment (community or hospital)
5. Immune status
6. Anatomical sites Skin or mucosa
(gastrointeslinal, respiratory or urogenital)
7. O2

9. • Beneficial effects:
1. Prevent colonization of pathogenic bacteria by
competing for attachment sites and nutrients.
2. Synthesize vitamins (B, K) which are absorbed as
nutrient.
3. Inhibits the growth of pathogenic bacteria by
secreting waste substances (fatty acids,
peroxidase, lactic acid, bacteriocin etc).
4. Immune stimulation
5. Prevent allergic diseases (Hygiene hypothesis)
6. Complement activation by endotoxin of normal
flora

11. • Harmful effects
1. Agent of disease
2. Transfer to susceptible host
3. Bacterial synergism
4. Contribute in spared of drug resistance
5. Competition for host’s nutrients

12. • Probiotics are live, nonpathogenic bacteria (or yeasts)
that may be effective in the treatment or prevention of
certain human diseases.
• They are useful in the condition where the normal
intestinal flora is suppressed.
• Examples: Bacillus coagulans, Bifidobacterium longum,
Lactobacillus acidophilus, Saccharomyces boulardii.

14. • In contrast to probiotics, prebiotics are the dietary non-
digestible fibres which when administered, stimulated the
growth and activity of normal flora.

15. Q1. The colon is the site of the largest number
of normal flora bacteria. Which one of the
following bacteria is found in the greatest
number in the colon?
(A) Bacteroides fragilis
(B) Clostridium perfringens
(C) Enterococcus faecalis
(D) Escherichia coli
(E) Lactobacillus species

16. Q2: Certain microorganisms are never
considered to be members of the normal flora.
They are always considered to be pathogens.
Which one of the following organisms fits into
that category?
(A) Streptococcus pneumoniae
(B) Escherichia coli
(C) Mycobacterium tuberculosis
(D) Staphylococcus aureus
(E) Neisseria meningitidis

17. Q3: Your patient is a 30-year-old woman with a
previous history of rheumatic fever who has
had fever for the past 2 weeks. On
examination, you find a new heart murmur. You
suspect endocarditis and do a blood culture,
which grows a viridans group streptococcus
later identified as S. sanguinis. Using your
knowledge of normal flora, what is the most
likely source of this organism?
(A) Duodenum
(B) Skin
(C) Throat
(D) Urethra
(E) Vagina

18. Q4: A 76-year-old woman with a prosthetic (artificial)
hip comes to you complaining of fever and pain in that
joint. You are concerned about an infection by S.
epidermidis. Using your knowledge of normal flora,
what is the most likely source of this organism?
(A) Dental plaque
(B) Mouth
(C) Skin
(D) Stomach
(E) Vagina

19. Q5: Antimicrobial therapy can decrease the
amount of susceptible bowel flora and allow
proliferation of relatively resistant colonic
bacteria. Which one of the following species
can proliferate and produce a toxin that causes
diarrhoea?
(A) Enterococcus species
(B) S epidermidis
(C) Pseudomonas aeruginosa
(D) Clostridium difficile
(E) B fragilis