1

Chapter 7.

NORMAL FLORA

Tiana Milanda

Normal Flora

• Microorganisms that colonize a host

without causing disease

• Two types of normal flora exist :

– resident flora are microorganisms that

inhabit sites on the body for extended

periods

– transient flora are microorganisms that

are temporary

3

RESIDENT FLORA

• Do NOT produce disease under normal conditions

• Includes bacteria, fungi, protozoa, viruses and arthropods in the most areas of the body in contact with the outside environment

• Large intestine has the highest numbers of bacteria

• Internal organs, tissues & fluids are microbe-free

4

TRANSIENT FLORA

• Cling to the skin surface, but does not ordinarily grow on it.

• It is acquired by routine contact, and it varies markedly from person to person and over time.

• May be present for several days, weeks, or months, and then disappear.

• It is greatly influenced by the hygiene of the person.

• May or may not cause disease.

5

RELATIONSHIP BETWEEN NORMAL

FLORA AND HOST

• Mutualism

• Commensalism

• Parasitism

Mutualism

• in this type of relationship, both

partners benefit

– E. coli synthesizes vitamin K in the

intestine

– in exchange the large intestine provides

nutrients necessary for survival of the

microorganisms

E. coli

Commensalism

• one organism is benefited and the other

is unaffected by this type of relationship

– many of the microorganisms that make up

our normal flora inhabit places like the eyes,

ears, and external genitalia

• these bacteria live on secretions and sloughed off

cells

• they bring no benefit to the host and yet the

microorganisms benefit greatly from the

environment they inhabit

Parasitism

• one organism benefits at the expense of the other

– all pathogens are parasites

• TRUE PATHOGENS – capable of causing disease in

healthy persons with normal immune defenses

– Influenza virus, plague bacillus, malarial

protozoan

parasitic microorganisms

Normal Flora

• the presence of normal flora

– cover potential adherence sites for invading

microorganisms

– consume the available nutrients

– produce compounds toxic to other

microorganisms

This is call microbial antagonism.

bacteria found on skin

Normal Flora

• when the balance between normal flora and pathogens

is upset, disease can result

– the normal bacterial microorganisms of the adult

human vagina maintain the pH at about 3.4 – 4.5

– the presence of this normal flora inhibits the

overgrowth of Candida albicans, yeast

– if the presence of the normal flora is eliminated by

antibiotics, or excessive douching, the pH of the

vagina becomes nearly neutral, creating an

environment very conducive to the growth of C.

albicans

C. albicans

11

OPPORTUNISTIC FLORA

• Are potentially pathogenic organisms that do not cause disease in their normal habitat in a healthy person

• Organisms that gain access through broken skin or mucous membranes can cause opportunistic infections

• If the host is already weakened or com-promised by infection.

• Pseudomonas sp & Candida albicans

Table 13.4

Normal flora established during birth process.

Once established, composition of flora is

dynamic :

• Changes result from physiological variation

within the host

• Each member of flora ecosystem is

influenced by presence and condition of

other members

Dynamic nature of normal flora

15

FLORA of the SKIN

• Staphylococcus, Micrococcus, Coryne-bacterium, Mycobacterium, Yeast.

• Most live in the upper dead layers of the epidermis, glands, and follicles.

• Present in sebaceous glands and hair follicles Propionibacterium acnes

• Dependent on skin lipids for growth.

16

FLORA of the SKIN

• Epidermis region normally unsuitable for growth due to periodic drying

• Breach of barrier can lead to disease

• Factors that influence flora: weather, age of host, personal hygiene

17

BACTERIA of the EYE

• The conjunctiva, a continuation of the skin and a mucous membrane, contains basically the flora of the skin.

• Staphylococcus aureus and Staphylococcus epidermidis.

• Lacrimal fluid contains mucus, antibodies, and lysozyme, an enzyme that destroys bacteria.

Flora of Oral Cavity

• Before teeth appear: streptococci and lactobacilli

• Teeth: change in microflora

• Streptococcus, Neisseria, Staphyloccoccus, Lactobaccillus, Actinomyces, Bacteroides.

• Saliva: lysozymes

• Food particles contributes to microbial growth

• Saliva creates a thin organic film of acidic glycoproteins which serves as a firm attachment site for microbes (anaerobic)

• Extensive attachment: dental plaque

• Resident microbes begin to release high concentrations of organic acids that decalcify enamel resulting in dental caries& gingivitis

19

FLORA of the GASTROINTESTINAL

TRACT

• Stomach, small intestine

and large intestine

• Stomach fluids are highly

acidic and act as a

protective barrier

• Helicobacter pylori

normally colonizes

stomach wall but can

cause ulcers in

susceptible individuals

Flora of Gastrointestinal Tract

• Large intestine: cecum and colon

• Colon has a large number of

microbes exp. E.coli

• Obligate anaerobes predominate:

Clostridium, Bacteroides and

Enterococcus faecalis

• Intestinal flora carry out essential

metabolic reactions, exp. vitamin

B12 and K

• Antibiotic therapy can sometimes

lead to destruction of normal

microflora and lead to

opportunistic infections and disease

21

FLORA of the UPPER

RESPIRATORY SYSTEM

• Enter upper respiratory tract

(nasopharynx, oral cavity and

throat) during respiration

• Trapped in nasal passage and

expelled with nasal

secretions

• Oral Streptococci,

Staphylococcus aureus,

Staphylococcus epidermidis,

Neisseria sp., and

Haemophilus.

• Most microbes are inhaled,

the filtered out, destroyed,

or expelled.

22

FLORA of the LOWER

RESPIRATORY SYSTEM

• Lower respiratory tract

(lungs, bronchi and

trachea))

• Usually no permanent

residents are present.

Flora of Urogenital Tract

• In males and females bladder is sterile

• Epithelial cells lining the urethra tend to be colonized by gram-negative microbes

• Normal flora can multiply due to changes such as pH and cause disease

• Flora changes in female from childhood-adulthood–menopause (alkaline-acidic)

24

FLORA of the URINARY SYSTEM

• Staphylococcus, Streptococcus, and coliforms.

• In females, flora exists only in the first portion of urethra, the remainder of the tract is sterile.

• In males, the entire reproductive and urinary tract is sterile except for a short portion of the

anterior urethra.

25

FLORA of the REPRODUCTIVE

SYSTEM

• In females and males,

flora occupies the external

genitalia.

• Internal reproductive

structures normally remain

sterile.

• Lactobacillus,

Streptococcus,

Corynebacterium,

Mycobacterium.

• Candida albicans