Chapter 5: Normal Flora of the Human Body

Microbial Ecology

study of the relationship between microorganisms and their environment

Normal flora

consists of the group of organisms that inhabit the body of a normal healthy individual in the community.

indigenous flora

may be non-pathogenic or pathogenic and may times behave as opportunistic pathogens

resident flora

transient flora

What are the two types of flora?

Resident flora

organisms that are relatively of fixed types and are regularly found in a given area of the body at given age.

Transient flora

inhabit the skin and mucous membrane temporarily for hours, days or weeks and are derived from the environment.

Normal flora are beneficial to human body because?

• inhibit the growth of pathogenic organisms by priming the immune system of newborns

• protects the body’s organs and systems that are in direct contact with external environment therefore subject to attack of invasive organisms

vitamin K

Normal intestinal flora secrete ______________ that are needed for the activity of some clotting factors.

mucin

Normal flora can prevent pathogenic organisms from attaching and penetrating the skin and other tissues by producing _________ which make it difficult for the pathogenic organisms to attach to the tissues to produce disease

cellulase, galactosidase, and glucosidase

Normal flora in the intestine aid in the digestion of food by producing enzymes such as

steroids

Intestinal flora help in the metabolism of?

cerebrospinal fluid (CSF)

synovial fluid

blood

Body fluids that are sterile

urinary bladder

uterus

fallopian tubes

middle ear

paranasal sinuses

Sterile tissues include

Skin

part of the human body that is constant contact with the environment making it the most exposed to microorganisms

1. lysozyme in the skin

2. acidic pH of the skin due to sweat

3. free fatty acids in sebaceous secretions

4. constants sloughing off of the skin

certain factors that eliminate non-resident flora from the skin

bacteria and fungi

normal flora of the skin consists mainly of

1. axilla, perineum, and toe webs

2. hand, face and trunk

3. upper arms and legs

Skin may be divided into three regions

axilla, perineum, and toe webs

1. These skin regions have more microorganisms

2. predominantly inhabited by gram-negative bacilli

3. characterized by having

• high moisture levels

• higher body temp

• higher levels of surface lipids

hands, forearms, feet, legs

1. Dry sites

2. have diverse flora because of their exposure to the environment

Staphylococcus epidermis and Staphylococcus hominis

Predominant flora in these dry site (hands, forearms, feet, legs) areas include ?

stratum corneum and hair follicles

Most microorganisms in the skin are found in its superficial layers such as?

• Staphylococcus epidermis

• Staphylococcus aureus

• Microcci (Micrococcus luteus)

• Diptheroids (Coryneforms)

• Gram-negative Bacilli (Enterobacter, Klebsiella, Escherichia coli, Proteus spp.)

• Nail flora

Enumerate: Normal flora found on the skin

Staphylococcus epidermis

• major skin inhabitant

• compromising approximately 90% of resident aerobic flora

Staphylococcus aureus

most commonly found in nose and perineum; in the nose, number varies with age (greater in newborns than in adults)

Microcci (Micrococcus luteus)

Accounts for 20%-80% in the skin

Diptheroids (Coryneforms)

classified into: lipophilic or non lipophilic

lipophilic

common in axilla

non-lipophilic

more common on glabrous or hairless skin such as palm of hands

Anaerobic diphtheroids (Propionibacterium acnes)

rich in sebaceous glands

Gram-negative Bacilli (Enterobacter, Klebsiella, Escherichia coli, Proteus spp.)

seen in most intertriginous areas such as toe webs and axilla

Nail flora

similar to that of the skin

fungi may also be present ( aspergillus, penicillium, cladosporium, mucor)

Streptococcus viridans group

tongue and buccal mucosa are inhabited mostly by

S. mutans

S. milleri

S. salivarius

S. sanguis

Enumerate: Streptococcus viridans group that part of the normal flora on the mouth

viridans streptococci

have been implicated in the pathogenesis of the dental caries.

gingival crevices and tonsillar crypts

primarily inhabited by anaerobic flora in the mouth

Haemophilus influenzae

Streptococcus pneumoniae

Nisseria meningitidis

Mycoplasma

Enumerate: Transient flora in the pharynx

Neisseria meningitidis

Corynebacterium diphtheriae

Bordetella pertussis

Enumerate: upper respiratory tract initial colonization by pathogenic organisms

lower respiratory tract

usually sterile and organisms that reach this region are usually destroyed by the defense mechanisms of the body such as alveolar macrophages

lysozyme

• the normal flora in the conjunctivae are very scanty because they are held in check by the flow of tears that contain?

• this may interfere with the cell wall synthesis of organisms

Neisseria

Moraxella

Corynebacterium

Staphylococci

Streptococci

Enumerate: Transient flora in the conjunctiva

transient mouth flora

The esophagus contains

bacteria

minimal_____ may be found in the stomach due to the relatively hostile environment in the stomach.

gastric acid

The acidity in the environment of the stomach is further increased after meals because of the release of

Helicobacter pylori

• survive in the acidic environment of the stomach

• most common cause of duodenal ulcer

• produces urease causes alkalinization of gastric acid thereby enabling it to colonize the stomach

streptococci

lactobacilli

bacteroids

Enumerate: Transient flora found in the small intestine

Bacteroides fragilis

Bifidobacterium/Lactobacillus bifidum

Eubacterium

Peptostreptococcus

Clostridium

Enumerate: The colon is inhabited predominantly by anaerobes which includes

Bifidobacterium/Lactobacillus bifidum

predominant in breast-fed infants

Bacteroides fragilis

most common in the human colon

Lactobacillus acidophilus

predominant intestinal flora n bottle-fed infants

Escherichia coli and other Enterobacteriaceae

about 1%-4% of the flora of the colon are facultative aerobes, predominantly include?

1. synthesis of vitamin B complex and vitamin K

2. conversion of bile into bile acids

3. competition with transient flora for nutrients

4. prevention of colonization of the intestines by transient flora

5. production of potentially pathogenic end-products of metabolism that are toxic to transient flora.

Intestinal flora play important role in the body, namely?

urinary tract

sterile above the distal 1 cm of the urethra

S. epidermidis

enterococci

diphtheroids

Enumerate: Flora of the anterior urethra

Mycobacterium smegmatis

• in both males and females

• may be found as normal commensals in their secretions

Gardnerella vaginalis

bacteroides

alpha streptococci

found in penile urethra

female urethra

either sterile or contains staphylococcus epidermidis

age, hormonal levels, vaginal pH of the host

Vaginal flora varies depending on the

Lactobacillus spp

predominant vaginal flora in female infants

Staphylococcus epidermidis

Streptococci

diephtheroids

Escherichia coli

from 1 month of age until puberty microorganisms that may inhabit vagina include

Lactobacillus acidophilus

corynebacteria

peptostreptococci

streptococci

Bacteroides

staphylococci

Enumerate: Predominant flora in vagina at puberty

Lactobacillus

plays a crucial role in preventing gonococcal infection by producing lactic acid that adds to the acidity of the vagina

Young girls

are more prone to the development of gonococcal infection compared to adult women because the normal acidic pH of vagina as well as the normal vaginal flora are not yet developed

glycogen

After menopause, the vaginal pH increases once more due to the lessened production of?

Torulpsis and Candida

• fungi such as ___________ and __________may also be found (10%-30%)

• overgrowth of these fungi can lead to vaginal infections such as vaginitis