objectives
• Define and classify normal microbiological
flora of human body
• Explain the beneficial role of microbial flora
• Explain endogenous and exogenous diseases
in reference to microflora
• The term "normal microbial
flora" denotes the population
of microorganisms that
inhabit the skin and mucous
membranes of healthy
normal persons.
• The skin and mucous
membranes always harbor a
variety of microorganisms
that can be arranged into two
groups:
(1) The resident flora relatively fixed types of microorganisms regularly found in a
given area at a given age; if disturbed, it promptly reestablishes itself
(2) The transient flora nonpathogenic or potentially pathogenic microorganisms that
inhabit the skin or mucous membranes for hours, days, or weeks;
• it is derived from the environment,
• does not produce disease, and
• does not establish itself permanently on the surface.
• Members of the transient flora are generally of little significance so long as the
normal resident flora remains intact.
• However, if the resident flora is disturbed, transient microorganisms may colonize,
proliferate, and produce disease.
Skin
•
Staphylococcus epidermidis
•
Staphylococcus aureus (in small numbers)
•
Micrococcus species
•
Nonpathogenic Neisseria species
•
Alpha-hemolytic and nonhemolytic streptococci
•
Diphtheroids
Nasopharynx
•
diphtheroids, nonpathogenic Neisseria ,S epidermidis, nonhemolytic streptococci, anaerobes
•
Lesser amounts of the following when accompanied by organisms listed above: yeasts, Haemophilus species,
pneumococci, S aureus,
GIT
•
Various Enterobacteriaceae except Salmonella, Shigella, Yersinia, Vibrio, and Campylobacter species
• Enterococci
• Alpha-hemolytic and nonhemolytic streptococci
• Diphtheroids
• S aureus in small numbers
• Yeasts in small numbers
• Anaerobes in large numbers (too many species to list)
Genitalia
• Corynebacterium species, Lactobacillus species, -hemolytic and nonhemolytic streptococci, nonpathogenic Neisseria species
• enterococci, Enterobacteriaceae and other gram-negative rods, S epidermidis, Candida & other yeasts
•
Anaerobes (too many to list); Prevotella, Clostridium, and Peptostreptococcus species
BENEFICIAL FUNCTIONS OF NORMAL
FLORA(commensals)
1. Prevent colonization by
pathogens
2. Produce antimicrobial
substances
3. In newborn it is a powerful
stimulus for the
development of the
immune system
4. Microflora of intestine
synthesize vitamin k and
several B vitamins
5. Certain bacteria
metabolize dietary
carcinogens
Haemorrhagic disease of the newborn
• Haemorrhagic disease of
the newborn is a
coagulation disturbance in
newborns due to vitamin K
deficiency
• Newborns have low vitamin
K stores at birth, vitamin K
passes the placenta poorly,
the levels of vitamin K in
breast milk are low and the
gut flora has not yet been
developed (vitamin K is
normally produced by
bacteria in the intestines).
Pseudomembranous colitis
• The harmless normal flora in the GIT protect
against colonization by harmful
exogenous(coming from outside) bacteria
because of nutritional competition
• Broad spectrum antibiotic usage especially in
the hospitals kills this normal flora in the GIT
• A bacteria called Clostridium difficile which is
widespread in the environment and resistant
to these antibiotics take the place of normal
flora
• The C. difficile cause the disease known as
“Pseudomembranous colitis” or “antibiotic
associated diarrhea”
• Most common symptom is diarrhoea
Vaginal candidiasis
• Candida vaginitis
– Vagina is colonized by a friendly
bacteria lactobacillus species that
produces lactic acid and lowers the
vaginal pH
– Lower pH prevents colonization by
harmful pathogens as most
organism do not grow in acidic pH
– Antibiotic usage kill normal flora
and colonization with a fungus
called candida takes place
– 75% of women may have an
episode of candidal vaginitis during
their lifetime
– intense itching of the vulva & thick
scanty curdlike discharge,
– The vagina and labia are usually
very red(erythematous)
Harmful effects of normal flora/DISEASE CAUSING ABILITY OF
MICROBIAL FLORA
1.
When organisms are displaced from
their normal site in the body to an
abnormal site For example, streptococci
of the viridans group, Bacteroides
species are the most common resident
bacteria of the large intestine. If
introduced into the free peritoneal cavity
or into pelvic tissues along with other
bacteria as a result of trauma, they cause
suppuration and bacteremia.
2. When potential pathogens gain a
competitive advantage due to diminished
populations of harmless competitors
example: by use of antibiotic therapy
3. Immunocompromised individuals
4. Drug resistance
Exogenous and endogenous diseases
• Endogenous infection is "due to reactivation of organisms
present in a dormant focus mainly by normal bacterial flora."
• Exogenous infection is "caused by organisms not normally
present in the body but which have gained entrance from the
environment."
• A prime example of this is when the residential bacterium E.
coli of the GI tract enters the urinary tract. This causes a
urinary tract infection. Infections caused by exogenous
bacteria occurs when microbes that are noncommensal enter
a host. These microbes can enter a host via inhalation of
aerosolized bacteria, ingestion of contaminated or illprepared foods, sexual activity, or the direct contact of a
wound with the bacteria
DISEASE CAUSING ABILITY OF
MICROBIAL FLORA
• Urinary tract
infection(UTI) in females
– UTI is very common in
females
– Fecal gram negative
bacteria inhabit the
perianal area
– With sexual thursting and
very short length of female
urethra these perianal
gram negative bacteria
gain assess to the urinary
bladder causing urinary
tract infection in females
DISEASE CAUSING ABILITY OF
MICROBIAL FLORA
• Some pathogenic bacteria
normally colonize the throat
;e.g Streptococcus
pneumoniae, Hemophilus
influenze etc.
• Loss of respiratory
defences(e.g cilia damage
by viruses,loss of cough
reflex etc.)make these
organism move to lungs,
sinuses and middle ear
causing pneumonia,sinusitis
, otitis media respectively
DISEASE CAUSING ABILITY OF
MICROBIAL FLORA
• Streptococci of the viridans
group are the most
common resident organisms
of the upper respiratory
tract. If large numbers of
them are introduced into
the bloodstream (eg,
following tooth extraction
or tonsillectomy), they may
settle on deformed or
prosthetic heartvalves and
produce infective
endocarditis.
NORMAL FLORA OF THE SKIN
• Staphylococcus epidermidis is most important(causes
infective endocarditis)
• Fungi and yeasts are often present in skin folds
• factors that may be important in eliminating nonresident
microorganisms from the skin are the low pH, the fatty
acids in sebaceous secretions, and the presence of
lysozyme.
• DISEASES Anaerobes and aerobic bacteria often join to
form synergistic infections (gangrene, necrotizing fasciitis,
cellulitis) of skin and soft tissues.
• Propionibacterium and Peptococcus-situated in the
deeper follicles in the dermis-cause of acne
NORMAL FLORA OF THE CONJUCTIVA
• It is relatively free from
organisms due to the
flushing action of tears.
• Examples: Diphtheroids
Staphylococcus
S epidermidis
• The conjunctival flora is
normally held in check by
the flow of tears, which
contain antibacterial
lysozyme.
The Role of the Normal Mouth Flora in Dental Caries
• Caries is a disintegration of the teeth
beginning at the surface and progressing
inward.
• First step: The formation of plaque on the
hard, smooth enamel surface. There appears
to be a strong correlation between the
presence of Streptococcus mutans and
caries on specific enamel areas.
• second step is the formation of large
amounts of acid (pH < 5.0) from
carbohydrates by streptococci and
lactobacilli in the plaque.
• The development of caries also depends on
genetic, hormonal, nutritional, and many
other factors
NORMAL FLORA OF THE NOSE,
NASOPHARYNX AND ACESSORY SINUSES
• In the nose: Corynebateria
Staphylococcus
• The nasopharynx of infant is sterile at birth
• But acquires the common commensal flora
and pathogenic flora carried form the mother
and hospital staff
• Examples: Peudomonas
E.coli
NORMAL FLORA OF THE MOUTH AND UPPER RESPIRATORY TRACT
• The flora of the nose consists of prominent corynebacteria, staphylococci (
S epidermidis, S aureus), and streptococci.
• The mucous membranes of the mouth and pharynx are often sterile at birth
but may be contaminated by passage through the birth canal.
• Within 4–12 hours after birth, viridans streptococci become established as the
most prominent members of the resident flora and remain so for life.
• When teeth begin to erupt, the anaerobic spirochetes, Prevotella species etc
establish themselves, along with some anaerobic vibrios and lactobacilli.
Actinomyces species are normally present in tonsillar tissue and on the
gingivae in adults, and various protozoa may also be present. Yeasts (Candida
species) occur in the mouth.
• Diseases: Periodontal infections, perioral abscesses, sinusitis, and mastoiditis
may involve predominantly Prevotella melaninogenica, fusobacteria, and
peptostreptococci. Aspiration of saliva (containing up to 102 of these organisms
and aerobes) may result in necrotizing pneumonia, lung abscess, and
empyema
NORMAL FLORA OF THE INTESTINAL TRACT
•
•
•
•
•
In 80-90 % newborn infants,the meconium is
sterile but in 10-20% a few orrganisms
probably acquired through labour may be
present.
In all cases,within 4-24 hours of birth an
intestinal flora is established
In bresstfed children the intestine contains
lactobacillus while bottle fed babies have
enterococci, colon bacilli and stahpylococci
Bowels of newborns in intensive care
nurseries tend to be colonized by
Enterobacteriaceae, eg, klebsiella, citrobacter,
enterobacter.
The normal acid pH of the stomach markedly
protects against infection with some enteric
pathogens, eg, cholera. As the pH of intestinal
contents becomes alkaline, the resident flora
gradually increases.
• Minor trauma (eg, sigmoidoscopy, barium enema) may
induce transient bacteremia in about 10% of procedures.
• Intestinal bacteria are important in synthesis of vitamin K,
conversion of bile pigments and bile acids, absorption of
nutrients and breakdown products, and antagonism to
microbial pathogens.
• Antimicrobial drugs taken orally suppress the drugsusceptible components of the fecal flora
• The drug-susceptible microorganisms are replaced by drugresistant ones, particularly staphylococci, enterobacters,
enterococci, protei, pseudomonads, Clostridium difficile,
and yeasts.
• The feeding of large quantities of Lactobacillus acidophilus
may result in the temporary establishment of this organism
in the gut and the concomitant partial suppression of other
gut microflora.
Normal Flora of the Vagina
•
•
•
•
•
At puberty, aerobic and anaerobic lactobacilli
reappear in large numbers and contribute to the
maintenance of acid pH through the production of
acid from carbohydrates, particularly glycogen.
This appears to be an important mechanism in
preventing the establishment of other, possibly
harmful microorganisms in the vagina.
If lactobacilli are suppressed by the administration
of antimicrobial drugs, yeasts or various bacteria
increase in numbers and cause irritation and
inflammation.
After menopause, lactobacilli again diminish in
number and a mixed flora returns
The cervical mucus has antibacterial activity and
contains lysozyme. In some women, the vaginal
introitus contains a heavy flora resembling that of
the perineum and perianal area. This may be a
predisposing factor in recurrent urinary tract
infections. Vaginal organisms present at time of
delivery may infect the newborn (eg, group B
streptococci).
BACTERIA IN THE BLOOD AND TISSUES
• Blood is sterile
• The commensals from the normal flora of the
mouth,nasopharynx and intestinal tract may
get into the blood and tissues but they are
usually quickly eliminated by the normal
defence mechanisms
THANK YOU
Self assessment
1. Which of the following sites of the human body does not have indigenous
microflora?
• a. bladder
• b. colon
• c. distal urethra
• d. vagina
2. The indigenous microflora of the external ear canal is most like the indigenous
microflora of the:
• a. colon.
• b. mouth.
• c. skin.
• d. distal urethra.
3.Microbial flora is also known as:
• Commensals
• Pathogens
• Microbes
• Infectious particles
MCQ
• Muhammad Talha 58-years-old man, smoker presents with
shortness of breath, cough, expectoration of rusty colored
sputum. His Chest X-rays showed consolidation of right lower
lobe of lung. Sputum and blood culture isolated Strep
pneumoniae. The most likely source of this pathogen in this
patient is
a. From another patient in community
b. Patient’s own GIT flora
c. Patient’s own throat flora
d. Ingestion of contaminated water from community
e. None of the above
Correct Answer: c
MCQ
A 25-years-young lady reported with upper respiratory tract
infection. General practitioner prescribed Tab Co-amoxiclav
for 3 days. On 4th day, lady experienced itching, thick curdy
discharge from vagina. Gram stain of the discharge reveal
numerous pus cells and gram positive budding
microorganism. The cause of this infection is most likely due
to:
a. Fecal contamination of vagina
b. Recto-vaginal fistula
c. Antimicrobial intake
d. Catheterization
e. Per-vaginal exam
Correct Answer: c
• Muhammad 24-years-young met a RTA. He sustained
multiple injuries and was hospitalized. At laparotomy, it was
found that there was a laceration in ascending colon 50 cm
from ceacum. The laceration was stiched but three days
later, he experienced pain right side of abdomen and fever.
USG revealed pus collection near stitched laceration of
ascending colon. The most likely organisms to be isolated
will be
1. Vibrio cholerae and Staph aureus
2. Strep pyogenes
3. Mycobacterium tuberculosis
4. Mixed normal gastrointestinal flora
5. Neisseria meningitidis
Correct Answer: 4
question: write the harmful effects of normal
flora