2. is the term used to describe the various bacteria and fungi that
are permanent residents of certain body sites
The viruses and parasites, which are the two other major groups of
microorganisms, are usually not considered members of the normal flora,
although they can be present in asymptomatic individuals.
The members of the normal flora vary in both number and kind from one site to
another.
Normal flora organisms inhabit the body surfaces exposed to the environment,
such as the skin, oropharynx, intestinal tract, and vagina. Members of the
normal flora differ in number and kind at various anatomic sites
3. the internal organs usually are sterile areas such as the
central nervous system, blood, lower bronchi and alveoli,
liver, spleen, kidneys, and bladder are free of all but the
occasional transient organism.
• Members of the normal flora are low-virulence organisms. In
their usual anatomic site, they are nonpathogenic. However, if they
leave their usual anatomic site, especially in an
immunocompromised individual, they can cause disease.
• Colonization resistance occurs when members of the
normal flora occupy receptor sites on the skin and mucosal
surfaces, thereby preventing pathogens from binding to those
receptors.
4. Sterile (Microbe-Free) Anatomical Sites
and Fluids
Sites That Harbor Normal Resident
Microbes
All Internal Tissues and Organs
Heart and circulatory system Bones
Liver Ovaries/testes
Kidneys and bladder Glands (pancreas,
salivary)
Lungs Sinuses
Brain and spinal cord Middle and inner ear
Muscles Internal eye
Fluids Within an Organ or Tissue
Blood
Urine in kidneys, ureters, bladder
Cerebrospinal fluid
Saliva prior to entering the oral cavity
Semen prior to entering the urethra
Amniotic fluid surrounding the embryo and fetus
• Skin and its contiguous mucous membranes
• Upper respiratory tract (oral cavity, pharynx, nasal
mucosa)
• Gastrointestinal tract (mouth, colon, rectum, anus)
• Outer opening of urethra
• External genitalia
• Vagina
• External ear and canal
• External eye (lids, lash follicles)
5. Resident NF – consists of relatively fixed types of microorganisms
regularly found in a given area at a given age; if disturbed, it promptly
reestablishes itself.
Transient NF –consists of 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.
7. Healthy fetus, in utero, is essentially free of MOs
Infant exposed immediately to MOs when passing
through mothers vaginal tract and then to MOs in
environment
Within few hours, oral and nasopharyngeal flora of
neonate established
Within one day, resident flora of lower intestinal tract
established
8. Protection from External Invaders
a) Because of the normal flora occupy body's epithelial surfaces, they are able to prevent other bacteria by
blocking receptors
b) competing for essential nutrients
c) producing anti-bacteria substances e.g : Fatty acids, peroxides , Bacteriocins
May be source of opportunistic infections
e.g : In Patients with impaired defense Mechanisms
Immunostimulation
a) They produce antibodies which may contribute to host defenses.
b) Some of these antibodies may cross react with normal tissue components.
Nutrition Some of the normal intestinal flora e.g. E. coli & Bacteroids produce Vitamin K in the gut
9. Important Members of the Normal Flora
Skin. The predominant member of the normal flora
of the skin is Staphylococcus epidermidis. It is
an important cause of infections of prosthetic heart
valves and prosthetic joints.
Candidia albicans, a yeast also found on the
skin, can enter the bloodstream and cause
disseminated infections, such as endocarditis in
intravenous drug users. S. aureus is also present
on the skin, but its main site is in the nose. It
causes abscesses in the skin and in many other
organs.
10. Oropharynx. The main members
of the normal flora of the mouth and
throat are the viridans
streptococci, such as S. sanguis
and S. mutans . Viridans
streptococci are the most common
cause of subacute endocarditis.
11. Examples of bacteria
that inhabit the
gastrointestinal tract.
Gastrointestinal tract. The stomach contains very few organisms
because of the low pH. The colon containsthe largest number of
normal flora and the most diverse species, including both anaerobic and
facultative bacteria. There are both gram-positive and gram-negative rods
and cocci.
The members of the colonic normal flora are an important cause of disease
outside of the colon. The two most important members of the colonic flora
that cause disease are the anaerobe Bacteroides fragilis and the
facultative Escherichia coli. Enterococcus faecalis, a facultative, is
also a very important pathogen.
12. Vagina. Lactobacilli are the
predominant normal flora organisms
in the vagina.They keep the pH of
the vagina low, which inhibits the
growth of organisms such as C.
albicans, an important cause of
vaginitis.
Urethra. The outer third of the
urethra contains a mixture of
bacteria, primarily S. epidermidis .
The female urethra can become
colonized with fecal flora such as E.
coli , which predisposes to urinary
tract infections.
13. Associations between microbes
and humans. Effects of contact
with microbes can progress in a
variety of directions, ranging from
no effect to colonization, and from
infection to disease and immunity.
The example shown here follows the
possible events in the case of contact
with a pathogen such as
Streptococcus pneumoniae (the
pneumococcus). This bacterium can
be harbored harmlessly in the upper
respiratory tract, but it may also
invade and infect the ear, cranium,
and respiratory tract.
14. •The two main ways in which an
individual will encounter a pathogen
are:
where the
normal microbiota can multiply and
develop due to a disruption of normal
defences
result when
infecting bacteria have been acquired
from an external source and is not part
of the natural microbiota
15.
16.
17. – Invasion
• e.g. Strep pyogenes pharyngitis
– Migration
• e.g. Escherichia coli urinary tract infection
– Innoculation
• e.g. Coagulase negative staphylococcus prosthetic
joint infection
– Haematogenous
• e.g. viridans Strep endocarditis
18. What is a surface?
Interface between a solid and either a liquid or gas.
Patient
Pathogen
Infection Management Outcome
Mechanism of infection
epithelium
hair
nails
conjunctiv
al
gastrointestinal
respiratory
genitourinary
27. Processes in the pathogenesis of infection at
surfaces
• Adherence to host cells or prosthetic
surface
• Biofilm formation
• Invasion and multiplication
• Host response
– Pyogenic (neutrophils -> pus)
– Granulomatous (fibroblasts, lymphocytes,
macrophages -> nodular inflammatory
28. What is Biofilm
Biofilms are multicellular aggregates of bacteria and
yeast that congregate on surfaces.
Biofilm formation is a nearly universal bacterial trait,
and biofilms are found on almost all natural and
artificial surfaces
Biofilms are formed to protect the bacteria from host
defenses, antibiotics, and from harsh environmental
conditions.
Some examples of biofilms are the plaque that forms
on teeth and the slime that forms on surfaces in
watery areas
29. A process that enables bacteria to
communicate using secreted signaling
molecules called auto inducers
This process enables a population of
bacteria to regulate gene expression
collectively and therefore, control
behavior on a community-wide scale.
30. Quorum Sensing helps
in
Bacteria use Quorum sensing to
mastermind behaviors or
(Controls)
– Sporulation
– Biofilm formation
– Virulence factor secretion
55*pp0
31. Three principles steps
1) production of small biochemical signal molecules by the bacterial cell.
2) release of the signal molecules, either actively or passively, into the
surrounding environment
3) recognition of the signal molecules by specific receptors once they
exceed a threshold concentration, leading to Gene expression ->co-
operative behaviours and more AI production.
32. Diagnosis
• Aim is to identify infecting organism and its antimicrobial
susceptibilities.
• Blood cultures
• Tissue/prosthetic material sonication and culture
• Treatment
• Aim:
– sterilise tissue
– reduce bioburden
• Antibacterials
• Remove prosthetic material
• Surgery – resect infected material
35. • Natural and prosthetic surfaces are frequent sites of
infection
• Biofilms are a common feature of surface infections
• Bacteria are protected from host and antibacterial attack
by biofilms.
