Microbes and human
diseases
, Characteristics Viruses Bacteria Fungi Protozoa and
Helminhs
1. Cells 1. No 1. Yes 1. Yes 1. Yes
2. Approximate 0.02-0.2 1 -5 3 – 10(Yeast) 15 – 25/Visible
diameter(µm)
3. Nucleic Acid 3. Either DNA 3. Both DNA or 3. Both DNA or 3. Both DNA or
or RNA. RNA. RNA. RNA.
4. Types of 4. None 4.Prokaryotic 4. Eukaryotic 4. Eukaryotic
nucleus
5. Ribosomes 5. Absents 5. Present 5. Present 5. Present
6. Mitochondria 6. Absent 6. Absent 6. Present 6. Present
7. Nature of outer 7. Protein 7. Rigid wall 7. Rigid wall 7. Flexible
surface capsid and containing containing membrane.
lipoprotein peptidoglycan. chitin.
envelop
,Characteristics Viruses Bacteria Fungi Protozoa and
Helminhs
8. Motility 8. None 8. Some 8. None 8. Most
9. Method of 9. Not binary 9. Binary 9. Budding or 9. Mitosis
replication fission. fission. Mitosis
,Some definitions:
• Host: An organism which harbors the parasite.
• Parasite: A living organism which receives nourishment and shelter
from another organism where it lives.
,• Symbiosis: An association in which both are so
dependent upon each other that one cannot live without
the help of the other. None of the partners suffers any
harm from the association.
• Parasitism: An association in which the parasite derives
benefit and the host gets nothing in return but always
suffers some injury, however slight the injury may be.
• Commensalism:
An association in which the parasite only is deriving
benefit without causing injury to its host. A commensal is
capable of leading an independent life.
,Normal flora
• The new born baby is sterile. But, very soon,different body sites
become colonized by microorganisms.
• The term ‘normal microbial flora’ or simply ‘normal flora’ denotes
the population of microorganisms that inhabit the skin and mucous
membranes of healthy normal persons.
• Bacteria and fungi but,usually no virus and parasites, are members of
normal flora.
,Normal flora
• In a healthy animal, the internal tissues, e.g. blood,
brain, muscle, etc., are normally free of
microorganisms.
• On the other hand, the surface tissues, e.g. skin and
mucous membranes, are constantly in contact with
environmental organisms and become readily
colonized by certain microbial species.
• The mixture of organisms regularly found at any
anatomical site is referred to as the normal flora.
,THE BENEFITS OF THE NORMAL
FLORA
1. The normal flora provide 1st line of defense against
microbial pathogens.
2. The normal flora prevent colonization by pathogens
3. The normal flora may antagonize other bacteria
4. The normal flora stimulate the development of
certain tissues
5. Bacteria of the gut provide important nutrients,such
as Vitamin-K and aid in digestion and absorption of
nutrients.
6. The normal flora produce some antimicrobial
substances like bacteriocins and antibiotics, which
prevent infection by pathogenic bacteria.
,THE BENEFITS OF THE NORMAL FLORA
CONT.
7.In new born baby, the normal flora act as powerful stimulus for the
development of the immune system. It leads to production of IgA that
is secreted through mucus membrane and give protection.
, Harmful effects of the normal flora
Competition with host for nutrients
Low grade toxemia produced in host
When individuals are immunocompromised , normal
flora can overgrow and become pathogenic.
If removed from normal habitat and introduced in new
environment they produce disease
• Ex: When viridans streptococci is introduced in blood
stream – cause bacterial endocarditis
• Escherichia coli in Urinary tract – cause UTI,
in wound – cause wound infection etc
diseases
, Characteristics Viruses Bacteria Fungi Protozoa and
Helminhs
1. Cells 1. No 1. Yes 1. Yes 1. Yes
2. Approximate 0.02-0.2 1 -5 3 – 10(Yeast) 15 – 25/Visible
diameter(µm)
3. Nucleic Acid 3. Either DNA 3. Both DNA or 3. Both DNA or 3. Both DNA or
or RNA. RNA. RNA. RNA.
4. Types of 4. None 4.Prokaryotic 4. Eukaryotic 4. Eukaryotic
nucleus
5. Ribosomes 5. Absents 5. Present 5. Present 5. Present
6. Mitochondria 6. Absent 6. Absent 6. Present 6. Present
7. Nature of outer 7. Protein 7. Rigid wall 7. Rigid wall 7. Flexible
surface capsid and containing containing membrane.
lipoprotein peptidoglycan. chitin.
envelop
,Characteristics Viruses Bacteria Fungi Protozoa and
Helminhs
8. Motility 8. None 8. Some 8. None 8. Most
9. Method of 9. Not binary 9. Binary 9. Budding or 9. Mitosis
replication fission. fission. Mitosis
,Some definitions:
• Host: An organism which harbors the parasite.
• Parasite: A living organism which receives nourishment and shelter
from another organism where it lives.
,• Symbiosis: An association in which both are so
dependent upon each other that one cannot live without
the help of the other. None of the partners suffers any
harm from the association.
• Parasitism: An association in which the parasite derives
benefit and the host gets nothing in return but always
suffers some injury, however slight the injury may be.
• Commensalism:
An association in which the parasite only is deriving
benefit without causing injury to its host. A commensal is
capable of leading an independent life.
,Normal flora
• The new born baby is sterile. But, very soon,different body sites
become colonized by microorganisms.
• The term ‘normal microbial flora’ or simply ‘normal flora’ denotes
the population of microorganisms that inhabit the skin and mucous
membranes of healthy normal persons.
• Bacteria and fungi but,usually no virus and parasites, are members of
normal flora.
,Normal flora
• In a healthy animal, the internal tissues, e.g. blood,
brain, muscle, etc., are normally free of
microorganisms.
• On the other hand, the surface tissues, e.g. skin and
mucous membranes, are constantly in contact with
environmental organisms and become readily
colonized by certain microbial species.
• The mixture of organisms regularly found at any
anatomical site is referred to as the normal flora.
,THE BENEFITS OF THE NORMAL
FLORA
1. The normal flora provide 1st line of defense against
microbial pathogens.
2. The normal flora prevent colonization by pathogens
3. The normal flora may antagonize other bacteria
4. The normal flora stimulate the development of
certain tissues
5. Bacteria of the gut provide important nutrients,such
as Vitamin-K and aid in digestion and absorption of
nutrients.
6. The normal flora produce some antimicrobial
substances like bacteriocins and antibiotics, which
prevent infection by pathogenic bacteria.
,THE BENEFITS OF THE NORMAL FLORA
CONT.
7.In new born baby, the normal flora act as powerful stimulus for the
development of the immune system. It leads to production of IgA that
is secreted through mucus membrane and give protection.
, Harmful effects of the normal flora
Competition with host for nutrients
Low grade toxemia produced in host
When individuals are immunocompromised , normal
flora can overgrow and become pathogenic.
If removed from normal habitat and introduced in new
environment they produce disease
• Ex: When viridans streptococci is introduced in blood
stream – cause bacterial endocarditis
• Escherichia coli in Urinary tract – cause UTI,
in wound – cause wound infection etc
