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Medical microbiology is the study of causative agents of infectious diseases of humans and their reactions to such infections. In other words it deals with etiology, pathogenesis, laboratory diagnosis, specific treatment and control of infection (immunization).
INTRODUCTION to MEDICAL
1. Medical microbiology
2. Classification of
3. Morphology of bacteria
4. Bacterial anatomy
5. Morphology of viruses
6. Morphology of
7. Morphology of chlamidia
8. Methods of laboratory
• Medical microbiology is the study of causative
agents of infectious diseases of humans and
their reactions to such infections. In other
words it deals with etiology, pathogenesis,
laboratory diagnosis, specific treatment and
control of infection (immunization).
Modern medical microbiology
• Bacteriology – the science of bacteria, the
causative agents of a member of infectious
• Virology – the science of viruses, non-cellular
living systems, capable of causing infectious
diseases in man.
• Immunology – the science which concerned
with mechanisms of body protection against
pathogenic microorganisms and foreign cells
• Mycology – the study of fungi pathogenic for
• Protozoology – which deals with pathogenic
unicellular animal organisms.
CLASSIFICATION OF MICROORGANISMS
• DNA-viruses and RNA-viruses
• Eukaryotes Prokaryotes
• Fungi Blue-green algae
• Algae Bacteria
• Protozoa Scotobacteria Photobacteria
• Slime moulds 1. Class Bacteria
2. Class Rickettsias
3. Class Mollicutes
A division of the kingdom Procaryotae comprising bacteria with a gram-negative type of
cell wall consisting of an outer membrane and a thin inner peptidoglycan layer
containing muramic acid. It contains three classes:
Scotobacteria, Anoxyphotobacteria & Oxyphotobacteria.
• In microbiology the binominal system of
nomenclature is accepted where each
species has a generic and a specific
name. The generic name is written with a
capital letter, and the specific name – with
a small letter. For example: the anthrax
bacillus – Bacillus anthracis; the tetanus
bacillus – Clostridium tetani.
The size of bacteria
• The size of bacteria is measured in micrometer
(m) or micron () (1 micron or micrometer is one
thousandth of a millimeter) and varies from 0.1 to
16-18 . Most pathogenic bacteria measure from
0.1 to 10 .
• The other units of measurement of microorganisms
are millimicron (m) or nanometer (nm) (one
millionth of a millimeter) and 1 Angstrom (Å) (one
tenth of nanometer).
Morphology of Bacteria
• Bacteria are intracellular free-living
organisms having both DNA and RNA. Their
biological properties and predominant
reproduction by binary fission relates them to
• Spherical (cocci)
(vibriones, spirilla, spirochaetes)
• Bacteria (1) include those
microorganisms, which, as rule,
do not produce spores (E.coli,
• Bacilli (2) (B.anthracis) and
clostridia (3) (C.tetani, C.botuli-
num) include organisms the
majority of which produce spores.
• Size of rod-shaped bacteria varies
2-10 μm: small rods are 2-4 μm;
long rods are 5-10 μm.
1. Single Rod
• 1. Vibrios – are cells, which resemble a
comma in appearance (curved rods).
Typical representative of this group is
2. Spirilla – are coiled forms of bacteria.
Pathogenic species: Spirillum minus (1) – which
is responsible for a disease in humans
transmitted through the bite of rats – rat-bite fever
– sodoku; Helicobacter pylori (2) – causative
agent of ulcer disease of stomach.
• Treponema – exhibits, thin, flexible cells
with 6-14 regular twists. The size of
Treponema varies from 10-18 μ (T.pallidum).
• Leptospira – are characterized by very thin
cell structure. The leptospirae form 12-18
regular coils (primary spirals)
(L.interrogans) and C- or S- shape according
• Borrelia – have large irregular spirals, the
number of which varies from 3 to 10.
3. Spirochaetes – are flexuous spiral forms which
include: Treponema (T.pallidum) (1), Borrelia
(B.recurrentis) (2), Leptospira (L.interrogans) (3)
• In addition to conferring rigidity upon
bacteria, the cell wall protects against
• Chemically, the rigid part of the cell wall is
• First described by Gram in 1884. It is' used
to study morphologic appearance of
bacteria. Gram's stain differentiates all
bacteria into two distinct groups:
• a. Gram-positive organisms
• b. Gram-negative organisms
The periplasm is a concentrated gel-like matrix in the space between the inner
cytoplasmic membrane and the bacterial outer membrane called the periplasmic
space in gram-negative bacteria. Using cryo-electron microscopy it has been found that
a much smaller periplasmic space is also present in gram-positive bacteria.
Bacteria with deficient cell walls
• Mycoplasma: a genus of naturally occurring bacteria
which lack cell walls
• L-forms: cell-wall-deficient forms of bacteria, usually
produced in the body of patients treated with penicillin
• Spheroplasts: derived from Gram-negative bacteria;
produced artificially by lysozyme or by growth with
penicillin or any other agent capable of breaking down the
• Protoplasts: derived from Gram-positive bacteria and
totally lacking cell walls; produced artificially by lysozyme
and hypertonic medium*
Hypertrophy (/haɪˈpɜːrtrəfi/, from Greek ὑπέρ
"excess" + τροφή "nourishment") is the increase in
the volume of an organ or tissue due to the
enlargement of its component cells. It is
distinguished from hyperplasia, in which the cells
remain approximately the same size but increase in
Electron micrograph mycoplasma
cells (1) and L-forms of Proteus
Morphology of viruses
• Do not possess cellular
• Contain one type of nucleic acid
either RNA or DNA
• Lack enzymes necessary for
protein and nucleic acid
synthesis machinery of host
• They multiply by complex
process and not by binary
• They are unaffected by
• They are sensitive to interferon.
Morphology of Rickettsiae.
• They are minute organisms having properties
in between bacteria and viruses.
• It contains both DNA and RNA.
• Contains enzymes for metabolic functions.
• Multiplies by binary fission.
• It is coccobacilli 300x600 nm in size, non-
motile, non-capsulated and is Gram-negative.
• Sensitive to many antibiotics.
• Can multiply only inside living cells.
Morphology of Rickettsiae
The morphological structures of the
rickettsiae of epidemic and endemic
typhus fever, Rocky Mountain
spotted fever, and Q fever are similar
to one another and to certain
The rickettsial organisms in common
with the elementary bodies of
vaccinia virus and all bacteria would
appear to have a limiting membrane
which surrounds a substance that
seems to be protoplasmic in nature;
numbers of dense granules are
embedded in the inner protoplasm.
Morphology of chlamydia.
• Chlamydiae are Gram-negative. They lack
some important mechanisms for the
production of metabolic energy, so they
are intracellular parasites. There are 2
morphological forms of chlamydia:
• Elementary bodies
• Initial bodies
Methods of laboratory diagnosis
3. Detection sensitivity of
bacteria to antibiotics
6. DNA-technology test
(PCR) Polymerase Chain
Reaction. It's a testing
technique that can detect either
DNA or RNA from any kind of
organism, such as HIV, for