This is prepared for Nursing and allied health students

1. Types Of Microorganism
Muhammad Azhar
MSc in Microbiology
BScN Generic
BscBiochemistry
+923066555308
Prepared by Muhammad Azhar MSc, BScN , BSc 1

2. • Microorganisms differ from each other not only in size, but also in structure, habitat,
metabolism, and many other characteristics. While we typically think of microorganisms
as being unicellular, there are also many multicellular organisms that are too small to be
seen without a microscope. Some microbes, such as viruses, are even acellular (not
composed of cells).
Until the late 1970s it was generally accepted that all bacteria are closely related in
evolutionary development. This concept was challenged in 1977 by Carl R. Woese and
coinvestigators at the University of Illinois, whose research on ribosomal RNA from a
broad spectrum of living organisms established that two groups of bacteria evolved by
separate pathways from a common and ancient ancestral form.
This discovery resulted in the establishment of a new terminology to identify the major
distinct groups of microbes—namely, the eubacteria (the traditional or “true” bacteria),
the archaea (bacteria that diverged from other bacteria at an early stage of evolution and
are distinct from the eubacteria), and the Eukarya (the eukaryotes).
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3. Microorganisms are found in each of the three domains of life:
i. Bacteria
ii. Archaea
iii.and Eukarya.
Microbes within the domains Bacteria and Archaea are all prokaryotes (their cells
lack a true membrane-bound nucleus), whereas microbes in the domain Eukarya are
eukaryotes (their cells have a nucleus and membrane bound organelles). Some
microorganisms, such as viruses, do not fall within any of the three domains of life.
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4. EUKARYOTES & PROKARYOTES:
Cells have evolved into two fundamentally different types, eukaryotic and prokaryotic, which can
be distinguished on the basis of their structure and the complexity of their organization.
Fungi, protozoa, and helminths are eukaryotic, whereas bacteria are prokaryotic.
i. The eukaryotic cell has a true nucleus with multiple chromosomes surrounded by a nuclear
membrane and associated proteins.
ii. The nucleoid of a prokaryotic cell consists of a single circular molecule of loosely organized
DNA, lacking a nuclear membrane and mitotic
iii. Eukaryotic cells contain organelles, such as mitochondria and lysosomes, and larger (80S)
ribosomes, whereas prokaryotes contain no organelles and smaller (70S) ribosomes.
iv. Most prokaryotes have a rigid external cell wall that contains peptidoglycan, a polymer of
amino acids and sugars, as its unique structural component. Eukaryotes, on the other hand, do
not contain peptidoglycan. Either they are bound by a flexible cell membrane, or, in the case of
fungi, they have a rigid cell wall with chitin
v. The eukaryotic cell membrane contains sterols, whereas prokaryotes does not have it, except
the wall-less Mycoplasma
vi. Motility is another characteristic by which these organisms can be distinguished. Most protozoa
and some bacteria are motile, whereas fungi and viruses are nonmotile
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6. Bacteria:
Bacteria are unicellular free-living organisms without chlorophyll having both DNA and
RNA. They are capable of performing all essential processes of life, e.g. growth,
metabolism and reproduction.
i. Bacteria are found in nearly every habitat on earth, including within and on humans.
ii. Most bacteria are harmless or helpful, but some are pathogens, causing disease in humans and
other animals.
iii.Bacteria are prokaryotic because their genetic material (DNA) is not housed within a true
nucleus. t
iv. Bacteria are microscopic, with a few extremely rare exceptions, such as Thiomargarita
namibiensis (750um) to be visible to the naked eye.
v. Most bacteria have cell walls that contain peptidoglycan.
vi. Bacteria are often described in terms of their general shape.
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8. Common shapes include
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9. Shapes of Bacteria
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10. vii.Shape of bacteria: On the basis of shape, bacteria are classified as under:
a. Cocci (from kakkos, meaning berry): They are spherical. On the basis of arrangement of
individual organisms, they are described as staphylococci (clusters like bunches of grapes),
streptococci (arranged in chains), diplococci (forming pairs), tetrads and sarcina are cocci
arranged in groups of four and cubical packet of eight cell respectivel
b. The cylindrical or rod shaped organisms are called bacilli (from baculus, meaning rods).
They are of following types. In some of the organisms length may approximate the width of
the organisms. These are called coccobacilli, e.g. brucella.
c. Vibrio: These are comma shaped, curved rods and derive the name from their characteristic vibratory
motility.
d. Spirochaetes (from speria meaning coil, chaete meaning hair). They are relatively longer, thin,
flexible organisms having several coils.
e. Actinomycetes (actis meaning ray, mykes, meaning fungus) are branching filamentous bacteria, so
called because of resemblance to radiating sunrays.
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11. f. Mycoplasma are organisms which lack cell wall and so do not possess a stable
morphology. They are round or oval bodies with interlacing filaments.
viii. Their genome is usually a circular bacterial chromosome – a single loop of DNA,
although they can also have small pieces of DNA called plasmids.
ix. Bacteria have an enclosing cell wall, which provides strength and rigidity to their cells.
x. They reproduce by binary fission or sometimes by budding, but do not
undergo meiotic sexual reproduction.
Examples of bacterial cells. Escherichia coli gut normal flora (UTI), Streptococcus mutans
(surfaces of teeth dental carries), Staphylococcus epidermidis (catheters HAI ), Mycoplasma
tuberculosis (TB)
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12. A Typical Bacterial cell
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13. Gram staining
i. Distinguishes two major classes of
bacteria
ii. Bacteria that have been starved or treated
with antibiotics exhibit variable staining.
iii. Gram-positive bacteria have a thick cell
wall and stain purple.
iv. Gram-negative bacteria have a thin cell
wall and stain red.
v. Gram-resistant bacteria (e.g.,
Mycobacterium and Mycoplasma species)
stain poorly or not at all with Gram stain
vi. Gram-positive and gram-negative bacteria
have similar internal structures but
structurally different cell envelopes
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14. Cell Walls of Acid-Fast
Bacteria
Mycobacteria (e.g.,
Mycobacterium
tuberculosis) have an
unusual cell wall, resulting
in their inability to be
Gram-stained . These
bacteria are said to be acid
-fast because they resist
decolorization with acid–
alcohol after being stained
with carbolfuchsin. This
property is related to the
high concentration of
lipids, called mycolic
acids, in the cell wall of
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16. Bacterial Spores:
These highly resistant structures which are formed in response to adverse conditions
by certain Bacteria.
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17. Bacterial growth curve:
When placed in a new medium, bacteria exhibit a typical pattern of growth and
multiplication marked by four phases. Bacteria reproduce by binary fission, a process
by which one parent cell divides to form two progeny cells. Because one cell gives rise
to two progeny cells, bacteria are said to undergo exponential growth (logarithmic
growth).
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18. Growth requirements
Different bacteria require different nutrients for growth in the body and in culture. Characteristic nutrient
requirements and metabolic products can be used to identify bacteria.
1. Oxygen requirement
i. Obligate aerobes require oxygen for growth.
ii. Anaerobes do not require oxygen for growth.
iii. Obligate anaerobes, which are damaged by oxygen, include normal colonizers of the gastrointestinal tract,
respiratory tract, and/or skin.
iv. Aerotolerant anaerobes can survive in the presence of small amounts of oxygen but grow best in its absence.
v. Facultative anaerobes can grow under aerobic or anaerobic conditions.
2. Nutrient requirements
i. Undemanding eaters can be cultured on simple media (e.g., E. coli, Salmonella species, and other gram-negative
enteric bacteria).
ii. Demanding eaters require complex media/Enriched media containing numerous growth factors (e.g.
Haemophilus and Neisseria species).
3. Temperature requirements
Most pathogenic bacteria of medical importance grow optimally at 35°C to 37°C, near
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19. The Archaea: are a group of organisms that were originally thought to be bacteria due
to their physical similarities. More reliable genetic analysis revealed that the Archaea
are distinct from both Bacteria and Eukaryotes, earning them their own domain in the
Three Domain Classification originally proposed by Woese in 1977.
i. Archaea are procaryotes differing from true bacteria in cell wall and plasma
membrane chemistry as well as 16S rRNA sequences.
ii. Plasma membrane in archaea is in the L-isomeric form, while bacteria and
eukaryotes have the D-isomeric form.
iii. An ether-linkage between the glycerol and the side chain present in Archaea while
the ester-linked lipids found in bacteria and eukaryotes.
The plasma membrane of Archaea is made up of monolayers while Bacteria and
eukaryotes only have lipid bilayers
archaea lack peptidoglycan and have pseudomurein
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