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
Prepared by Muhammad Azhar MSc, BScN , BSc 4
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.
Prepared by Muhammad Azhar MSc, BScN , BSc 6
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.
Prepared by Muhammad Azhar MSc, BScN , BSc 10
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)
Prepared by Muhammad Azhar MSc, BScN , BSc 11
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
Prepared by Muhammad Azhar MSc, BScN , BSc 13
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
mycobacteria. Prepared by Muhammad Azhar MSc, BScN , BSc 14
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
normal body temperatures Prepared by Muhammad Azhar MSc, BScN , BSc 18