Exhaustive historical evidences based on the survey of literatures, amply stress and reveal the
fact that
‘bacteria’
‘world of living organisms’.
A
bacterium may be regarded as a one-celled organism without true nucleus or functionally
specific components of metabolism that essentially belongs to the kingdom
Prokaryotae (Monera), a
name which means primitive nucleus. However, all other living organisms are termed as
Eukaryotes, a
name that precisely implies a true or proper nucleus.
It has been duly observed and established that
‘bacteria’ are exclusively responsible for the
causation of several painful ailments in humans, namely :
tonsillitis, pneumonia, cystitis, school sores,
and
conjunctivitis.
Alternatively, one may define
bacteria as microscopic single-celled organisms that can penetrate
into healthy tissues and start multiplying into vast numbers. Interestingly, when they do this, they
invariably damage the tissue that they are infecting, causing it to break down into the formation of
pus.**
Due to the damage they (bacteria) cause, the affected and involved area becomes red, swollen,
hot and painful. In this manner, the waste products of the damaged tissue, together with the bacteria,
rapidly spread into the blood stream, and this virtually stimulates the brain to elevate the body temperature
so as to fight off the contracted infection; and this ultimately gives rise to the development of
‘fever’ (normal body temperature being 37°C or 98.4°F).
Salient Features
The various
salient features of ‘bacteria’ are as stated under:
(1) The body is invariably invaded by millions of organisms every day, but very few surprisingly
may ever succeed in causing serious problems by virtue of the fact that
body’s defence
mechanisms
usually destroy the majority of the invading microbes.
In fact, the white-blood cells (WBCs) are the main line of defence against the prevailing
infections. Evidently, the WBCs rapidly migrate to the zone of ‘unwanted bacteria’ and do
help in engulfing them and destroying them ultimately. Importantly, when these defence
mechanisms get overwhelmed, that a specific infection develops and noticed subsequently.
(2)
Nomenclature: Each species of organisms or bacteria (and fungi but not viruses) has two
names
: first — a family name (e.g., Staphylococcus) that essentially makes use of a capital
initial letter and comes first always; and
secondly — a specific species name (e.g., aureus)
which uses a lower case initial letter and comes second.
Example
: The golden staph bacteria that gives rise to several serious throat infections is
therefore termed as
Staphylococcus aureus, but should be normally abbreviated to S. aureus.
(3) As different types of bacteria invariably favour different segments of the body and thereby
lead to various glaring symptoms; therefore, it is absolutely necessary to choose and pick-up
an appropriate educated guess about the antibiotic(s) to be administered by a
‘physician’. In
the event of any possible doubt it is always advisable to take either a
‘sample’ or a ‘swab’
being sent to a
‘microbiological laboratory’ for an expert analysis, so that the precise organism
may be identified, together with the most suitable antibiotic to destroy it completely.
(4) Obviously, there are a plethora of organisms (bacteria), specifically those present in the
‘gut’,
observed to be quite useful with respect to the normal functioning of the body. These
organisms usually help in the digestive process, and prevent infections either caused by
fungi
(e.g., thrush) or sometimes by viruses. Importantly, antibiotics are capable of killing
these so called
‘good bacteria’ also, which may ultimately give rise to certain apparent sideeffects
due to the prolonged usage of antibiotics, such as :
diarrhoea, fungal infections ofthe mouth and vagina.
Structure and Form of the Bacterial Cell:
These characteristic form of the bacterial cell may
be sub-divided into
two heads, namely:
(
i) Size and shape, and
(
ii) StructureThese two categories shall now be dealt with separately in the sections that follows :
Size and Shape:
The size and shape of bacteria largely vary between the dimensions of 0.75
– 4.0
μm. They are invariably obtained as definite unicellular structures that may be essentially found
either as
spherical forms (i.e., coccoid forms) or as cylindrical forms (i.e., rod-shaped forms). However,
the latter forms, in one or two genera, may be further modified into
two sub-divisions, namely:
(
a) With a single twist (or vibrios), and
(
b) With several twists very much akin to ‘cork screw’ (or spirochaetes).
In actual practice, there prevails another predominant characteristic feature of the bacterial form
i.e.,
the inherent tendency of the coccoid cells to exhibit growth in aggregates. It has been duly observed
that these
‘assemblies’ do exist in four distinct manners, such as:
(
i) As ‘pairs’ (or diplococci),
(
ii) As ‘groups of four systematically arranged in a cube’ (or sarcinae),
(
iii) As ‘unorganized array like a bunch of grapes’ (or staphylococci), and
(
iv) As ‘chains like a string of beads’ (or streptococci).
In general, these
‘aggregates’ are so specific and also characteristic that they usually assign aparticular generic nomenclature to the group, for instance :
(
a) Diplococcus pneumoniae — causes pneumonia,
(
b) Staphylococcus aureus — causes ‘food-poisoning’ and boils, and(c) Streptococcus pyogenes — causes severe sore throat.
Structure:
There exists three essential divisions of the so called ‘bacterial cell’ that normally
occur in all species, such as:
cell wall or cytoplasmic membrane and cytoplasm.
Based upon the broad and extensive chemical investigations have evidently revealed
two fundamental
components in the structure of a bacterial cell, namely :
(
a) Presence of a basic structure of alternating N-acetyl-glucosamine, and
(
b) N-acetyl-3-0-1-carboxyethylglucosamine molecules. In fact, the strategic union of the said
two
components distinctly give rise to the polysaccharide backbone.
Salient Features:
The salient features of the structure of a bacterial cell are as stated under:
(1) The two prominent and identified chemical entities
viz., N-acetyl glucosamine (A), and Nacetyl-3-0-1- carboxymethylglucosamine (B) are usually cross-linked by peptide chains.
(2) The combined structure of [A] and [B] as shown in (1) above basically possesses an
enormous
mechanical strength
, and, therefore, essentially represents the target for a specific
group of
‘antibiotics’, which in turn via different modes, categorically inhibit the biosynthesis
that eventually take place either in the course of
cell growth or in the cell division prominently.
(3) The fundamental
peptidoglycan moiety (also known as murein or mucopeptide) besides
contains other chemical structures that particularly gets distinguished by the presence of
two
kinds of bacteria, namely :
(
a) Gram-negative organism, and
(
b) Gram-positive organisms.
However, these
two variants of organisms may be identified distinctly and easily by treating a
thin-film of bacteria, duly dried upon a microscopic slide with a separately prepared solution of a
basic
dye
i.e., gentian violet, and followed soon shape after by the application of a solution of iodine. Thus,we may have:
Gram-negative bacteria —
by alcohol washing the dye-complex from certain types of cells, and
Gram-positive bacteria
— by retaining the dye-complex despite the prescribed alcohol-washing.
Further, the prevailing marked and pronounced differences in behaviour, just discovered by a
stroke of luck, are now specifically recognized to be a glaring reflection of wall structure variants in the
two kinds of cell
Gram-positive Cell Wall [Y] :
In this particular instance, the walls of bacteria essentially comprise
of the molecules of a
polyribitol or polyglycerophosphate that are found to be strategically
attached by means of
covalent bonds (G) to the prevailing oligosaccharide backbone; and these chemical
entities are nothing but
teichoic acids [D]. It is, however, pertinent to mention here, that the said teichoic
acids
do not give rise to any sort of additional rigidity upon the ensuing cell wall, but as they are acidic
in character,
they are capable of sequestering essential metal cations derived from the culture media
upon which the bacterial cells are growing. Importantly, this could be of immense value in such circumstances
wherein the
‘cation concentration’ in the environment is apparently at a low ebb.
Gram-negative Cell Wall :
Interestingly, the Gram-negative cell wall is observed to be much
more complex in character by virtue of the presence of the lipoprotein molecules (F) strategically attached
covalently to the respective vital oligosaccharide backbone. Besides, on its outer region, a layer
of lipopolysaccharide (E) along with the presence of protein critically attached by hydrophobic interactions
and divalent metal cations
e.g., Ca2+, Fe2+, Mg2+, Cu2+, whereas, in its inner side is a layer ofphospholipid.