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General Bacteriology
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0:00
In this video, I will explain General Bacteriology, or General Microbiology. General Bacteriology is quite hard, so we need to simplify it as much as we can.
0:15
Let's talk about the bacterial cell. Why is it classified as Prokaryotic and not Eukaryotic cell?
0:25
The Eukaryotic cell composes the human body or Mamilians in general.
0:31
The Eukaryotic cell differs from the Prokaryotic in many aspects. The first difference is that the Prokaryotic cells have very defined thick cell wall. Its cell wall is so strong as it contains some structures called: Peptidoglycans. We will discuss those in a moment. The Eukaryotic cell
0:59
has a very primitive cell wall. So, what does primitive mean? It means that it is so simple, why? Because Eukaryotic cells in humans
1:13
are attached to each other to protect one another. So there is no need for a rigid cell wall.
1:27
This cell lives in complete isolation; there is nothing attached to it so it must have a rigid cell wall. That's the first difference between the Prokaryotic and Eukaryotic cells. Let's find another difference. The Prokaryotic cell has one chromosome folded upon itself in its cytoplasm. A ribbon of chromosome: DNA
1:51
The Eukaryotic cell has nucleus and has more than one chromosome; 22-23 chromosomes.
2:02
Generally, it has more than one chromosome. Ok, what else? Here you have a definite nuclear membrane, there you don't have it.
2:17
In the Eukaryotic cells, you have nucleoli inside the nucleus. But in the Prokaryotic cells, you don't have them. So we have 4 differences now: Rigid cell wall
2:28
one chromosome folded upon itself, but here you have more than one chromosome, nuclear membrane and nucleoli. This cell is very primitive, not thick or rigid.
2:47
Ok, what else? The nucleus over here synthesises mRNA which produces ribosomes responsible for protein synthesis. Same with the Eukaryotic cell. The Eukaryotic cell has mitochondria which is responsible for oxidation phosphorylation (respiration).
3:19
But here, you don't have mitochondria so how does the cell respire? The cytoplasmic membrane has some invaginations. Those invaginations are called mesosomes. Those invaginations are the site of respiratory mechanisms or oxidation phosphorylation. That is the difference between Prokaryotic and Eukaryotic cells. Now we will discuss the Prokaryotic cell (or bacterial cell) in further detail.
4:00
The bacterial cell has a rigid cell wall
4:08
enclosing a very fine cytoplasmic membrane
4:16
which shows some invaginations or mesosomes, the sites of oxidation phosphorylation and it has one chromosome folded upon itself,
4:30
in addition to ribosomes that are signaled by RNA to synthesise cell protein required for metabolism.
4:46
Alright?
4:48
Let's discuss an important topic now which is the bacterial cell wall. The bacterial cell wall is very rigid but elastic. How come? You know those large electrical cables? They are very rigid. But they can place them underground or move them to any side, so they are flexible.
5:18
Alright So it is rigid and elastic.
5:25
What's is the reson behind this rigidity then? The reason behind the rigidity of the bacterial cell wall is a compound called N-acetyl muramic acid attached to N-acetyl glucosamine along with teichoic acid. Those two compounds are responsible for rigidity. If we break their union, we will end up with a damaged cell wall. I will tell you now the significance of having a fragile cell wall. Those two compounds form a large layer called peptidoglycan.
6:20
So the cell wall has a very rigid layer of peptidoglycan formed of N-acetyl muramic acid and N-acetyl glucosamine.
6:31
If any of these compounds experiences leakage, the bacterial cell wall will experience leakage too and it will be broken, so the cytoplasmic membrane leaves the cell by osmosis, the cell bursts and dies. This is the mechanism of the antibiotic Penicillin. The penicillin breaks the peptidation of N-acetyl glycosamine and N-acetyl muramic acid. So the cytoplasm leaves the cell by osmosis then it bursts and the cell gets destroyed. Alright We are still studying the cell wall.
7:27
Is the cell wall completely closed? No, it has some small pores.
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They allow the passage of nutrition and get rid of waste products. Alright? But it allows the passage of anything
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so it is non-selective, it is a passive permeable membrane.
7:54
Even if there are toxins they will enter, but the cytoplasmic membrane is selective or active permeable membrane. So we have passive permeability and active permeability.
8:11
Alright? This is a very important note. The bacterial cell wall forms invaginations to divide the cell. There we have another difference between Prokaryotic and Eukaryotic cells that is the Prokaryotic cells can be divided by binary fission. Imagine this is a cell, it divides like this into two. So that is binary fission. One cell divides into two, 2 into 4, 4 into 8, 8 into 16, 16 into 32 and so on. Alright
8:53
So how can I benefit of the bacterial cell wall in medicine? I have certain antibiotics to kill this type of bacteria by breaking its cell wall, like Penicillin as we mentioned previously. The second thing is Cephalosporine.
9:22
They both act on the bacterial cell wall, in addition to Cycloserine. But we are more concerned with Penicillin and Cephalosporine in the Antibiotics lecture.
9:40
Alright Does the bacterial cell wall differ from one cell to the other? Yes, of course. A scientist called Gram developed a staining method called: Gram stain to distinguish bacterial species that can be either Gram positive or Gram negative.
10:02
The Gram positive bacteria absorbs the color of methyl-violet, giving a light violet colour. But the Gram negative doesn't absorb the violet colour as it experiences decolorization by acid so it is stained by Karbul fuchsin stain, we will explain this later on, to give a red colour in the end.
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Violet and red colours
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So, is there a difference between Gram positive and negative bacteria types? Of course. The Gram positive bacteria has a very thick layer of peptidogylcan.
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And a very thin layer
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of lipopolysaccharides
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which are called endotoxins, meaning the toxins attached to the cell wall of the Gram negative bacilli. Moving on to the Gram negative bacilli, we find a thick layer of lipopolysaccharides and very thin layer of peptidoglycan. Let's think together now, when I treat someone infected with Gram positive bacteria, I can successfully administer Penicillin, Cephalosporines or any other antibiotics which can act on the bacterial cell wall.
11:42
But with Gram negative bacteria, I can't treat the patient with Penicillin. We have to administer other drugs which I will discuss in the Antimicrobial drugs Lecture,
11:57
as they have a totally different method of administration. You can never treat Gram negative bacteria like E.Coli with Penicillin. The patient shall never cure.
12:11
But I can treat bacteria like Staphelococcus, Streptococcus and Pneumococcus with antibiotics that act on the bacterial cell wall.
12:29
Now we are done with the Bacterial cell wall. I am not going to get into much details like our doctors in the Faculty of Science. When we study any subject related to the Faculty of Science, we only memorise what we can make use of in the Faculty of Medicine.
12:49
No, let's move on to the cytoplasmic membrane. This cytoplasmic membrane is very fine. That's why Allah created a rigid cell wall for the bacteria to protect the fine or weak cytoplasmic membrane. This layer performs selective permeability; meaning that it takes in what the cell needs and gets rid of what the cell doesn't want. All of those materials enter through the bacterial cell wall pores. That is the cytoplasmic membrane. The reason behind giving it this name is that it encloses
13:31
cytoplasm, this area defines the cytoplasm with all its contents.
13:37
Alright, what else? This membrane is targeted by some antibiotics as well. We will study the antibiotics that act on this layer. Sometimes this cytoplasmic membrane contains Ergosterol like in fungus, where it becomes the target of antifungal drugs.
14:05
Alright? The antibiotics that act on the cytoplasmic membrane include polymyxins. But this is a nephrotoxin.
14:18
That is in bacteria, but in fungus the ergosterol is the target of antifungal drugs like Nystatin, which is one of the important antifungal drugs.
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Alright?
14:34
Ok Now we are done with the cytoplasmic membrane. What does the cytoplasm contain? It has ribosomes, which are signaled by mRNA released from a nuclear body, to synthesise protein.
14:51
So the ribosomes are also a target, as we need to stop their synthesis action.
14:57
Some people treat bacteria by administering drugs which act on ribosomes.
15:08
Therefore, bacteria won't be able to translate the signals received from the mRNA. Examples of drugs that act on ribosomes are: Chloramphenicol, Streptomycin and Erythromycin. Some, and only some, bacteria contain
15:37
bodies called: Inclusion
15:45
bodies.
15:49
Or we would better say: Inclusion granules. Inclusion bodies are found in virus.
16:00
The inclusion granules store nutrition for the use of bacteria. We can identify certain types of bacteria by the presence or absence of such granules, like the metachromatic granules found in diphtheria microbe,which we will study later on. There is also another structure called Plasmid
16:28
This Plasmid is extra chromosomal DNA. It is a regular DNA but not attached to chromosome. This plasmid can be transferred from one bacterial cell to the other, carrying a certain drug resistant gene, which can convert one bacterial cell from being drug sensitive, easily treated by a certain drug, to be drug resistant, through the transfer of plasmid from one cell to the other. So the other bacterial cell becomes resistant. We call this Conjugation.
17:20
What else do we have in this structure? We have very thin hairs originating from the area between the cell wall and cytoplasm, and we have very long hairs originating from the cytoplasm. We call those long hairs originating from the cytoplasm: flagella. Those resemble the legs of the bacteria.
17:45
But we call those short hairs: pilli or phymbria. Those hairs are responsible for adhesion to the host cell, they adhere strongly to the host cell to be able to form a colony on the organ attached to it. For example, if the bacteria of the urinary tract infection doesn't attach to the mucus membrane of the urethra it will be released with urine. That is why it is attached to the host cell by phymbria. We aslo have sex pilli
18:30
so pilli can be used for adhesion or sex, how? Bacteria are classified into males and females so they attach to one another using sex pilli, and the plasmid is then transferred through this tube called phymbria from one bacterial cell to the other. So this process is included in the conjugation as well.
19:03
Alright Anthing else? Yes. When the bacteria first enters your body, it faces the phagocytes. So some bacteria form capsules around themselves. Can you see it? Sorry, the white board is now full.
19:20
This capsule is antiphagocyte, it repels the phagocytes,
19:33
preventing them from engulfing the bacterial cell. So they rapidly increase in number like the pneumococcus. Again this microbe is called: Pneumo, from Pneumonia, coccus. Those are the cocci responsible for the inflammation of the lungs.
19:57
Ok In the unfavorable environmental conditions, where the bacterial cell can't eat or drink or do anything, the medium pH is bad, no nutrition or anything else, at this point some bacteria start forming capsules. This is called the spore form of bacteria. We will explain all of this later on.
20:27
Now let's discuss another important topic. What is a car composed of?
20:36
Body, motor, chairs and derexion. That's it.
20:51
Of course the motor is formed of other things.
20:54
Those are defined as the essential structures of bacteria. So when you are asked about the essential structures of bacteria, you must reply with the cell wall, the cytoplasmic membrane, and the nuclear body, right? And the ribosomes, too. The cell wall protects the bacterial cell, the cytoplasmic membrane for selective permeability the nucleus signals the ribosomes
21:27
and so on as we previously mentioned. Those are essential structures. There are some bacteria that can't move (non-motile). They don't have flagella, so will they die? No, they live normally. This means that structures like flagella are accessory ones, like car accessories [seat covers and others]. So in the bacterial cell, the flagella is accessory in addition to the capsule and spore, which are not found in all bacterial cells. The phymbria, inclusion granules and plasmids
22:10
are to be added to the accessory structures. So when I ask you: All the following are essential structures of bacteria except: a. Cell wall (essential) b. Cytoplasmic membrane (essential) c. Nuclear body (essential) d. Ribosomes (essential) Alright? Those are all essential, but if the choices included Flagella, then it is the exception, same with phymbria, capsule and spore so we have various questions to be discussed later on.
22:45
One more important thing, everything has a target of antibiotics so what? I can prevent the delivery of messages signaled by the nuclear body. So I can act on the nuclear body using antibiotics and antimicrobial drugs. Every part of the bacteria has a target site of antibiotics. We will discuss this in more detail in the Antibiotics lecture. Let's discuss the accessories of the bacterial cell. The first accessory structure is the flagella.
23:28
Here is the bacterial cell wall, cytoplasmic membrane, nuclear body and flagella. This flagella is made of a protein called flagin.
23:40
This is an antigen and you know any antigen protein has large molecular weight and large molecular surface. So the phymbria is an antigen and the body releases antibodies for it. When there is one flagellum at one side, the bacterial cell is classified as monotrichous or monotrichate. It can also show two flagella on opposite sides. This is classified as amphitrichate.
24:17
Alright The flagella can surround the whole bacterial cell. What surrounds the heart? The pericardium. Peri means around, so we call this Peritrichate. The flagella may also look like fiber,
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from one side
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as you can see or from two sides. It looks like fiber, so it is called: Lophotrichate. Either on one side or both, it is called lophotrichate. Those are all antigenic and we call the flagella's antigen H-Ag instead of saying flagellar antigen. That is the H-Ag. Alright
25:08
Let's move on to the pneumococcus, we said that it is surrounded by a capsule. This capsule is a polysaccharide.
25:21
So it is a hapten not an antigen. It can only be antigen if the cocci are inside the protein. The hapten must attach to a carrier anyway. Alright? The capsule surrounding this bacteria is antiphagocytic, released from the cell wall. All the secretions will gather to form a capsule. I told you that the bacteria is classified into Gram positive and Gram negative. Definitely! So how can we stain the capsule then? Not with Gram, it has special stains like pmeu-rise stain for pneumococcal capsule.
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Anything else other than the cocci? Yes, we have another very dangerous bacillus used in wars nowadays. It is called Bacillus anthracis.
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Bacillus anthracis
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It results in anthrax disease. There is another type called pulmonary anthrax that kills immediately when inhaled. They used to accuse Iraqi people of using it in war by firing bombs containing this type of bacillus. This type of bacteria has a capsule to protect it from phagocytosis. This capsule is formed of polypeptides not polysaccharides. This has a special stain called polychromic methylene blue, it is normally stored for 5-8 years in the laboratory before use.
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All of these structures are accessories.
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When the medium is not suitable, no nutrition, no oxygen,
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bad pH and all the cell's requirements are absent, the cell will gather all of its cytoplasm around the nuclear body; forming a keratinized wall resistant to the environmental conditions. The rest of the cell breaks off. This spore contains concentrated cytoplasm and the nuclear body. Alright? This spore can form in the middle of the bacteria, or at one side of it or it can be terminal, resembling a drumstick. We actually call it a drumstick spore type.
28:10
The site of spore formation helps us identify the bacterial cell type. An example of the drumstick bacteria is the Tetanus.
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The anthrax microbe forms its spore in the middle of the cell. It is very dangerous since it forms a spore outside the body
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and it forms a capsule inside the body to prevent phagocytosis action. And it forms spores outside the body to live normally despite the bad environmental conditions.
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The spore can be oval and sub-terminal like gas gangrene microbe. Gas gangrene
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So the spore is antigenic. The capsule is also antigenic and is called C-Ag. The cell wall of the bacteria is an antigen as well. It is called O-Ag. Today we studied the types of bacterial antigen: Body antigen --> O, Flagellum --> H, Capsule --> C Flagella --> H, Cell wall --> O, Phymbria --> F So every part of the bacteria is an antigen. Imagine that a pen (bacteria) entered the body, the body will form anti-pen (antibacteria) to get rid of it. In fact it forms anti-plastic anti-ink
29:45
and anti-metal so every part of it is an antigen. Alright? Those are the things that you should be aware of in the bacterial Prokaryotic cell.
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