As-salamu alaykum everyone. Welcome to another ATP video. In this video, we'll talk about some basics in microbiology to get you introduced to this subject.
So, what is microbiology? Microbiology is the study of microscopic organisms, such as bacteria, viruses, fungi, and protozoa. Most of these microorganisms are beneficial to us. In humans, we have normal microbiota that helps in digestion. In plants, the bacteria is responsible for nitrogen fixation.
and in animals it helps in cellulose digestion. Also, these microorganisms are used in industries. Generally, we divide the organisms, these bacterial viruses and fungi, according to their characteristics.
So in bacteria, we use gram stain, either positive or negative, to categorize them. In viruses, we depend on their genome, DNA or RNA, whether it's single-stranded or double-stranded, to categorize them. In fungi, they're either divided into molds, which is multicellular, or yeasts, which are unicellular.
We also have the hierarchy of classification. We used to put each organism, including us humans, into its category. We took it in high school, if you remember.
So from highest to lowest, it's domain, kingdom, phylum, class, order, family, genus, and species. You can use this mnemonic to help you remember it. Dina's kids prefer candy over fried green spinach.
Spinach is pretty underrated by the way. So if we start from the top, we have three domains on this planet. Bacteria, Archaea and Eukarya.
Both bacteria and the archaea are considered as prokaryotes. Whereas Eukarya are considered as eukaryotes. The main differences between prokaryotes and eukaryotes are Absence of cytoplasmic structures such as mitochondria, golgi apparatus and endoplasmic reticulum in prokaryotes.
And then we have absence of cell wall in eukaryotes except for fungi and plants. Also they differ in the structure of the ribosomes. After that we go to the kingdom. Both bacteria and archaea have only one single kingdom which are bacteria and archaea respectively. And then we have the eukarya and it has four kingdoms.
Protists, fungi, plants and animals. And then we continue the classification like this, like we mentioned before. Phylum, class, order, family, genus, and then species.
For now, we will focus on bacteria. How do we name them, basic structures, and gram staining? Any bacteria's name is composed of two words.
The first one refers to the name of the genus, and the second one refers to the species name. We'll take Staphylococcus aureus as an example. So Staphylococcus is the genus, and aureus is species. Also...
The name of the microorganism might refer to its shape, like in our example. Staphyla means a bunch of grapes, or a cluster. And Cocos means round cells.
Aureus means it looks like gold in color when we culture it. Other than cocci, the round cells, we have rods, or bacilli. And then we have spiroshets, which are curved.
And then we have diplococci, which is basically two cocci, or basically two round cells. And then we have cocobacilli. which is a mixture of both a rod and a round cell.
And then we have Vibrious, which is a curved rod. Then we have Streptococci, which are cocci in chains. And then we have the Staphylococci, like we mentioned in our example, which are large cocci in irregular clusters.
And then we have Tetrads, which are cocci in a packet of four, from the name Tetrads, tetra, which means four. Now we're going to discuss the bacterial architecture. Since bacteria are considered as cells, that means they have genetic material, a cell membrane, and a cytoplasm.
In addition to that, they have a cell wall, a flagella, which is used for locomotion, and then we have pili, which is used for attachment, and then we have plasmid, which is an extra-chromosomal genetic material, so it's not part of the DNA, and then we have a glycocalyx, which is used for protection. The glycocalyx can be either capsule, which is neatly organized and protects the bacterium from phagocytes, or biofilm, which is an unorganized, loose structure, yet important for attachment. Bacteria also have porins.
These porins are transmembrane proteins that selectively allow some molecules to pass the cytosol of the bacteria. Porins can mediate antibiotic resistance by inhibiting some antibiotics from entering the bacteria. They also have mesosomes that are equivalent to mitochondria and eukaryotes. Remember, bacteria doesn't have mitochondria, so they have mesosomes instead.
Bacteria depend on these mesosomes for respiration. Mesosomes are formed by the invagination of the plasma membrane into the cytosol. Generally speaking, this is how a bacterium looks like. However, each bacterium has its special characteristics that distinguish it from the rest.
Now we'll move on to Gram staining. In Gram staining, we can classify bacteria into either Gram positive or Gram negative, and that depends on the cell wall constituents and its ability to react with the Gram stain. To classify them, Gram positive react with the stain and give blue color.
while gram-negative react with a stain and give red or pink color. If we look at the membranes of both gram-positive and gram-negative bacteria from the inner layer, we see that both of them have plasma membrane. However, on the outside, the differences start to appear. In gram-positive, it has a thick peptidoglycan layer. This layer has techoic and lipotechoic acids.
In gram-negative bacteria, and outer to the plasma membrane, we have thin layer of peptidoglycan. And then we have outer membrane composed of phospholipids that has trans-systable proteins and lipoproteins embedded into it. And the last layer in gram-negative bacteria is the lipopolysaccharide. The lipopolysaccharide layer is composed of three structures O antigen, corpolysaccharide, lipid A which is also known as endotoxin. So we can conclude that the endotoxins are only present in gram-negative bacteria.
These endotoxins are antigenic which means they can elicit an immune response causing some symptoms of fever, weakness, aches or shock to the patient. So that's it for the intro, hope you enjoyed. Please give us your feedback so we can improve in the next videos.
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