Biological sciences, Microbiology

Introduction To Microbiology

Introduction to Microbiology by Assalamu Alaikom, which is the study of microscopic organisms or microbes such as bacteria, viruses, fungi, and protozoa.

Introduction To Microbiology

Assalamu Alaikom everyone welcome: today we’ll talk about some basic concepts in microbiology to get you introduced to this subject.

What is microbiology?

Microbiology is the study of microscopic organisms or microbes 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 and other aspects of human. In plants, the bacteria are responsible for nitrogen fixation, and in animals it helps in cellulose digestion. Also, these microorganisms are used in industries. Generally, we divide the organisms (bacteria, viruses, and fungi) according to their characteristics.

Introduction to Microbiology: how to categorize Bacteria, fungi, viruses
So in bacteria (can be viewed under a high-resolution microscope), we use Gram stain either: gram 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 are 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 Dina’s kids prefer candy over fried green spinach. Spinach is pretty underrated by the way. If we start from the top, we have three domains on this planet bacteria, archaea, and Eukarya. Both bacteria and archaea are considered as prokaryotes, whereas Eukarya are considered as eukaryotes. The main differences between prokaryotes and eukaryotes are the absence of cytoplasmic structures (organelles) such as mitochondria Golgi apparatus, and endoplasmic reticulum in prokaryotes, and then we have the 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.

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Introduction To Microbiology: let’s talk about Biological kingdoms

Both bacteria and archaea have only one single kingdom, which are bacteria and archaea, respectively. Eukarya has four kingdoms: protists, fungi, plants, and animals. And then we continue the classification like this: as 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 in gram staining. Any bacterium’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.

Gram-positive bacteria

We’ll take Staphylococcus aureus as an example. Staphylococcus is the genus and aureus is species. Note that both the genus and the species are italicized. Also, the name of the microorganism might refer to its shape. Like our example, staphylo means a bunch of grapes or a cluster, and coccus means round cells. Aureus means it looks like gold in color when we culture it. Other than cocci or the round cells, we have rods or bacilli. We also have spirochete, which are curved. And then we have diplococci, which are basically two cocci or basically two round cells. There are also have Coccobacilli, which are a mixture of both rod and around cell. We have vibrios which is a curved rod, and then we have streptococci which are cocci in chains. About staphylococci? As we mentioned in our example, staphylococci are large cocci in irregular clusters (like grapes), and then we have tetrads, which are cocci in a packet of four. From the name tetrads, we have tetra, which means four.

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Bacterial architecture

Now we’re going to discuss the bacterial architecture. Since bacteria are considered as cells that means they have a genetic material, a cell membrane, and a cytoplasm. In addition to that, they have a cell wall and flagella, which are used for locomotion. We also have pili, which are used for attachment. We have plasmid, which is an extra chromosome of 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. But here we 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. Bacteria also have Mesosomes that are equivalent to mitochondria in eukaryotes. Remember that bacteria do not have mitochondria. So they have Mesosomes instead. Bacteria depend on these Mesosomes for respiration. Mesosomes are formed by the invaginations of a plasma membrane into the cytosol. Generally speaking this is how a bacterium looks like; however, each bacterium has the special characteristics that distinguish it from the rest.

Introduction To Microbiology: Gram staining

Now let us 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 (they retain violet stain), while gram-negative react with the 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. Gram-positive bacteria have a thick peptidoglycan layer. This layer has two teichoic and lipoteichoic acids. In gram-negative bacteria and outer to the plasma membrane, we have a thin layer of peptidoglycan, and then we have an outer membrane composed of phospholipids that have trans-proteins and lipoproteins embedded into it, and the last layer in gram-negative bacteria is a lipolysaccharide.

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The lipopolysaccharide or LPS layer is composed of three structures: O-antigen, core polysaccharide, and 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 introduction to microbiology. I hope you enjoyed! And don’t forget to check out more eLearning videos here!

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