Subtitles section Play video Print subtitles 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 bacteria 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. Dina's kids prefer candy over fried green spinach . Spinach is pretty underrated. 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 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 in 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. 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. Other than cocci the round cells, we have rods or bacilli, and then we have spirochete, which are curved. And then we have diplococci which is basically two cocci or basically two round cells, and then we have cocco-bacilli which is a mixture of both a rod and a round cell. And then we have vibrios 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 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 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 in eukaryotes. Remember bacteria doesn't 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 its special characteristics that distinguish it from the rest. Now 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 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 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-proteins and lipoproteins embedded into it and the last layer in gram-negative bacteria is a polysaccharide. The lipopolysaccharide layer is composed of three structures: o-antigen, core polysaccharide, 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 you can improve in the next videos. And don't forget to like and subscribe to get our latest new videos and explanations!