What are Microbes?
Microbes are tiny living organisms that may or may not cause disease. Germs, or pathogens are the category of microbes that can cause disease. These single-cell organisms are so tiny that millions can fit into the eye of a needle. They are the oldest and most abundant form of life on earth. Microbe fossils date back more than 3.5 billion years to a time when the Earth was covered with oceans that regularly reached the boiling point, hundreds of millions of years before dinosaurs roamed the Earth. Without microbes, we couldn’t eat or breathe. Without us, they’d probably be just fine.
Understanding how microbes operate is vital to understanding the past and the future of ourselves and our planet. Microbes are in the air we breathe, the ground we walk on, the food we eat, and inside our bodies. We, along with other animals, could not digest food without them. Plants couldn’t grow, garbage wouldn’t decay and there would be less oxygen for us to breathe. Without these seemingly invisible organisms, our planet would not survive as we know it.
Students naturally have microbes on their hands and collect more and more throughout the day. Many microbes are normal and help keep us healthy; some are viruses and bacteria that make us sick. Within a classroom, students interact with each other and with common surfaces they share in the learning spaces they occupy. When they touch things, some of the microbes on their hands transfer to the things they touch, and the microbes from the things they touch are transferred onto their hands and body.
Bacteria
Bacteria are small single-celled organisms found almost everywhere on Earth and vital to the planet's ecosystems. Some species can live under extreme temperature and pressure conditions, making it possible for them to be found in every habitat on Earth: soil, rock, oceans, and even arctic snow.
They are microbes with a cell structure simpler than many other organisms. Their control center, which holds the genetic information, is contained in a single loop of DNA, rather than a nucleus. Some bacteria have an extra circle of genetic material called a plasmid. The plasmid often contains genes that give the bacterium some advantage over other bacteria. For example, it may contain a gene that makes the bacterium resistant to a certain antibiotic.7
Bacteria are classified into five groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), comma (vibrios), or corkscrew (spirochaetes). They can exist as single cells, in pairs, chains, or clusters.8
Some live in or on other organisms including plants, animals, and humans. The human body is full of bacteria and other microbes such as viruses and fungi, which collectively comprise the human microbiome estimated to contain more bacterial cells than human cells. Most bacteria in the body are harmless, and some are even helpful. Amazingly, there are approximately 10 times as many bacterial cells as human cells in the human body. Many of these bacterial cells are found lining the digestive system. Bacteria live in the soil or on dead plant matter where they play an important role in the cycling of nutrients. Other types of bacteria cause food spoilage and crop damage while some are incredibly useful in the production of fermented foods such as yogurt and soy sauce. Relatively few bacteria are parasites or pathogens that can cause disease in animals and plants.9
All bacteria reproduce by binary fission, in which the bacterium, a single cell, divides into two identical daughter cells. Binary fission begins when the DNA of the bacterium divides into two (replicates). The bacterial cell then elongates and splits into two daughter cells with identical DNA to the parent cell. Each daughter cell is essentially a clone of the parent cell.
Under favorable conditions (temperature and available nutrients), some bacteria like Escherichia coli (often called E. coli) can divide every 20 minutes. This means that in just seven hours one bacterium can generate 2,097,152 bacteria. After one more hour, the number of bacteria will have risen to an incredible 16,777,216. That’s why we can become ill quickly when harmful microbes invade our bodies.10
Bacteria can play important useful roles in our daily lives. Lactic acid bacteria, such as Lactobacillus and Lactococcus together with yeast and molds, or fungi, are used to prepare foods such as cheese, soy sauce, natto (fermented soybeans), vinegar, yogurt, and pickles. Fermentation is useful for preserving foods and some of these foods may offer health benefits. For example, some fermented foods contain types of bacteria similar to those linked with gastrointestinal health. Some fermentation processes lead to new compounds, such as lactic acid, which appear to have an anti-inflammatory effect. Bacteria can break down organic compounds. This is useful for waste processing and cleaning up oil spills and toxic waste. The pharmaceutical and chemical industries use bacteria in the production of certain chemicals. Bacteria are used in molecular biology, biochemistry, and genetic research because they can multiply quickly and are relatively easy to manipulate. Scientists use bacteria to study how genes and enzymes work. Bacteria are necessary to make antibiotics. Bacillus thuringiensis (Bt) is a bacterium that can be used in agriculture instead of pesticides and does not have the detrimental environmental consequences associated with pesticide use.11
In 1900, pneumonia, tuberculosis, and diarrhea were the three biggest killers in the United States. Strategies for sterilization techniques and the development of antibiotic medications have led to a significant drop in deaths from bacterial diseases. Bacteria are needed to make antibiotics. But the overuse of antibiotics is making bacterial infections harder to treat. As the bacteria mutate, they become more resistant to existing antibiotics, which makes infections harder to treat. Bacteria evolve naturally, but the overuse of antibiotics is speeding up the process of bacteria evolution to resist antibiotic drugs.
Some types of bacteria can cause diseases in humans, such as cholera, diphtheria, dysentery, bubonic plague, pneumonia, tuberculosis (TB), typhoid, and many more. If the human body is exposed to bacteria that the body does not recognize as helpful, the immune system will attack them.12
General Timeline of Understanding Bacteria
Over 2,000 years ago, a Roman author, Marcus Terentius Varro, warned against locating homesteads in the proximity of swamps ‘because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases’. 13
Fracastoro stated that there were diseases that could be caused by a contagion that ‘passes from one thing to another’. These were transmitted in three ways: by direct contact with the infected, by contact with their clothes or carried by the air. Fracastoro described this agent of contagion as seminaria, a word which has often been translated as germs. Its literal meaning, however, is breeding ground or nursery. Although he stated contagion was affected by ‘small imperceptible particles’, Fracastoro never perceived these particles to be living creatures. He did speculate, however, that each disease had its own specific seminaria, an idea that was overlooked for more than 300 years.
In the 17th century, a Dutch scientist, Antonie van Leeuwenhoek created a single-lens microscope with which he saw what he called “animalcules,” later known as bacteria. He is considered to be the first microbiologist. The Dutch shopkeeper Leeuwenhoek had an obsession with microscopes and a talent for lens grinding. For more than 50 years he made important observations across every branch of natural science. After studying samples of plaque and spittle, Leeuwenhoek wrote to the Royal Society that he found ‘an unbelievably great company of living animalcules… in such enormous numbers, that all the water … seemed to be alive’. Although he never connected these creatures with disease, his observations and drawings are the first recorded descriptions of micro-organisms.14
In the 19th century, the chemist Louis Pasteur said that diseases were caused by germs. Pasteur’s discoveries on fermentation in wine, beer, and milk demonstrated that it was microorganisms in the atmosphere that produced fermentation diseases. His proof of external contamination was to finally overturn the theory of the spontaneous generation of microorganisms caused by internal or systematic imbalances. The report of his experiments has been called ‘the manifesto of the germ theory’. It established the fundamental concepts from which the science of microbiology would develop. This was known as the Germ Theory.15
In 1910, the scientist Paul Ehrlich announced the development of the first antibiotic, Salvarsan. He used it to cure syphilis. His aim was, as he put it, to find chemical substances which have special affinities for pathogenic organisms, to which they would go, as antitoxins go to the toxins to which they are specifically related, and would be, as Ehrlich expressed it, «magic bullets» which would go straight to the organisms at which they were aimed. He was also the first scientist to detect bacteria by using stains.16
In 2001, Joshua Lederberg coined the term “gut microbiome.” Scientists worldwide are currently seeking to describe and understand more precisely the structures, types, and uses of “gut flora,” or bacteria in the human body.17
Lederberg’s discoveries greatly increased the utility of bacteria as a tool in genetics research, and it soon became as important as the fruit fly Drosophila and the bread mold Neurospora. His discovery of transduction, the process of carrying a bacterial gene from one bacterium to another provided the first hint that genes could be inserted into cells. The realization that the genetic material of living things could be directly manipulated eventually bore fruit in the field of genetic engineering, or recombinant DNA technology.18
Culture of eight-year-old’s hand19
The Facebook page for the American Society for Microbiology (ASM) shared a photo of a large bacterial culture plate bearing a handprint made of microbial colonies. Tasha Sturm, who works as a lab tech at Cabrillo College in California, created this culture by pressing her eight-year-old son’s hand into an agar plate after he had been playing outside. Agar is commonly used to culture microbes because it provides a nutrient-rich base for microorganisms to grow. She then incubated the handprint for 48 hours and let it sit for another few days, photographing the final result.20
Sturm added some tentative IDs in the comment section of the original post: white colonies are probably a form of Staphylococcus, which lives in people’s noses and skin and some colonies of fungi and yeast. Most strains are harmless or even beneficial, but some can cause disease when they grow where they shouldn’t, especially when they develop antibiotic resistance. Sturm also posted two close-ups of colonies that are either species of Bacillus — a common soil bacterium. Researchers are working to explain exactly what this abundance of microbes on the body and its stunning diversity means for human health and disease.21
Viruses
A virus is an infectious agent that can only replicate within a host organism, small germs (pathogens) that can infect you and make you sick. They can infect humans, plants, animals, bacteria, and fungi. Each one infects only specific types of hosts.
Viral infections in humans can span the spectrum from causing no symptoms to making you extremely ill. Types of diseases and conditions caused by viruses include respiratory illnesses, diarrhea and vomiting, sexually transmitted infections, and skin conditions.22
As infectious agents, viruses are small pieces of genetic information in a “carrying case” — a protective coating called a capsid. When a virus particle is independent of its host, it essentially consists of the viral genome, or genetic material, contained within a protein shell, the capsid. In some viruses, the protein shell is enclosed within a membrane called an envelope. Viral genomes are very diverse since they can be DNA or RNA, single- or double-stranded, linear or circular, and vary in length and in the number of DNA or RNA molecules.
Since viruses aren’t made up of cells, they do not have all the equipment that cells use to make more copies of themselves. Instead, they carry instructions and use a host cell’s equipment to replicate themselves.
It’s like someone breaking into your house to use your kitchen. The virus brought its own recipe, but it needs to use your dishes, measuring cups, mixer, and oven to make it. (Unfortunately, they usually leave a big mess when they finally leave.23
The viral replication process begins when a virus infects its host by attaching to the host cell and penetrating the cell wall or membrane. The process by which a lytic phage (virus that lethally infects bacteria) attacks its host cell illustrates many basic steps in virus replication. Here, the virus's genome is uncoated from the protein and injected into the host cell. Then the viral genome hijacks the host cell's machinery, forcing it to replicate the viral genome and produce viral proteins to make new capsids. Next, the viral particles are assembled into new viruses. The new viruses burst out of the host cell during a process called lysis, which kills the host cell. Some viruses take a portion of the host's membrane during lysis to form an envelope around the capsid.24
Following viral replication, the new viruses may move on to infect new hosts. Many viruses cause diseases in humans, such as influenza, chicken pox, AIDS, the common cold, and rabies. Vaccination is the primary way to prevent viral infections, which administers a vaccine made of inactive viral particles to an uninfected individual, to increase the individual's adaptive immune response to the virus if it infects later in time.25
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