Anaerobic bacteria will die around oxygen. Facultative anaerobes function best with oxygen but do not need it. Some bacteria are good for you, including the bacteria in your digestive system, or gut. These bacteria help to break down food and keep you healthy. Other good bacteria can produce oxygen are used to create antibiotics. Bacteria are used in food production to make yogurt and fermented foods. The ecosystem relies on bacteria to function properly. For example, bacteria break down dead matter in the environment, like dead leaves, releasing carbon dioxide and nutrients in the process.
Without the release of carbon dioxide, plants are unable to grow. Though there are many more good bacteria than bad, some bacteria are harmful. Harmful bacteria are called pathogenic bacteria because they cause disease and illnesses like strep throat, staph infections, cholera, tuberculosis, and food poisoning. Temperature is one of the ways you can kill pathogenic bacteria in your home. You can do this by boiling water and cooking food to the correct….
Many of the bacteria in the body play an important role in human survival. Bacteria in the digestive system break down nutrients, such as complex sugars, into forms the body can use.
Non-hazardous bacteria also help prevent diseases by occupying places that the pathogenic, or disease-causing, bacteria want to attach to. Some bacteria protect us from disease by attacking the pathogens. Bacteria take in nitrogen and release it for plant use when they die. Plants need nitrogen in the soil to live, but they cannot do this themselves.
To ensure this, many plant seeds have a small container of bacteria that is used when the plant sprouts. Lactic acid bacteria, such as Lactobacillus and Lactococcus together with yeast and molds, or fungi, are used to prepare foods such as as cheese, soy sauce, natto fermented soy beans , vinegar, yogurt, and pickles. Not only is fermentation useful for preserving foods, but some of these foods may offer health benefits.
For example, some fermented foods contain types of bacteria that are similar to those linked with gastrointestinal health. Some fermentation processes lead to new compounds, such as lactic acid, which that appear to have an anti-inflammatory effect. More investigation is needed to confirm the health benefits of fermented foods.
Bacteria can break down organic compounds. This is useful for activities such as waste processing and cleaning up oil spills and toxic waste.
Bacteria are used in molecular biology, biochemistry and genetic research, because they can grow quickly and are relatively easy to manipulate. Scientists use bacteria to study how genes and enzymes work. Bacillus thuringiensis Bt is a bacterium that can be used in agriculture instead of pesticides. It does not have the undesirable environmental consequences associated with pesticide use. Some types of bacteria can cause diseases in humans, such as cholera , diptheria, 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. This reaction can lead to the symptoms of swelling and inflammation that we see, for example, in an infected wound. In , pneumonia, TB, and diarrhea were the three biggest killers in the United States. Sterilization techniques and antibiotic medications have led to a significant drop in deaths from bacterial diseases. However, the overuse of antibiotics is making bacterial infection harder to treat.
As the bacteria mutate, they become more resistant to existing antibiotics, making infections harder to treat.
Bacteria transform naturally, but the overuse of antibiotics is speeding up this process. For this reason, scientists and health authorities are calling on doctors not to prescribe antibiotics unless it is necessary, and for people to practice other ways of preventing disease, such as good food hygiene, hand washing, vaccination, and using condoms.
Recent research has led to a new and growing awaress of how the human body interacts with bacteria, and particularly the communities of bacteria living in the intestinal tract, known as the gut microbiome, or gut flora.
In , researchers published findings suggesting that women with obesity were more likely to have a particular kind of bacteria, Selenomonas noxia S. The culture density in a stationary culture is constant. During the stationary phase, cells switch to a survival mode of metabolism.
As growth slows, so too does the synthesis of peptidoglycans, proteins, and nucleic-acids; thus, stationary cultures are less susceptible to antibiotics that disrupt these processes. In bacteria capable of producing endospores, many cells undergo sporulation during the stationary phase.
Secondary metabolites, including antibiotics, are synthesized in the stationary phase. For example, quorum sensing in Staphylococcus aureus initiates the production of enzymes that can break down human tissue and cellular debris, clearing the way for bacteria to spread to new tissue where nutrients are more plentiful. As a culture medium accumulates toxic waste and nutrients are exhausted, cells die in greater and greater numbers.
Soon, the number of dying cells exceeds the number of dividing cells, leading to an exponential decrease in the number of cells Figure 4. This is the aptly named death phase, sometimes called the decline phase. Many cells lyse and release nutrients into the medium, allowing surviving cells to maintain viability and form endospores.
A few cells, the so-called persisters, are characterized by a slow metabolic rate. Persister cells are medically important because they are associated with certain chronic infections, such as tuberculosis, that do not respond to antibiotic treatment. The growth pattern shown in Figure 4 takes place in a closed environment; nutrients are not added and waste and dead cells are not removed. In many cases, though, it is advantageous to maintain cells in the logarithmic phase of growth. One example is in industries that harvest microbial products.
A chemostat Figure 6 is used to maintain a continuous culture in which nutrients are supplied at a steady rate. A controlled amount of air is mixed in for aerobic processes. Bacterial suspension is removed at the same rate as nutrients flow in to maintain an optimal growth environment. Figure 6. A chemostat is a culture vessel fitted with an opening to add nutrients feed and an outlet to remove contents effluent , effectively diluting toxic wastes and dead cells.
The addition and removal of fluids is adjusted to maintain the culture in the logarithmic phase of growth. If aerobic bacteria are grown, suitable oxygen levels are maintained. Estimating the number of bacterial cells in a sample, known as a bacterial count, is a common task performed by microbiologists. The number of bacteria in a clinical sample serves as an indication of the extent of an infection. Quality control of drinking water, food, medication, and even cosmetics relies on estimates of bacterial counts to detect contamination and prevent the spread of disease.
Two major approaches are used to measure cell number. The direct methods involve counting cells, whereas the indirect methods depend on the measurement of cell presence or activity without actually counting individual cells. Both direct and indirect methods have advantages and disadvantages for specific applications.
Direct cell count refers to counting the cells in a liquid culture or colonies on a plate. It is a direct way of estimating how many organisms are present in a sample. The simplest way to count bacteria is called the direct microscopic cell count, which involves transferring a known volume of a culture to a calibrated slide and counting the cells under a light microscope.
The calibrated slide is called a Petroff-Hausser chamber Figure 7 and is similar to a hemocytometer used to count red blood cells. The central area of the counting chamber is etched into squares of various sizes. A sample of the culture suspension is added to the chamber under a coverslip that is placed at a specific height from the surface of the grid.
It is possible to estimate the concentration of cells in the original sample by counting individual cells in a number of squares and determining the volume of the sample observed. The area of the squares and the height at which the coverslip is positioned are specified for the chamber.
The concentration must be corrected for dilution if the sample was diluted before enumeration. Figure 7. A grid is etched on the slide to facilitate precision in counting.
The enlarged view shows the square within which bacteria red cells are counted. If the coverslip is 0. Cells in several small squares must be counted and the average taken to obtain a reliable measurement.
The advantages of the chamber are that the method is easy to use, relatively fast, and inexpensive. On the downside, the counting chamber does not work well with dilute cultures because there may not be enough cells to count. Figure 8. Fluorescence staining can be used to differentiate between viable and dead bacterial cells in a sample for purposes of counting. Viable cells are stained green, whereas dead cells are stained red.
Using a counting chamber does not necessarily yield an accurate count of the number of live cells because it is not always possible to distinguish between live cells, dead cells, and debris of the same size under the microscope.
However, newly developed fluorescence staining techniques make it possible to distinguish viable and dead bacteria. These viability stains or live stains bind to nucleic acids, but the primary and secondary stains differ in their ability to cross the cytoplasmic membrane. The primary stain, which fluoresces green, can penetrate intact cytoplasmic membranes, staining both live and dead cells. The secondary stain, which fluoresces red, can stain a cell only if the cytoplasmic membrane is considerably damaged.
Thus, live cells fluoresce green because they only absorb the green stain, whereas dead cells appear red because the red stain displaces the green stain on their nucleic acids Figure 8.
Another technique uses an electronic cell counting device Coulter counter to detect and count the changes in electrical resistance in a saline solution. A glass tube with a small opening is immersed in an electrolyte solution.
A first electrode is suspended in the glass tube. A second electrode is located outside of the tube. As cells are drawn through the small aperture in the glass tube, they briefly change the resistance measured between the two electrodes and the change is recorded by an electronic sensor Figure 9 ; each resistance change represents a cell.
The method is rapid and accurate within a range of concentrations; however, if the culture is too concentrated, more than one cell may pass through the aperture at any given time and skew the results. This method also does not differentiate between live and dead cells. Direct counts provide an estimate of the total number of cells in a sample. However, in many situations, it is important to know the number of live, or viable, cells.
Counts of live cells are needed when assessing the extent of an infection, the effectiveness of antimicrobial compounds and medication, or contamination of food and water.
Figure 9. A Coulter counter is an electronic device that counts cells. It measures the change in resistance in an electrolyte solution that takes place when a cell passes through a small opening in the inside container wall. A detector automatically counts the number of cells passing through the opening. The viable plate count, or simply plate count, is a count of viable or live cells. It is based on the principle that viable cells replicate and give rise to visible colonies when incubated under suitable conditions for the specimen.
Furthermore, samples of bacteria that grow in clusters or chains are difficult to disperse and a single colony may represent several cells. Some cells are described as viable but nonculturable and will not form colonies on solid media.
For all these reasons, the viable plate count is considered a low estimate of the actual number of live cells. These limitations do not detract from the usefulness of the method, which provides estimates of live bacterial numbers. Microbiologists typically count plates with 30— colonies. Also, counts in this range minimize occurrences of more than one bacterial cell forming a single colony.
Thus, the calculated CFU is closer to the true number of live bacteria in the population. There are two common approaches to inoculating plates for viable counts: the pour plate and the spread plate methods.
Although the final inoculation procedure differs between these two methods, they both start with a serial dilution of the culture. The serial dilution of a culture is an important first step before proceeding to either the pour plate or spread plate method. The goal of the serial dilution process is to obtain plates with CFUs in the range of 30—, and the process usually involves several dilutions in multiples of 10 to simplify calculation.
The number of serial dilutions is chosen according to a preliminary estimate of the culture density. Figure 10 illustrates the serial dilution method.
Figure Serial dilution involves diluting a fixed volume of cells mixed with dilution solution using the previous dilution as an inoculum. The result is dilution of the original culture by an exponentially growing factor. A fixed volume of the original culture, 1. This step represents a dilution factor of 10, or , compared with the original culture. From this first dilution, the same volume, 1.
The dilution factor is now compared with the original culture. This process continues until a series of dilutions is produced that will bracket the desired cell concentration for accurate counting. From each tube, a sample is plated on solid medium using either the pour plate method Figure 11 or the spread plate method Figure The plates are incubated until colonies appear.
Two to three plates are usually prepared from each dilution and the numbers of colonies counted on each plate are averaged. In all cases, thorough mixing of samples with the dilution medium to ensure the cell distribution in the tube is random is paramount to obtaining reliable results. This process is repeated for each serial dilution prepared. The resulting colonies are counted and provide an estimate of the number of cells in the original volume sampled.
Tuberculosis TB is a debilitating multi-organ disease caused by the bacterium Mycobacterium tuberculosis. The most important form of the disease is pulmonary TB, an infection of the lungs and respiratory tract. The threat of antimicrobial resistance AMR has now been recognised globally and it is estimated that 10 million people a year will die due to antimicrobial resistance by if no urgent action is taken. Species within the genus Pseudomonas are amongst the most researched bacteria in the scientific community.
Bacteria in this genus are widely used as model organisms in microbial research, and include a range of important species in fields such as plant pathogenicity, bioremediation, and environmental microbiology. As well as being hugely important in the medical and pharmaceutical industries, Streptomyces also play a significant environmental role; contributing to the decomposition of organic matter, and fertility of the soil.
Microbiology Today : Mycobacteria. Science Photo Library. Building bacterial bridges. Tuberculosis Explainer. Antimicrobial resistance. Pseudomonas - friend and foe. Homepage Why Microbiology Matters What is microbiology?
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