Feature Function Reason Steam inlet Hot steam sterilises the inside of the fermenter An aseptic precaution to prevent contamination by unwanted microorganisms Nutrient inlet Allows sterile nutrients to enter the fermenter Microorganisms need nutrients so that they can grow and reproduce Water jacket with cooling water Keeps the temperature inside constant Microorganisms grow best at an optimum temperature Air inlet Provides a source of oxygen Microorganisms need oxygen for aerobic respiration Filter on air inlet Stops microorganisms getting inside the fermenter An aseptic precaution to prevent contamination by unwanted microorganisms Stirring paddles Keeps the mixture inside the fermenter agitated stirred Mixes the microorganisms with the nutrients and keeps the temperature even The pH inside the fermenter is monitored to check it is at the optimum value for the particular microorganism being grown.
Steam inlet. Hot steam sterilises the inside of the fermenter. An aseptic precaution to prevent contamination by unwanted microorganisms. Nutrient inlet. Allows sterile nutrients to enter the fermenter. Microorganisms need nutrients so that they can grow and reproduce. Water jacket with cooling water. Keeps the temperature inside constant. Microorganisms grow best at an optimum temperature.
Air inlet. Provides a source of oxygen. Microorganisms need oxygen for aerobic respiration. When working with cultures of living organisms, it is extremely important to maintain the environments in which cells are cultured and manipulated as free of other organisms as possible. This means passing rims and lids through the flame produced by a Bunsen burner in order to kill microorganisms coming in contact with those surfaces.
Sterile technique, in general, is a learned state-of-being, or mantra, where every utilization of any sterile material comes with the caveat of taking every precaution to ensure it remains as free of contaminants as possible for as long as possible. A serial dilution is the step-wise dilution of a substance in solution. Usually the dilution factor at each step is constant, resulting in a geometric progression of the concentration in a logarithmic fashion.
A ten-fold serial dilution could be 1 M, 0. A culture of microbes can be diluted in the same fashion. For a ten-fold dilution on a 1 mL scale, vials are filled with microliters of water or media, and microliters of the stock microbial solution are serially transferred, with thorough mixing after every dilution step.
The dilution of microbes is very important to get to microbes diluted enough to count on a spread plate described later. Streak plate : Four streak plates. Successful streaks lead to individual colonies of microbes. In microbiology, streaking is a technique used to isolate a pure strain from a single species of microorganism, often bacteria. Samples can then be taken from the resulting colonies and a microbiological culture can be grown on a new plate so that the organism can be identified, studied, or tested.
The streaking is done using a sterile tool, such as a cotton swab or commonly an inoculation loop. This is dipped in an inoculum such as a broth or patient specimen containing many species of bacteria.
The sample is spread across one quadrant of a petri dish containing a growth medium, usually an agar plate which has been sterilized in an autoclave. Choice of which growth medium is used depends on which microorganism is being cultured, or selected for.
Growth media are usually forms of agar, a gelatinous substance derived from seaweed. Spread plates are simply microbes spread on a media plate.
Microbes are in a solution, and can be diluted. They are then transferred to a petri dish with media specific for the growth of the microbe of interest.
The solution is then spread uniformly through a number of possible means, the most popular is the use of sterile glass beads that are shook on top of the media, spreading the microbe-containing liquid evenly on the plate. Also common is the use of a bent-glass rod, often referred to as a hockey stick, due to its similar shape. The glass rod is sterilized and used to spread the microbe-containing liquid uniformly on the plate.
Many microbes have special growth conditions or require precautions to grow in a laboratory setting, leading to special culture techniques. Microbiologists would prefer to use well-defined media to grow a microbe, making the microbe easier to control.
However, microbes are incredibly varied in what they use as a food source, the environments they live in, and the danger levels they may have for humans and other organisms they may compete with. Therefore they need special nutrient and growth environments. To grow these difficult microbes, microbiologists often turn to undefined media which is chosen based on price and more-so in this case by necessity as some microorganisms have never been cultured on defined media.
Some special culture conditions are relatively simple as demonstrated by microaerophile. Many microphiles are also capnophiles, as they require an elevated concentration of carbon dioxide. In the laboratory they can be easily cultivated in a candle jar. Many labs also have access directly to carbon dioxide and can add the desired carbon dioxide levels directly to incubators where they want to grow microaerophiles.
Candle jar : A candle is lit in a jar with a culture plate. The lid is put on, as the burns it increases the carbon dioxide levels in the jar. Animals can often be used to culture microbes. For example, armadillos are often used in the study of leprosy. They are particularly susceptible due to their unusually low body temperature, which is hospitable to the leprosy bacterium, Mycobacterium leprae.
Likewise, humans can acquire a leprosy infection from armadillos by handling them or consuming armadillo meat. Additionally, Syphillis which is caused by the bacteria Treponema pallidum is difficult to grow with defined media, so rabbits are used to culture Treponema pallidum.
Treponema pallidum belongs to the Spirochaetesphylum of bacteria. To date Spirochaetes are very difficult if not impossible to rear in a controlled laboratory environment. This also includes other human pathogens like the bacterium that causes Lyme disease.
Using animals to culture human-pathogens has problems. First, the use of animals is always difficult for technical and ethical reasons. Also, a microbe growing on animal other than a human may behave very differently from how that same microbe will behave on a human.
Some human pathogens are grown directly on cells cultured from humans. Exemplified by the bacteria Chlamydia trachomatis , the bacteria responsible for the sexually transmitted infection STI in humans known as Chlamydia.
As Chlamydia trachomatis only grows in humans. The human cell culture known as McCoy cell culture is used to culture this bacteria. Chlamydias bacteria group : Light microscope view of cells infected with chlamydiae as shown by the brown inclusion bodies. A large concern of microbiology is trying to find ways in which humans can avoid or get rid of microbrial infections.
As typified by some of the above examples, some microbes have to be grown in the lab, and some of them can infect humans. To deal with this, microbiologists use a classification of biosafety levels. A biosafety level is the level of the biocontainment precautions required to isolate dangerous biological agents in an enclosed facility.
Biosafety Level 1 : This level is suitable for work involving well-characterized agents not known to consistently cause disease in healthy adult humans, with minimal potential hazard to laboratory personnel and the environment.
Biosafety Level 2 : This level is similar to Biosafety Level 1 and is suitable for work involving agents of moderate potential hazard to personnel and the environment. It includes various bacteria and viruses that cause only mild disease to humans or are difficult to contract via aerosol in a lab setting such as chlamydia. Biosafety Level 3 : This level is applicable to clinical, diagnostic, teaching, research, or production facilities in which work is done with indigenous or exotic agents that may cause serious or potentially lethal disease after inhalation.
It includes various bacteria, parasites, and viruses that can cause severe to fatal disease in humans, but for which treatments exist eg. Biosafety Level 4 : This level is reserved for work with dangerous and exotic agents that pose a high individual risk of aerosol-transmitted laboratory infections, agents that cause severe to fatal disease in humans for which vaccines or other treatments are not available, such as Bolivian and Argentine hemorrhagic fevers, Marburg virus, and the Ebola virus.
Very few laboratories are biosafety level 4. Positive pressure suit : A scientist puts on a positive pressure suit, something needed to work with the most dangerous human pathogens in a biosafety level 4 laboratory. Privacy Policy. Skip to main content. Culturing Microorganisms. Search for:. Culturing Bacteria. Culture Media Culture media is the food used to grow and control microbes.
Learning Objectives Classify culture media. Key Takeaways Key Points Culture media contains the nutrients needed to sustain a microbe. Culture media can vary in many ingredients allowing the media to select for or against microbes.
Glucose or glycerol are often used as carbon sources, and ammonium salts or nitrates as inorganic nitrogen sources in culture media. Key Terms culture : The process of growing a bacterial or other biological entity in an artificial medium.
Complex and Synthetic Media In defined media all the chemical compounds are known, while undefined media has partially unknown chemical constituents. Learning Objectives Differentiate complex and synthetic medias. Key Takeaways Key Points Defined media is made from constituents that are completely understood.
Undefined media has some part of which is not entirely defined. The presence of extracts from animals or other microbes makes a media undefined as the entire chemical composition of extracts are not completely known. Key Terms recombinant : This term refers to something formed by combining existing elements in a new combination.
Also called blood serum. Selective and Differential Media Selective media allows for the growth of specific organisms, while differential media is used to distinguish one organism from another.
Learning Objectives Compare selective and differential media. Key Takeaways Key Points Selective media generally selects for the growth of a desired organism, stopping the growth of or altogether killing non-desired organisms. Differential media takes advantage of biochemical properties of target organisms, often leading to a visible change when growth of target organisms are present. Differential media, unlike selective media, does not kill organisms.
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