Incubator- Definition, Parts, Working, Types, Uses, Precautions

An incubator in microbiology is a device that creates and maintains optimal conditions of temperature, humidity, and other environmental factors for the growth of microorganisms. An incubator can be used to culture both unicellular and multicellular organisms, such as bacteria, fungi, algae, protozoa, animal cells, and plant cells. An incubator is an essential piece of laboratory equipment for many experimental and diagnostic purposes in microbiology, cell biology, molecular biology, and biotechnology.

An incubator is composed of various parts that work together to create and maintain the optimal conditions for the growth of microorganisms. The following are some of the main components and parts of an incubator:

• Cabinet: The cabinet is the main body of the incubator that encloses the chamber where the cultures are placed. It is usually made of metal sheets with insulation between them to prevent heat loss and reduce electricity consumption. The cabinet has a capacity that ranges from 20 to 800 liters, depending on the size and type of the incubator. The cabinet also has inward projections that support the shelves inside the chamber.
• Door: The door is used to close and open the cabinet. It also has insulation and a glass window that allows the observation of the cultures without disturbing the temperature and humidity inside the chamber. The door has a handle and a lock to ensure proper sealing and security.
• Control panel: The control panel is located on the outer wall of the cabinet. It has switches, indicators, and knobs that allow the user to set and monitor the parameters of the incubator, such as temperature, humidity, CO2 level, airflow, etc. The control panel also has a switch to control the thermostat of the device.
• Thermostat: The thermostat is a device that regulates the temperature inside the chamber by turning on and off the heating element. The thermostat can be set to a desired temperature by using a knob on the control panel. The thermostat maintains a constant temperature by alternating between heating and cooling cycles.
• Heating element: The heating element is a coil or a rod that generates heat when electricity passes through it. It is located at the bottom or at the back of the chamber. The heating element heats up the air inside the chamber and creates a convection current that distributes heat evenly throughout the chamber.
• Perforated shelves: The perforated shelves are metal racks that are attached to the inner wall of the chamber. They are used to hold the culture plates or flasks in an upright position. The perforations on the shelves allow air circulation and heat distribution inside the chamber. Some incubators have removable shelves that can be adjusted or cleaned as needed.
• Asbestos door gasket: The asbestos door gasket is a strip of material that seals the gap between the door and the cabinet. It prevents outside air from entering or escaping from the chamber. It also reduces heat loss and maintains a stable environment inside the chamber.
• L-shaped thermometer: The L-shaped thermometer is a device that measures and displays the temperature inside the chamber. It has two ends: one end with gradations that remains outside of the cabinet for easy reading, and another end with a mercury bulb that protrudes slightly into the chamber.
• HEPA filters: Some advanced incubators have HEPA filters that filter out dust, microbes, and other contaminants from the air entering or leaving the chamber. They are usually connected to an air pump that creates a closed-loop system of airflow inside the chamber. HEPA filters reduce contamination and improve air quality inside the chamber.
• Humidity and gas control: Some specialized incubators have devices that control humidity and gas levels inside the chamber. For example, CO2 incubators have a reservoir underneath the chamber that contains water. The water is vaporized to maintain relative humidity inside the chamber. They also have gas chambers that supply CO2 gas to adjust its concentration inside the chamber. Humidity and gas control are important for some organisms that require specific levels of moisture and carbon dioxide for their growth.

An incubator is based on the principle that microorganisms require a particular set of parameters for their growth and development. All incubators are based on the concept that when organisms are provided with the optimal condition of temperature, humidity, oxygen, and carbon dioxide levels, they grow and divide to form more organisms.

In an incubator, the thermostat maintains a constant temperature that can be read from the outside via the thermometer. The temperature is maintained by utilizing the heating and no-heating cycles. During the heating cycle, the thermostat heats the incubator, and during the no-heating period, the heating is stopped, and the incubator is cooled by radiating heat to the surrounding. Insulation from the outside creates an isolated condition inside the cabinet, which allows the microbes to grow effectively.

Similarly, other parameters like humidity and airflow are also maintained through different mechanisms that create an environment similar to the natural environment of the organisms. For example, some advanced incubators are provided with HEPA filters to lower the possible contamination created due to airflow. An air-pump with filters creates a closed-loop system so that the air flowing inside the incubator generates less contamination.

Some incubators also have humidity and gas control systems to provide the desired level of moisture and carbon dioxide inside the chamber. The CO2 incubators have a reservoir underneath the chamber that contains water. The water is vaporized to maintain the relative humidity inside the chamber. Similarly, these incubators have gas chambers to give the desired concentration of CO2 inside the incubator. This is important for balancing the pH and humidity required for the growth of some organisms.

Variation of the incubator like a shaking incubator is also available, which allows for the continuous movement of the culture required for cell aeration and solubility studies. A thermostatically controlled shaker incubator provides a rapid and uniform transfer of heat to the culture vessel, and its agitation provides increased aeration, resulting in acceleration of growth. This type of incubator can only be used for broth or liquid culture media.

Once the cultures of organisms are created, the culture plates are to be placed inside an incubator at the desired temperature and required period of time. In most clinical laboratories, the usual temperature to be maintained is 35–37°C for bacteria. The following are the steps to be followed while running an incubator:

1. Before using the incubator, it should be made sure that no remaining items are present in the incubator from the previous cycles. However, in some cases, if the same incubator is being used for multiple organisms, and they require the same set of parameters, they can be placed together in the same incubator.
2. The door of the incubator is then kept closed, and the incubator is switched on. The incubator has to be heated up to the desired temperature of the growth of the particular organism. The thermometer can be used to see if the temperature has reached.
3. In the meantime, if the organism requires a particular concentration of CO2 or a specific humidity, those parameters should also be set in the incubator.
4. Once all the parameters are met, the petri dish cultures are placed on the perforated shelves upside down, i.e., media uppermost. This is necessary because if the plates are incubated normally, condensation collects on the surface of the medium and prevents the formation of isolated colonies.
5. If it is necessary to incubate Petri dish cultures for several days, the plates are sealed with adhesive tapes or are placed in plastic bags or plastic food containers.
6. Now, the door is locked, and the plates are kept inside for the required time before taking them out.

There are different types of incubators based on the purpose, design, and parameters of the incubation. Some of the common types of incubators used in microbiology are:

• Benchtop incubators: These are the basic and most common type of incubators used in most laboratories. They are insulated boxes with an adjustable heater that can provide temperatures above ambient temperature only. They are suitable for growing bacterial and eukaryotic cells that require moderate temperatures, such as 37°C for E. coli or 30°C for yeast.
• CO2 incubators: These are special types of incubators that have automatic control of CO2 and humidity levels. They are used for growing mammalian cells that require a slightly acidic pH and high relative humidity. They also have a water reservoir underneath the chamber to maintain the humidity and a gas chamber to regulate the CO2 concentration.
• Cooled incubators: These are incubators that have both heating and cooling systems that can provide temperatures below or above ambient temperature. They are used for growing microorganisms that have a prolonged growth rate in the natural environment or that require low temperatures, such as psychrophiles. They also have a balance between heating and cooling controls to prevent temperature fluctuations.
• Shaker incubators: These are incubators that have a shaking mechanism that allows for continuous movement of the culture vessels. They are used for growing liquid or broth cultures that require increased aeration and solubility. They also have temperature control and insulation like other incubators.
• Portable incubators: These are small and compact incubators that can be used for fieldwork or remote locations. They are used for growing microorganisms from environmental samples or water examination. They have battery-powered heating systems and simple temperature control.

Each type of incubator has its own advantages and disadvantages depending on the application and the requirements of the microorganisms. Therefore, it is important to select the right type of incubator for the desired outcome.

Incubators have a wide range of applications in various areas including cell culture, pharmaceutical studies, hematological studies, and biochemical studies. Some of the uses of incubators are given below:

• Incubators are used to grow microbial culture or cell cultures. Microorganisms and cells require specific environmental conditions such as temperature, humidity, oxygen, and carbon dioxide levels for their optimal growth and development. Incubators provide these conditions artificially and allow the cultivation of different types of organisms such as bacteria, fungi, algae, protozoa, animal cells, plant cells, etc.
• Incubators can also be used to maintain the culture of organisms to be used later. Some organisms have a short lifespan or lose their viability quickly after being isolated from their natural environment. Incubators can preserve these organisms by providing them with suitable conditions until they are needed for further experiments or applications.
• Some incubators are used to increase the growth rate of organisms that have a prolonged growth rate in the natural environment. For example, some bacteria that cause tuberculosis or leprosy have a slow generation time and take weeks or months to form visible colonies on solid media. Incubators can accelerate their growth by providing them with optimal temperature and nutrients.
• Specific incubators are used for the reproduction of microbial colonies and subsequent determination of biochemical oxygen demand (BOD). BOD is a measure of the amount of oxygen consumed by microorganisms in breaking down organic matter in water samples. Incubators can provide a controlled condition for incubating water samples inoculated with microorganisms and measuring the change in dissolved oxygen levels over time.
• Incubators are also used for breeding of insects and hatching of eggs in zoology. Some insects such as mosquitoes or flies are used as vectors for transmitting diseases or as biological control agents for pest management. Incubators can provide a suitable environment for their reproduction and development. Similarly, some eggs such as chicken eggs or reptile eggs require specific temperature and humidity for successful hatching. Incubators can simulate these conditions and facilitate the incubation process.
• Incubators also provide a controlled condition for sample storage before they can be processed in the laboratories. Some samples such as blood samples or tissue samples need to be stored at a certain temperature and prevent contamination or degradation before they can be analyzed or tested. Incubators can keep these samples at a stable temperature and protect them from external factors.

The following precautions are to be followed while running an incubator:

• As microorganisms are susceptible to temperature change, the fluctuations in temperature of the cabinet by repeatedly opening the door should be avoided. Opening the door can also introduce contaminants into the chamber and affect the humidity and CO2 levels.
• The required parameters for the growth of the organism should be met before the culture plates are placed inside the cabinet. The incubator should be preheated to the desired temperature and the CO2 and humidity levels should be adjusted accordingly.
• The plates should be placed upside down with the lid at the bottom to prevent the condensation of water onto the media. This can interfere with the formation of isolated colonies and affect the results.
• The inside of the incubators should be cleaned regularly to prevent the organisms from settling on the shelves or the corners of the incubator. A disinfectant solution should be used to wipe down the surfaces and any spills should be cleaned immediately.
• While running the incubator for an extended period of time, sterile water should be placed underneath the shelves to prevent the culture media from drying out. Alternatively, a humidifying tray can be used to maintain a constant humidity level inside the chamber.
• A second thermometer should be used to verify the temperature reading of the incubator sensor. If there is a discrepancy, the sensor should be recalibrated or replaced. A CO2 analyzer can also be used to check the accuracy of the CO2 control system.
• A risk assessment should be carried out before doing any microbiological investigation. Not all microbiological research is safe to conduct and some organisms may pose a health hazard to the users or the environment. Appropriate biosafety measures should be followed according to the level of risk involved.

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