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Have you heard of Escherichia coli? E. coli is a gram-negative rod bacterium found in the normal flora of the colon in humans and other animals. However, this bacterium can be pathogenic and lead to serious intestinal infections. E. coli is a rapidly growing species, and a single cell can produce 10 million cells in just 8 hours! Interested in learning about the growth of bacteria? Keep reading!
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Jetzt kostenlos anmeldenHave you heard of Escherichia coli? E. coli is a gram-negative rod bacterium found in the normal flora of the colon in humans and other animals. However, this bacterium can be pathogenic and lead to serious intestinal infections. E. coli is a rapidly growing species, and a single cell can produce 10 million cells in just 8 hours! Interested in learning about the growth of bacteria? Keep reading!
Bacterial growth is referred to as an increase in the number of bacterial cells that occurs during binary fission.
Binary fission is the main method by which bacterial cells reproduce. Binary fission is a simple type of cell division in which the cell duplicates its genetic material, elongates and divides into two new daughter cells that are identical to the parent cell. Thanks to binary fission, bacterial growth can lead to the production of colonies containing millions of bacterial cells!
Fig. 1. Binary fission in bacteria. The process starts with the duplication of the genetic material (the pink bundle gives way to another, green bundle, and the single plasmid gives way to another). The cell then elongates and constricts until it divides into two.
Bacteria were first discovered in the late 1600s by a Dutch scientist called Antonie van Leeuwenhoek. He discovered them by viewing plaque from his own teeth under the microscope, and named them "animalcules" because of how they moved!
Bacteria are microorganisms that can grow and reproduce in a variety of environments. However, each bacteria strain requires certain conditions regarding moisture, warmth, and its source of nutrients.
Bacteria thrive in moist environments, such as soil, water, and organic matter. They also prefer temperatures between 4-60°C, with most species growing optimally at temperatures between 25-40°C. Finally, bacteria require a source of nutrition, such as sugars, amino acids, and minerals, in order to grow and reproduce. Without these essential conditions, bacterial growth will be limited or may not occur at all.
Firstly, bacteria require a suitable temperature range in which to grow. We will discuss this in more detail later in the article, but the optimal temperature for bacterial growth varies depending on the strain, but most bacteria grow best at temperatures between 20-45°C. Extreme temperatures, such as those above 60°C or below 0°C, can inhibit or even kill bacteria.
However, not even freezing kills all bacteria!
Now that we learned about the different phases of bacterial growth, let's look at some factors affecting bacterial the growth of bacteria.
Let's start with temperature. Bacteria have optimal temperatures in which they grow best, and this optimal temperature range differs between bacterial species. Bacteria can be divided into groups depending on their optimal temperature range:
Psychrophiles are bacteria that prefer to grow at temperatures below 20°C.
Mesophiles are bacteria that prefer temperatures within 25-40°C.
Most pathogenic bacteria prefer to grow at 37°C and are, therefore, mesophiles.
Thermophiles are bacteria that grow at high temperatures ranging from 55-80 °C.
Bacteria also need a source of energy and nutrients to survive. Most bacteria are heterotrophic, meaning they obtain their energy and nutrients by consuming organic matter. This can include simple carbohydrates, amino acids, and other organic compounds. Oxygen can also be required by some bacteria, but many others are anaerobic, meaning that they don't need (or might even die in the presence of) oxygen. Of course, bacteria need water to survive, with most species requiring at least 60% relative humidity to grow.
Oxygen, as well as temperature, also has effects on the growth of bacteria. Some bacteria might thrive when there is plenty of oxygen, while other strains might prefer environments with low or no oxygen levels. Depending on their oxygen requirements, we give them different names.
| Classification based on Oxygen Requirement | Definition |
Obligate aerobes | Bacteria that can only grow in the presence of oxygen. Examples: M. tuberculosis, Pseudomonas, and Bacillus. |
| Obligate anaerobes | Bacteria that can only grow without oxygen. Example: C. tetani |
| Facultative anaerobes | Aerobic bacteria that can also grow without oxygen present. Examples: E. coli, and S. aureus. |
| Facultative aerobes | Anaerobic bacteria that can also grow in the presence of oxygen. Example: Lactobacillus. |
| Aerotolerant anaerobes | Bacteria that do not use oxygen, but can tolerate its presence. Example: C. histolyticum |
| Microaerophilic bacteria | Bacteria that have the ability to growth in the present of low oxygen tension (5-10% oxygen) Examples: Helicobacter, andCampylobacter. |
The pH also plays a critical role in bacterial growth. This is because the pH of a particular environment can affect the activity of enzymes necessary for bacterial growth and metabolism. Therefore, an appropriate pH range is crucial for bacterial growth and survival.
Remember that the measure of pH is a logarithmic scale of the number of protons in a solution.
Most bacteria thrive in a neutral pH environment, between 6.5 and 7.5. However, some bacteria have adapted to grow in extremely acidic or basic conditions.
Generally, most pathogenic bacteria grow between pH 7.2 and 7.6. However, some bacteria (ex. Lactobacilli) is capable of growth in pH less than 4, while others such as V. cholerae can grow in basic pH (8.2-8.9).
Bacteria growth can be divided into four phases:
Lag phase
Log phase
Stationary phase
Death phase
It's important to note that the duration of each phase may vary depending on the specific bacteria and the environment they are in. Additionally, not all individual bacteria will pass through all the phases.
For example some bacteria may die before reaching the death phase.
Bacterial growth starts at the lag phase. In this stage, the microorganism have just been introduced to the culture medium and are trying to acclimate to it. So, there is metabolic activity going on, but no cell division.
Then, we have the log phase. In this phase, we see bacteria dividing exponentially. Here, the bacterium is small in its size, and biochemically active. The number of bacterial cells also starts rising due to cell division.
The third phase is called the stationary phase. In this stage, bacterial growth stops almost entirely because of the exhaustion of nutrients and elevation of toxin levels. Also, the number of viable cells formed, and the number of dying cells are in balance. Another important thing to know is that, during this phase, the bacterium becomes gram-variable. Bacteria might also produce exotoxins, antibiotics, and bacteriocins at this phase.
Lastly, we have the death phase, also known as the decline phase. Here, the bacteria completely stops dividing, and cell death continues due to running out of nutrients and the accumulation of toxin products, so the bacterial population numbers decrease.
Bacteria need time to grow and reproduce. The time it takes for a bacterial population to double in size is known as the generation time and this varies depending on the species and the growth conditions. Some bacteria have generation times as short as 20 minutes, while others can take several hours or even days. The population of bacteria will continue to grow until the nutrients and other conditions become limiting.
Regardless, the general graph for bacterial growth includes all four phases described above.
When dealing with bacterial growth, we might need to determine generation time. By calculating generation time, we can measure the growth rate of a microbial population.
Generation time (or doubling time) is the time a microbial population needs to double in number.
The formula for generation time is as follows:
$$ \text{generation time}(t_{g}) = \frac{\text{time elapsed}(t)}{\text{number of generations}(n)} $$
But, how do we use generation time to find out the number of cells in a certain period of time? We can use the formula below:
$$ n_{t} = n_{0} \times 2^{n} $$
where,
\( n_{0} \) is the initial number of cells.
\( n_{t} \) is the final number of cells after a certain period of time.
\( n \) is the number of new generations over a given amount of time. \( n = \frac{\text{given amount of time}}{\text{generation time}} \)
Let's solve an example!
Calculate the number of cells after 2 hours of growth, starting with five cells (Generation time = 20 minutes).
The first thing we need to do is calculate \( n \). So:
$$ n = \frac{\text{given amount of time}}{\text{generation time}} = \frac{120min}{20min} = 6 $$
Now, all we have to do is use the formula:
$$ n_{t} = n_{0} \times 2^{n} $$
$$ n_{t} = 5\times 2^{6} = 320 \text{ cells} $$
We can use direct and indirect measures of bacterial growth and determine bacterial population size.
First, let's talk about the method of direct microscopic counting for total cell count. In this method, scientists use a specialized slide called the Petroff-Hausser counting chamber (Figure 4). This counting chamber has a grid, facilitating the counting of cells when observed under the microscope.
Direct count is a method used to calculate population size by counting the cells within a sample of the population.
This method is easy and quick to use. However, there are some limitations. For example, we cannot distinguish between live and dead cells unless special staining techniques are used. Also, if the cells are too small, it can be hard to count them.
Now, a common method used to count viable cells is known as plate count or viable count. Viable cells are referred to as cells that are alive and able to grow on laboratory culture media. Basically, scientists spread the microbes in solid media and then count the colonies. There are two ways to do this (Figure 5):
Spread-plate method: adding 0.1 ml or less of sample to the surface of an agar plate, spreading it evenly and then incubating until colonies are seen in the surface. Then, plates containing between 30 and 300 colonies are counted and the number of viable cells is expressed in units of CFU (colony forming units).
Pour-plate method: a known volume of culture (0.1 - 1.0 mL) is added to a sterile plate. Then, sterile molten agar medium is added to it, and evenly mixed. After solidification of the agar and incubation, the surface colonies and subsurface colonies are counted.
Preventing bacterial growth is important in order to maintain a safe and hygienic environment, as well as to prevent the spread of illness and disease. There are several methods that can be used to prevent bacterial growth:
Sanitation: Regularly cleaning and disinfecting surfaces and equipment can help to remove bacteria and prevent them from growing. This is especially important in places where there are people with weak or underdeveloped immune systems (e.g. children, older people and people with autoimmune diseases) or where there is high risk of infection (hospitals, restaurants, etc.).
Temperature control: Bacteria are sensitive to temperature changes. Many species cannot survive at high temperatures and cannot reproduce easily at low temperatures. Heating food to the appropriate temperature or refrigerating and freezing food can help to prevent bacterial growth.
Humidity control: Bacteria thrive in moist environments, so maintaining low humidity levels can help to prevent bacterial growth.
pH control: Many bacteria have a narrow range of pH levels at which they can grow. By controlling the pH of a product, bacteria growth can be prevented.
Preservation: Using preservatives such as salt, sugar, vinegar, and alcohol can help to prevent bacterial growth by making the environment inhospitable for them.
Personal hygiene: Proper handwashing, showering and other personal hygiene practices can help to prevent the spread of bacteria. This is especially relevant when someone is sick (for example, when someone has diarrhoea).
Use of antimicrobial agents: There are several antimicrobial agents that can be used to prevent bacterial growth, such as antibiotics, antiseptics, and disinfectants. Each product has a different use and not all of them work against all bacteria. Thus, especially for antibiotics, we should not use them when it's not recommended by a doctor. They can provide us with the correct type of antimicrobial for each situation.
Sterilization: This is the process of destroying or eliminating all forms of life and microorganisms. This is used in the medical, laboratory and food industries. There are different types of sterilization, like temperature- or agent-dependent sterilization methods.
It's important to note that different bacteria have different requirements for growth and not all of these methods will be effective in preventing the growth of all types of bacteria.
The temperature danger zone for bacterial growth is the range of temperatures between 5-57°C in which bacteria can grow and multiply rapidly.
This range of temperatures is particularly dangerous as it is within the range of temperatures that are commonly used to store and prepare food. Bacteria can double in number every 20 min in the danger zone, which means that even a small amount of bacteria can quickly multiply and reach dangerous levels for human health.
In order to prevent bacterial growth, it is important to keep food out of the danger zone by either keeping it at temperatures above 57°C or below 5°C, or by heating or cooling it quickly through the danger zone.
After reading this article, I'm sure you feel as relieved as we do that we have fridges and freezers now!
The 4 stages of bacterial growth are:
Most bacteria grow well in a moist protein-rich and pH-neutral or slightly acidic environment, although each bacteria strain is different and may require special conditions to thrive.
Bacterial growth can be prevented or slowed down by the use of antibiotics, as well as nutrient restriction, a dry environment or hostile temperatures.
In terms of preventing bacterial growth in food, keeping food in the fridge or freezer, or in a dry location according to the instructions on the label can help prevent food decay due to bacteria.
Most bacteria grow well in a moist protein-rich and pH-neutral or slightly acidic environment, although each bacteria strain is different and may require special conditions to thrive.
Bacterial growth is the generation of two genetically identical daughter bacteria cells from a single mother cell through a process called binary fission. Binary fission is a type of asexual reproduction.
Most bacteria grow well in a moist, protein-rich and pH-neutral or slightly acidic environment, although each bacteria strain is different and may require special conditions to thrive.
To prevent bacterial growth in food, it should be stored in the appropriate conditions depending on what type of food it is. Some foods will require storage in a cold space, such as the fridge or freezer, while others might require storage in a dry and dark place, like a cupboard. Another option is to heat the food up above the usual bacterial growth threshold, higher than 60°C.
The ideal temperature for bacterial growth depends on the strain of bacteria. Most bacteria, though, are mesophiles, which means they prefer moderate temperatures of 20 - 45°C, ideally 37ºC.
Bacteria can be divided into groups depending on their optimal temperature range:
Psychrophiles are bacteria that prefer to grow at temperatures below 20°C.
Mesophiles are bacteria that prefer temperatures within 25-40°C.
Most pathogenic bacteria prefer to grow at 37°C and are, therefore, mesophiles.
Thermophiles are bacteria that grow at high temperatures ranging from 55-80 °C.
The Temperature Danger Zone for bacterial growth is the range of temperatures at which food poisoning bacteria grow more easily. This range is between 5°C and 60°C. Between those temperatures, bacteria can double in less than 20 min.
Freezing stops bacterial growth but doesn't necessarily kill all the microorganisms present in the food. Therefore, when frozen food is defrosted, the bacteria might start growing again and cause food poisoning.
Salt and sugar prevent bacterial growth by creating an osmotic gradient, which causes water to flow out of the bacterial cells and dry them up.
Spices inhibit bacterial growth through several distinct mechanisms. Some spices, like garlic, can kill bacteria, while others might just decrease their growth rate. The way by which they do this is extremely varied: some spices damage the cell membrane, others inhibit ATPases or motility, among other methods.
In general, bacteria grow well at temperatures between 5°C and 60°C, ideally at 37°C. Temperatures above of below that range impede bacterial growth.
The lag phase is the first stage of bacterial growth. In this stage, the microorganisms have just been introduced to the culture medium and are trying to acclimate to it. So, there is metabolic activity going on, but no cell division.
Antibiotics usually disrupt bacterial cell functioning, which in turn slows down or stops bacterial growth. Antibiotics can also kill bacteria.
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SIGNUP SIGNUPFlashcards in Bacterial Growth16
Start learningBacteria are _______ organisms.
prokaryotic
Prokaryotes have all of the following except:
Ribosomes
Prokaryotic cells have _____ ribosomes.
70S
Which type of bacteria has a thick, peptidoglycan layer?
Gram-positive bacteria
Which type of bacteria has an outer membrane composed of LPS and protein?
Gram-negative bacteria
True or false: Bacterial growth is referred to as an increase in the number of bacterial cells that occur during binary fission.
True
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