Bacteria are the simplest organisms on Earth, yet they can pack a punch. One of today’s hottest topics in medical research is the rise of antibiotic-resistant strains of bacteria. These are harder to kill, as most antibiotics do not affect them anymore.
Antibiotic resistance arises from the transfer of genes from one bacterial cell to another. As they grow and reproduce, the resistance traits are passed on, leading to greater numbers of resistant bacteria. This is a huge public health concern. As a result, more research is being done to discover new antibiotics.
For students taking biology classes or those looking into a medical degree, this topic is important for them to know. But students learning genetic transfer in bacteria for the first time might find the lessons daunting. Thankfully, there are many ways to make it more engaging and approachable. Read on to find out how.
First of all, let’s take a look at why students find it challenging to learn genetic transfer in bacteria. Here are the top three reasons experienced by both students and teachers.
Bacterial gene transfer involves plasmids, which are tiny pieces of DNA inside bacterial cells. Bacteria themselves are already microscopic, so their DNA is even smaller. The minute nature of these molecules can make them a huge challenge for students to appreciate.
Experiments related to gene transfer in bacteria are risky. They can inadvertently create superbugs, or bacteria that are resistant to many antibiotics. This is a potentially huge health risk not just for students and teachers in the lab, but for the larger population.
Studying gene transfer in bacteria uses techniques that are difficult to master. DNA extraction, transduction, and transformation are complex procedures for many students, especially those who have no background in any of these techniques. The sheer volume of protocols students need to be familiarized with is intimidating to many of them.
Based on the difficulties students have when studying genetic transfer in bacteria, here are five tips for educators to make the topic more interesting. Each piece of advice addresses a particular challenge that students face.
Genetic transfer in bacteria confers different characteristics to them. One of the most concerning is antibiotic resistance, giving rise to so-called “superbugs.” Superbugs are bacteria that are resistant to many kinds of antibiotics, making them harder to control. Diseases caused by superbugs are also much harder to treat. Examples of these superbugs are methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and multidrug-resistant Pseudomonas aeruginosa.
Antibiotic resistance usually appears when bacteria are exposed to sub-lethal concentrations of a specific antibiotic. Due to selective pressure, the surviving microbes’ DNA may mutate, and some of those mutations may confer antibiotic resistance mechanisms. The resistant bacteria survive and pass on their resistance genes across several generations.
These resistance mechanisms can be sorted into four categories:
The modification of the primary target of the antibiotic, such as the transpeptidase for ampicillin resistance.
The inactivation of the antibiotic compound itself, such as the production of 𝝱-lactamase enzymes to degrade penicillin-G inside the cell.
Preventing the antibiotic from reaching the target by reducing the permeability of the membrane or using efflux pumps to keep the drug outside the cell, as observed against ciprofloxacin.
Using alternative metabolic pathways to compensate for the action of the antibiotic and ensure the survival of the bacteria.
A particular concern is the transmission of these drug-resistant genes across species. A drug-resistant bacterial strain can transfer its resistance genes to other strains of the same species. Other times, it can also transfer those genes to individuals of a different species that have never been exposed to the drug in the first place. This way, antibiotic resistance can spread widely and compromise whole antibiotic therapies.
The accumulation of antibiotic resistance genes leads to the creation of "superbugs" – bacterial strains that are immune to all but the most drastic treatments.
To overcome antibiotic resistance, the current strategies are to discover new antibiotics with novel modes of action or to use different antibiotics in "cocktails" – presuming that a bacteria might survive facing one, but not two or three antibiotics simultaneously.
Pictures, diagrams, illustrations, and videos are helpful in making students better comprehend concepts regarding genetic transfer in bacteria. Moreover, students can better understand this topic and related concepts when their learning is aided by graphics, animations, and videos.
Videos, in particular, can make teaching practical concepts easier. Students can replay video demonstrations as often as needed until they have a good grasp of the concepts they need. They can learn streak plating, incubation, DNA extraction, and other important lab techniques. By the time they work on a real lab bench, they already know everything they need to do.
Interactive simulations are even better. They let students manipulate lab instruments and reagents virtually, so it’s as if they’re doing the real thing. If they make mistakes, there is no risk to themselves or others. Once they master the technique in the virtual world, they will be more confident as they perform actual experiments in the real lab. The image below is from Labster’s simulation entitled Genetic Transfer in Bacteria: Prevent the rise of superbugs.
Students must first master fundamental concepts like the bacterial genome, mutations, and gene transfer modes to fully understand this topic. Here is an overview of these basics.
The entirety of genetic information in a cell is called a genome. Bacteria have a genome mainly consisting of a chromosome and plasmids. Both are made up of DNA.
The main genetic element of bacteria is a chromosome. Bacteria usually have circular DNA, unlike the linear DNA of plant and animal cells. The chromosome is coiled and tightly packed inside the bacterial cell.
Plasmids are extrachromosomal DNA, which are also circular. Plasmids are mostly found in bacteria, and there are often more than one of them present in every bacterial cell. Plasmids usually encode extra genes that confer additional traits to bacteria, but these are not necessary for survival under normal conditions. These extra genes include those responsible for antibiotic resistance.
Structure of the bacterial genome (Image source: Labster Theory)
Mutations are variations in the sequence of a genome. They can occur because of errors during DNA replication or DNA damage.
A mutation is the ultimate source of new genetic variation. They can be passed onto the offspring if the mutations occur in gametes (germ cells). The genetic changes caused by mutation can have one of three outcomes on the phenotype.
The mutation reduces fitness — i.e. causes lower likelihood of survival or fewer offspring.
The mutation increases fitness (e.g. in the case of antibiotic resistance)
The mutation has no effect on fitness. These are called neutral mutations.
Vertical gene transfer
Vertical gene transfer refers to the inheritance of the parental gene to the offspring. In bacteria, the chromosomes of the daughter cells are identical to those of the parent cells.
In vertical gene transfer, genetic variation is made possible through mutation. This may be useful if bacteria are exposed to harsh environments, such as a human body with antibiotics. Bacterial cells with mutations that result in antibiotic resistance would survive. Eventually, they will be the dominant population, and the antibiotic will no longer be effective for the patient.
Horizontal gene transfer
Horizontal gene transfer is the movement of genetic elements between cells that are not direct progeny. Unlike vertical gene transfer, this allows gene transfer between different species of bacteria.
Horizontal gene transfer may occur through conjugation, where two bacterial cells exchange plasmids with each other. Conjugation is considered to have the most significant influence is the spread of antibiotic-resistance genes.
There are many methods of microbial control, including sterilization, irradiation, and using antimicrobial agents. Each method has a different level of control and uses different equipment and reagents. Below is an overview of each one.
Sterilization is a type of decontamination that leaves no microbial load on an item. In other words, there are zero bacteria, fungi, spores, or even proteins present to transmit infection. Sterilization is the highest level of decontamination, and it is valuable in healthcare settings.
Different sterilization methods include wet heat (steam), dry heat, irradiation, and chemical sterilization. The gold standard and most effective way to sterilize lab equipment is through wet heat, where instruments and reagents are put inside an autoclave. The autoclave generates intense heat and pressure (121ºC, 15 psi) that can destroy all infectious material.
Some lab instruments and reagents may be damaged by heat and pressure, so they cannot be placed in an autoclave. For these purposes, dry heat (baking) is used. The temperature and cycle time is higher than an autoclave (160-190ºC for up to two hours).
Irradiation is also an effective method of microbial control. Surfaces exposed to ultraviolet (UV) light are effectively disinfected. Exposure to UV light is a common method of disinfecting cell culture hoods. UV light does not generate much heat, making it useful for disinfecting heat-sensitive items.
Antimicrobial agents can be used to control microbial load without heat or radiation. They can have general effects, destroying any microorganism, or they can have specific targets. Chemical disinfectants like 70% ethanol, 10% hypochlorite bleach, or 0.2% glutaraldehyde can be used to clean lab equipment and surfaces. They are indiscriminate, killing all microorganisms they come in contact with.
Antibiotics, on the other hand, are selectively toxic. Different antibiotics act on specific kinds of bacteria, targeting different parts of bacterial cells.
Virtual lab simulations are excellent tools for teaching control of microbial growth. Labster is determined to deliver fully interactive advanced laboratory simulations that make use of gamification elements like storytelling and scoring systems while exposing students to an immersive, realistic, 3D environment.
Check out this simulation called Genetic Transfer in Bacteria: Prevent the rise of superbugs at Labster. This virtual lab allows students to experience molecular events like bacterial conjugation and the growth of antibiotic-resistant strains in a safe, computer-generated environment. With this, students will gain the confidence to eventually perform the procedures on their own in an actual lab.
The GIF below is an example of what students can explore in the simulation.
Please take a moment to check out Labster’s Virtual Lab called Genetic Transfer in Bacteria: Prevent the rise of superbugs or get in touch to find out how you can start using virtual labs with your students.
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