What is R Factor Structure Function and Transfer Mechanism
R-factor, or resistance factor, are plasmids that allow specific bacteria to gain resistance against antibiotics. They are mostly available in a set of genetic codes which can transfer themselves from one cell to another of a bacterium via means of conjugation or non-conjugation. Through bacterial conjugation, many r-factors can pass from bacterium to another.
R factor is accountable for coding of antimicrobial resistance against specific drugs. Moreover, they often code restriction for more than a single antibiotic, up to eight different resistances at times. The standard means of spreading antimicrobial resistance among various bacterial species, chromosomes, etc. occur via conjugation.
Define Plasmid
Plasmids are small, extra-chromosomal structure found in bacteria that can replicate itself. These circular molecules of DNA have a double-stranded format, and they are also found in multi-cellular organisms and archaea.
R plasmid is a DNA molecule that grants bacterial resistivity to one antibiotic or more. It comprises of two components primarily – a resistance transfer factor (RTF) and resistance determinants. RTF is a necessary factor responsible for the transmission of plasmids among bacteria, and r-determinants are genetic codes promoting antibiotic resistivity.
What are the Types of Plasmids?
Resistance or R Plasmid: These allow antimicrobial resistance against drugs. They have self-replication capabilities and can be resistant to multiple drugs. It comprises of two types – narrow and broad host range group. The narrow group enables replication within a species, whereas broad one allows transmission among different bacteria.
F-Plasmids: The fertility factor enables genetic coding transmission from one bacterium to another through conjugation. It is a form of a large plasmid and available mostly in Escherichia coli. The ones that contain F factor are termed as F+, and those lacking it are known as F-.
Virulence: They help bacteria to adapt efficiently with their surroundings. Similar to other plasmids, they can also travel from one bacterium to another.
Col Plasmids: They grant the bacteria a capacity to produce venomous proteins called colicines. Specific bacteria use these toxins to destroy other bacteria, thereby thriving in hostile environments.
Degradative: In contrast to other plasmids, they allow the host bacterium to decay xenobiotic components.
Structure of Resistance Plasmid
The resistance plasmid can be said to resemble a circular structure of DNA fragments, and its length varies in the spectrum of 80-95 kb and constitutes of the larger segment of a factor known as the R-RTF or Resistance Transfer Factor molecules. This plasmid is known to be majorly homologous to the F factor and contains quite like genes. It also constitutes a gene known as the fin 0 gene that restrains the task of transferring of the operon. These R factors come in varying sizes and also the kinds of resistance they offer to drugs. The R determinant is smaller in size as compared to the RTF. The RTF as well as the R determinants bind to develop a single unit and are split up from one another by the presence of IS 1 elements on both the sides. The presence of these IS 1 elements encourages the interchange of R determinant amongst the variants of R-RTF units present.
Functions of Resistance Plasmid
Following are the functions of the resistance plasmid -
The resistance plasmids are extremely important in playing a significant part in the transferral of the MDR genes in the bacteria.
The Resistance plasmids are also a part of the gene carrier process for the self-multiplication procedure, uniting and offering resistance against ampicillin.
Resistance is also built to offer against the antibiotics and encourage bacteria to manufacture Pilli, by the resistance plasmids which contain a specific gene which promotes the above-mentioned function
Horizontal Gene Transfer
Bacteria which consists of the F factors, can build a sex pilus which encourages the transmission of the horizontal gene between the bacteria, which is the donor and the bacteria, which is the recipient. The resistance to an antibiotic can quickly and without much hassle and expand amongst the rest of the bacterial community as well. This is because the F factor is present in several R factors too. Due to the presence of the gene known as the RTF or the Resistance Transfer Factor, several R factors can also be consumed by the DNA through the process of transduction or transformation.
Fun Fact
There are more than 100 types of antibiotic drugs! Some most commonly used antibiotics are amoxicillin, azithromycin, penicillin, streptomycin, etc.
Wrack Your Brains
Here are specific questions on r factor and its functioning. Use your knowledge to crack them.
What does fertility plasmids grant to a host bacterium?
Antimicrobial resistance
Ability to conjugate
Multi-drug resistance ability
None of the above
For being able to exist simultaneously in a single cell, non-identical plasmids require
Compatibility
Conjugation
Stability
High in numbers
None of them
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FAQs on R Factor in Bacteria and Antibiotic Resistance
1. What is R factor in bacteria?
The R factor is a plasmid in bacteria that carries genes responsible for antibiotic resistance. It is an extra-chromosomal, circular DNA molecule that can replicate independently of the bacterial chromosome. R factors often contain:
- Resistance genes that protect bacteria against specific antibiotics.
- Transfer genes (tra genes) that enable movement between bacteria.
2. What does R factor stand for?
The term R factor stands for Resistance factor. It refers to a plasmid that provides resistance to one or more antibiotics in bacteria. These resistance factors are commonly found in pathogenic bacteria and contribute significantly to the global problem of antimicrobial resistance.
3. How does the R factor spread antibiotic resistance?
The R factor spreads antibiotic resistance primarily through bacterial conjugation. During conjugation:
- A donor bacterium forms a sex pilus to attach to a recipient cell.
- The R plasmid DNA is replicated.
- A copy of the plasmid is transferred to the recipient bacterium.
4. What are the components of an R plasmid?
An R plasmid typically consists of two main components: the resistance transfer factor (RTF) and resistance genes (r genes).
- The RTF contains genes required for plasmid replication and conjugation.
- The r genes encode resistance to specific antibiotics such as penicillin or tetracycline.
5. What is the difference between R factor and F factor?
The main difference is that the R factor carries antibiotic resistance genes, while the F factor controls bacterial conjugation without conferring resistance.
- R factor: Provides resistance to antibiotics and may also enable transfer.
- F factor (Fertility factor): Contains genes for formation of sex pili and DNA transfer but usually lacks resistance genes.
6. Where are R factors found?
R factors are found in the cytoplasm of bacteria as extra-chromosomal plasmids. They are especially common in pathogenic bacteria such as Escherichia coli, Salmonella, and Staphylococcus. These plasmids can exist independently or sometimes integrate into the bacterial chromosome.
7. Why is the R factor important in medicine?
The R factor is medically important because it causes the spread of multidrug resistance among bacteria. This leads to:
- Reduced effectiveness of common antibiotics.
- Longer and more severe infections.
- Increased healthcare costs and mortality.
8. Can R factors carry resistance to multiple antibiotics?
Yes, many R factors carry genes that confer resistance to multiple antibiotics at the same time. These plasmids may contain several r genes, each coding for resistance to a different drug such as streptomycin, chloramphenicol, or tetracycline. This results in multidrug-resistant (MDR) bacterial strains.
9. How do R factors replicate inside bacteria?
R factors replicate independently using their own origin of replication within the bacterial cell. The plasmid DNA undergoes replication using the host’s enzymes, ensuring copies are passed to daughter cells during binary fission. This stable inheritance maintains antibiotic resistance within bacterial populations.
10. Are R factors involved in horizontal gene transfer?
Yes, R factors are key agents of horizontal gene transfer in bacteria. They move between unrelated bacterial cells mainly through conjugation, enabling rapid genetic exchange. This process increases genetic variation and accelerates the spread of antibiotic resistance across species and environments.
