Question

The most frequent mechanism of transferable drug resistance. (A) transduction (B) transformation (C) transmission (D) plasmid exchange (E) mutation and selection

Short answer

The most frequent mechanism of transferable drug resistance is plasmid exchange.

Step-by-step solution

Understanding Transferable Drug Resistance

First, let's understand what "transferable drug resistance" means. It refers to the ability of bacteria to acquire resistance to drugs (usually antibiotics) and transfer this ability to other bacteria. This transfer can happen between different bacterial species or within the same species.

Identifying the Mechanisms

In order to solve the problem, we need to know the common mechanisms through which drug resistance can be transferred among bacteria. The options provided are: (A) transduction - transfer of genetic material via bacteriophages, (B) transformation - uptake of free DNA fragments from the environment, (C) transmission - not a specific mechanism in genetic terms, (D) plasmid exchange - direct transfer of plasmids containing resistance genes between bacteria, (E) mutation and selection - genetic mutations that confer resistance, subsequently selected under drug pressure. Out of these, plasmid exchange is particularly known for horizontal gene transfer, especially involving antibiotic resistance genes.

Evaluating Each Option

Let's evaluate each option: - (A) Transduction: This process involves bacteriophages and is not the most common method for resistance gene transfer. - (B) Transformation: While some bacteria can uptake free DNA, it's limited to species capable of transformation. - (C) Transmission: This is not a correct term in the context of genetic exchange. - (D) Plasmid Exchange: This is a very common method for transferring antibiotic resistance, as plasmids can move between bacteria. - (E) Mutation and Selection: While mutation can lead to resistance, it is not considered a 'transfer' mechanism. Thus, the most frequent mechanism of transferable drug resistance is (D) plasmid exchange.

Key concepts

Plasmid Exchange

Plasmid exchange involves the transfer of plasmids, which are small DNA molecules, from one bacterium to another. These plasmids can carry genes that confer resistance to antibiotics. This process allows bacteria to quickly adapt to their environment by sharing survival traits.
Plasmids can move between bacteria through a process called conjugation. In conjugation, two bacterial cells connect via a tube-like structure known as a pilus. The plasmid is then copied and transferred to the recipient cell, granting it new abilities.

• Plasmids often carry multiple resistance genes, making this transfer highly efficient for spreading drug resistance.
• This mechanism is not limited by bacterial species, meaning resistance can spread across diverse bacterial groups.

Plasmid exchange is a powerful tool for bacteria in hostile environments, such as during antibiotic treatment, where survival depends on these genetic changes.

Horizontal Gene Transfer

Horizontal gene transfer (HGT) is a process where genetic material is transferred between organisms in a manner other than traditional reproduction. In bacteria, this is a primary way to quickly acquire new traits, like antibiotic resistance.
There are several methods of HGT:

• **Conjugation:** Direct transfer of DNA through contact between bacterial cells, often involving plasmids.
• **Transformation:** Uptake of free DNA fragments from the environment by a bacterium.
• **Transduction:** Transfer of DNA from one bacterium to another via a virus (bacteriophage).

HGT allows bacteria to rapidly respond to new pressures, such as antibiotics, making it a critical factor in the spread of antibiotic resistance genes. It essentially lets bacteria "borrow" successful survival strategies from each other.

Antibiotic Resistance Mechanisms

Antibiotic resistance mechanisms enable bacteria to survive in the presence of drugs designed to kill them. These mechanisms can occur through several biological changes:

• **Enzyme production:** Bacteria produce enzymes that inactivate the antibiotic. An example is β-lactamase, which targets penicillins.
• **Efflux pumps:** Proteins that pump antibiotics out of the cell before they can do harm.
• **Target modification:** Changes in bacterial structures that antibiotics target, reducing the drug's effectiveness.
• **Reduced permeability:** Alteration of membrane channels to prevent antibiotics from entering the cell.

Antibiotic resistance can arise through spontaneous mutations, but is often spread via mechanisms like plasmid exchange, as plasmids can carry multiple resistance genes. This makes understanding these processes crucial in the fight against antibiotic-resistant infections.