Chapter 19, Problem 15STP

Summary Introduction

To analyze : 

The characteristics of bacteria that contribute to the development of antibiotic resistance.

Introduction :

Bacteria also possess small extrachromosomal, self-replicating, double-stranded, circular DNA apart from chromosomal DNA. R-plasmids carry genes for resistance against antibiotics. They can pass from one bacterium to another through horizontal gene transfer. This transfer of resistance results in the spread of resistance to the neighboring bacterial cells. Through this primary mechanism, bacteria evolve themselves to degrade the novel compounds such as drugs by acquiring resistance. It results in a medically challenging condition to deal with.

Explanation of Solution

Antibiotics eliminate the pathogenic bacteria either by killing it or by inhibiting its growth. However, bacteria are capable of acquiring resistance against antibiotics through horizontal gene transfer. It is a non-genealogical transmission of the genes coding for antibiotic resistance in the neighboring bacteria. These genes are mostly located on bacterial plasmid through which the resistance is spread. Methods through which resistance genes can be transferred horizontally are conjugation, transformation, and transduction. Most commonly, a bacterial cell spread resistivity through conjugation. The pili present on the surface of the bacterial cell helps to form a conjugation tube between a donor and recipient bacterial cell. Through the conjugation tube, the genes for resistance are transferred to the neighboring bacterial cells. All these methods involve passing of the traits from the donor cell to the recipient cell that results in alteration of the genetics of a competent bacterial cell. 

Apart from this, bacteria can also acquire resistance because of mutation caused due to selective pressure of antibiotic use. A high rate of replication is the cause of these genetic mutations. The faster the rate of replication, the faster the chances of acquiring the changes in the genome according to the changing environment. Bacteria evolve and adapt to antibiotics to survive in a hostile environment. The rate of acquiring resistance is also very high. Once it acquires resistance to first-line antibiotics, it further becomes resistant to second and third-line drugs too. It leads to the development of multi-drug resistant conditions.

Conclusion

Bacteria acquire drug resistance through horizontal gene transfer. They commonly transfer the genes for resistance present on the plasmid through conjugation. The pilus forms a conjugation tube and the genes are transferred from the donor cell to the recipient cell. It causes the spread of resistivity. They can also evolve due to selective pressure to survive in a hostile environment that contains antibiotics. They acquire changes in their genome and evolve to gain resistivity against antibiotics.