Pathogenic bacteria gain resistance to antibiotics due to changes in their 

Plasmids are small, circular DNA molecules that can carry antibiotic resistance genes. Bacteria gain resistance to antibiotics when they acquire plasmids containing these resistance genes.

(1) Cosmids are hybrid plasmid vectors that can carry larger fragments of DNA. However, they are not directly
related to the development of antibiotic resistance in bacteria.

(3) Antibiotic resistance in bacteria is not related to changes in the nucleus. Bacteria lack a true nucleus, as found in eukaryotic cells.

(4) The nucleoid is the region in the bacterial cell where the bacterial chromosome is located. Antibiotic resistance is not directly related to changes in the nucleoid.