R-plasmid conjugation is a means of genetic recombination (def) in bacteria. R-plasmids often contain resistance genes coding for multiple antibiotic resistance, as well as resistance transfer genes coding for the production of a conjugation (sex) pilus. The conjugation pilus enables the donor bacterium to transfer a copy of the R-plasmid to a recipient bacterium, making it also multiple antibiotic resistant and able to produce a conjugation pilus.
During R-plasmid conjugation, the sex pilus of the donor bacterium attaches to a recipient bacterium as one strand of the R-plasmid breaks. The sex pilus retracts and a bridge is created between the two bacteria. One plasmid strand enters the recipient bacterium while one strand remains in the donor. Each strand then makes a complementary copy (see Fig. 1A through 1D). As a result, the recipient becomes multiple antibiotic resistant and able to make a conjugation pilus, and is now able to transfer R-plasmids to other bacteria.
This is a big problem in treating opportunistic gram-negative infections (urinary tract infections, wound infections, pneumonia, septicemia) by such organisms as E. coli, Proteus, Klebsiella, Enterobacter, Serratia, and Pseudomonas, as well as with intestinal infections by organisms like Salmonella and Shigella.
Genetic recombination is discussed in greater detail in Unit 4.