Question: Why is gene transfer important in antibiotic resistance?
About the article "Bacteria", section "DNA transfer".

Candidate passages:
One of the most worrisome characteristics of "P. aeruginosa" is its low antibiotic susceptibility, which is attributable to a concerted action of multidrug efflux pumps with chromosomally encoded antibiotic resistance genes (e.g., "mexAB", "mexXY" etc.)
and the low permeability of the bacterial cellular envelopes.
In addition to this intrinsic resistance, "P. aeruginosa" easily develops acquired resistance either by mutation in chromosomally encoded genes or by the horizontal gene transfer of antibiotic resistance determinants.
Development of multidrug resistance by "P. aeruginosa" isolates requires several different genetic events, including acquisition of different mutations and/or horizontal transfer of antibiotic resistance genes.
Hypermutation favours the selection of mutation-driven antibiotic resistance in "P. aeruginosa" strains producing chronic infections, whereas the clustering of several different antibiotic resistance genes in integrons favors the concerted acquisition of antibiotic resistance determinants.
Some recent studies have shown phenotypic resistance associated to biofilm formation or to the emergence of small-colony variants may be important in the response of "P. aeruginosa" populations to antibiotics treatment. 
Horizontal gene transfer (HGT) refers to the transfer of genes between organisms in a manner other than traditional reproduction.
Also termed "lateral gene transfer" (LGT), it contrasts with "vertical transfer", the transmission of genes from the parental generation to offspring via sexual or asexual reproduction.
HGT has been shown to be an important factor in the evolution of many organisms.
Horizontal gene transfer is the primary reason for bacterial antibiotic resistance, and plays an important role in the evolution of bacteria that can degrade novel compounds such as human-created pesticides and in the evolution, maintenance, and transmission of virulence.
This horizontal gene transfer often involves temperate bacteriophages and plasmids.
Genes that are responsible for antibiotic resistance in one species of bacteria can be transferred to another species of bacteria through various mechanisms (e.g., via F-pilus), subsequently arming the antibiotic resistant genes' recipient against antibiotics, which is becoming a medical challenge to deal with.
This is the most critical reason that antibiotics must not be consumed and administered to patients without appropriate prescription from a medical physician.
Most thinking in genetics has focused upon vertical transfer, but there is a growing awareness that horizontal gene transfer is a highly significant phenomenon and among single-celled organisms perhaps the dominant form of genetic transfer.
Artificial horizontal gene transfer is a form of genetic engineering. 
Being Gram-negative bacteria, most "Pseudomonas spp."
are naturally resistant to penicillin and the majority of related beta-lactam antibiotics, but a number are sensitive to piperacillin, imipenem, ticarcillin, or ciprofloxacin.
Aminoglycosides such as tobramycin, gentamicin, and amikacin are other choices for therapy.
This ability to thrive in harsh conditions is a result of their hardy cell wall that contains porins.
Their resistance to most antibiotics is attributed to efflux pumps, which pump out some antibiotics before the antibiotics are able to act.
"Pseudomonas aeruginosa" is increasingly recognized as an emerging opportunistic pathogen of clinical relevance.
One of the most worrying characteristics of "P. aeruginosa" is its low antibiotic susceptibility.
This low susceptibility is attributable to a concerted action of multidrug efflux pumps with chromosomally encoded antibiotic resistance genes (e.g., "mexAB-oprM", "mexXY", etc.,) and the low permeability of the bacterial cellular envelopes.
Besides intrinsic resistance, "P. aeruginosa" easily develops acquired resistance either by mutation in chromosomally encoded genes or by the horizontal gene transfer of antibiotic resistance determinants.
Development of multidrug resistance by "P. aeruginosa" isolates requires several different genetic events that include acquisition of different mutations and/or horizontal transfer of antibiotic resistance genes.
Hypermutation favours the selection of mutation-driven antibiotic resistance in "P. aeruginosa" strains producing chronic infections, whereas the clustering of several different antibiotic resistance genes in integrons favours the concerted acquisition of antibiotic resistance determinants.
Some recent studies have shown phenotypic resistance associated to biofilm formation or to the emergence of small-colony-variants may be important in the response of "P. aeruginosa" populations to antibiotic treatment. 
Public health applications.
Bacterial survival on surfaces.
Studies have found prolonged viability of bacteria on stainless-steel surfaces at room temperature.
In a specific study, stainless steel was inoculated with 107 CFU/cm2 "E. coli" and "K. pneumonia", containing blaCTX-M-15 and blaNDM-1 (antibiotic-resistant genes) respectively.
Thirty days later (at room temperature, 22˚ C), 104 viable cells remained; and, after 100 days, 100 CFU/cm2 of "E. coli" remained.
In contrast, on copper and copper alloy surfaces, rapid death of antibiotic-resistant bacterial strains, as well as destruction of plasmid and genomic DNA, can be observed.
Studies suggest that exposure to dry copper surfaces inhibits the respiration and growth of producers by releasing copper ions.
Increased horizontal gene transfer (HGT) is observed simultaneously with cell viability on stainless steel surfaces.
HGT is one of the major factors responsible for creating antibiotic resistance in bacteria.
This suggests that immediate decontamination of surfaces is important in preventing the spread of antibiotic resistance genes.
It has also been shown that horizontal transfer of antibiotic-resistant β-lactamase genes does not occur on antimicrobial copper surfaces.
As copper surfaces degrade naked DNA (and plasmid DNA in antibiotic-resistant "E. coli" and "K. pneumonia"), copper surfaces would halt HGT.
Horizontal gene transfer has been demonstrated to occur readily on dry surfaces such as stainless steel, but not on copper and copper alloy surfaces.
The rate of bacterial death increased proportionally with the percentage of copper in the copper alloy surface.
This can be very important in future clinical and community settings, as an increase in copper utilization in hospital room equipment could help to greatly reduce the spread of antibiotic-resistant infection and the horizontal gene transfer of this antibiotic resistance. 
SCC"mec", or staphylococcal cassette chromosome "mec", is a mobile genetic element of "Staphylococcus" bacterial species.
This genetic sequence includes the "mecA" gene coding for resistance to the antibiotic methicillin and is the only known way for "Staphylococcus" strains to spread the gene in the wild by horizontal gene transfer.