Copper Restricts Spread of Antibiotic-Resistant Infections

A new study shows how copper can prevent horizontal gene transfer (HGT) in bacteria, which has contributed to the increasing number of antibiotic-resistant infections worldwide.

Researchers at the University of Southampton (United Kingdom) investigated the ability of pathogens to persist in the environment, particularly on touch surfaces. They found that the virulent clone Escherichia coli ST131 and Klebsiella pneumoniae exhibited prolonged survival on stainless steel, with approximately 104 viable cells remaining from an inoculum of 107 Colony Forming Units (CFU) per cm² after 1 month at 21 °C. They also found that HGT to an antibiotic-sensitive but azide-resistant recipient E. coli strain occurred on stainless steel dry touch surfaces and in suspension, but not on dry copper. The gene conjugation frequency was approximately 10–50 times greater and occurred immediately, and the resulting transconjugants were more stable with E. coli as the donor cell than with K. pneumonia.

The transconjugants also exhibited the same resistance profile as the donor, suggesting multiple gene transfer. On the other hand, rapid death, inhibition of respiration, and destruction of genomic and plasmid DNA of both pathogens occurred on copper alloys, accompanied by a reduction in copy number. Naked E. coli DNA degraded on copper at 21 °C and 37 °C but more slowly at 4 °C, suggesting a direct role for the metal. The researchers concluded that the use of copper alloys as antimicrobial touch surfaces may help reduce infection and HGT. The study was published in the November 2012 issue of the journal mBio.

“People with inadequate hand hygiene could exchange their bugs and different antibiotic resistance genes just by touching a stair rail or door handle, ready to be picked up by someone else and passed on,” said lead author Prof. Bill Keevil, PhD, chair of environmental healthcare. “Copper touch surfaces have promise for preventing antibiotic resistance transfer in public buildings and mass transportation systems. Copper substantially reduces and restricts the spread of these infections, making an important contribution to improved hygiene and, consequently, health.”

HGT conferring resistance to many classes of antimicrobials has resulted in a worldwide epidemic of nosocomial and community infections caused by multidrug-resistant microorganisms, which has led to an increasing number of difficult-to-treat healthcare-associated infections (HCAIs). Installations of copper touch surfaces have already taken place around the world, harnessing copper's ability to continuously reduce biological burden and consequently the risk of HCAI transmission.

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