Horizontal Transfer of Antibiotic Resistance Genes on Abiotic Touch Surfaces: Implications for Public Health

Horizontal gene transfer (HGT) is largely responsible for increasing the incidence of antibiotic-resistant infections worldwide. While studies have focused on HGT in vivo, this work investigates whether the ability of pathogens to persist in the environment, particularly on touch surfaces, may also play an important role. Escherichia coli, virulent clone ST131, and Klebsiella pneumoniae harboring extended-spectrum-β-lactamase (ESBL) bla(CTX-M-15) and metallo-β-lactamase bla(NDM-1), respectively, exhibited prolonged survival on stainless steel, with approximately 10(4) viable cells remaining from an inoculum of 10(7) CFU per cm(2) after 1 month at 21°C. HGT of bla 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 conjugation frequency was approximately 10 to 50 times greater and occurred immediately, and resulting transconjugants were more stable with ESBL E. coli as the donor cell than with K. pneumoniae, but bla(NDM-1) transfer increased with time. Transconjugants also exhibited the same resistance profile as the donor, suggesting multiple gene transfer. Rapid death, inhibition of respiration, and destruction of genomic and plasmid DNA of both pathogens occurred on copper alloys accompanied by a reduction in bla copy number. Naked E. coli DNA degraded on copper at 21°C and 37°C but slowly at 4°C, suggesting a direct role for the metal. Persistence of viable pathogenic bacteria on touch surfaces may not only increase the risk of infection transmission but may also contribute to the spread of antibiotic resistance by HGT. The use of copper alloys as antimicrobial touch surfaces may help reduce infection and HGT.