Multidrug-Resistant CTX-M-(15, 9, 2)- and KPC-2-Producing and Isolates Possessed a Set of Acquired Heavy Metal Tolerance Genes Including a Chromosomal Operon (for Acquired Silver Resistance).

Bacterial resistance to antibiotics is concern in healthcare-associated infections. On the other hand, bacterial tolerance to other antimicrobials, like heavy metals, has been neglected and underestimated in hospital pathogens. Silver has long been used as an antimicrobial agent and it seems to be an important indicator of heavy metal tolerance. To explore this perspective, we searched for the presence of acquired silver resistance genes ( operon: , and ) and acquired extended-spectrum cephalosporin and carbapenem resistance genes ( and ) in Complex (EcC) ( = 27) and ( = 8) isolated from inpatients at a general hospital. Moreover, the genetic background of the (silver-efflux pump) and the presence of other acquired heavy metal tolerance genes, (copper-efflux pump), (arsenite-efflux pump), (tellurite resistance protein), and (mercuric reductase) were also investigated. Outstandingly, 21/27 (78%) EcC isolates harbored gene located in the chromosome. Complete operon was found in 19/21 -positive EcC isolates. Interestingly, 8/20 (40%) and 5/6 (83%) co-harbored genes and and/or genes. Frequent occurrences of , and genes were detected, especially in -positive, multidrug-resistant (MDR) and/or CTX-M-producing isolates. Our study showed co-presence of antibiotic and heavy metal tolerance genes in MDR EcC isolates. In our viewpoint, there are few studies regarding to bacterial heavy metal tolerance and we call attention for more investigations and discussion about this issue in different hospital pathogens.