AUTHOR=Andrade Leonardo N. , Siqueira Thiago E. S. , Martinez Roberto , Darini Ana Lucia C. 

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

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00539

DOI=10.3389/fmicb.2018.00539

ISSN=1664-302X

ABSTRACT=<p>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 (<italic>sil</italic> operon: <italic>silE, silS, silR, silC, silF, silB, silA</italic>, and <italic>silP</italic>) and acquired extended-spectrum cephalosporin and carbapenem resistance genes (<italic>bla</italic><sub>CTX−M</sub> and <italic>bla</italic><sub>KPC</sub>) in <italic>Enterobacter cloacae</italic> Complex (EcC) (<italic>n</italic> = 27) and <italic>Enterobacter aerogenes</italic> (<italic>n</italic> = 8) isolated from inpatients at a general hospital. Moreover, the genetic background of the <italic>silA</italic> (silver-efflux pump) and the presence of other acquired heavy metal tolerance genes, <italic>pcoD</italic> (copper-efflux pump), <italic>arsB</italic> (arsenite-efflux pump), <italic>terF</italic> (tellurite resistance protein), and <italic>merA</italic> (mercuric reductase) were also investigated. Outstandingly, 21/27 (78%) EcC isolates harbored <italic>silA</italic> gene located in the chromosome. Complete <italic>sil</italic> operon was found in 19/21 <italic>silA</italic>-positive EcC isolates. Interestingly, 8/20 (40%) <italic>E. hormaechei</italic> and 5/6 (83%) <italic>E. asburiae</italic> co-harbored <italic>silA/pcoD</italic> genes and <italic>bla</italic><sub>CTX−M−(15,2,or9)</sub> and/or <italic>bla</italic><sub>KPC−2</sub> genes. Frequent occurrences of <italic>arsB, terF</italic>, and <italic>merA</italic> genes were detected, especially in <italic>silA/pcoD</italic>-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.</p>