<p>Plasmids in agriculturally-impacted bodies of
water may play a significant role in the dissemination of antibiotic resistance
(AR). High bacterial loads in stream sediment and selective pressures
introduced by agricultural practices may facilitate the exchange and
recombination of genetic material, creating reservoirs of AR genes that can
potentially be accessed by fecal and other animal and human pathogens. </p>
<p> Transmissible
plasmids were captured “exogenously” from stream sediment samples by
conjugating sediment cells with a rifampicin-resistant strain of Escherichia
coli.
Transconjugants were tested for decreased antibiotic susceptibility using a
modified Stokes disk diffusion method. Twenty-three of thirty captured
plasmids conferred decreased susceptibility to multiple antibiotics in addition
to tetracycline. </p>
<p> One
plasmid, pEG1-1, conferred resistance to tetracycline, tobramycin, kanamycin, ticarcilin, piperacillin, piperacillin-tazobactam, and
cefepime. A
method to sequence multi-drug resistance plasmids using both Oxford Nanopore
MinION and Ion Torrent Personal Genome Machine sequencers was developed to
sequence plasmid pEG1-1. A hybrid assembly generated a single 73,320 bp contig.
Analysis of the genome revealed pEG1-1 to be an IncP-1β plasmid with two mobile
genetic elements – a tn21-related transposon and an in104
complex
integron – both of which carry multiple antibiotic resistance genes. </p>
<p> These
findings suggest that plasmids in stream sediment are prone to the
incorporation of mobile genetic elements that introduce a broad range of
antibiotic resistance genes into their genome. This could cause serious risk to
human health since IncP-1β plasmids are capable of transferring into nearly all
Gram-negative bacteria, including fecal pathogens that get introduced to stream
sediment.</p
