AUTHOR=Chen Wenyao , Fang Tingzi , Zhou Xiujuan , Zhang Daofeng , Shi Xianming , Shi Chunlei 

TITLE=IncHI2 Plasmids Are Predominant in Antibiotic-Resistant Salmonella Isolates

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.01566

DOI=10.3389/fmicb.2016.01566

ISSN=1664-302X

ABSTRACT=<p>The wide usage of antibiotics contributes to the increase in the prevalence of antibiotic-resistant <italic>Salmonella</italic>. Plasmids play a critical role in horizontal transfer of antibiotic resistance markers in <italic>Salmonella</italic>. This study aimed to screen and characterize plasmid profiles responsible for antibiotic resistance in <italic>Salmonella</italic> and ultimately to clarify the molecular mechanism of transferable plasmid-mediated antibiotic resistance. A total of 226 <italic>Salmonella</italic> isolates were examined for antimicrobial susceptibility by a disk diffusion method. Thirty-two isolates (14.2%) were resistant to at least one antibiotic. The presence of plasmid-mediated quinolone resistance (PMQR) genes and <italic>β</italic>-lactamase genes were established by PCR amplification. PCR-based replicon typing revealed that these 32 isolates represented seven plasmid incompatibility groups (IncP, HI2, A/C, FIIs, FIA, FIB, and I1), and the IncHI2 (59.4%) was predominant. Antibiotic resistance markers located on plasmids were identified through plasmid curing. Fifteen phenotypic variants were obtained with the curing efficiency of 46.9% (15/32). The cured plasmids mainly belong to the HI2 incompatibility group. The elimination of IncHI2 plasmids correlated with the loss of <italic>β</italic>-lactamase genes (<italic>bla</italic><sub>OXA-1</sub> and <italic>bla</italic><sub>TEM-1</sub>) and PMQR genes (<italic>qnrA</italic> and <italic>aac(6′)-Ib-cr</italic>). Both IncHI2 and IncI1 plasmids in a <italic>S. enterica</italic> serovar Indiana isolate SJTUF 10584 were lost by curing. The <italic>bla</italic><sub>CMY -2</sub>-carrying plasmid pS10584 from SJTUF 10584 was fully sequenced. Sequence analysis revealed that it possessed a plasmid scaffold typical for IncI1 plasmids with the unique genetic arrangement of IS<italic>1294</italic>-ΔIS<italic>Ecp1</italic>-<italic>bla</italic><sub>CMY -2</sub>-<italic>blc</italic>-<italic>sugE</italic>-Δ<italic>ecnR</italic> inserted into the colicin gene <italic>cia</italic>. These data suggested that IncHI2 was the major plasmid lineage contributing to the dissemination of antibiotic resistance in <italic>Salmonella</italic> and the activity of multiple mobile genetic elements may contribute to antibiotic resistance evolution and dissemination between different plasmid replicons.</p>