AUTHOR=Xiao Linlin , Wang Xiaotong , Kong Nana , Cao Mei , Zhang Long , Wei Quhao , Liu Weiwei 

TITLE=Polymorphisms of Gene Cassette Promoters of the Class 1 Integron in Clinical Proteus Isolates

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.00790

DOI=10.3389/fmicb.2019.00790

ISSN=1664-302X

ABSTRACT=<sec><title>Objective</title><p>To describe the polymorphisms of gene cassette promoters of the class 1 integron in clinical <italic>Proteus</italic> isolates and their relationship with antibiotic resistance.</p></sec><sec><title>Methods</title><p>Polymorphisms of the gene cassette promoter in 153 strains of <italic>Proteus</italic> were analyzed by PCR and nucleotide sequencing. Variable regions of atypical class 1 integrons were detected by inverse PCR and nucleotide sequencing. Enterobacterial repetitive intergenic consensus (ERIC)-PCR was used to analyze the phylogenetic relationships of class 1 integron-positive clinical <italic>Proteus</italic> isolates. Representative beta-lactamase genes (<italic>bla</italic>), including <italic>bla</italic><sub>TEM</sub>,<italic>bla</italic><sub>SHV</sub>,<italic>bla</italic><sub>CTX-M-1</sub>,<italic>bla</italic><sub>CTX-M-2</sub>,<italic>bla</italic><sub>CTX-M-8</sub>,<italic>bla</italic><sub>CTX-M-9</sub>,<italic>bla</italic><sub>CTX-M-25</sub> and <italic>bla</italic><sub>OXA-1</sub>, and plasmid-mediated quinolone resistance (PMQR) genes including <italic>qnrA, qnrB, qnrC, qnrD, qnrS, oqxA, oqxB, qepA</italic>, and <italic>aac(6′)-Ib</italic> were also screened using PCR and sequence analysis.</p></sec><sec><title>Results</title><p>Fifteen different gene cassette arrays and 20 different gene cassettes were detected in integron-positive strains. Of them, <italic>aadB-aadA2</italic> (37/96) was the most common gene cassette array. Two of these gene cassette arrays (<italic>estX-psp-aadA2-cmlA1, estX-psp-aadA2-cmlA1-aadA1a-qacI-tnpA-sul3</italic>) have not previously been reported. Three different Pc-P2 variants (PcS, PcW<sub>TGN-10</sub>, PcH1) were detected among the 96 <italic>Proteus</italic> strains, with PcH1 being the most common (49/96). Strains carrying the promoters PcS or PcW<sub>TGN-10</sub> were more resistant to sulfamethoxazole, gentamicin and tobramycin than those carrying PcH1. Strains with weak promoter (PcH1) harbored significantly more intra- and extra-integron antibiotic resistance genes than isolates with strong promoter (PcW<sub>TGN-10</sub>). Further, among 153 isolates, representative beta-lactamase genes were detected in 70 isolates (<italic>bla</italic><sub>TEM-1</sub>, 54; <italic>bla</italic><sub>OXA-1</sub>, 40; <italic>bla</italic><sub>CTX-M-3</sub>, 12; <italic>bla</italic><sub>CTX-M-14</sub>, 12; <italic>bla</italic><sub>CTX-M-65</sub>, 5; <italic>bla</italic><sub>CTX-M-15</sub>, 2) and representative PMQR genes were detected in 87 isolates (<italic>qnrA</italic>, 6; <italic>qnrB</italic>, 3; <italic>qnrC</italic>, 5; <italic>qnrD</italic>, 46; <italic>qnrS</italic>, 5; <italic>oqxA</italic>, 7; <italic>aac(6′)-Ib</italic>, 13; <italic>aac(6′)-Ib-cr</italic>, 32).</p></sec><sec><title>Conclusion</title><p>To the best of our knowledge, this study provides the first evidence for polymorphisms of the class 1 integron variable promoter in clinical <italic>Proteus</italic> isolates, which generally contain relatively strong promoters. Resistance genotypes showed a higher coincidence rate with the drug-resistant phenotype in strong-promoter-containing strains, resulting in an ability to confer strong resistance to antibiotics among host bacteria and a relatively limited ability to capture gene cassettes. Moreover, strains with relatively weak integron promoters can “afford” a heavier “extra-integron antibiotic resistance gene load”. Furthermore, the gene cassettes <italic>estX</italic>, <italic>psp</italic> and the gene cassette arrays <italic>estX-psp-aadA2-cmlA1, estX-psp-aadA2-cmlA1-aadA1a-qacI-tnpA-sul3</italic> have been confirmed for the first time in clinical <italic>Proteus</italic> isolates. Beta-lactamase genes and PMQR were investigated, and <italic>bla</italic><sub>TEM-1</sub> and <italic>bla</italic><sub>OXA-1</sub> were the most common, with <italic>qnrD</italic> and <italic>aac (6′)-Ib-cr</italic> also being dominant.</p></sec>