| The emergence of new oxazolidinone resistance gene optr A after multi-resistance gene cfr, as the second transferable resistance gene, has received great attention. Meanwhile The different resistance mechanism and the characteristic of resistant to oxazolidinones and phenicols also attracted people's attention. This study was carried out to investigate the epidemic characteristics of optr A among different species from pigs, the soil, and workers in close contact with them in a farm in Guang dong.513 samples collected from a farm in Guangdong, China in 2015, including252 samples from the pig nasal swab, 241 samples from the pig rectal swab, 12 samples from the soil and 8 samples from human. Whole genome DNA was screened for optr A gene by polymerase chain reaction(PCR) amplification. As a result, 86 samples were screened by using selective medium supplemented with 10?g/m L florfenicol, meanwhile optr A-positive isolates were obtained by PCR and sequencing. The species were identified by 16 S r RNA amplification and sequencing. The results showed that 17 optr A positive strains were obtained, including 11 Enterococcus species(2 Enterococcus faecalis, 3Enterococcus faecium, 2 Enterococcus durans, 4 Enterococcus gallinarum) and 6 Proteus mirabilis.The 17 optr A-positive isolates were tested for their susceptibility to commonly clinical used antimicrobial agents by broth microdilution. The results showed that all the 17 optr A-positive isolates were resistant to commonly clinical used broad-spectrum antibiotic(tetracycline and florfenicol). Of the 17 optr A-positive isolates, 11 optr A-positive Enterococcus species were resistant to erythromycin, amoxicillin and gentamycin, but were susceptible to vancomycin. The resistance rates of ampicillin, ciprofloxacin,chloramphenicol, linezolid and penicillins were more than 50.0%. 6 optr A-positive Proteus mirabili were resistant to doxycycline, ampicillin, cefazolin, imipenem, strepomycin,tetracycline and trimethoprim/sulfamethoxazole and the resistance rates of gentamycin and cefotaxime were over 60.0%. Additionally, the resistance rates of the rest were between30.0% to 50.0%.The 17 optr A-carrying isolates were screened for resistance genes by PCR. The vancomycin-resistant-related genes(van A, van B, van C), erythromycin resistance-associated gene(erm C) and the ATP efflux pump gene(msr A/msr B) were negative. However, The positive rate of multi-resistance gene cfr and florfenicol resistant gene fex A, fex B and flo R were 35.3%, 70.6%, 52.9% and 29.4%, respectively. The relatively prominent gene was erm A(88.2%) and erm B(82.4%), which were almost consistent with the resistant phenotype.The optr A-carrying Enterococcus faecalis(2) and Enterococcus faecium(3) isolated from pigs were characterized by multilocous sequence typing(MLST). 4 sequence types were yielded of 5 strains, ST116, ST480, ST486 and ST874, respectively. Pulsed-field gel electrophoresis(PFGE) was carried out to analyze the clonal relatedness of 17 optr A-positive isolates. The 11 optr A-carrying Enterococcus species obtained 10 different patterns and 6 optr A-carrying Proteus mirabilis had 4 different patterns with 1 failed in typing. S1-PFGE-Southern results showed that optr A of Enterococcus species was harbored in plasmid DNA(9 isolates) and chromosomal DNA(1 isolates). Meanwhile the cfr of Enterococcus species was harbored in the different plasmid DNA.In summary, The oxazolidinone resistance gene optr A may be transferable in Enterococcus species from pigs and soil in pig farm. |
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