| Glaesserella parasuis?G.parasuis?is an opportunistic pathogen that colonizes the porcine upper respiratory tract and is the etiological agent of Gl?sser's disease.However,the structural organization of genetic information,antibiotic resistance genes,potential pathogenicity,and evolutionary relationships among global G.parasuis strains remain unclear.The aim of this study was to better understand patterns of genetic variation,antibiotic resistance factors,and virulence mechanisms of this pathogen,so as to guide the prevention and treatment of disease caused by G.parasuis.In this study,we sequenced a multidrug-resistant isolate from diseased swine in Dongguan,China,then compared this genome sequence with those of 54 isolates from China sequenced by us and 39 strains sequenced by other researchers in order to improve our understanding of genomic diversity in G.parasuis.In addition,comparative genome analyses were used to identify genomic differences between two phenotypically distinct isolates with same serotype and close relationship.The results are as follows:1.The genomic feature of G.parasuis HPS-1 contained one circular chromosome of2 326 414 bp with a 40.03%GC content,a total of 2 288 predicted open reading frames?ORFs?,and a circular plasmid of 7 777 bp which could encode seven genes,including bla ROB-1and aac?6'?-Ie-aph?2''?-Ia,which confer to?-lactams and aminoglycosides resistance.2.Multilocus sequence typing?MLST?analysis assigned the 94 G.parasuis isolates to70 different STs,including 42 new STs.Most?85.13–91.74%?of the genetic variation between G.parasuis isolates was observed in the accessory genomes.The results of this study enrich the G.parasuis MLST databases and highlight the wide distribution of G.parasuis strains.Phylogenetic trees based on single-copy core genes and whole-genome single nucleotide polymorphisms?SNPs?both resolved two well-supported lineages and both contained both Asian and North American isolates.Besides,the trees showed that G.parasuis HPS-1 and HPS-2 were closely related,both isolated from Guangdong province.Novel virulence factors?gig P,mal Q,and gmh A?and drug resistance genes?nor A,bac A,ksg A,and bcr?in G.parasuis were identified.Resistance determinants?sul2,aph?3''?-Ib,nor A,bac A,ksg A,and bcr?were widespread across isolates,regardless of serovar,isolation source,or geographical location.3.A comparative genomic analysis of a multidrug-resistant isolate HPS-1 and a susceptible isolate HPS-2 showed that these two isolates are closely related,although there was a large-scale genomic rearrangement.The 14.7%and 13.5%strain-specific genes were detected for HPS-1 and HPS-2,respectively.Notably,only the two genes bla ROB-1and aac?6'?-Ie-aph?2''?-Ia in a plasmid were specific to HPS-1 by investigation of antibiotic resistance genes.Nonsynonymous SNPs in resistance genes aph?3''?-Ib,fus A,rpo C and rpo B were observed and some of mutations have been reported.4.The p YL1 transformed into S.aureus isolate RN4220 at a frequency of 10-9cells per recipient cell by electroporation.The transformants had increased MICs for oxacillin,gentamicin,amikacin,kanamycin,and streptomycin as compared with those of the parental strain.This finding indicated that plasmid p YL1 contributed to the?-lactam resistance and aminoglycoside antibiotic resistance in G.parasuis HPS-1. |
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