Antibiotic Susceptibilities And Virulence Genes Of Clinically Isolated Salmonella Enterica Serovars Schwarzengrund

Objective: Investigating antimicrobial resistance,molecular typing,virulence genes of Salmonella Schwarzengrund(S.Schwarzengrund)and clinical characteristics of patients infected by S.Schwarzengrund to provide evidences for learning the etiological characteristics,developing prevention and control measures of S.Schwarzengrund infection and rational use of antibiotics.Methods: 1.The clinical data were recorded from patients with acute diarrhea who received treatment in the Second Hospital of Tianjin Medical University between May and October 2014.And their stool samples were collected for the culture of pathogenic baterica,isolation and identification of Salmonella with biochemical tests and serotyping studies.2.Susceptibility to 11 antimicrobial agents of S.Schwarzengrund infection was performed as Kirbty-Bauer and MIC determination.3.Multi-locus sequence typing(MLST): seven housekeeping genes(thr A,pur E,suc A,his D,aro C,hem D,dna N)of S.Schwarzengrund were amplified,sequenced and analyzed.The nucleotide sequences were unloaded to MLST database to confirm the allele number and sequence type(ST).4.Pulsed-field gel electrophoresis(PFGE): S.Schwarzengrund isolates were analyzed by pulsed-field gel electrophoresis with restriction enzyme Xba I.PFGE patterns of isolates were clustered by Bio Numerics software.5.To analyze clinical history and features of 16 patients with S.Schwarzengrund infection and the association between clinical characteristics and molecular typing of isolates.6.Virulence gene PCRs: the representative genes of SPI1~5(inv A,sit C,hil A,sse L,sif A,mgt C,sii E,sop B),virulent plasmids(pef A,prot6 E,spv B)and the regulatory gene(pho P)were detected by PCR with specific primers.Results: 1.A total of 108 non-repetitive non-typhoidal Salmonella isolates were collected,14.8 %(16 isolates)of which were S.Schwarzengrund.2.The susceptible rates to 11 antimicrobial agents were 100 % in 16 S.Schwarzengrund strains.3.All 16 isolates of S.Schwarzengrund showed identical MLST type which was ST241.The allelic profile of 7 housekeeping genes(thr A,pure,suc A,his D,aro C,hem D,dna N)were 43?47?49?16?41?15 and 3,respectively.4.With the criterion of 100 % similarity,3 different PFGE patterns were found among the 16 isolates of S.Schwarzengrund including A pattern 14 strains,B pattern 1 strain and C pattern 1 strain.The similarity between A and B was 94.2 % and among A,B,and C was77.8 %.5.Among the 16 patients infected by S.Schwarzengrund,10 were male and 6 were female.The median age was 35.5 years old.All cases reported acute diarrhea and 1 case with high fever.13 patients were diagnosed with acute gastroenteritis and 3 bacillary dysenteries.8 patients who ate the same food got illness during June 17 th to 19 th,2014,and S.Schwarzengrund strains isolated from them showed identical A pattern of PFGE.6.All 16 isolates of S.Schwarzengrund were positive for the representative genes carried by SPI1~5 and the regulatory gene(pho P)but negative for pef A,prot6 E and spv B which were located on plasmids.Conclusions: 1.Multiple clinical cases infected by S.Schwarzengrund occurred in Tianjin in 2014,which contained an outbreak.2.ST241 S.Schwarzengrund clinical isolates with multiple PFGE patterns in this study were susceptible to common antibiotics but carried SPI1~5 and regulatory genes,suggesting their high virulence and public health threats.3.Attention should be paid to the tendency and threat of clinical S.Schwarzengrund infection and continuous surveillance and investigation should be performed.