Functional and molecular characterization of pSE34 encoding a type IV secretion system in Salmonella enterica serotype Enteritidis phage type 34.
Salmonella enterica serotype Enteritidis infection remains a serious public health threat to humans. Salmonella Enteritidis phage type 4 (PT4) is a clone that has already caused a global pandemic for years. To investigate why PT34 becomes a subdominantly emerging phage type, molecular characterizations, including serotyping, pulsed-field gel electrophoresis (PFGE), phage typing, and plasmid profiling, were carried out on PT34. The results indicated that relative to PT4, PT34 contained an additional 32-kb DNA segment in PFGE and a 33-kb plasmid pSE34 in plasmid profiling. Southern blot hybridization showed that the DNA segment was the major part of pSE34. All of the S. Enteritidis PT34 clinical isolates possessed pSE34, while PT4 and PT21 did not. Sequencing analysis revealed that pSE34 is 32 950 bp long, with a G+C% content of 41.2%, and contains a total of 53 orfs. Transposon mutagenesis demonstrated that taxB, taxC, and the pilX operon on this plasmid participated in the process of conjugation. In virulence testing, PT34 that harbored pSE34, compared with PT4, showed no increased invasion to tissue culture cells in vitro. The presence of conjugative pSE34 in PT4 caused the conversion of phage type from PT4 to PT34, suggesting that the emergence of PT34 was a result of the introduction of the conjugative pSE34 into its common progenitor PT4.
Chen
Chyi-Liang
CL
Molecular Infectious Diseases Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
Wang
Chen-Yu
CY
Chu
Chishih
C
Su
Lin-Hui
LH
Chiu
Cheng-Hsun
CH
D001426:Bacterial Proteins / Q000235:genetics*; D001434:Bacteriophage Typing; D001482:Base Composition; D016172:DNA Fingerprinting; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D005798:Genes, Bacterial; D005838:Genotype; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016366:Open Reading Frames; D010957:Plasmids / Q000032:analysis / Q000235:genetics*; D012480:Salmonella Infections / Q000382:microbiology; D012477:Salmonella enteritidis / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D017422:Sequence Analysis, DNA; D012703:Serotyping; D037521:Virulence Factors / Q000235:genetics*
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D037521:Virulence Factors