創傷弧菌為海洋性革蘭氏陰性菌，可以在人類和鰻魚造成疾病。只有一部分的創傷弧菌對於鰻魚是有致病力的，而這類的創傷弧菌被歸類為生物二型。這一型的創傷弧菌對鰻魚的致病力是由一普遍存在於此型菌株內的質體所帶來的。過去的研究發現，生物二型毒力質體本身雖然不會散播至其他細菌，但可以在另一存在於大多數生物二型菌株內之接合質體的幫助下，在此型菌株間以約10-2的頻率傳送。在本研究中，我探討了生物二型毒力質體pR99由一株生物二型野生株CECT4999轉移至三株生物一型臨床株SW058、SW059、YJ016和三株生物一型環境株CG024、CG027、CG028的頻率。為了方便篩選出帶有毒力質體pR99、接合質體pC4602-1，或兩者兼具之接合株(transconjugants)，我們將氯黴素抗藥基因cat和安比西林(ampicillin)抗藥(Apr)基因分別插入pR99和pC4602-1中。結果顯示，pR99::cat確實可以由生物二型菌株傳送至生物一型環境株和臨床中。pR99::cat或者是pR99::cat和pC4602-1::Apr兩者同時轉移的頻率在CG024、CG028、SW059約為10-3，在另三株則約為10-5~10-6。將帶有pC4602-1::Apr之YJ016接合菌株和YJ016進行接合作用後，發現該質體之轉移頻率並沒有提高，排除了限制修飾系統(restriction modification)阻礙pC4602-1::Apr轉移的可能性。此外，和生物二型野生株CECT4999相比，帶有pR99::cat之接合株對鰻魚血清的殺菌作用只有部分的抗性。進一步觀察pR99質體套數和此質體上一傳遞對鰻魚血清的抗性之基因vep07 的mRNA的表現量，發現均與CECT4999相似。然而，部份接合株的外膜上Vep07的表現量較CECT4999低許多，其它的接合株則是和CECT4999相當。此外，將生物一型接合株HC131和HC147的vep07刪除，並不影響此兩菌株對鰻魚血清中的抗性。由此推測，Vep07可能與生物一型接合株對鰻魚血清的抗性無關。

Vibrio vulnificus, a gram-negative estuarine bacterial species, is pathogenic to humans and eels. Only a fraction of V. vulnificus strains, classified as biotype (BT) 2, is virulent for the eel, and the virulence is conferred by a common plasmid in the BT2 strains. It has been shown previously that the BT2 virulence plasmid, though itself is not transmissible, could be transferred between the BT2 strains with a frequency of about 10-2 in the presence of a conjugative plasmid found in most of BT2 strains. In this study, we investigated the transmissibility of a BT2 virulence plasmid, pR99 possessed by strain CECT4999, to three clinical BT1 strains, SW058, SW059 and YJ016, and three environmental BT1 isolates, CG024, CG027 and CG028. The plasmids pR99 and pC4602-1, a BT2 conjugative plasmid, were inserted with chloramphenicol- and ampicillin-resistance cassettes, respectively, for the selection of transconjugants with either or both plasmids. The results indicate that pR99 could be transferred from a BT2 strain into both environmental and clinical BT1 isolates. The frequency of transferring pR99 alone or both pR99 and pC4602-1 were about 10-5~10-6 except for CG024, CG028 and SW059, which showed a frequency of about 10-3. The role of restriction modification systems in preventing uptake of the BT2 plasmid pC4602-1 by the BT1 strains has been excluded as the conjugation frequency of transferring this plasmid from the transconjugant of strain YJ016 back to YJ016 was not elevated. Compared to the BT2 strain, CECT4999, the pR99-possessing BT1 derivatives were only partially resistant to eel serum killing effect. The copy number of pR99 and the mRNA level of vep07, a gene in pR99 that confers the resistance to eel serum, in the BT1 transconjugants were similar to those in strain CECT4999. However, some transconjugants expressed much less Vep07 than strain CECT4999 on the outer membrane while the others expressed similar amount of Vep07 to that of CECT4999. In addition, deletion of vep07 in BT1 transconjugants HC131 and HC147 did not affect the resistance of these two strains to eel serum. These results suggest that Vep07 may not be associated with the resistance of BT1 transconjugants to eel serum killing effect.

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