Ahmed H J, Svensson L A, Cope L D, Latimer J L, Hansen E J, Ahlman K, Bayat-Turk J, Klamer D, Lagergård T
Department of Medical Microbiology and Immunology, University of Göteborg S-413 46 Göteborg, Sweden and *Department of Microbiology, Southwestern Medical Center, University of Texas, Dallas, USA.
J Med Microbiol. 2001 Oct;50(10):860-864. doi: 10.1099/0022-1317-50-10-860.
The aim of this study was to investigate the presence of the three cdtABC genes responsible for production of cytolethal distending toxin (CDT) in Haemophilus ducreyi and Actinobacillus actinomycetemcomitans strains. Of 100 H. ducreyi strains from the culture collection of the University of Göteborg (CCUG), 27 strains with low or intermediate cytotoxic titre (< 1 in 10(4)) and 23 of the remaining isolates with a high cytotoxic titre (> or = 1 in 10(4)) were selected. Twenty-nine strains of H. ducreyi were isolated recently from patients with chancroid and 50 A. actinomycetemcomitans strains from patients with periodontitis. The cytotoxic activity on HEp-2 cells and the presence of cdtABC genes were studied by cytotoxicity assay of bacterial sonicates and PCR with primers specific for individual cdtA, B, and C genes of H. ducreyi in bacterial DNA preparations, respectively. All strains that manifested a cytotoxic titre in sonicate > or = 1 in 100 possessed all the three cdt genes. Eighteen of the 50 strains selected from the culture collection were negative and 32 positive for cdt genes. As all strains with a high cytotoxic titre gave positive PCR results, it can be assumed that the remaining 50 strains, which have high cytotoxic titre, would have been positive as well. Thus, it can be estimated that 82% of the culture collection strains had cdtABC genes. Similarly, 24 (83%) of 29 recent H. ducreyi isolates expressed the CDT activity and displayed all cdtABC genes. Forty-three (86%) of 50 strains of the closely related A. actinomycetemcomitans, expressing a cytotoxic activity > or = 1 in 100, also possessed all three genes. Furthermore, the nucleotide sequence of the cdtABC genes was highly conserved among H. ducreyi strains from different geographic areas. These results indicate that the majority of pathogenic H. ducreyi and A. actinomycetemcomitans strains express a CDT activity encoded by all three cdtABC.
本研究旨在调查引起细胞致死性膨胀毒素（CDT）产生的三种cdtABC基因在杜克雷嗜血杆菌和伴放线放线杆菌菌株中的存在情况。从哥德堡大学培养物保藏中心（CCUG）的100株杜克雷嗜血杆菌中，选择了27株细胞毒性滴度低或中等（<1/10⁴）的菌株以及其余23株细胞毒性滴度高（≥1/10⁴）的分离株。最近从软下疳患者中分离出29株杜克雷嗜血杆菌，从牙周炎患者中分离出50株伴放线放线杆菌。分别通过细菌超声裂解物的细胞毒性测定以及在细菌DNA制剂中使用针对杜克雷嗜血杆菌单个cdtA、B和C基因的特异性引物进行PCR，研究了对HEp-2细胞的细胞毒性活性和cdtABC基因的存在情况。所有超声裂解物中细胞毒性滴度≥1/100的菌株均具有全部三种cdt基因。从培养物保藏中心选择的50株菌株中，18株cdt基因呈阴性，32株呈阳性。由于所有细胞毒性滴度高的菌株PCR结果均为阳性，可以推测其余50株细胞毒性滴度高的菌株也会呈阳性。因此，可以估计培养物保藏中心82%的菌株具有cdtABC基因。同样，29株近期分离的杜克雷嗜血杆菌中有24株（83%）表达了CDT活性并显示出全部cdtABC基因。50株密切相关的伴放线放线杆菌中，43株（86%）细胞毒性活性≥1/100，也具有全部三种基因。此外，不同地理区域的杜克雷嗜血杆菌菌株中，cdtABC基因的核苷酸序列高度保守。这些结果表明，大多数致病性杜克雷嗜血杆菌和伴放线放线杆菌菌株表达由全部三种cdtABC编码的CDT活性。
