Escande F, Gerbaud G, Martel J L, Courvalin P
Unité d'Ecologie Bactérienne, Centre National des Pasteurella, Institut Pasteur, Paris, France.
Vet Microbiol. 1991 Jan;26(1-2):107-14. doi: 10.1016/0378-1135(91)90047-j.
Thirteen strains of Pasteurella haemolytica resistant to moderate levels of trimethoprim (MICs from 8 to 64 micrograms/ml) and 0/129 (MICs from 16 to 64 micrograms/ml) were isolated from bovine specimens. Two strains, CNP330 and CNP334, were studied and found to harbour various plasmids but all attempts to cure trimethoprim resistance were unsuccessful. Resistance characters were not transferable to Escherichia coli or to Pasteurella multocida by conjugation and to E. coli by transformation. The resistance gene(s) was therefore tentatively assigned to a chromosomal location and cloned into E. coli where it conferred trimethoprim resistance. Trans-complementation analysis of a dihydrofolate reductase-deficient mutant of E. coli showed that trimethoprim resistance was secondary to synthesis of a dihydrofolate reductase. DNA/DNA hybridization of the hybrid plasmid and of strains CNP330 and CNP334 with probes specific for dihydrofolate reductase types I to V were negative, indicating that cross-resistance to trimethoprim and 0/129 in P. haemolytica was due to the acquisition by P. haemolytica of a new resistance determinant.
从牛标本中分离出13株对中等水平甲氧苄啶具有抗性（最低抑菌浓度为8至64微克/毫升）和0/129（最低抑菌浓度为16至64微克/毫升）的溶血巴斯德菌。对两株菌CNP330和CNP334进行了研究，发现它们含有各种质粒，但所有消除甲氧苄啶抗性的尝试均未成功。抗性特征不能通过接合转移至大肠杆菌或多杀巴斯德菌，也不能通过转化转移至大肠杆菌。因此，抗性基因初步定位在染色体上，并克隆到大肠杆菌中，在那里它赋予了甲氧苄啶抗性。对大肠杆菌二氢叶酸还原酶缺陷型突变体的反式互补分析表明，甲氧苄啶抗性是由于二氢叶酸还原酶的合成所致。用针对I至V型二氢叶酸还原酶的探针，对杂交质粒以及CNP330和CNP334菌株进行DNA/DNA杂交，结果均为阴性，这表明溶血巴斯德菌对甲氧苄啶和0/129的交叉抗性是由于溶血巴斯德菌获得了一种新的抗性决定簇。
