Barg N L, Hutson F S, Wheeler L A, Thomson C J, Amyes S G, Wharton M, Schaffner W
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee.
J Infect Dis. 1990 Aug;162(2):466-73. doi: 10.1093/infdis/162.2.466.
Two strains of trimethoprim-resistant Shigella sonnei bearing R plasmids pBH600 and pBH700 each elaborated a dihydrofolate reductase (DHFR) and were moderately resistant to trimethoprim (minimum inhibitory concentrations, 128 and 256 micrograms/ml, respectively). Neither plasmid hybridized to probes for DHFR types I, II, or III. The trimethoprim resistance genes from the R plasmids resided on a 1600-base pair (bp) PstI fragment of pBH600 and an 1800-bp PstI fragment of pBH700. Isoelectric focusing showed distinct isoelectric points for the enzymes coded for on pBH600 (5.3) and pBH700 (5.6-5.7). Trimethoprim-resistant S. sonnei from 10 locations in nine states were examined. Isolates from 8 locations hybridized only to a pBH700-derived probe and one isolate hybridized to a pBH600-derived probe. These two trimethoprim resistance genes appear novel. The gene on plasmid pBH700 codes for an enzyme that seems widespread among S. sonnei isolates in the USA.
携带R质粒pBH600和pBH700的两株耐甲氧苄啶宋内志贺菌分别产生了一种二氢叶酸还原酶（DHFR），并且对甲氧苄啶具有中度抗性（最小抑菌浓度分别为128和256微克/毫升）。这两种质粒均未与I型、II型或III型DHFR的探针杂交。来自R质粒的甲氧苄啶抗性基因位于pBH600的一个1600碱基对（bp）的PstI片段和pBH700的一个1800 bp的PstI片段上。等电聚焦显示pBH600（5.3）和pBH700（5.6 - 5.7）编码的酶具有不同的等电点。对来自九个州10个地点的耐甲氧苄啶宋内志贺菌进行了检测。来自8个地点的分离株仅与pBH700衍生的探针杂交，一个分离株与pBH600衍生的探针杂交。这两个甲氧苄啶抗性基因似乎是新的。质粒pBH700上的基因编码一种在美国宋内志贺菌分离株中似乎广泛存在的酶。
