Ashraf M M, Ahmed Z U, Sack D A
Bacterial Genetics Laboratory, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka.
Can J Microbiol. 1991 Jan;37(1):59-63. doi: 10.1139/m91-009.
The association of a 20-MDa plasmid with nalidixic acid resistant (Nalr) strains of Shigella dysenteriae 1 has been examined. The plasmid, which is readily transferable, does not itself code for nalidixic acid resistance but offers a survival advantage to its host under nalidixic acid stress. The plasmid-containing cultures of S. dynsenteriae 1 produced Nalr mutants in vitro at a frequency 1000-fold higher than their plasmidless parent strains, after two exposures to nalidixic acid. Using a similar procedure, mutants resistant to other antibiotics such as chloramphenicol, tetracycline, or ciprofloxacin could not be isolated. The genome of S. dysenteriae 1 appears to carry a heavy load of the insertion sequence IS1. The propensity of the plasmid-containing strains to readily mutate to nalidixic acid resistance and its possible relevance to the observed association of the plasmid with Nalr clinical isolates is discussed.
对一个20兆道尔顿的质粒与痢疾志贺氏菌1型耐萘啶酸（Nalr）菌株之间的关联进行了研究。该质粒易于转移，其本身并不编码对萘啶酸的抗性，但在萘啶酸胁迫下能为宿主提供生存优势。在两次暴露于萘啶酸后，含该质粒的痢疾志贺氏菌1型培养物在体外产生耐萘啶酸突变体的频率比其无质粒亲代菌株高1000倍。使用类似的程序，无法分离出对其他抗生素如氯霉素、四环素或环丙沙星耐药的突变体。痢疾志贺氏菌1型的基因组似乎携带大量插入序列IS1。讨论了含质粒菌株易于突变为耐萘啶酸的倾向及其与观察到的质粒与耐萘啶酸临床分离株之间关联的可能相关性。
