title: Unusual association of a plasmid with nalidixic acid resistance in an epidemic strain of Shigella dysenteriae type 1 from Asia.
abstract: 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.
authors.affiliation: Bacterial Genetics Laboratory, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka.
authors.forename: M M
authors.initials: MM
authors.lastname: Ashraf
authors.forename: Z U
authors.initials: ZU
authors.lastname: Ahmed
authors.forename: D A
authors.initials: DA
authors.lastname: Sack
mesh_terms: D001208:Asia / Q000453:epidemiology; D004196:Disease Outbreaks; D004352:Drug Resistance, Microbial / Q000235:genetics; D004405:Dysentery, Bacillary / Q000453:epidemiology / Q000382:microbiology; D006801:Humans; D009268:Nalidixic Acid / Q000494:pharmacology*; D010957:Plasmids; D012762:Shigella dysenteriae / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D009268:Nalidixic Acid