title: Instability of multiple drug resistance plasmids in Salmonella typhimurium isolated from poultry.
abstract: Plasmids in five strains of Salmonella typhimurium resistant to ampicillin, chloramphenicol, gentamicin, neomycin/kanamycin, streptomycin, sulphonamides, tetracyclines and trimethoprim (ACGKSSuTTm), CGKSSuTTm, ACSSuT or CSSuT which had been isolated from poultry in the first 3 months of 1989 have been characterized and compared with plasmids in two strains of R-types ACGKSSuTTm and ASSuTTm isolated from two patients later in the year. With the exception of the human isolate of R-type ASSuTTm, all strains carried two non-conjugative plasmids, one coding for SSu and belonging to incompatibility group Q, and a second coding for multiple resistance and belonging to the FIme incompatibility group. The human isolate of R-type ASSuTTm did not carry the IncQ SSu plasmid but like the poultry isolates, carried a non-conjugative FIme plasmid. Restriction endonuclease digestion with the enzymes EcoR I, Pst I and Hind III demonstrated that the FIme plasmids from strains of different R-types showed a high degree of homology but exhibited numerous fragment size polymorphisms. The restriction digest fingerprint of plasmids in the human isolate of R-type ACGKSSuTTm was indistinguishable from a poultry isolate of the same R-type. Analysis of segregants of one of the poultry isolates of R-type ACGKSSuTTm demonstrated that resistance determinants could be rapidly lost from the FIme plasmid to give rise to a number of R-types and fingerprint patterns. Loss of tetracycline resistance from this plasmid appeared to be correlated with the integration of other plasmid-mediated resistances into the bacterial chromosome. Evidence is presented for the rapid loss of antimicrobial resistance determinants from a multiple resistance plasmid of the FIme incompatibility group in response to withdrawal of antibiotic selective pressure.
authors.affiliation: Division of Enteric Pathogens, Central Public Health Laboratory, London.
authors.forename: D J
authors.initials: DJ
authors.lastname: Brown
authors.forename: E J
authors.initials: EJ
authors.lastname: Threlfall
authors.forename: B
authors.initials: B
authors.lastname: Rowe
mesh_terms: D000818:Animals; D001434:Bacteriophage Typing; D002645:Chickens / Q000382:microbiology; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000032:analysis; D004352:Drug Resistance, Microbial / Q000235:genetics; D006801:Humans; D006877:Hydroxamic Acids / Q000378:metabolism; D007502:Iron Chelating Agents / Q000378:metabolism; D011201:Poultry Diseases / Q000382:microbiology*; D011815:R Factors; D015183:Restriction Mapping; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000145:classification / Q000187:drug effects* / Q000235:genetics; D014422:Turkeys / Q000382:microbiology
chemical_list: D004269:DNA, Bacterial; D006877:Hydroxamic Acids; D007502:Iron Chelating Agents; C031819:aerobactin