title: Plasmid characterization and pulsed-field electrophoretic analysis demonstrate that ampicillin-resistant strains of Salmonella enteritidis phage type 6a are derived from Salm. enteritidis phage type 4.
abstract: Plasmid incompatibility studies have demonstrated that strains of Salmonella enteritidis phage type (PT) 6a resistant to ampicillin possess a 36 megadalton incompatibility group (Inc) X plasmid coding for resistance to ampicillin which is capable of converting strains of Salm. enteritidis belonging to PTs 1 and 4 to PT 6a, and PT 8 to PT 13. However, pulsed-field gel electrophoresis (PFGE) has demonstrated that all clinical isolates of PT 6a have a characteristic XbaI pulsed-field profile which is distinct from that of PT 1 and which can only be differentiated from that of PT 4 by the presence of plasmid-associated fragments of less than 45 kb. It is concluded that ampicillin-resistant strains of Salm. enteritidis PT 6a are derived from strains of Salm. enteritidis PT 4 by acquisition of an Inc X ampicillin resistance plasmid.
authors.affiliation: Laboratory of Enteric Pathogens, Central Public Health Laboratory, London, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Ridley
authors.forename: P
authors.initials: P
authors.lastname: Punia
authors.forename: L R
authors.initials: LR
authors.lastname: Ward
authors.forename: B
authors.initials: B
authors.lastname: Rowe
authors.forename: E J
authors.initials: EJ
authors.lastname: Threlfall
mesh_terms: D000667:Ampicillin / Q000494:pharmacology*; D001434:Bacteriophage Typing / Q000379:methods; D004587:Electrophoresis, Agar Gel; D016521:Electrophoresis, Gel, Pulsed-Field; D010406:Penicillins / Q000494:pharmacology*; D010957:Plasmids; D012483:Salmonella Phages / Q000235:genetics* / Q000302:isolation & purification; D012477:Salmonella enteritidis / Q000187:drug effects / Q000821:virology*
chemical_list: D010406:Penicillins; D000667:Ampicillin