Plasmid and restriction endonuclease patterns in Pasteurella multocida isolated from a swine pyramid Xavier Ru´bies a,* , Jordi Casal b , Carlos Pijoan c a Laboratorios HIPRA S.A., Av. La Selva No. 135, 17170 Amer Girona, Spain b Facultat de Veterina`ria, Patologia Infecciosa i Epidemiologia, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Barcelona, Spain c Clinical and Population Sciences, University of Minnesota, 1988 Fitch Avenue, St. Paul, MN 55108, USA Received 28 September 2000; received in revised form 15 June 2001; accepted 7 July 2001 Abstract Restriction endonuclease analysis (REA) and plasmid profile were used to study the epidemiology of Pasteurella multocida in a swine pyramid structure. The studied pyramid was comprised of a group of 12 swine farrow-to-finish farms related by unidirectional animal movement. P. multocida isolates were obtained from the lungs of 275 slaughtered pigs. Serotyping was performed by hyaluronidase sensitivity test and toxicity was investigated by the ELISA test. HpaII was used to cleave the P. multocida extracted DNA. REA patterns relationships were studied using the Sokal–Michener coefficients, and the dendrogram was built using the UPGMA system. The 218 P. multocida isolates obtained were distributed in 17 REA patterns. In 9 of the 12 farms studied only 2–3 REA patterns were detected, with one clearly predominant pattern. The 81 strains with plasmids were assigned to six plasmid profiles. REA and plasmid profiles proved to be good epidemiological tools for identifying different strains of P. multocida with the same phenotype. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Pasteurella multocida; Swine; REA patterns; Plasmid 1. Introduction Pasteurella multocida plays a central role in pneumonic pasteurellosis, which is one of the most common and costly diseases in pigs (Pijoan, 1992). P. multocida is considered as a secondary agent that follows primary infections with other agents (Pijoan, 1992). It has Veterinary Microbiology 84 (2002) 69–78 * Corresponding author. Tel.: þ34-72-430660; fax: þ34-72-430661. E-mail address: xrf@hipra.com (X. Ru´bies). 0378-1135/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0378-1135(01)00440-0