Genetic characterization of Streptococcus phocae strains isolated from Atlantic salmon, Salmo salar L., in Chile I ValdØs 1 , B Jaureguiberry 1 , J L Romalde 2 , A E Toranzo 2 , B MagariÇos 2 and R AvendaÇo-Herrera 1 1 Laboratorio de Investigacio ´n y Desarrollo-Veterquı ´mica, Cerrillos, Santiago, Chile 2 Departamento de Microbiologı ´a y Parasitologı ´a, Facultad de Biologı ´a-CIBUS and Instituto de Acuicultura, Universidad de Santiago de Compostela, Spain Abstract Streptococcus phocae is a beta-haemolytic bacterium frequently involved in disease outbreaks in seals causing pneumonia or respiratory infection. Since 1999, this pathogen has been isolated from diseased Atlantic salmon, Salmo salar, causing serious eco- nomic losses in the salmon industry in Chile. In this study, we used different molecular typing methods, such as pulsed-field gel electrophoresis (PFGE), randomly amplified polymorphic DNA (RAPD), enterobacterial repetitive intergenic consensus se- quence PCR (ERIC-PCR), repetitive extragenic palindromic PCR (REP-PCR) and restriction of 16S–23S rDNA intergenic spacer regions to eval- uate the genetic diversity in S. phocae. Thirty-four strains isolated in different years were analysed. The S. phocae type strain ATCC 51973 T was included for comparative purposes. The results demonstrated genetic homogeneity within the S. phocae strains isolated in Chile over several years, suggesting the existence of clonal relationships among S. phocae isolated from Atlantic salmon. The type strain ATCC 51973 T presented a different genetic pattern with the PFGE, RAPD, ERIC-PCR and REP-PCR methods. However, the fingerprint patterns of two seal isolates were distinct from those of the type strain. Keywords: Streptococcus phocae, Salmo salar, strep- tococcosis, genotyping, Chile. Introduction The beta-haemolytic Streptococcus phocae is the aetiological agent of a serious bacterial disease affecting different species of seal in several countries of northwest Europe and the Caspian Sea, causing pneumonia or respiratory infection (Skaar, Gaus- tad, Tonjum, Holm & Stenwing 1994; Henton, Zapke & Basson 1999; Raverty & Fiessel 2001; Vossen, Abdulmawjood, La ¨mmler, Weiß & Siebert 2004; Kuiken, Kennedy, Barret, Van de Bildt, Borgsteede, Brew, Codd, Duck, Deaville, Eybatov, Forsyth, Foster, Jepson, Kydyrmanov, Mitrafanov, Ward, Wilson & Osterhaus 2006). Streptococcus phocae had been isolated exclusively from pinni- peds, until Gibello, Mata, Blanco, Casamayor, Domı ´nguez & Ferna ´ndez-Garayzabal (2005) iden- tified strains from the FRS Marine Laboratory bacterial collection (Aberdeen, Scotland) and orig- inally isolated from Atlantic salmon, Salmo salar L., as belonging to this bacterial species. Since 1999, economic losses caused by streptococcal infections in Chile have decreased; however, S. phocae remains one of the most important risk factors in the salmon industry in Chile during the summer months (Romalde, Ravelo, Valde ´s, Magarin ˜os, de la Fuente, San Martı ´n, Avendan ˜o-Herrera & Toranzo 2008). Numerous studies report that S. phocae consti- tutes a biochemically homogeneous taxon with typical characteristics useful in the identification of this pathogen (Skaar et al. 1994; Gibello et al. 2005). Serological analysis demonstrated antigenic heterogeneity within this species, with the seal isolates classified into LancefieldÕs serogroups C and F (Skaar et al. 1994; Vossen et al. 2004). Previous Journal of Fish Diseases 2009, 32, 351–358 doi:10.1111/j.1365-2761.2008.01014.x Correspondence Dr R Avendan ˜o-Herrera, Laboratorio de Investigacio ´ n y Desarrollo-Veterquı ´mica, Camino Melipilla 5641, Cerrillos, Santiago, Chile (e-mail: reavendano@yahoo.com) 351 Ó 2009 The Authors. Journal compilation Ó 2009 Blackwell Publishing Ltd