Although Shewanella is usually considered an environmental genus, different clinical infections have appeared in recent years (4, 7). Treatment of such infections is difficult due to the lack of knowledge concerning the natural antimicrobial resistance as well as the recommended antibiotic treatment of their infections (11). The aim of our study was to investigate the antimicrobial resistance mechanisms acquired by this genus in the nosocomial environment. All isolates identified as Shewanella spp. (n 10) by the use of standard biochemical tests were collected in a public hospital of Argentina during 2005 and 2006. Three isolates were identified as Shewanella putrefaciens and seven as Shewanella algae. PCR amplifications using total DNA were performed according to the instructions of the manufacturer (Promega) by the use of specific primers for evaluation of the presence of antimicrobial resistance determinants associated with horizontal gene transfer: (i) integron integrase genes (intI1, intI2, and intI3) (6, 10); (ii) 13 β-lactamase-like genes, namely, the blaOXA-58, blaOXA-48, blaTEM-1, blaCTX-M-2, blaSHV-like, blaSCO-1, blaPER-2, blaGES-like, blaVEB-like, blaIMP-like, blaVIM-like, blaSPM-1, and blaOXA-23 genes (5, 6, 9); and (iii) sul1, sul2, and sul3 genes (1). We found the type 1 integrase gene in 9 isolates, while the type 2 integrase gene was found in 6 isolates (Table 1). Concerning the variable region of class 1 integrons (vr-1), we found the presence of the dfrA1 gene cassette in isolates Sa9, Sa82, and Sa392 and the dfrA1-aadA1 array in isolates Sa74, Sa10, and Sa2 (Table 1). Concerning class 2 integrons, only the variable region of Sa2 harboring dfrA1-sat2-aadA1-orfX-ybfA-ybfB-ybgA, Sa9 harboring dfrA1-sat2, and Sa10 harboring the dfrA1 gene cassette could be identified (Table 1). When we investigated the presence of 13 β-lactamase genes, positive amplification was obtained for the 3 isolates of S. putrefaciens (Table 1) by the use of primers for the amplification of the carbapenemase blaOXA-48 gene previously found harbored in a transposon of a Klebsiella pneumoniae isolate from France (9). No clear contribution of this gene to carbapenem resistances could be established. We found that plasmids were present in 2 out of 10 isolates (Sa2 and Sp95). Given that Shewanella is well known as an environmental genus and that almost all isolates from our study harbored integrons and other relevant determinants of resistance (such as the carbapenemase blaOXA-48) usually associated with horizontal gene transfer, species of this genus could be considered to represent not only a potential reservoir but also a vector of antimicrobial resistance mechanisms in hospital settings and the environment, with transmission occurring in both directions.