Emergence of extended-spectrum -lactamases and AmpC-type -lactamases in human Salmonella isolated in Spain from 2001 to 2005

Abstract

To study the resistance to third-generation cephalosporins in Salmonella strains isolated from humans in a 5 year period in Spain, and to identify the responsible genes and their dissemination. Twenty-seven isolates were analysed by PCR and sequencing to identify the genes responsible for the β-lactamase resistance phenotypes. The transferability of the phenotypes was tested by conjugation to Escherichia coli K12J53, plasmid detection with S1-PFGE, hybridization and PCRs of the transconjugants. The genetic relationship was determined by PFGE. We found bla_CTX-M-9 and bla_CTX-M-10 in Salmonella Virchow PT19. bla_CTX-M-14 was detected in Salmonella (IV) 44:z₄,z₂₃:-, Salmonella Enteritidis PT6a, Salmonella Typhimurium DT193 and Salmonella Typhimurium DT104B. bla_CTX-M-1 was found in Salmonella Litchfield. bla_CTX-M-15 and bla_CTX-M-32 were found in Salmonella Enteritidis PT1. bla_SHV-12 was found in Salmonella Blockley, Salmonella Hadar PT2, Salmonella Enteritidis PT21, Salmonella Enteritidis PT1 and Salmonella Bredeney. bla_SHV-2 was found in Salmonella Livingstone. bla_CMY-2 was detected in Salmonella Bredeney, Salmonella Newport, Salmonella Enteritidis PT5b and Salmonella Heidelberg. bla_DHA-1 was detected for the first time in Spain in Salmonella Newport. One strain of Salmonella Senftenberg harboured two extended-spectrum β-lactamases, bla_SHV-12 and bla_CTX-M-9. We have found a large variety of β-lactamase families as well as several members of major relevance, such as CTX-M-15, CTX-M-32, CMY-2 and DHA-1. XbaI-PFGE, conjugation assays and S1-PFGE hybridization showed that all these β-lactamases were mediated by plasmids. This study demonstrates the emergence of a public health risk related to resistance to β-lactams in Salmonella. The resistance trends need to be monitored carefully.