05). Imipenem selection did not modify the conjugation frequencies (Table 2). We showed that all the blaNDM-1-carrying plasmids were transferred to K. pneumoniae and S. typhimurium with frequencies ranging from 10−5 to 10−8 transconjugants per donor, showing a variable potential of transfer of blaNDM-1 plasmids in Enterobacteriaceae

(Table 2). As observed using E. coli JM109 as recipient, plasmids p419 and pKp7 were transferred to K. pneumoniae CIP53153 and S. typhimurium LT2 at the lowest frequencies (10−7 to 10−8 transconjugants per donor) and were not transferred to P. mirabilis CIP103181 (Table 2). Only two types of broad-host range plasmids (p601 and p271) were transferred into P. mirabilis CIP103181 but at low frequencies (Table 2), which is consistent with what has been observed Trametinib mouse previously (Naas et al., 2003). CTX 10 μg mL−1 NA 20 μg mL−1b CTX 10 μg mL−1 NA 20 μg mL−1 CTX 10 μg mL−1 NA 20 μg mL−1 IMP 0.25 μg mL−1 NA 20 μg mL−1 IMP 0.75 μg mL−1 NA 20 μg mL−1 CTX 10 μg mL−1 NA 20 μg mL−1 CTX 10 μg mL−1 RA 250 μg mL−1 CTX 10 μg mL−1 TE 30 μg mL−1 Transconjugants expressed variable levels of carbapenem resistance (Table 3), as previously observed (Kumarasamy et al., 2010). According to the updated breakpoints of the CLSI (Clinical and Laboratory Standards Institute, 2010) for imipenem, meropenem, doripenem (susceptible, ≤ 1 μg mL−1; resistant,

≥ 4 μg mL−1) and ertapenem (susceptible, ≤ 0.25 μg mL−1; resistant ≥ 1 μg mL−1), those transconjugants could be classified as susceptible, intermediate susceptibility or resistant to carbapenems. MICs of carbapenems were always the highest for K. pneumoniae used Selleck Crizotinib as the recipient species that fits with its lower natural susceptibility to carbapenems compared to that of E. coli (Table 3). The lowest MIC values of carbapenems were obtained with P. mirabilis used as Avelestat (AZD9668) a recipient, which is consistent with the previous findings showing low MIC values of β-lactams when other β-lactamase genes,

such as blaTEM, are expressed in P. mirabilis (Kontomichalou et al., 1974). Those low MIC values of carbapenems may explain further difficulties to identify NDM-1 producers in P. mirabilis. None of the five plasmids was transferred to A. baumannii and to P. aeruginosa by conjugation. One cannot exclude that conjugative transfer could have been obtained using clinical NDM-1 producers as donors that may contain helper plasmids for mobilization, providing conjugation proteins in trans. None of the five plasmids was transferred by electroporation in P. aeruginosa. A single plasmid type (p271) was transferred successfully by electroporation in A. baumannii CIP70.10 reference strain indicating that at least this untypeable plasmid can replicate in A. baumannii. This transformant was highly resistant to carbapenems (MICs of imipenem, meropenem and doripenem > 32 μg mL−1). They mirror published data with NDM-1 and NDM-2-positive A.