Molecular characterization of plasmid-encoded ACC-1a4 beta-lactamase produced by Salmonella strains isolated from water in a Tunisian hospital

International audienceA collection of non-typhoidal Salmonella strains, designated MMB1 to MMB18, resistant to third generation cephalosporins were isolated from water in a Tunisian hospital. Isolates harbored a new bla(ACC) gene located on a small transmissible plasmid of 5 kb. The ACC-1a4 enzyme was produced in Escherichia coli, purified and characterized. Compared to the chromosomal bla(ACC-1a) gene, the bla(ACC-1a4) exhibit three mutations. We determined the kinetic parameters of our enzyme for a representative series of beta-lactam substrates. The ACC-1a4 enzyme was active on penicillins and cephalosporins, nitrocefin and cephalothin being its best tested substrates. This is a real cause for alarm since these mutations showed that the DNA sequence of bla(ACC) is an intermediate between those of bla(ACC-1a) and bla(ACC-4) and might increase the probability of the appearance and spreading of ACC-4-mediated resistance in the hospital environment