Stability of meropenem and doripenem solutions for administration by continuous infusion.

the same pI—despite the negative diffusion test for ESBL detection—we carried out a search for bla SHV using PCR (see Table S2); this, however, was negative for both strains. Another possible explanation for the aztreonam resistance observed in our strains might be overproduction of their chromosomal class A OXY b-lactamase. 5 The promoter region of the OXY b-lactamase was amplified by PCR (see Table S2), and the sequences revealed a mutation in the 210 consensus region of the promoter in both strains; this consisted of the transition (G!A) of the fifth base, described as the most frequent among in vitro mutants and clinical isolates of aztreonam-resistant K. oxytoca. 5 The bla OXY gene was also amplified by PCR (see Table S2), and the sequence analysis indicated that both strains carried a bla OXY-2-type very similar to bla OXY-2-8 (GenBank accession no. AY055205) with only two substitutions, a serine to glycine at position 23 and an aspartic acid to alanine at position 38, considering position 1 as the starting methionine.