Polymorphisms of the pbp5 gene and correlation with ampicillin resistance in Enterococcus faecium isolates of animal origin.

The C-terminal region of the pbp5 gene was sequenced in 11 ampicillin-resistant and 5 ampicillin-susceptible Enterococcus faecium isolates of animal origin, and compared with a pbp5 reference sequence (GenBank accession no. X84860). Eight different pbp5 alleles (designated A-H) were detected when amino acid changes in the region 461-629 were considered. Three of these alleles (A-C) were detected in ampicillin-susceptible isolates (MIC range 1-8 microg ml-1), and included the changes 470H-->Q, 471V-->I, 487Q-->L, 581I-->V, 595E-->A or 622E-->D. The remaining five alleles (D-H) were found in ampicillin-resistant isolates (MIC range 32-256 microg ml-1); three of these alleles (F-H) presented a serine insertion at position 466', in addition to other important amino acid changes (485M-->A, 496N-->K, 499A-->T, 525E-->D, 586V-->L or 629E-->V). The other two alleles presented the amino acid changes 496N-->K and 629E-->V (allele D), and 470H-->Q (allele F). A correlation between deduced amino acid changes in PBP5 and ampicillin MICs was detected in animal E. faecium isolates.