Polymorphisms of the pbp5 gene and correlation with ampicillin resistance in Enterococcus faecium clinical isolates

Introduction and Objectives: Recently, the proportion of E. faecium isolates from enterococcal infections has increased, largely due to the spread of resistance to antibiotics. Acquired resistance to higher levels of ampicillin has been shown to be associated with increased production of penicillin binding protein 5 (PBP5) or mutations in the pbp5 gene. The current study was conducted to sequence the C-terminal ends of pbp5s from isolates with different ampicillin minimum inhibitory concentrations (MICs) in order to determine possible mechanism of resistance to ampicillin.Materials and Methods: MICs of ampicillin against 19 isolates of E. faecium were determined using broth macro-dilution method. The presence of pbp5 gene was confirmed by PCR and the C-terminal ends of pbp5s for each isolates were sequenced.Results: Sequencing analysis of 19 clinical isolates of E. faecium including 17 ampicillin-resistant (MIC range 128-˃512) and 2 ampicillin-susceptible (MIC 1 μg/ml) revealed 5 different pbp5 alleles (designated A-E) having differences in 18 amino acid positions spanning from residue 426 to 642 in comparison with reference sequence E.faecium X84860.1. All of these alleles except D with only one resistant isolate, harbored serine insertion at position 466ʹ, different from susceptible isolates. Both of susceptible isolates were categorized in allele E. They presented only four amino acid changes. However, these substitutions were also found in all other alleles.Conclusion: A correlation between deduced amino acid changes in PBP5 and ampicillin MICs was detected in clinical E. faecium isolates.

کلیدواژه ها:

Enterococcus faecium ، penicillin binding protein 5 ، ampicillin resistance ، amino acid substitutions