Polymorphism in pbp5 Gene Detected in Clinical Enterococcus faecium Strains with Different Ampicillin MICs from a Tunisian Hospital

Abstract

The polymorphism in pbp5 gene was investigated in nine unrelated clinical gentamicin-resistant Enterococcus faecium strains with different minimal-inhibitory-concentration values for ampicillin (six ampicillin-resistant and three ampicillin-susceptible). Five alleles were detected when the pbp5 C-terminal region was analysed, two of them in the ampicillin-susceptible strains. Two of our high-ampicillin-resistant strains showed a new allele characterised by the Thr416Ala and Val462Ala substitutions. Two different alleles were identified when the pbp5 N-terminal region was studied; one of them in the unique strain (E. faecium 83) that presented very low ampicillin MIC (<0.125 μg/ml) and a nucleotidic mutation implicating a stop codon at 451 position. RT-PCR experiments carried out on five E. faecium strains belonging to each of the different pbp5 alleles (including E. faecium 83) gave positive results indicating the expression of this gene. Specific mutations in pbp5 gene could be responsible of the high MIC values of some of the E. faecium strains.

Keywords:

• Enterococcus faecium
• pbp5
• penicillin resistance
• Tunisia