Polymorphism in ftsI gene and {beta}-lactam susceptibility in Portuguese Haemophilus influenzae strains: clonal dissemination of beta-lactamase-positive isolates with decreased susceptibility to amoxicillin/clavulanic acid

J Antimicrob Chemother. 2011 Apr;66(4):788-96. doi: 10.1093/jac/dkq533. Epub 2011 Jan 25.

Abstract

Objectives: The aim of this study was to characterize ampicillin resistance mechanisms in clinical isolates of Haemophilus influenzae from Portugal. Association between specific patterns of amino acid substitutions in penicillin-binding protein 3 (PBP3) (with or without β-lactamase production) and β-lactam susceptibility as well as genetic relatedness among isolates were investigated.

Methods: Two-hundred and forty non-consecutive H. influenzae isolates chosen according to their different ampicillin MICs [101 β-lactamase-non-producing ampicillin-resistant (BLNAR) isolates, 80 β-lactamase-producing ampicillin-resistant (BLPAR) isolates and 59 β-lactamase-non-producing ampicillin-susceptible (BLNAS) isolates] were analysed. The β-lactamase-encoding bla(TEM-1) gene was detected by PCR. The ftsI gene encoding PBP3 was sequenced. Genetic relatedness among isolates was examined by PFGE.

Results: Of the 240 H. influenzae isolates, 141 had mutations in the transpeptidase domain of the ftsI gene, including most BLNAR strains (94/101, 93.1%) and a high percentage of BLPAR strains (47/80, 58.8%). As previously reported, the latter have been described as β-lactamase-positive amoxicillin/clavulanic acid resistant (BLPACR). The most common amino acid substitutions were identified near the KTG motif: N526K (136/141, 96.5%), V547I (124/141, 87.9%) and N569S (121/141, 85.8%). The 141 strains were divided into 31 ftsI mutation patterns and included six groups (I, IIa, IIb, IIc, IId and III-like). BLNAR strains were genetically diverse but close genetic relationships were demonstrated among BLPACR strains.

Conclusions: This study shows that the non-enzymatic mechanism of resistance to β-lactams is widespread among H. influenzae isolates in Portugal. Clonal dissemination of BLPACR strains showing high resistance to ampicillin and reduced susceptibility to amoxicillin/clavulanic acid was documented.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Amoxicillin-Potassium Clavulanate Combination / pharmacology*
  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / genetics*
  • Bacterial Typing Techniques
  • Child
  • Cluster Analysis
  • DNA, Bacterial / genetics
  • Electrophoresis, Gel, Pulsed-Field
  • Genotype
  • Haemophilus Infections / epidemiology*
  • Haemophilus Infections / microbiology
  • Haemophilus influenzae / classification*
  • Haemophilus influenzae / genetics
  • Haemophilus influenzae / isolation & purification
  • Humans
  • Microbial Sensitivity Tests
  • Molecular Typing
  • Penicillin-Binding Proteins / genetics
  • Polymerase Chain Reaction
  • Polymorphism, Genetic*
  • Portugal / epidemiology
  • Sequence Analysis, DNA
  • beta-Lactam Resistance*
  • beta-Lactamases / biosynthesis

Substances

  • Anti-Bacterial Agents
  • Bacterial Proteins
  • DNA, Bacterial
  • Penicillin-Binding Proteins
  • Amoxicillin-Potassium Clavulanate Combination
  • beta-Lactamases