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Polymyxin B Heteroresistance and Adaptive Resistance in Multidrug- and Extremely Drug-Resistant Acinetobacter

Gabrielle Limeira Genteluci1,2, Paula Araujo de Souza3, Daniela Betzler Cardoso Gomes3,4

  • 1Department of Microbiology, National Institute of Quality Control in Heath, Fiocruz, Rio de Janeiro, Brazil. genteluci2@hotmail.com.

Current Microbiology
|June 5, 2020
PubMed

Insights

Multidrug-resistant Acinetobacter baumannii infections are a growing concern. This study found widespread oxacillinase genes and polymyxin B heteroresistance in clinical isolates, but no adaptive resistance, highlighting treatment challenges.

Area of Science:

  • Medical Microbiology
  • Infectious Diseases
  • Antimicrobial Resistance

Background:

  • Acinetobacter baumannii is a significant cause of hospital-acquired infections.
  • Multidrug resistance (MDR) in A. baumannii complicates treatment options.
  • Polymyxin B is a last-resort antibiotic, but resistance is emerging.

Purpose of the Study:

  • To investigate the genetic diversity and antimicrobial susceptibility of A. baumannii clinical isolates.
  • To determine the prevalence of polymyxin B heteroresistance and adaptive resistance.
  • To analyze the presence of oxacillinase genes and insertion sequences in MDR A. baumannii.

Main Methods:

  • Identification of 72 A. baumannii isolates using rpoB gene sequencing.
  • Genetic diversity assessed by pulsed-field gel electrophoresis.
  • Detection of oxacillinase genes (blaOXA) and ISAba1 using PCR.
  • Polymyxin B heteroresistance evaluated by population analysis profile.
  • Adaptive resistance assessed through serial passage in increasing polymyxin B concentrations.

Main Results:

  • 62% of isolates were multidrug-resistant (MDR), and 35% were extensively drug-resistant (XDR).
  • All isolates harbored blaOXA-23-like and blaOXA-51-like genes; 96% showed ISAba1-blaOXA-23 association.
  • Polymyxin B heteroresistance was detected in 36% of isolates; no adaptive resistance was observed.
  • Respiratory tract infections were the most common source (49% of isolates).

Conclusions:

  • High levels of antimicrobial resistance and the spread of oxacillinase genes are evident in A. baumannii clinical isolates.
  • The presence of polymyxin B heteroresistance poses a significant challenge for treating MDR A. baumannii infections.
  • Further strategies are needed to combat the increasing resistance of this opportunistic pathogen.

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