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Gram-negative bacteria as causative agents of ventilator-associated pneumonia and their respective resistance

Daniela Bandić-Pavlović1,2, Tajana Zah-Bogović1,2, Marta Žižek3

  • 1Department of Anesthesiology, School of Medicine, University of Zagreb, Zagreb, Croatia.

Journal of Chemotherapy (Florence, Italy)
|July 31, 2020
PubMed

Insights

Multidrug-resistant Gram-negative bacteria, including Acinetobacter baumannii and Pseudomonas aeruginosa, are a significant threat in intensive care units (ICUs). This study identified high rates of resistance and diverse resistance mechanisms, highlighting the urgent need for effective antimicrobial strategies.

Area of Science:

  • Clinical Microbiology
  • Infectious Diseases
  • Intensive Care Medicine

Background:

  • Ventilator-associated pneumonia (VAP) is a critical complication in intensive care units (ICUs), contributing significantly to patient mortality.
  • Multidrug-resistant Gram-negative bacteria, particularly Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae, are frequently implicated in ICU-acquired VAP.
  • Understanding the prevalence and resistance mechanisms of these pathogens is crucial for developing effective treatment and prevention strategies.

Purpose of the Study:

  • To investigate the antibiotic susceptibility patterns of Gram-negative bacteria isolated from VAP patients in Croatian ICUs.
  • To identify the prevalence of specific resistance genes, including those for extended-spectrum beta-lactamases (ESBLs) and carbapenemases.
  • To elucidate the genetic mechanisms underlying multidrug resistance in key Gram-negative pathogens causing VAP.

Main Methods:

  • Prospective study conducted in four ICUs between September 2017 and March 2018.
  • Antibiotic susceptibility testing performed using broth microdilution.
  • Detection of ESBLs, carbapenemases (Hodge test, carbapenem inactivation method), and resistance genes (PCR for bla genes, qnr genes).

Main Results:

  • High resistance rates observed in Pseudomonas aeruginosa against imipenem (74%) and meropenem (68%).
  • Acinetobacter baumannii isolates exhibited extensive resistance, with most strains resistant to carbapenems and other antibiotics, except colistin and amikacin.
  • Prevalence of specific resistance genes: blaOXA-23/24 in A. baumannii, CTX-M group 1 in K. pneumoniae and E. cloacae, CMY family in P. mirabilis, and OXA-48/VIM-1 in K. pneumoniae and E. cloacae.

Conclusions:

  • A high proportion of multidrug-resistant Pseudomonas aeruginosa, Klebsiella pneumoniae, and extensively resistant Acinetobacter baumannii were identified.
  • Acquired resistance mechanisms, primarily carbapenemase and ESBL production, were dominant in A. baumannii and K. pneumoniae.
  • Resistance in P. aeruginosa likely involves efflux pump upregulation or porin loss, with significant diversity of beta-lactamases found in Enterobacteriaceae.
Keywords:
Acinetobacter baumanniiKlebsiella pneumoniaePseudomonas aeruginosaVentilator-associated pneumonia

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