Molecular Epidemiology of Multidrug-Resistant Pseudomonas aeruginosa Acquired in a Spanish Intensive Care Unit: Using Diverse Typing Methods to Identify Clonal Types

Abstract

The increasing number of infections from multidrug-resistant P. aeruginosa (MDRPA) has compromised the selection of appropriate treatment in critically ill patients. Recent investigations have shown the existence of MDRPA global clones that have been disseminated in hospitals worldwide. We aimed to describe the molecular epidemiology and genetic diversity of the MDRPA acquired by Intensive Care Units (ICU) patients in our hospital. We used phenotypic methods to define the MDRPA and molecular methods were used to illustrate the presence of carbapenemase encoding genes. To characterize the MDRPA isolates, we used MALDI-TOF biomarker peaks, O-antigen serotyping, and multi-locus sequence typing analyses. Our data show that the most widely distributed MDRPA clone in our ICU unit was the ST175 strain. These isolates were further investigated by the whole-genome sequencing technique to determine the resistome profile and phylogenetic relationships, which showed, as previously described, that the MDR profile was due to the intrinsic resistance mechanisms and not the carbapenemase encoding genes. In addition, this study suggests that the combination of environmental focus and cross-transmission are responsible for the spread of MDRPA clones within our ICU unit. Serotyping and MALDI-TOF analyses are useful tools for the early detection of the most prevalent MDRPA clones in our hospital. Using these methods, semi-directed treatments can be introduced at earlier stages and healthcare professionals can actively search for environmental foci as possible sources of outbreaks.

Keywords: Pseudomonas aeruginosa; ST175; genotyping; high-risk clone; molecular characterization; multidrug-resistant; whole-genome sequencing.

Figure 1

The MLST, O-antigen determination, MALDI-TOF biomarker peaks, and PCR carbapenemase encoding genes results of the MDRPA strains that were isolated from acquisition-positive ICU patients. MDRPA: multidrug-resistant P. aeruginosa; GE: genetically heterogeneous; NA: no agglutination.

Figure 2

A minimum spanning tree based on the number of allelic differences between the isolates. The number of allelic differences are indicated on the lines connecting the isolates.

Figure 3

Dendrogram. High and low similarity coefficient cut-offs were established at >98% and 95%, respectively. Four isolates were classified as probably related and formed Cluster 1. Two isolates were considered possibly related and another two isolates were considered probably not related.