New Sequence Type ST3449 in Multidrug-Resistant Pseudomonas aeruginosa Isolates from a Cystic Fibrosis Patient.

Catalina Díaz-Ríos,Alain A Ocampo-Sosa,David Abad,Marta Hernández,Jorge Calvo,David Iturbe,Laura Álvarez-Montes,Athanasia Varsaki

doi:10.3390/antibiotics10050491

Abstract

Pseudomonas aeruginosa is one of the most critical bacterial pathogens associated with chronic infections in cystic fibrosis patients. Here we show the phenotypic and genotypic characterization of five consecutive multidrug-resistant isolates of P. aeruginosa collected during a month from a CF patient with end-stage lung disease and fatal outcome. The isolates exhibited distinct colony morphologies and pigmentation and differences in their capacity to produce biofilm and virulence potential evaluated in larvae of Galleria mellonella. Whole genome-sequencing showed that isolates belonged to a novel sequence type ST3449 and serotype O6. Analysis of their resistome demonstrated the presence of genes blaOXA-396, blaPAO, aph(3’)-IIb, catB, crpP and fosA and new mutations in chromosomal genes conferring resistance to different antipseudomonal antibiotics. Genes exoS, exoT, exoY, toxA, lasI, rhlI and tse1 were among the 220 virulence genes detected. The different phenotypic and genotypic features found reveal the adaptation of clone ST3449 to the CF lung environment by a number of mutations affecting genes related with biofilm formation, quorum sensing and antimicrobial resistance. Most of these mutations are commonly found in CF isolates, which may give us important clues for future development of new drug targets to combat P. aeruginosa chronic infections.

Highlights

Pseudomonas aeruginosa is among the most dreaded opportunistic human pathogens that affect the airways of cystic fibrosis (CF) individuals
P. aeruginosa isolates MS6000, MS6002, MS6003, MS6004 and MS6005 were sequentially collected during a month from a CF patient with end-stage pulmonary disease who died before lung transplantation
Five consecutive P. aeruginosa isolates were collected during a month from respiratory samples from a cystic fibrosis patient with end-stage respiratory failure who died before lung transplantation

Summary

Introduction

Pseudomonas aeruginosa is among the most dreaded opportunistic human pathogens that affect the airways of cystic fibrosis (CF) individuals. This bacterium is notorious for its metabolic versatility and innate resistance to many antibiotics due to the permeability barrier conferred by its Gram-negative outer membrane. Respiratory tract infection in CF patient usually initiates with persistent infections by P. aeruginosa that are frequently eradicated by antibiotic treatments. P. aeruginosa displays high virulence at initial stages of infection and it is relatively susceptible to antibiotics, but during the transition to a chronic way of survival it undergoes several adaptations to overcome the hostile environment of the lung. Among the characteristics P. aeruginosa exhibits at chronic phases of infection the presence of a mucoid phenotype, reduced expression of virulence factors, reduced motility, enhanced biofilm formation ability, high mutation rates, appearance of small colony variants (SCV), pigmentation changes and resistance to antimicrobial agents [3,4]

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