Comparison of type III secretion system virulence among fluoroquinolone-susceptible and -resistant clinical isolates of Pseudomonas aeruginosa

Abstract

Fluoroquinolone resistance and type III secretion system (TTSS) virulence are independently associated in Pseudomonas aeruginosa infections with poor patient outcomes. In the present study, the virulence of fluoroquinolone-susceptible and -resistant isolates of P. aeruginosa was compared, focusing on TTSS virulence. Clinical isolates (n = 45) exhibiting a broad range of susceptibilities to fluoroquinolones, with differing mechanisms of resistance and associated with varying disease sites, were selected for the study. PCR, Southern blot and western immunoblot analyses were performed to determine the presence of TTSS-encoding genes and secretion of gene products. The cytotoxicity of the clinical isolates towards human lung epithelial cells was also determined. Clinical isolates encoding only the exoS cytotoxin gene occurred more frequently than those encoding only exoU (62% vs. 27%; p 0.0007). Compared with exoS(+) isolates, exoU(+) isolates were more likely to be fluoroquinolone-resistant (92% vs. 61%, p 0.05) and to exhibit both a gyrA mutation and the efflux pump over-expressed (EPO) phenotype (91% vs. 59%; p 0.06). Almost all exoU(+) strains secreted ExoU and exhibited increased cytotoxicity compared with ExoS-secreting strains (7% vs. 92.5%, relative to a PA103 reference strain control). These data suggest that exoU(+) and fluoroquinolone resistance may be co-selected traits that result in highly virulent and resistant strains. Adverse outcomes associated with infections caused by fluoroquinolone-resistant strains may, in part, be attributable to this co-association, which warrants further clinical investigation.

An investigation of type 3 secretion toxins encoding-genes of Pseudomonas aeruginosa isolates in a University Hospital in Egypt

“…The prevalence of exoU was 62.4% in all examined P. aeruginosa isolates which was third in prevalence to exoT and exoY in the T3SS genotypes of isolates tested, contrasting with a number of studies 11,12,18 that reported exoU prevalence to be the lower one in P. aeruginosa isolates compared to the other secretion toxins genes. It was stated that exoU gene was acquired via horizontal transmission on a plasmid, and then integrated in the P. aeruginosa genome.…”

“…7,10 Deletion of exoU severely limits the toxicity of P. aeruginosa strain in lung, and the enzyme has been implicated as an agent associated with septic shock and increased disease severity and mortality in pneumonia. 7,11 Interestingly, the genes encoding P. aeruginosa T3SS toxins are found in some isolates but not in others. 12 The distribution of these genes among isolates of P. aeruginosa and the frequency in populations of isolates from different disease sites has not been thoroughly examined in our country…”

Molecular Detection of the VirulentExoUGenotype ofPseudomonas aeruginosaIsolated from Infected Surgical Incisions

“…All ExoU isolates were MDR, which is consistent with Mitov et al [30], who found a higher frequency of MDR among ExoU isolates compared with ExoS isolates. Consistent with the current finding regarding the high prevalence of fluoroquinolone resistance in ExoU isolates (100%), Wong-Beringer et al [38] found that 92% of ExoU were fluoroquinolone-resistant compared with 61% resistance in ExoS. The association between MDR and the presence of the ExoU genotype has been associated with poor clinical outcome in patients with pneumonia in two different studies, particularly in immunocomporomised patients [39,40], with no clear genetic explanation.…”

Molecular epidemiological survey of the quinolone- and carbapenem-resistant genotype and its association with the type III secretion system in Pseudomonas aeruginosa

“…Some published studies have reported that exoU-positive P. aeruginosa strains are most often multi-resistant compared with exoS strains (Garey et al, 2008;Wong-Beringer et al, 2008). In our study, this relationship was not observed as the strains with the TTSS genotype were also multiresistant, suggesting again that these bacteria could exhibit other additional resistance mechanisms that make these strains present multiple antimicrobial co-resistance.…”