Type III secretion system characterization of Pseudomonas aeruginosa isolates associated with cystic fibrosis

Abstract

Pseudomonas aeruginosalung infection is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). The type III secretion system is an important and identified virulence determinant of P. aeruginosa that delivers effector proteins into targeted host cells. Three effector proteins have been described in P. aeruginosa: exoS, exoT, exoU. Unlike many studies that have been done on bacterial virulence factors in acute conditions, fewer studies have been done on virulence factors of bacteria in chronic disease and conditions such as cystic fibrosis.

this study investigated 51 sputum samples containing P. aeruginosa from child patients with cystic fibrosis for their possession of genes associated with the type III secretion system (exoU, exoS, exoT). PCR assays using specific primers were used to determine the distribution of the type III secretion toxin-encoding genes exoU, exoT and exoS for the test strains.

In this study from 51 samples, 34 of samples (6.66%) were resistant to trimethoprim, 19 of samples (2.37%) were resistant to gentamicin, and 11 samples (5.21%) were resistant to amikacin and cefepime, 10 samples (6.19%) were resistant to tobramycin, 8 cases (6.15%) were resistant to ciprofloxacin, 7 samples (7.13%) were resistant to imipenem, 5 (8/9%) were resistant to ceftazidime and 3 cases (8.5%) were resistant to meropenem. In the current study, from the total of 51 sputum samples, 46 samples (90%) possessed the exoT gene, 40 samples (75%) possessed the exoS genewhereas 13 samples (25%) possessed the exoU gene.

In this study, the resistance against antibiotics of aminoglycosides (gentamicin), fluoroquinolone (ciprofloxacin) and broad-spectrum cephalosporins (cefepime or Ceftazidime) was observed in 13/7% of the samples showing the emergence of multi-drug resistance in these samples. Our results demonstrated that most of our isolates harbored type III secretion toxin-encoding genes, but isolates containing the ExoS-encoding gene are significantly more common among CF patient isolates indicating that ExoS-secreting strains are selected for survival in CF patient airways.