The Frequency of Exotoxin A and Exoenzymes S and U Genes Among Clinical Isolates of Pseudomonas aeruginosa in Shiraz, Iran

Pseudomonas aeruginosa as an opportunistic pathogen produces several virulence factors. The most important
of these factors are exotoxin A and type III secretion system (T3SS). The aim of this study was to determine the
frequency of toxA, exoU and exoS genes among clinical isolates of P. aeruginosa. In this cross-sectional study
from September 2011 to February 2012, 156 P. aeruginosa isolates were recovered from different clinical
samples. Susceptibility testing against 10 antibiotics was performed on individual isolates by the disc diffusion
method according to CLSI guidelines. Extracted DNA was subjected to PCR assay for determining the presence
of toxA, exoU and exoS genes. Overall, the frequency of toxA, exoU and exoS genes were 90.4%, 66.7% and 65.4%, respectively. All of the abdominal and eye isolates were exoS+. The frequency of exoS+/exoU- and exoS- /exoU+ genotypes was estimated 19.2% and 16.2%, respectively. Indeed, genotypes exoS+/exoU+ and exoS-/exoU-
were found with frequencies of 48.7% and 15.3%, respectively. The highest and lowest antibiotic resistance rate
was seen against azteroenam (94.2%) and amikacin (44.9%), respectively. Fluoroqinolone-resistant isolates were
isolated with frequency of 45.8%. Multi-drug resistant (MDR) isolates were detected in 62.8% of isolates. The resistance rate in exoU+ isolates was 86% compared to 66% in exoS+ isolates. The high frequencies of virulence
genes detected in our clinical isolates with notable antibiotic resistance rates indicate the potential risk of these
isolates in nosocomial infections.