Significant role of pyocyanin and exotoxin A in the pathogenesis of Pseudomonas aeruginosa isolated from hospitalized patients

Abstract

Aim: Due to the importance of exotoxin A and pyocyanin in the pathogenicity of this bacterium, we decided to evaluate the prevalence of genes encoding these virulence factors in clinical isolates of P. aeruginosa. Materials and methods: In this study, 100 clinical isolates were collected and identified by conventional biochemical tests. The ability to produce pyocyanin was determined by culture in a specific liquid medium (GSNB) at 37°C. The DNAs of the bacteria were extracted by the SDS method and a PCR test was performed to identify the exoA, phzA1B1C1D1E1F1G1, phzM, and phzS genes. Results: In this study, 90 isolates were pyocyanin-producing in phenotypic test. Also, 96%, 98%, 92%, and 96% of the isolates carried exoA, phzM, phzS, and phzA1B1C1D1E1F1G1 genes, respectively. Interestingly, 2 isolates lacking the exoA gene did not have the phzM and phzS genes at the same time, but the other 2 isolates carrying all three gene loci required for pyocyanin synthesis. Also, among the strains that lacked the ability to produce pyocyanin, 2 isolates concurrently lacked the phzS and phzA1B1C1D1E1F1G1 genes and 2 isolates simultaneously lacked the phzM and phzS genes, while the 2 isolates did not carry only the phzS gene. The other 2 isolates did not contain only phzA1B1C1D1E1F1G1 operon. Conclusion: The presence of the phzA1B1C1D1E1F1G1 operon, along with the phzM and phzS genes, plays a significant role in the production of pyocyanin pigment. However, the high prevalence of exoA gene in this study indicates the importance of this factor for vaccine designing.