The effect of Staphylococcus aureus on the antibiotic resistance and pathogenicity of Pseudomonas aeruginosa based on crc gene as a metabolism regulator: An in vitro wound model study

Abstract

Background: The cooperation of Pseudomonas aeruginosa and Staphylococcus aureus in various infections results in increased pathogenicity and antibiotic resistance. However, the mechanism controlling such a phenomenon is still unclear. In this study, the effects of S. aureus on the metabolism, antibiotic resistance, and pathogenicity of P. aeruginosa were investigated.

Material and methods: The biofilm and the planktonic states of growth of P. aeruginosa and S. aureus were investigated using the co-culture method in the L929 cell line. Then, the antibiotic resistance and virulence factors production of the recovered colonies of P. aeruginosa were examined by phenotypic methods. Quantitative Real-Time PCR was used to determine the expression level of crc, lasI/R, and rhlI/R genes. Two way ANOVA test and student's t-test were used to analyze the effect of S.aureus on metabolism, virulence, and resistance of P.aeruginosa.

Results: P. aeruginosa strains in a single-species planktonic culture on the L929 cell line indicated higher CFU counts than the biofilm. Conversely, in the biofilm state of co-culture, the CFU counts increased in comparison to the planktonic condition. Also, the expression level of crc increased two fold in the PA-1 and PA-2 strains compared to the single-species cultures on the L929 cell line. However, the PA-3 strain indicated a sharp decrease in the expression of crc (3 fold decrease). Besides, a 3-4 fold increase in susceptibility to amikacin was observed as the expression level of crc declined. The QS-regulated factors were diminished as rhlR and lasI were downregulated in both states of growth.

Conclusion: In polymicrobial wound infection, Staphylococcus aureus plays a vital role in the metabolic changes of Pseudomonas aeruginosa. However, the levels of antibiotic susceptibility and pathogenicity of Pseudomonas aeruginosa also changed due to metabolism.

Keywords: Biofilm; Catabolite repression regulator; Metabolism; Pseudomonas aeruginosa; Staphylococcus aureus; Virulence.