Vegetables and rhizospheres as the reservoir for extensively drug-resistant (XDR) Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosais an urgent threat pathogen due to its evolving resistance to multiple antibiotics. Agricultural soil and plants are the vast reservoirs of this much-dreaded opportunistic bacterium. A few human isolates of P. aeruginosa are known to infect plants and insects. However, there is no report on the occurrence of multi-drug resistant P. aeruginosa in edible vegetable crops. This study compared 18 P. aeruginosa isolates from the rhizosphere and endophytic niches of four different vegetable crops (cucumber, tomato, eggplant, and chili) with three known clinical strains. All the isolates were tested for virulence traits such as resistance to various antibiotics classes, motility, biofilm, and production of virulence factors (rhamnolipid, pyocyanin, hemolysin, proteases, and lipases). Hierarchical clustering based on Ward minimum variance with Manhattan distance matrix grouped the strains into three clusters based on their phenotypic traits. Strains were exhibiting the highest virulence co-clustered with the human pathogenic isolates. These strains were resistant to cephalosporins, aminoglycosides, macrolides, nitrofurans, tetracyclines, and sulfonamides. These extensively drug-resistant (XDR) strains were only susceptible to polymyxin (colistin) and quinolone (cephalosporin). This study shows that the virulence traits are shared between plant- and human-isolates of P. aeruginosa. More importantly, the occurrence of XDR strains in vegetable crops is a serious global threat.