Motility, biofilm, and endotoxin in Ralstonia pickettii isolates obtained from purified and ultrapure pharmaceutical water systems.

This study aimed to examine the motility, biofilm production, endotoxin release, and antibiotic resistance of 81 Ralstonia pickettii isolates collected from different pharmaceutical water systems in Croatia. Swimming and twitching motility were detected in all isolates, while swarming was not observed. Biofilm production was detected in approximately 40 % of the isolates under the tested conditions. Notably, extracellular polymeric substance (EPS) production was a common trait among all isolates. Endotoxin production was detected with the Limulus Amoebocyte Lysate test. Antibiotic susceptibility testing revealed consistent resistance to colistin, as well as significant resistance rates to β-lactam antibiotics, ertapenem, amoxicillin/clavulanic acid, ticarcillin and ampicillin. High susceptibility to first-generation cephalosporins, cephalexin, cefoxitin and chloramphenicol was observed. All isolates were susceptible to tigecycline and tetracycline. The isolates were grouped into three genetically closely related clusters, yet notable phenotypic diversity in biofilm production and antibiotic susceptibility persisted within these groups. The study highlights R. pickettii's adaptability in pharmaceutical water systems, marked by its motility, biofilm-forming capabilities, and multidrug resistance. These results emphasise the importance of rigorous monitoring of water systems to reduce transmission risks and prevent the emergence of resistant strains in clinical environments.