Last update:
11-Nov-2004

OBJECTIVE The comparative virulence properties of susceptible and multidrug-resistant Pseudomonas aeruginosa isolates in vitro and in vivo.

METHOD Eight susceptible and 12 multidrug-resistant genetically distinct isolates were tested, as defined by PFGE. Production of elastase and release of endotoxins were defined by chromogenic assays. Human monocytes were stimulated in vitro by the selected isolates for the production of pro-inflammatory (TNFα, IL-1β, IL-6, IL-8, IL-12) and anti-inflammatory (IL-10) cytokines, of malondialdehyde (MDA) and of procalcitonin. Cytokines were estimated by EIA, MDA by the thiobarbiturate assay and procalcitonin by immunochemiluminescence. Survival of 20 Wistar rats was recorded after intraperitoneal injection of one susceptible isolate in 10 and one resistant isolate in the other 10.

RESULTS Statistically significantly higher production of MDA, of IL-1β and of IL-6 from monocytes was observed after stimulation by susceptible isolates than after stimulation by multidrug-resistant isolates. Similar differences were found for elastase, TNFα and IL-8, but these were not statistically significant. No production of IL-10 or IL-12 was detected after stimulation with any isolate. Levels of procalcitonin were similar after induction with either susceptible or multidrug-resistant isolates. Mean (±SE) survival of rats after inoculation with the susceptible isolate was 21.80 (±7.87) hours and after inoculation with the multidrug-resistant isolate 61.8±11.81 hours (Ρ=0.0065).

CONCLUSIONS Considerable differences were encountered in the virulence properties of susceptible and resistant isolates of P. aeruginosa, according to both in vitro and in vivo evidence. These results could influence therapeutic decision.

Key words: Cytokines, Pseudomonas aeruginosa, Resistance, Sepsis, Virulence.