Stimulation of innate immunity by susceptible and multidrug-resistant Pseudomonas aeruginosa:: an in vitro and in vivo study

In attempt to investigate the stimulatory effect of Pseudomonas aeruginosa on innate immunity and to correlate it to its level of resistance to antimicrobials, 20 isolates were applied; 8 isolates were susceptible and 12 multidrug-resistant. Genetic diversity was defined by PFGE. Human monocytes of two healthy volunteers were in vitro stimulated by the isolates for the production of pro-inflammatory (TNF-alpha, IL-1beta, IL-6, IL-8 and IL-12) and anti-inflammatory cytokines (IL-10), of malondialdehyde and of procalcitonin. Cytokines were estimated by EIA, malondialdehyde by the thiobarbiturate assay and procalcitonin by an immunochemiluminometric assay. Survival of 48 Wistar rats was recorded after induction of sepsis by the intraperitoneal injection of three susceptible and three multidrug-resistant isolates. To test whether comparative effect of the latter isolates on survival correlates with any difference of monocyte-mediated release of pro-inflammatory mediators, monocytes of two rats were in vitro stimulated for the production of TNF-alpha and of malondialdehyde. In vitro stimulation of human monocytes by the susceptible isolates elicited elevated production of malondiadeheyde, of IL-1beta and of IL-6 compared to stimulation by multidrug-resistant isolates. Similar differences were found for TNF-alpha and IL-8, but they were not statistically significant. Production of IL-10 and IL-12 was not detected after stimulation with any isolate. Levels of procalcitonin were similar after induction with either susceptible or multidrug-resistant isolates. Mean survival of animals was 7.56, 21.80 and 55.20 h, respectively, after challenge by the susceptible isolates and 28.89, 61.8 and more than 120 h, respectively, after challenge by the multidrug-resistant isolates. Differences of survival were accompanied by greater rodent monocyte-release of TNF-alpha and malondialdehyde after stimulation by the susceptible isolates compared to multidrug-resistant ones. It is concluded that considerable differences are encountered on the stimulation of human monocytes by susceptible and resistant isolates of Pseudomonas aeruginosa. These results correlate with in vivo evidence and might influence decision on therapeutics.