Background: Outcomes of patients with Pseudomonas aeruginosa bacteremia (Pab) have been attributed to appropriateness of antibiotic therapy and/or host factors. However, given the large number of virulence factors produced by this bacterium, we hypothesize that these may play roles in determining outcomes, little about which is known in humans with bacteremia.
Methods: Clinical data, antibiotic therapy as well as bacterial isolates were collected concurrently from 75 patients with Pab over 20 months. Strains were analyzed for the presence of known toxin genes, proteolytic activity, motility and pyocyanin production. The data were analyzed to ascertain which factors correlated with septic shock (SS) or death within a 7day period.
Results: 25 of 75 patients developed SS. Univariate analysis of host and bacterial factors was performed. The mean age of the SS group was 62.5 yr vs 54.1 yr in the non shock group (p=.046). Treatment with ineffective antibiotics in the first 24 hours or the presence of MDR Pa did not influence the occurrence of SS. Bacterial factors such as proteolytic activity, presence of lasB, exoA, exoS, exoU, plcH were not statistically significant determinants of poor outcomes. However, of the 75 patients, 8 were infected with non-motile isolates, 6 of whom developed SS (75%) p=0.014. Six of the 75 patient isolates were high pyocyanin producers (>18ug/ml), 5 of which resulted in SS (83.3%) p=0.014 (Figure 1).
Multivariate analysis, to assess the potential predictors of SS indicated that the OR for development of SS with a non-motile isolate was 6.8, 95% CI=(1.37,51.5), p=0.030. The OR for high pyocyanin producing isolates for development of SS was 16.9, 95% CI=(2.27,360), p=.017. There was no correlation between the absence of motility and high pyocyanin production (Figure 2).
Conclusion: This study to evaluate the role of host as well as microbial factors in poor outcomes due to Pab indicates that besides age, microbial determinants, hitherto unexpected, such as the lack of motility and high pyocyanin production, independently increase the risk of a poor outcome.
Figure 1: The plot shows pyocyanin levels (ug/ml) by SS status for all 75 subjects. The rate of SS was 83% among 6 subjects who had a pyocyanin level above 18 ug/ml.
Figure 2: High Pyocyanin production and absence of motility are independent of each other in Pab isolates with SS.
R. Ramphal, None