The impact of multidrug resistance on the pathogenicity of Escherichia coli: an experimental study

In Vitro Reduction of Interleukin-8 Response to Enterococcus faecalis by Escherichia coli Strains Isolated from the Same Polymicrobial Urines

Urinary tract infections are often polymicrobial and are mainly due to uropathogenic Escherichia coli (UPEC). We previously demonstrated a link among clinical fluoroquinolone susceptible E. coli reducing in vitro urothelial interleukin-8 (CXCL8) induced by E. coli K-12, polymicrobial cystitis, and pyuria absence. Here, we evaluated whether fifteen clinical fluoroquinolone susceptible UPEC were able to reduce CXCL8 induced by Enterococcus faecalis that had been isolated from the same mixed urines, other than CXCL8 induced by E. coli K-12. We also evaluated the connection between fluoroquinolone susceptibility and pathogenicity by evaluating the immune modulation of isogenic gyrA, a mutant UPEC resistant to ciprofloxacin. Using the 5637 bladder epithelial cell line, we observed that lower CXCL8 induced the most UPEC isolates than K-12 and the corresponding E. faecalis. During coinfections of UPEC/K-12 and UPEC/E. faecalis, we observed lower CXCL8 than during infections caused by K-12 and E. faecalis alone. UPEC strains showed host–pathogen and pathogen–pathogen interaction, which in part explained their persistence in the human urinary tract and coinfections, respectively. Mutant UPEC showed lower modulating activity with respect to the wildtypes, confirming the connection between acquired fluoroquinolone resistance and the decrease of innate microbial properties.

Colistin loading dose: evaluation of the published pharmacokinetic and clinical data

Colistin (polymyxin E) has been widely used since the beginning of the century as a last-option antibiotic for the treatment of patients with multidrug-resistant and extensively-drug resistant bacterial infections. However, colistin dosing is troublesome because each batch of the drug contains a mixture of components and because it is administered as the inactive pro-drug colistimethate sodium (CMS), which has different pharmacokinetic (PK) properties from the active drug. Significant inter-individual and intra-individual variability in colistin plasma concentrations have been observed in all available studies. Low plasma concentrations of the drug during the first hours from initiation of administration suggested that a loading dose would be appropriate. However, other PK studies challenge this approach. Clinical data from randomised controlled trials are not available, whilst data from observational studies do not support higher effectiveness of a loading dose. In this review, we summarise the available data regarding the administration of a loading dose and discuss the issues surrounding the potential advantages and disadvantages as well as the context within which such an approach could be beneficial to patients.

Interactions of Klebsiella pneumoniae with the innate immune system vary in relation to clone and resistance phenotype

Apart from inadequate antimicrobial treatment, specific virulence factors contribute to the high attributable mortality of infections caused by multidrug-resistant (MDR) Klebsiella pneumoniae. We explored the roles of MDR and clones as virulence determinants of K. pneumoniae and their interaction with innate immunity. Twenty isolates were studied and characterized by resistance phenotype and multilocus sequence type (MLST). Human peripheral blood mononuclear cells (PBMCs) were stimulated for the production of proinflammatory cytokines by live and heat-killed isolates and plasmid DNA; modulation by cellular pathway inhibitors was explored. Survival of 30 mice was recorded after intraperitoneal challenge with susceptible and K. pneumoniae carbapenemase (KPC)-producing isolates. Splenocytes of mice were stimulated for the production of pro- and anti-inflammatory cytokines. Isolates were divided into different patterns of production of tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) poststimulation in relation to both the MLST clone and resistance phenotype. The sequence type 383 (ST383) clone producing Verona integron-encoded metallo-β-lactamase (VIM) stimulated high production of both TNF-α and IL-1β. Clone ST17 producing KPC elicited low TNF-α production; this was reversed by Toll-like receptor 9 (TLR9) antagonists, indicating an effect of plasmid DNA. This isolate was linked with early death of mice compared to high-TNF-α-producing isolates. We conclude that KPC-producing isolates seem to be highly virulent in a low-TNF-α-release environment, suggesting an immunoparalysis induction mechanism. KPC plasmids may directly contribute to the immune system stimulation.

Comparison of host response mechanisms evoked by extended spectrum beta lactamase (ESBL)--and non-ESBL-producing uropathogenic E. coli

Background

Infections caused by extended spectrum beta-lactamases (ESBL)-producing bacteria have been emerging worldwide and the majority of ESBL-producing E. coli strains are isolated from patients with urinary tracts infections. The purpose of this study was to compare the host-response mechanisms in human polymorphonucleated leukocytes (PMN) and renal epithelial cells when stimulated by ESBL- or non-ESBL-producing uropathogenic E. coli (UPEC) isolates. The host-pathogen interaction of these ESBL-producing strains in the urinary tract is not well studied.

Results

The ability of ESBL strains to evoke ROS-production from PMN cells was significantly higher than that of the non-ESBL strains. The growth of ESBL strains was slightly suppressed in the presence of PMN compared to non-ESBL strains after 30 min and 2 h, but the opposite was observed after 5 and 6 h. The number of migrating PMN was significantly higher in response to ESBL strains compared to non-ESBL strains. Stimulation of A498 cells with ESBL strains elicited lower production of IL-6 and IL-8 compared to non-ESBL strains.

Conclusion

Significant differences in host-response mechanisms were identified when host cells were stimulated by ESBL- or non-ESBL producing strains. The obtained results on the early interactions of ESBL-producing strains with the host immune system may provide valuable information for management of these infections.

Predictors of mortality in patients with infections due to multi-drug resistant Gram negative bacteria: the study, the patient, the bug or the drug?

OBJECTIVE

To study the predictors of mortality among patients with multi-drug resistant Gram negative (MDRGN) infections and the role of MDRGN bacteria in the outcome of such patients.

METHODS

PubMed and Scopus databases were searched (until June 30, 2012). Data were extracted and analyzed using the technique of meta-analysis.

RESULTS

30 studies (25 retrospective) were included in the analysis; 9 provided data on predictors of mortality for MDRGN infections only, while 21 provided data for MDRGN vs non-MDRGN infections. Acinetobacter spp were the most commonly studied bacteria followed by Pseudomonas aeruginosa and Enterobacteriaceae. Significant diversity was observed among studies regarding the evaluated predictors of mortality. Infection severity and underlying diseases were the most commonly reported independent predictors of mortality followed by multidrug resistance, inappropriate treatment and increasing age. In studies that included only patients with MDRGN infections, cancer (RR 1.65, 95% CI 1.13-2.39) and prior or current ICU stay (1.27, 1.02-1.56) were associated with mortality. In studies that included patients with MDRGN and non-MDRGN infections, septic shock (3.36, 2.47-4.57), ICU stay (2.15, 1.45-3.20), pneumonia (1.65, 1.09-2.52), isolation of MDRGN bacteria (1.49, 1.21-1.83), inappropriate definitive (2.05, 1.12-3.76) and empirical treatment (1.37, 1.25-1.51), and male gender (1.13, 1.05-1.21) were most commonly observed in patients who died than patients who survived.

CONCLUSION

Significant diversity and statistical heterogeneity was observed. Beyond comorbidity and severity scores, MDR and inappropriate treatment were also identified as predictors of mortality.