Performance evaluation of InfectID-BSI: A rapid quantitative PCR assay for detecting sepsis-associated organisms directly from whole blood.

BACKGROUND: Bloodstream infections (BSIs) (presence of pathogenic organism in blood) that progress to sepsis (life-threatening organ dysfunction caused by the body's dysregulated response to an infection) is a major healthcare issue globally with close to 50 million cases annually and 11 million sepsis-related deaths, representing about 20% of all global deaths. A rapid diagnostic assay with accurate pathogen identification has the potential to improve antibiotic stewardship and clinical outcomes. METHODS: The InfectID-Bloodstream Infection (InfectID-BSI) test is a real-time quantitative PCR assay, which detects 26 of the most prevalent BSI-causing pathogens (bacteria and yeast) directly from blood (without need for pre-culture). InfectID-BSI identifies pathogens using highly discriminatory single nucleotide polymorphisms located in conserved regions of bacterial and fungal genomes. This report details the findings of a patient study which compared InfectID-BSI with conventional blood culture at two public hospitals in Queensland, Australia, using 375 whole blood samples (from multiple anatomical sites, eg. left arm, right arm, etc.) from 203 patients that have been clinically assessed to have signs and symptoms of suspected BSI, sepsis and septic shock. FINDINGS: InfectID-BSI was a more sensitive method for microorganism detection compared with blood culture (BacT/ALERT, bioMerieux) for positivity rate (102 vs 54 detections), detection of fastidious organisms (Streptococcus pneumoniae and Aerococcus viridans) (25 vs 0), detection of low bioburden infections (measured as genome copies/0.35 mL of blood), time to result (<3 h including DNA extraction for InfectID-BSI vs 16 h-48 h for blood culture), and volume of blood required for testing (0.5 mL vs 40-60 mL). InfectID-BSI is an excellent 'rule out' test for BSI, with a negative predictive value of 99.7%. InfectID-BSI's ability to detect 'difficult to culture' microorganisms re-defines the four most prevalent BSI-associated pathogens as E. coli (28.4%), S. pneumoniae (17.6%), S. aureus (13.7%), and S. epidermidis (13.7%). INTERPRETATION: InfectID-BSI has the potential to alter the clinical treatment pathway for patients with BSIs that are at risk of progressing to sepsis.

Pseudomonas aeruginosa Trent and zinc homeostasis.

Pseudomonas aeruginosa is a Gram-negative pathogen and the major cause of mortality in patients with cystic fibrosis. The mechanisms that P. aeruginosa strains use to regulate intracellular zinc have an effect on infection, antibiotic resistance and the propensity to form biofilms. However, zinc homeostasis in P. aeruginosa strains of variable infectivity has not been compared. In this study, zinc homeostasis in P. aeruginosa Trent, a highly infectious clinical strain, was compared to that of a laboratory P. aeruginosa strain, ATCC27853. Trent was able to tolerate higher concentrations of additional zinc in rich media than ATCC27853. Further, pre-adaptation to additional zinc enhanced the growth of Trent at non-inhibitory concentrations but the impact of pre-adaption on the growth of ATCC27853 under the same conditions was minimal. The results establish clear differences in zinc-induced responses in Trent and ATCC27853, and how zinc homeostasis can be a promising target for the development of novel antimicrobial strategies for P. aeruginosa infection in cystic fibrosis patients.