Enhanced Klebsiella pneumoniae Carbapenemase Expression from a Novel Tn4401 Deletion.

The Klebsiella pneumoniae carbapenemase gene (blaKPC) is typically located within mobile transposon Tn4401 Enhanced KPC expression has been associated with deletions in the putative promoter region upstream of blaKPC Illumina sequences from blaKPC-positive clinical isolates from a single institution were mapped to a Tn4401b reference sequence, which carries no deletions. The novel isoform Tn4401h (188-bp deletion [between istB and blaKPC]) was present in 14% (39/281) of clinical isolates. MICs showed that Escherichia coli strains containing plasmids with Tn4401a and Tn4401h were more resistant to meropenem (≥16 and ≥16, respectively), ertapenem (≥8 and 4, respectively), and cefepime (≥64 and 4, respectively) than E. coli strains with Tn4401b (0.5, ≤0.5, and ≤1, respectively). Quantitative real-time PCR (qRT-PCR) demonstrated that Tn4401a had a 16-fold increase and Tn4401h a 4-fold increase in blaKPC mRNA levels compared to the reference Tn4401b. A lacZ reporter plasmid was used to test the activity of the promoter regions from the different variants, and the results showed that the Tn4401a and Tn4401h promoter sequences generated higher ß-galactosidase activity than the corresponding Tn4401b sequence. Further dissection of the promoter region demonstrated that putative promoter P1 was not functional. The activity of the isolated P2 promoter was greatly enhanced by inclusion of the P1-P2 intervening sequence. These studies indicated that gene expression could be an important consideration in understanding resistance phenotypes predicted by genetic signatures in the context of sequencing-based rapid diagnostics.

Cost-Effectiveness of 30- Compared to 20-Milliliter Blood Cultures: a Retrospective Study.

The importance of blood culture (BC) volume for detection of bloodstream infections (BSIs) is documented. Recently, improved diagnostic sensitivity was demonstrated for 30- versus 20-ml BCs in adults (Cockerill FR, Wilson JW, Vetter EA, Goodman KM, Torgerson CA, Harmsen WS, Schleck CD, IIstrup DM, Washington JA, Wilson WR. Clin Infect Dis 38:1724-1730, 2004, http://dx.doi.org/10.1128/JCM.01314-11). Hospitals receive higher reimbursement for patients with documented septicemia. We determined the cost-effectiveness of 30-ml versus 20-ml BCs using results from our institution and previously published data. Positive BC results from 292 bacteremic episodes were reviewed. The costs of the reagents, equipment, phlebotomist, and technologist time were determined. The medical records department provided Medicare reimbursement (MR) data for patients with selected ICD-9 codes. These data provided an estimate of the annualized increase in MR versus costs associated with conversion to 30-ml BCs. MR for 464 annual primary BSIs was $24,808/episode. An expected 7.2% increase in BSIs detected using 30-ml BCs would add 34 additional cases annually and increase MR by $843,472. Comparative MR data for cases where septicemia complicated another diagnosis were available for 4 International Classification of Diseases, Ninth Revision (ICD-9) codes: laparoscopic cholecystectomy, biliary tract disorders, pneumonia, and cellulitis. The mean incremental MR was $9,667 per episode, which projected to a $483,350 revenue increase annually. The annual cost associated with conversion to 30-ml BCs was estimated to be $157,798. Thus, the potential net increase in hospital revenue would be $1,169,031 for 30-ml versus 20-ml BCs. Our results suggest that conversion to 30-ml BCs may not only improve patient care by detecting more BSIs but also increase hospital revenue substantially.

Urinary exosomal transcription factors, a new class of biomarkers for renal disease.

Urinary exosomes are excreted from all nephron segments and constitute a rich source of intracellular kidney injury biomarkers. To study whether they contain transcription factors, we collected urine from two acute kidney injury models (cisplatin or ischemia-reperfusion), two podocyte injury models (puromycin-treated rats or podocin-Vpr transgenic mice) and from patients with focal segmental glomerulosclerosis, acute kidney injury and matched controls. Exosomes were isolated by differential centrifugation and found to contain activating transcription factor 3 (ATF3) and Wilms Tumor 1 (WT-1) proteins detected by Western blot. These factors were found in the concentrated exosomal fraction, but not in whole urine. ATF3 was continuously present in urine exosomes of the rat models following acute injury at times earlier than the increase in serum creatinine. ATF3 was found in exosomes isolated from patients with acute kidney injury but not from patients with chronic kidney disease or controls. Urinary WT-1 was present in animal models before significant glomerular sclerosis and in 9/10 patients with focal segmental glomerulosclerosis but not in 8 controls. Our findings suggest that transcription factor ATF3 may provide a novel renal tubular cell biomarker for acute kidney injury while WT-1 may detect early podocyte injury. Measurement of urinary exosomal transcription factors may offer insight into cellular regulatory pathways.

Rapid isolation of urinary exosomal biomarkers using a nanomembrane ultrafiltration concentrator.

Urinary exosomes are excreted from all nephron segments and may serve as biomarkers for classifying renal diseases. Isolation of urinary exosomes by the established ultracentrifugation method has some limitations for use in a clinical laboratory. We sought a rapid and simple way to obtain urinary exosomes. We used a commercially available nanomembrane concentrator to enrich exosomes from urine by centrifugation at 3,000 g for 10-30 min. Urinary exosomal markers tumor susceptibility gene 101, aquaporin-2, neuron-specific enolase, annexin V, angiotensin-converting enzyme, and podocalyxin (PODXL) were recovered from the nanomembrane concentrator and detected by Western blotting, and typical features of urinary vesicles were found by electron microscopy. Exosomal markers were detected in as little as 0.5 ml of urine. By the nanomembrane method, exosomal proteins could be recovered from urine samples frozen at -80 degrees C or refrigerated overnight at 4 degrees C then stored at -80 degrees C. By enriching exosomes we could detect PODXL, a podocyte marker, which decreased by 71% in five male patients with focal segmental glomerulosclerosis and abundant proteinuria. We conclude that 1) use of a nanomembrane concentrator simplifies and accelerates the enrichment of urinary exosomes; and 2) the nanomembrane concentrator can concentrate exosomal proteins from clinical urine samples. This enhanced method may accelerate the translation of urinary exosomal biomarkers from bench to bedside for the diagnosis, classification, and prognostication of renal diseases.