High prevalence of colistin heteroresistance in specific species and lineages of Enterobacter cloacae complex derived from human clinical specimens.

BACKGROUND: Colistin (CST) is a last-line drug for multidrug-resistant Gram-negative bacterial infections. CST-heteroresistant Enterobacter cloacae complex (ECC) has been isolated. However, integrated analysis of epidemiology and resistance mechanisms based on the complete ECC species identification has not been performed. METHODS: Clinical isolates identified as "E. cloacae complex" by MALDI-TOF MS Biotyper Compass in a university hospital in Japan were analyzed. Minimum inhibitory concentrations of CST were determined by the broth microdilution method. The population analysis profiling (PAP) was performed for detecting the heteroresistant phenotype. The heat shock protein 60 (hsp60) cluster was determined from its partial nucleotide sequence. From the data of whole-genome sequencing, average nucleotide identity (ANI) for determining ECC species, multilocus sequence type, core genome single-nucleotide-polymorphism-based phylogenetic analysis were performed. phoPQ-, eptA-, and arnT-deleted mutants were established to evaluate the mechanism underlying colistin heteroresistance. The arnT mRNA expression levels were determined by reverse transcription quantitative PCR. RESULTS: Thirty-eight CST-resistant isolates, all of which exhibited the heteroresistant phenotype by PAP, were found from 138 ECC clinical isolates (27.5%). The prevalence of CST-resistant isolates did not significantly differ among the origin of specimens (29.0%, 27.8%, and 20.2% for respiratory, urine, and blood specimens, respectively). hsp60 clusters, core genome phylogeny, and ANI revealed that the CST-heteroresistant isolates were found in all or most of Enterobacter roggenkampii (hsp60 cluster IV), Enterobacter kobei (cluster II), Enterobacter chuandaensis (clusters III and IX), and Enterobacter cloacae subspecies (clusters XI and XII). No heteroresistant isolates were found in Enterobacter hormaechei subspecies (clusters VIII, VI, and III) and Enterobacter ludwigii (cluster V). CST-induced mRNA upregulation of arnT, which encodes 4-amino-4-deoxy-L-arabinose transferase, was observed in the CST-heteroresistant isolates, and it is mediated by phoPQ pathway. Isolates possessing mcr-9 and mcr-10 (3.6% and 5.6% of total ECC isolates, respectively) exhibited similar CST susceptibility and PAP compared with mcr-negative isolates. CONCLUSIONS: Significant prevalence (approximately 28%) of CST heteroresistance is observed in ECC clinical isolates, and they are accumulated in specific species and lineages. Heteroresistance is occurred by upregulation of arnT mRNA induced by CST. Acquisition of mcr genes contributes less to CST resistance in ECC.

Selective Detection of DNA from Viable Mycobacterium tuberculosis Complex Strains Using the EMA-PCR Method.

In this study, the ability to discriminate viable from dead cells of Mycobacterium tuberculosis complex (MTC), using an ethidium monoazide (EMA) treatment-dependent viable bacteria selection PCR kit was examined. Detection of dead bacteria was possible for bacterial concentrations in the range 1.5 × 107-3.0 × 107 CFU/mL, which was equivalent to McFarland No. 0.05-0.10. There was a significant difference between the results for viable and dead bacteria, and the sensitivity and specificity of this method for culture-negative samples from patients were 83% and 100%, respectively. To the best of our knowledge, this is the first successful selective detection of DNA from viable cells of MTC by EMA-PCR, using the viable bacteria selection kit for PCR (gram-positive), an EMA treatment kit. We believe that application of this method could promote earlier discharge of patients undergoing tuberculosis treatment by discriminating dead from viable cells.

Risk Factors for Postoperative Delirium in Abdominal Surgery: A Proposal of a Postoperative Delirium Risk Score in Abdominal Surgery.

BACKGROUND/AIMS: Despite the presence of several diagnosis scales for delirium, no prediction scale that is specific for postoperative delirium after abdominal surgery is available. We sought to create a novel delirium prediction system that is specific for abdominal surgery. METHODS: This study included 213 consecutive patients who required management in the surgical ICU following abdominal surgery. The Neelon and Champagne (NEECHAM) Confusion score was monitored throughout the postoperative course and patients with low NEECHAM score (≤26) were diagnosed as having delirium. RESULTS: Seventy-three patients (34%) were categorized in the delirium group. Multivariate analyses indicated that an age >70 years, hypertension, those undergoing hepatopancreatobiliary or upper gastrointestinal surgeries, a serum albumin level <2.5 g/dl on postoperative day (POD) 3 or 5 and a ≥6 mEq/l gap in the serum sodium level between the preoperative value and that on POD 3 were independently associated with a low NEECHAM score (≤26). When the presence of each risk was counted as 1 point, 21 patients had ≥4 points and 15 of them (71%) had low NEECHAM score. CONCLUSION: The scoring system combining multiple risk factors may be useful for predicting patients with an elevated risk for postoperative delirium after abdominal surgery.