anzctr.org.au Identifiers: ACTRN12613000532707 and ACTRN12615000403538 and ClinicalTrials.gov Identifier: NCT02176122.

Introduction This study aims to assess the association of piperacillin/tazobactam and meropenem minimum inhibitory concentration (MIC) and beta-lactam resistance genes with mortality in the MERINO trial. Methods Blood culture isolates from enrolled patients were tested by broth microdilution and whole genome sequencing at a central laboratory. Multivariate logistic regression was performed to account for confounders. Absolute risk increase for 30-day mortality between treatment groups was calculated for the primary analysis (PA) and the microbiologic assessable (MA) populations. Results 320 isolates from 379 enrolled patients were available with susceptibility to piperacillin/tazobactam 94% and meropenem 100%. The piperacillin/tazobactam non-susceptible breakpoint (MIC > 16 mg/L) best predicted 30-day mortality after accounting for confounders (odds ratio 14.9, 95% CI 2.8 – 87.2). The absolute risk increase for 30-day mortality for patients treated with piperacillin/tazobactam compared with meropenem was 9% (95% CI 3% – 15%) and 8% (95% CI 2% – 15%) for the original PA population and the post-hoc MA populations, which reduced to 5% (95% CI -1% – 10%) after excluding strains with piperacillin/tazobactam MIC values > 16 mg/L. Isolates co-harboring ESBL and OXA-1 genes were associated with elevated piperacillin/tazobactam MICs and the highest risk increase in 30-mortality of 14% (95% CI 2% – 28%). Conclusion After excluding non-susceptible strains, the 30-day mortality difference was from the MERINO trial was less pronounced for piperacillin/tazobactam. Poor reliability in susceptibility testing performance for piperacillin/tazobactam and the high prevalence of OXA co-harboring ESBLs suggests meropenem remains the preferred choice for definitive treatment of ceftriaxone non-susceptible E. coli and Klebsiella.

The incidence of and average time to detection for Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella (HACEK) bacteria in blood cultures with standard incubation and the utility of extended incubation of blood culture bottles were reviewed at four tertiary care microbiology laboratories. HACEK organisms were isolated from 35 (<0.005%) of 59,203 positive blood cultures. None of 407 blood cultures with extended incubation grew HACEK or other bacteria. Bacteremia from HACEK bacteria is rare, and extended incubation of blood cultures to recover HACEK bacteria is unnecessary.The Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella (HACEK) group of microorganisms comprises bacteria that commonly colonize the human oropharynx as normal, indigenous flora. Included are Haemophilus spp. (except H. influenzae), Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae. HACEK bacteria infrequently cause bacteremia but, when present, usually are clinically significant and are responsible for approximately 2 to 5% of culture-positive, infective endocarditis cases (6,20,21,29). Traditionally, most laboratories have followed the standard practice of extending the incubation of blood culture bottles for 14 to 21 days to improve the recovery of HACEK bacteria, particularly for patients diagnosed clinically with culture-negative endocarditis. Improvements in blood culture media and implementation of automated blood culture systems that increase recovery of these fastidious pathogens, however, raise questions about the need for extended incubation. The purpose of our study was to determine the incidence of and average time to detection for HACEK bacteria with standard blood culture incubation and to evaluate the utility of extended incubation of blood culture bottles.

We evaluated the accuracy of the BD Phoenix system for the identification (ID) and antimicrobial susceptibility testing (AST) of 251 isolates of the family Enterobacteriaceae representing 31 species. Organisms were inoculated onto the Phoenix panel according to the manufacturer's instructions. The results from conventional biochemical tests were used for the reference method for ID. Agar dilution, performed according to the CLSI guidelines, was the reference AST method. Essential and categorical agreements were determined. The overall levels of agreement for the genus-and species-level identifications were 95.6% and 94.4%, respectively. Fourteen isolates were incorrectly identified by the Phoenix system; 10 of these were incorrectly identified to the species level. Three of these were Enterobacter (Pantoea) species and four of these were Shigella spp. misidentified as Escherichia coli. For AST results, the essential and categorical agreements were 98.7% and 97.9%, respectively. The very major error, major error, and minor error rates were 0.38%, 0.33%, and 1.8%, respectively. Six isolates (three E. coli isolates and three Klebsiella isolates) were extended-spectrum ␤-lactamase producers. All six were flagged by the Phoenix system expert rules. The Phoenix system compares favorably to traditional methods for ID and AST of Enterobacteriaceae.As hospitals face the continuing challenge of treating sicker patients, the burden falls to clinical microbiology laboratories to provide accurate and rapid identification (ID) of the pathogens recovered and, more importantly, to detect antimicrobial resistance. To accomplish this goal, many laboratories rely upon automated microbial identification and antimicrobial susceptibility testing (AST) systems. The newer-generation instruments have more extensive databases; data management tools, including expert systems; and other features unique to each manufacturer. The BD Phoenix automated microbiology system (BD Diagnostic Systems, Sparks, MD) is the newest system to obtain clearance from the Food and Drug Administration.We evaluated the performance of the Phoenix instrument for the identification and susceptibility testing of challenge and clinical isolates of the family Enterobacteriaceae isolated from a variety of specimen sources in a busy tertiary-care medical center. MATERIALS AND METHODSBacterial strains. A total of 251 bacterial isolates were used for this evaluation. A total of 76 archived "challenge" gram-negative bacilli, including 19 isolates of Shigella spp. from Bangladesh, and 175 clinical isolates recovered from routine cultures in the Clinical Microbiology Laboratory of the Johns Hopkins Hospital (JHH) were included in this comparison.Reference identification. The laboratory's routine method for the identification of gram-negative organisms includes testing with the following conventional biochemicals. For Enterobacteriaceae, the following biochemicals incorporated into an in-house agar system were used: colistin, cefazolin, oxidase, phenylalanine deaminase, urea...