In vitro activity of eravacycline compared with tigecycline against carbapenem-resistant Enterobacteriaceae.

Eravacycline has been shown to have broad-spectrum activity against Gram-negative bacteria, including carbapenem-resistant Enterobacteriaceae (CRE). We compared the activity of eravacycline with that of tigecycline in CRE isolates cultured from patients at an academic medical centre. Eravacycline was more potent than tigecycline [mean minimum inhibitory concentration (MIC) ratio = 0.76, 95% confidence interval 0.66-0.87]; however, the MIC90 observed for eravacycline was higher than previously reported at 4 µg/mL. Future studies are necessary to elucidate the mechanism driving this difference.

In vitro activity of plazomicin compared to other clinically relevant aminoglycosides in carbapenem-resistant Enterobacteriaceae.

We evaluated the in vitro activity of plazomicin against other aminoglycosides in 122 clinical carbapenem-resistant Enterobacteriaceae isolates using several clinical susceptibility breakpoints. Plazomicin had excellent in vitro activity with 98% overall susceptibility. Amikacin was the next most active with 86% overall susceptibility. This dropped to 55% when switching from Clinical Laboratory and Standards Institute to US Committee on Antimicrobial Susceptibility Testing breakpoints.

Imipenem/relebactam activity compared to other antimicrobials against non-MBL-producing carbapenem-resistant Enterobacteriaceae from an academic medical center.

BACKGROUND: Carbapenem-resistant Enterobacteriaceae (CRE) cause significant mortality and are resistant to most antimicrobial agents. Imipenem/relebactam, a novel beta-lactam/beta-lactamase inhibitor combination, and 16 other antimicrobials were evaluated against non-metallo-beta-lactamase-producing carbapenem-resistant Enterobacteriaceae clinical isolates from a United States tertiary academic medical center. OBJECTIVES: To evaluate imipenem/relebactam and other commonly utilised antimicrobial agents against carbapenem-resistant Enterobacteriaceae. METHODS: Clinical isolates (n  = 96) resistant to ertapenem or meropenem by BD Phoenix (Becton, Dickinson and Company, Franklin Lakes, NJ, USA) and negative for metallo-beta-lactamase-production by an EDTA (Sigma-Aldrich Corp., St. Louis, MO, USA)/phenylboronic acid (Sigma-Aldrich Corp., St. Louis, MO, USA) disk diffusion assay were identified and collected from January 2012 to January 2017. In vitro susceptibility by broth microdilution was performed according to CLSI guidelines using CLSI susceptibility breakpoints for 17 antimicrobials (Sigma-Aldrich Corp., St. Louis, MO, USA). RESULTS: CRE primarily produced Klebsiella pneumoniae carbapenemase (KPC) and consisted primarily of K. pneumoniae (55%) and Enterobacter spp. (25%), followed by Citrobacter spp. (10%), Escherichia coli (5%), and others (5%). CRE were most susceptible to imipenem/relebactam (100%), followed by amikacin (85%), tigecycline (82%), and polymyxin B/colistin (65%). The median reduction of imipenem minimum inhibitory concentrations (MICs) of non-MBL-producing CRE was 16-fold but ranged from 0.5 to >512-fold. The MIC50, MIC90 and MIC range of imipenem/relebactam was 0.5/4, 1/4 and 0.06/4-1/4 mg/L, respectively. CONCLUSIONS: Imipenem/relebactam exhibits excellent activity against CRE that produce KPC.

Evaluation of the BD Phoenix automated system for determining antimicrobial susceptibility against carbapenem-resistant Enterobacteriaceae compared with broth microdilution.

PURPOSE: Carbapenem-resistant Enterobacteriaceae (CRE) are increasingly widespread in the healthcare system, resulting in infections associated with mortality of up to 50%. Many laboratories use automated systems to identify CRE isolates and determine susceptibility. The aim of this study was to evaluate categorical agreement between the BD Phoenix automated system and the gold standard - broth microdilution - in determining minimum inhibitory concentrations of CRE. METHODOLOGY: The activity of amikacin, aztreonam, cefepime, ceftazidime, ertapenem, gentamicin, levofloxacin, meropenem, nitrofurantoin, piperacillin-tazobactam and tobramycin on 125 CRE isolates collected from an academic medical centre was evaluated. Categorical agreement between BD Phoenix and broth microdilution was determined, as well as minor error rates, major error rates and very major error rates. RESULTS: BD Phoenix significantly overestimates susceptibility of CRE isolates to amikacin, aztreonam, cefepime, ceftazidime, gentamicin, levofloxacin, meropenem, nitrofurantoin and tobramycin compared with broth microdilution. Overall, categorical agreement of 76% between testing methods indicates the potential diminished ability of BD Phoenix to predict resistance accurately in highly drug-resistant isolates. All tested antimicrobials had higher major error rates compared with previous literature. CONCLUSIONS: BD Phoenix has diminished ability to determine susceptibility of CRE isolates. Further studies are warranted in order to validate BD Phoenix susceptibility testing in highly resistant CRE isolates. The mechanism by which isolates are resistant to carbapenems does not impact the ability of BD Phoenix to determine susceptibility.

Killing activity of meropenem in combination with amikacin against VIM- or KPC-producing Enterobacteriaceae that are susceptible, intermediate, or resistant to amikacin.

Amikacin is administered with a carbapenem to treat serious infections caused by carbapenem-resistant Enterobacteriaceae (CRE). The varying degrees of activity of the individual agents correspond to differences in activity of the 2 in combination. Amikacin and meropenem are not bactericidal against amikacin-resistant CRE.

Staggering the administration of polymyxin B and meropenem in time-kill against carbapenem-resistant Enterobacteriaceae exhibiting a wide range of meropenem MICs.

Little is known regarding the appropriate timing and sequencing of a carbapenem and polymyxin in combination against carbapenem-resistant Enterobacteriaceae. Meropenem and polymyxin B were administered simultaneously or 1 agent 2 h prior to the other, in vitro. The carbapenem should be administered prior to the polymyxin when used in combination.

Effect of increasing meropenem MIC on the killing activity of meropenem in combination with amikacin or polymyxin B against MBL- and KPC-producing Enterobacter cloacae.

Carbapenem resistant Enterobacteriaceae (CRE) are a growing threat worldwide. Infections caused by these organisms have exhibited high rates of mortality (50%) for which there is no standard of care and a dearth of clinical trials. Most in vitro data on CRE focus on Klebsiella pneumoniae, but it is known that effective therapy may depend on species or even strain. To address this, meropenem, amikacin, and polymyxin B alone and in combination were evaluated by time kill against four carbapenem-producing Enterobacter cloacae clinical isolates representing a range of meropenem nonsusceptibility (2-32 mg/L) and resistance mechanisms (KPC 2 and/or VIM 1). As meropenem minimum inhibitory concentration (MIC) increased, bactericidal activity and synergy were maintained for 48 hours in isolates exposed to meropenem and amikacin, but synergy and bactericidal activity were not maintained in all isolates exposed to meropenem and polymyxin B.

Comparison of sensory neuron growth cone and filopodial responses to structurally diverse aggrecan variants, in vitro.

Following spinal cord injury, a regenerating neurite encounters a glial scar enriched in chondroitin sulfate proteoglycans (CSPGs), which presents a major barrier. There are two points at which a neurite makes contact with glial scar CSPGs: initially, filopodia surrounding the growth cone extend and make contact with CSPGs, then the peripheral domain of the entire growth cone makes CSPG contact. Aggrecan is a CSPG commonly used to model the effect CSPGs have on elongating or regenerating neurites. In this study, we investigated filopodia and growth cone responses to contact with structurally diverse aggrecan variants using the common stripe assay. Using time-lapse imaging with 15-s intervals, we measured growth cone area, growth cone width, growth cone length, filopodia number, total filopodia length, and the length of the longest filopodia following contact with aggrecan. Responses were measured after both filopodia and growth cone contact with five different preparations of aggrecan: two forms of aggrecan derived from bovine articular cartilage (purified and prepared using different techniques), recombinant aggrecan lacking chondroitin sulfate side chains (produced in CHO-745 cells) and two additional recombinant aggrecan preparations with varying lengths of chondroitin sulfate side chains (produced in CHO-K1 and COS-7 cells). Responses in filopodia and growth cone behavior differed between the structurally diverse aggrecan variants. Mutant CHO-745 aggrecan (lacking chondroitin sulfate chains) permitted extensive growth across the PG stripe. Filopodia contact with the CHO-745 aggrecan caused a significant increase in growth cone width and filopodia length (112.7% ± 4.9 and 150.9% ± 7.2 respectively, p<0.05), and subsequently upon growth cone contact, growth cone width remained elevated along with a reduction in filopodia number (121.9% ± 4.2; 72.39% ± 6.4, p<0.05). COS-7 derived aggrecan inhibited neurite outgrowth following growth cone contact. Filopodia contact produced an increase in growth cone area and width (126.5% ± 8.1; 150.3% ± 13.31, p<0.001), and while these parameters returned to baseline upon growth cone contact, a reduction in filopodia number and length was observed (73.94% ± 5.8, 75.3% ± 6.2, p<0.05). CHO-K1 derived aggrecan inhibited neurite outgrowth following filopodia contact, and caused an increase in growth cone area and length (157.6% ± 6.2; 117.0% ± 2.8, p<0.001). Interestingly, the two bovine articular cartilage aggrecan preparations differed in their effects on neurite outgrowth. The proprietary aggrecan (BA I, Sigma-Aldrich) inhibited neurites at the point of growth cone contact, while our chemically purified aggrecan (BA II) inhibited neurite outgrowth at the point of filopodia contact. BA I caused a reduction in growth cone width following filopodia contact (91.7% ± 2.5, p<0.05). Upon growth cone contact, there was a further reduction in growth cone width and area (66.4% ± 2.2; 75.6% ± 2.9; p<0.05), as well as reductions in filopodia number, total length, and max length (75.9% ± 5.7, p<0.05; 68.8% ± 6.0; 69.6% ± 3.5, p<0.001). Upon filopodia contact, BA II caused a significant increase in growth cone area, and reductions in filopodia number and total filopodia length (115.9% ± 5.4, p<0.05; 72.5% ± 2.7; 77.7% ± 3.2, p<0.001). In addition, filopodia contact with BA I caused a significant reduction in growth cone velocity (38.6 nm/s ± 1.3 before contact, 17.1 nm/s ± 3.6 after contact). These data showed that neuron morphology and behavior are differentially dependent upon aggrecan structure. Furthermore, the behavioral changes associated with the approaching growth cone may be predictive of inhibition or growth.