Impact of borderline minimum inhibitory concentration on the outcome of invasive infections caused by Enterobacteriaceae treated with β-lactams: a systematic review and meta-analysis

Broth Microdilution and Gradient Diffusion Strips vs. Reference Agar Dilution Method: First Evaluation for Clostridiales Species Antimicrobial Susceptibility Testing

Antimicrobial susceptibility testing of anaerobes is challenging. Because MIC determination is recommended by both CLSI and EUCAST, commercial broth microdilution and diffusion strip tests have been developed. The reliability of broth microdilution methods has not been assessed yet using the agar dilution reference method. In this work, we evaluated two broth microdilution kits (MICRONAUT-S Anaerobes^® MIC and Sensititre Anaerobe MIC^®) and one gradient diffusion strip method (Liofilchem^®) for antimicrobial susceptibility testing of 47 Clostridiales isolates (Clostridium, Clostridioides and Hungatella species) using the agar dilution method as a reference. The evaluation focused on comparing six antimicrobial molecules available in both microdilution kits. Analytical performances were evaluated according to the Food and Drug Administration (FDA) recommendations. Essential agreements (EA) and categorical agreements (CA) varied greatly according to the molecule and the evaluated method. Vancomycin had values of essential and categorical agreements above 90% for the three methods. The CA fulfilled the FDA criteria for three major molecules in the treatment of Gram-positive anaerobic infections (metronidazole, piperacillin/tazobactam and vancomycin). The highest rate of error was observed for clindamycin. Multicenter studies are needed to further validate these results.

Breakpoint to MIC quotient: A parameter to rapidly evaluate the in vitro bactericidal activity of β-lactams on Enterobacteriaceae

Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) do not completely predict the bactericidal nature of the antimicrobial agent. Patients with pathogens having MICs near the clinical breakpoint experience a higher risk of clinical failure. This study defined an indicator, breakpoint to MIC quotient (BMQ), that incorporates MIC and the European Committee on Antimicrobial Susceptibility Testing breakpoint. The BMQ was inversely correlated with MBC in antibiotic combinations against Enterobacteriaceae strains (Spearman coefficient ≤ -0.96). This new parameter may provide timely additional insight for choosing an antibiotic for a severe bacterial infection.

Is It Time to Rethink the Notion of Carbapenem-Sparing Therapy Against Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae Bloodstream Infections? A Critical Review

OBJECTIVE

To present systematic recommendations for carbapenem-sparing therapy against extended-spectrum β-lactamases (ESBLs) Enterobacteriaceae bloodstream infections (BSIs) derived from a critical review of clinical data.

DATA SOURCES

A systematic literature search using PubMed and MEDLINE databases (January 1, 2012, to June 30, 2017) was performed using key MESH terms: ESBL or extended-spectrum β-lactamases and bacteremia or bloodstream infection with piperacillin/tazobactam, ciprofloxacin, levofloxacin, cefepime, cephamycins, carbapenem, doripenem, meropenem, and ertapenem. References within articles of interest were also evaluated.

STUDY SELECTION AND DATA EXTRACTION

All English language trials were considered, and results were limited to clinical efficacy trials. Articles were screened by title and abstract for inclusion.

DATA SYNTHESIS

Studies comparing noncarbapenem versus carbapenem therapy for ESBL BSIs were critically analyzed to identify heterogeneity among studies. Data abstracted included empirical or definitive therapy, patient population, dosing, source of infection and severity, infectious etiology, and outcome.

CONCLUSIONS

Completely sparing carbapenem therapy cannot be justified among patients with ESBL BSIs. Determining the source of infection is critical to identify patients for whom carbapenem-sparing therapy is appropriate.

Comparative Activity of Ciprofloxacin, Levofloxacin and Moxifloxacin against Klebsiella pneumoniae, Pseudomonas aeruginosa and Stenotrophomonas maltophilia Assessed by Minimum Inhibitory Concentrations and Time-Kill Studies

The aim of this study was to compare the in vitro susceptibility of Klebsiella pneumoniae, Pseudomonas aeruginosa and Stenotrophomonas maltophilia to three fluoroquinolones. The minimum inhibitory concentrations (MICs) to ciprofloxacin, levofloxacin and moxifloxacin were examined by E-test^® for a total of 40 K. pneumoniae strains, 40 S. maltophilia strains and 40 P. aeruginosa strains. Then, the bactericidal activity of these fluoroquinolones was investigated on five strains of each bacterial species by means of time-kill curves. For K. pneumoniae and P. aeruginosa, the distance of the measured MIC from the clinical break-point is a good indicator of the bactericidal activity for ciprofloxacin and levofloxacin as obtained in our experiments. The lower the MIC, the better the bactericidal activity in term of CFU Log decreases. If MIC of ciprofloxacin and levofloxacin against the considered bacteria are far from clinical breakpoint, these two antibiotics are equivalent. According to our MIC₅₀ and modal MIC, the breakpoints of both ciprofloxacin and levofloxacin seem to be somewhat high and data suggest reducing them. On S. maltophilia, none of the tested antibiotics showed a satisfactory activity.

Impact of the MIC of piperacillin/tazobactam on the outcome for patients with bacteraemia due to Enterobacteriaceae: the Bacteraemia-MIC project

OBJECTIVE

Our objective was to evaluate the impact of low versus borderline MIC of piperacillin/tazobactam on the clinical outcomes of patients with bacteraemia caused by Enterobacteriaceae who were treated with that antimicrobial.

PATIENTS AND METHODS

A prospective observational multicentre cohort study was conducted in 13 Spanish university hospitals. Patients >17 years old with bacteraemia due to Enterobacteriaceae who received empirical piperacillin/tazobactam treatment for at least 48 h were included. Outcome variables were clinical response at day 21, clinical response at end of treatment with piperacillin/tazobactam and all-cause 30 day mortality. Univariate and multivariate logistic regression analyses were performed.

RESULTS

Overall, 275 patients were included in the analysis; 248 (90.2%) in the low MIC group (≤ 4 mg/L) and 27 (9.8%) in the borderline MIC group (8-16 mg/L). The biliary tract was the most common source of infection (48.4%) and Escherichia coli was the most frequent pathogen (63.3%). Crude 30 day mortality rates were 10.5% and 11.1% for the low MIC group and the borderline MIC group, respectively (relative risk = 1.06, 95% CI = 0.34-3.27, P = 1). Multivariate analysis of failure at day 21 and at end of treatment with piperacillin/tazobactam and 30 day mortality showed no trend towards increased clinical failure or mortality with borderline MICs (OR = 0.96, 95% CI = 0.18-4.88, P = 0.96; OR = 0.47, 95% CI = 0.10-2.26, P = 0.35; OR = 1.48, 95% CI = 0.33-6.68, P = 0.6).

CONCLUSIONS

We did not find that higher piperacillin/tazobactam MIC within the susceptible or intermediate susceptibility range had a significant influence on the outcome for patients with bacteraemia due to Enterobacteriaceae.