Evaluation of Microscan WalkAway for determination of ceftazidime/avibactam and ceftolozane/tazobactam susceptibility in carbapenem-resistant Gram-negative bacilli

Background: We evaluated the performance of ceftazidime/avibactam and ceftolozane/tazobactam MicroScan Neg multidrug-resistant MIC 1 NMR1 panel for clinical carbapenem-nonsusceptible Gram-negative bacilli isolates. Methods: We evaluated 212 clinically significant carbapenem-nonsusceptible Gram-negative bacilli 139 Pseudomonas aeruginosa and 73 KPC-producing Enterobacterales from 71 Brazilian hospitals 2013-2020. Ceftazidime/avibactam and ceftolozane/tazobactam MICs from the panel were compared with broth microdilution BMD test as the reference method. Essential agreement EA and categorical agreement CA were assessed. For P. aeruginosa , antimicrobial susceptibility testing error rates were calculated using the error-rate bound method. Results: Discrepancies were initially observed with 11 isolates, 4 resolved after retesting, 2 in favor of the NMR1 and 2 in favor of the BMD method. The ceftazidime/avibactam EA overall and evaluable was 100% for P. aeruginosa and Enterobacterales. CA was 100% for Enterobacterales , and 98.6% for P. aeruginosa . The ceftolozane/tazobactam EA was 98.6% and 100% overall and evaluable, respectively, and CA was 96.4% for P. aeruginosa . For ceftazidime/avibactam, no VME was found, and the ME rate was 4.2% 2/48. For ceftolozane/tazobactam and P. aeruginosa , using the CLSI breakpoints, the minor error mE was 11.4% and no VME or ME was found. While using EUCAST breakpoints, VME was 11.4% with no ME. The mE becomes ME or VME in the absence of the intermediate category. All categorical errors were also within 1 log of MIC variation, and the adjusted error rate for CLSI/EUCAST was 0% 0/212. Conclusions: The NMR1 panel is an option to test ceftazidime–avibactam for KPC-producing Enterobacterales and carbapenem-nonsusceptible P. aeruginosa . When ceftolozane–tazobactam MIC 4 mg/L are obtained using this method, an alert could be created, and the results could be confirmed by alternative method.

Evaluation of antimicrobial susceptibility testing methods for Burkholderia cenocepacia and Burkholderia multivorans isolates from cystic fibrosis patients

The Burkholderia cepacia complex (BCC) is known for causing serious lung infections in people with cystic fibrosis (CF). These infections can require lung transplantation, eligibility for which may be guided by antimicrobial susceptibility testing (AST). While the Clinical and Laboratory Standards Institute recommends AST for BCC, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) does not due to poor method performance and correlation with clinical outcomes. Furthermore, limited data exists on the performance of automated AST methods for BCC. To address these issues, reproducibility and accuracy were evaluated for disk diffusion (DD), broth microdilution (BMD), and MicroScan WalkAway using 50 B. cenocepacia and 50 B. multivorans isolates collected from people with CF. The following drugs were evaluated in triplicate: chloramphenicol (CAM), ceftazidime (CAZ), meropenem (MEM), trimethoprim-sulfamethoxazole (TMP-SMX), minocycline (MIN), levofloxacin (LVX), ciprofloxacin (CIP) and piperacillin-tazobactam (PIP-TAZ). BMD reproducibility was ≥ 95% for MEM and MIN only, and MicroScan WalkAway reproducibility was similar to BMD. DD reproducibility was < 90% for all drugs tested when a 3 mm cut-off was applied. When comparing the accuracy of DD to BMD, only MEM met all acceptance criteria. TMP-SMX and LVX had high minor errors, CAZ had unacceptable very major errors (VME), and MIN, PIP-TAZ, and CIP had both unacceptable minor errors and VMEs. For MicroScan WalkAway, no drugs met acceptance criteria. Analyses also showed that errors were not attributed to one species. In general, our data agree with EUCAST recommendations that routine AST should not be performed for BCC CF isolates.

GC-mass determination for the biodegradative products of 2,6-dimethylpyridine using Dead-Sea bacterial isolate

Dead sea soil is known for its hypersaline environment and it is a promising location for isolating extremophilic bacteria with interesting metabolic features. In the current study, we isolated a gram-positive bacterium with the ability to degrade 2,6-dimethyl pyridine (2,6-DMP), also known as 2,6-lutidine, a chemical pollutant. The isolated bacteria were identified using the automated Microscan Walkaway system and the different biochemical reactions were determined. In minimal media using the 2,6-DMP as a sole carbon source, the bacterial isolate showed the ability to convert approximately 40 % of 2,6-DMP within 5 days. The GC-Mass analysis for the degradation products indicated that mono- and dihydroxylation for the pyridine ring and oxidation of one or both of the terminal methyl groups have occurred. Based on this finding, this isolated bacterial can further be utilized for bioremediation purposes.

Evaluation of the Vitek 2, Phoenix and Microscan for Antimicrobial Susceptibility Testing of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia causes high mortality infections in immunocompromised hosts with limited therapeutic options. Many U.S. laboratories rely on commercial automated antimicrobial susceptibility tests (cASTs) and use CLSI breakpoints (BPs) for S. maltophilia. However, contemporary data on these systems is lacking. We assessed performances of Vitek2, MicroScan Walkaway and Phoenix relative to reference broth microdilution for trimethoprim-sulfamethoxazole (SXT), levofloxacin (LEV), minocycline (MIN) and ceftazidime (CAZ), with 109 S. maltophilia bloodstream isolates. Using CLSI breakpoints, categorical agreement (CA) was below 90% on all systems and drugs, with the exception of SXT by MicroScan (98.1%) and Phoenix (98.1%) and MIN by MicroScan (100%) and Phoenix (99.1%). For SXT, Vitek2 yielded a 77.1% CA. LEV and CAZ CA ranged from 67% - 85%. Very major errors (VME) were >3% for SXT (MicroScan, Phoenix), LEV (MicroScan) and CAZ (all systems). Major errors (ME) were >3% for SXT (Vitek 2), LEV (Phoenix) and CAZ (MicroScan, Phoenix). Minor errors were >10% for CAZ and LEV on all systems. Data were analyzed with EUCAST pharmacokinetic/pharmacodynamic CAZ, LEV, ciprofloxacin (CIP) and tigecycline (TGC) breakpoints when possible. CA was <90% for all. VME were >3% for CAZ (all systems), LEV (MicroScan), and TGC (Vitek2) and ME were >3% for LEV (MicroScan), CAZ (all systems), ciprofloxacin (Vitek2 and MicroScan) and TGC (Vitek 2, Phoenix). Minor errors (MI) were >10% for all agents and systems, by EUCAST breakpoints with an intermediate category (LEV, CAZ, CIP). Laboratories should use caution with cASTs for S. maltophilia as a high rate of errors may be observed.

Identification of selected primary bloodstream infection pathogens in patients attending Kisii level five and Homa Bay county hospitals

Background: Bloodstream infection (BSI) contributes to a substantial proportion of mortality in sub-Saharan Africa and is marked by the presence of bacterial and/or fungal microorganisms in the blood. Because BSI can be life threatening, it requires a timely, reliable and accurate diagnosis. This study retrospectively analyzed data of identified BSI pathogens and compared the performance of the different diagnostic technologies used in terms of accuracy, sensitivity, turnaround time (TAT) and cost. Methods: Currently, culture followed by analytical profile index biochemical strips (API), (BioMerieux) are used as the conventional standard diagnostics in Kenyan public hospitals and labs. We compared the results of this standard to that of the BioFire FilmArray (FA) (BioFire Diagnostics) and MicroScan WalkAway-40 plus System (MS) (Beckman Coulter) used in diagnosis of BSI. The FA technology was able to identify 150/152 bacterial and yeast isolates with an overall accuracy of 99.04% (95% CI: 96.59-99.88%), sensitivity of 98.68% (95% CI: 95.33-99.84%), mean TAT of 8 hours 40 minutes per eight samples and running cost per sample of USD 140.11. The MS identified 150/152 isolates with an overall accuracy of 98.56% (95% CI: 95.86-99.70%), sensitivity of 98.68% (95% CI: 95.30-99.84%), mean TAT per sample was 42 hours and running cost per sample of USD 28.05. API detected 150/152 isolates, with an overall accuracy of 99.04% (95% CI: 96.59-99.88%), sensitivity of 98.68% (95% CI: 95.33-99.84%) and the mean TAT per sample was 53 and 103 hours for bacterial and yeast samples, respectively, with a running cost per sample of USD 28.05.Conclusions: The findings in this paper suggest that the FA and MS platforms should be able to perform adequately in Kenya referral hospitals and medical clinics as a rapid diagnostic tool.

Resistencia a colistín mediado por el gen mcr-1 identificado en cepas de Escherichia coli y Klebsiella pneumoniae. Primeros reportes en el Perú

Introducción. Ante la aparición de reportes de la presencia del gen mcr-1 y su posible diseminación por plásmidos en los países de la región y dado que este gen confiere resistencia a colistín, fármaco que es la última línea de tratamiento contra bacterias multirresistentes, es importante conocer su presencia en nuestro país en microorganismos que lo expresen. Métodos. Se realizó un estudio descriptivo y transversal. Se incluyeron microorganismos aislados de urocultivos de pacientes ambulatorios de un centro de salud privado en Lima, Perú, en agosto del año 2017. De 326 urocultivos positivos se seleccionaron 10 aislamientos entre cepas de Escherichia coli y Klebsiella pneumoniae que presentaron concentración mínima inhibitoria ≥4μg/mL (interpretado como resistente para colistín) por el sistema automatizado Microscan Walkaway 96 plus. Se utilizaron los siguientes métodos: colistín agar spot, predifusión con tabletas de colistín, microdilución en caldo colistin y PCR para el gen mcr-1. Resultados. Se determinó que 7 aislamientos, todas Escherichia coli, expresaron la presencia del gen mcr-1 por PCR, el cual confiere resistencia plasmídica a polipéptidos. De las cepas restantes, dos Escherichia coli y una Klebsiella pneumoniae, resultaron positivos para resistencia a colistín en las pruebas fenotípicas pero no en la PCR para gen mcr-1 lo cual sugiere un mecanismo de resistencia a colistín no asociado a gen mcr-1. Conclusiones. Se obtuvieron 7 aislamientos de Escherichia coli resistentes a colistín y con expresión del gen mcr-1.