Commercial Broth Microdilution Research Articles

Implementation of the Rapid Polymyxin™ NP test directly to positive blood cultures bottles

The present study assessed the performance of Rapid Polymyxin™ NP test to detect colistin resistance directly from 132 blood cultures found positive for Enterobacterales by FilmArray. Additionally, colistin MICs of isolated microorganisms were determined by the commercial broth microdilution method ComASP™ Colistin, used as the gold standard comparator. The Rapid Polymyxin™ NP test correctly detected all colistin-resistant isolates. However, the test has misidentified as resistant 4 colistin-susceptible isolates (1 Escherichia coli and 3 Klebsiella pneumoniae). Molecular characterization of colistin-resistant isolates showed that K. pneumoniae, which belonged to ST15 and ST147, carried alterations in the mgrB. Moreover, the first Greek mcr-1–positive colistin-resistant E. coli was detected. The rapidity (2–3 h) of the results, combined with its excellent negative predictive value (100%), allows implementation of the test for routine testing of blood cultures mainly in the clinical settings that are endemic for carbapenem-resistant bacteria, avoiding misuse of colistin and preventing the spread of colistin-resistant bacteria.

Evaluation of six commercial products for colistin susceptibility testing in Enterobacterales

ObjectivesThe recommended technique for colistin susceptibility testing by both EUCAST and CLSI is broth microdilution (BMD). However, many routine laboratories still use other methods such as gradient strips or semi-automated systems. The objective of this study was to compare six of the most widespread commercial products for colistin susceptibility testing in Europe with in-house prepared BMD. MethodsA collection of 325 carbapenemase-producing Enterobacterales was tested for colistin susceptibility with three semi-automated systems (Vitek 2, BD Phoenix, MicroScan WalkAway), one gradient-strip test (Etest®) and two commercial BMD products (MICRONAUT-S, TREK Sensititre). BMD, in-house prepared according to ISO standard 20776-1, served as reference. ResultsThe MICRONAUT-S BMD performed best with only one false-resistant (major error, ME) and four false-susceptible (very major error, VME) results while the TREK BMD performed poorer with 16 ME and seven VME. The semi-automated systems Vitek 2 and Phoenix performed poorly with 31 and 26 VME, respectively. The WalkAway semi-automated system showed 16 and 13 false results, depending on the inoculation method. The Etest® showed six ME and 10 VME. ConclusionsThis study shows that colistin susceptibility testing remains a challenging task for laboratories. It emphasizes the need for selecting the most reliable test method to advocate proper treatment and shows that critical evaluation and precautious usage of colistin susceptibility testing results is constantly required.

Susceptibility Testing of Exophiala dermatitidis to Inform Peri-Operative Prophylaxis at Time of Lung Transplantation

Purpose Exophiala dermatitidis is a black fungus that frequently colonises the lungs of people with cystic fibrosis (CF). Mucoid and non-mucoid variants can be detected from the same sputum for some patients, but their role in chronic CF lung disease is not fully understood and attempts at early eradication are not routinely performed. Invasive infections with this species are rare; however in 2014 we reported our first case of fatal, invasive infection with a highly mucoid strain of E. dermatitidis in a 34 year old post lung transplant patient with CF. This prompted us to include peri-operative antifungal prophylaxis for all patients colonised with this species. To inform the choice of optimal antifungal, we performed susceptibility testing of 38 isolates from 34 patients including lung transplant patients. The ability of these isolates to produce biofilm was also investigated. Methods The minimum inhibitory concentration (MIC) of 8 antifungal agents was measured using a commercial broth microdilution assay. Biofilm formation was assessed using a standard in vitro assay using staining with crystal violet. Results Using breakpoints for Candida albicans, all isolates were susceptible to voriconazole and amphotericin B with most isolates also susceptible to itraconazole (89% of isolates) and posaconazole (71% of isolates). In contrast, all isolates were non-susceptible to caspofungin and most isolates (92%) non-susceptible to fluconazole. All strains were inhibited by ketoconazole at ≤0.25 mg/ L whereas MICs of 5-fluorocytosine ranged from 1->64 mg/ L. 31 of 38 isolates were biofilm producers including 4 isolates that were classified as strong biofilm producers. We did not find a correlation between mucoid phenotype and biofilm production. Conclusion E. dermatitidis is commonly found to colonise the lungs of patients with CF, typically produces biofilm, and may rarely produce serious infection post transplantation. We demonstrate in vitro susceptibility to voriconazole and amphotericin B. For patients colonised with this species, we now elect to include voriconazole as part of the peri-operative prophylactic regimen.

2441. Outcomes of Patients With Vancomycin-Resistant Enterococcus Blood Stream Infections (BSI) Treated With Daptomycin

BackgroundReports of poor outcomes in patients (patients) infected with VRE strains with daptomycin (DAP) minimum inhibitory concentrations (MIC) near the susceptible breakpoint (<=4 μg/ml) are noted in the literature. We assessed the relationship of clinical outcomes for patients treated with DAP to the initial MIC.MethodsRetrospective study of consecutive adult patients with VRE BSI treated with DAP for at least 48 hours (November 2011–January 2015) in a tertiary hospital in Cleveland, OH. Patients were grouped based on the initial DAP MIC (MIC ≤ 2 μg/mL and MIC = 4 μg/mL) determined by a commercial broth microdilution method (Sensititre). Demographic and clinical data were extracted via EMR. Outcomes for all-cause mortality at 30 days (30-D mortality) and 90 days (90-D mortality), 30-day mortality attributed directly to VRE BSI (30-D mortality VRE) and microbiological failure (MF) were measured. MF was defined as duration of bacteremia ≥4 days after at least 48 hours of DAP use and achievement of source control when possible. We also assessed the impact of concomitant β-lactam use on MF.ResultsA total of 192 patients were identified. Baseline characteristics are shown in Table 1. Outcomes for MF, 30-D mortality VRE, 30-D mortality and 90-D mortality are shown in Table 2. Impact of concomitant β-lactam use on MF is shown in Figure 1.ConclusionIn this retrospective study, MF and mortality were not significantly higher for BSI caused by VRE with DAP MICs of 4 μg/ml, regardless of concomitant β-lactam use. Disclosures S. S. Richter, bioMerieux: Grant Investigator, Research grant. BD Diagnostics: Grant Investigator, Research grant. Roche: Grant Investigator, Research grant. Hologic: Grant Investigator, Research grant. Diasorin: Grant Investigator, Research grant. Accelerate: Grant Investigator, Research grant. Biofire: Grant Investigator, Research grant.

Presence of L701 M mutation in the FKS1 gene of echinocandin-susceptible Candida krusei isolates

Resistance of Candida krusei isolates to echinocandins, the recommended drugs to treat candidemia, has been associated with mutations in hot spot (HS) regions of the FKS1 gene or L701 M mutation in a region between HS1 and HS3 of FKS1. However, the role of L701 M mutation alone in causing reduced echinocandins susceptibility is still unclear. We analyzed a region between HS1 and HS3 of FKS1 of 25 C. krusei isolates from clinical samples. Susceptibility to echinocandins was determined by a commercial broth microdilution assay and by the microdilution method according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST). The L701 M mutation was detected in 22/25 (88%) C. krusei isolates with low MIC values in the absence of other HS mutations. The presence of isolated L701 M mutation in C. krusei clinical isolates susceptible to echinocandins suggests that this mutation may be just associated to polymorphism in the C. krusei population.

Molecular characterization and antimicrobial susceptibility pattern of Streptococcus agalactiae isolated from clinical mastitis in dairy cattle.

The objectives of this study were to: (a) genotypically characterize Streptococcus agalactiae isolates recovered from clinical mastitis (CM) cases in dairy cows and, (b) determine the association of antimicrobial susceptibility (AMS) and genotypes of Strep. agalactiae clustered according to the genetic similarity. A total of 89 Strep. agalactiae isolates recovered from bovine CM were genotyped using random amplified polymorphic DNA (RAPD) analysis. In addition, the AMS of the isolates was determined using a commercial broth microdilution test composed of 10 antimicrobials (penicillin, ampicillin, oxacillin, cephalothin, ceftiofur, penicillin/novobiocin, erythromycin, pirlimycin, tetracycline, and sulfadimethoxine). Descriptive analysis was used to report the frequency of RAPD-types and genotypic clusters within herd, housing system, season and CM severity scores. The minimal antimicrobial concentrations that inhibited 50% (MIC50) and 90% (MIC90) of the isolates were calculated and survival analysis was completed to verify the differences of AMS among genotypic clusters. Results of RAPD showed a great genotypic diversity of Strep. agalactiae (45 RAPD-types) and three clusters (Ia, Ib and II) were created based on the genetic similarity among genotypes. After clustering, a high genetic similarity was observed within and between herds. Overall, Strep. agalactiae showed high susceptibility to most antimicrobials, except to tetracycline and erythromycin. Differences in the AMS among clusters were observed for ampicillin, ceftiofur, erythromycin, pirlimycin, sulfadimethoxine and tetracycline. In conclusion, Strep. agalactiae is still highly susceptible to most antimicrobials, although differences in susceptibility to certain antimicrobials were observed among genotypic clusters.

Antimicrobial susceptibility testing of colistin – evaluation of seven commercial MIC products against standard broth microdilution for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter spp.

ObjectiveBoth EUCAST and CLSI recommend broth microdilution (BMD) for antimicrobial susceptibility testing of colistin, but BMD is rarely used in routine microbiology laboratories. The objective of this study was to evaluate five commercially available BMD products and two brands of gradient tests for colistin MIC determination using BMD according to ISO standard 20776-1 as reference. MethodsColistin MIC determination was performed according to the manufacturer's instructions on five commercially available BMD products (Sensititre, MICRONAUT-S, MICRONAUT MIC-Strip, SensiTest, and UMIC) and two gradient tests (Etest and MIC Test Strip). Colistin reference MICs were determined using frozen panels according to ISO standard 20776-1. An international collection of Gram-negative bacteria (n=75) with varying levels of colistin susceptibility was tested. ResultsThe colistin BMD products correlated well with reference tests, in particular for Sensititre and the two MICRONAUT products (essential agreement ≥96%: 66/69 (96%, CI 88–99%), 72/75 (96%, CI 88–99%) and 74/75 (99%, CI 92–100%)). The results were somewhat poorer for the BMD products SensiTest and UMIC: EA 88% (51/58, CI 77–95%) and 82% (61/74, CI 72–89%), respectively), and considerably poorer for the gradient tests (EA 43–71% depending on gradient test and Mueller-Hinton agar manufacturer). The gradient tests generally underestimated colistin MICs, resulting in a significant number of false susceptible results (9–18 of total 75 tests, compared with 1–3 for the BMD products). ConclusionsBased on the results of this study, we advise laboratories not to trust gradient tests for colistin susceptibility testing and to use broth microdilution methods for this purpose. There are several commercial broth microdilution tests available and in principle they perform well.

Susceptibility Testing for the Polymyxins: Two Steps Back, Three Steps Forward?

Optimizing and standardizing susceptibility testing for the polymyxins have become pressing issues, given the rise in multidrug-resistant Gram-negative bacilli. Recently, both the CLSI and EUCAST have recommended broth microdilution (BMD) (without polysorbate) as the reference method for polymyxin susceptibility testing. In this issue, K. L. Chew et al. (J Clin Microbiol 55:2609-2616, 2017, https://doi.org/10.1128/JCM.00268-17) compare the performances of three commercial BMD panels and the Etest to the reference, BMD, for polymyxin B and colistin, using 76 Enterobacteriaceae isolates (21 of which were mcr-1 positive). Although none of the commercial BMD panels strictly met FDA performance standards in this evaluation, possibly because of the small number isolates tested, the Sensititre panel achieved >90% categorical agreement for both polymyxin compounds. These results also reaffirm CLSI and EUCAST guidance that gradient diffusion testing, which had unacceptable error rates, should be abandoned. In a simulated analysis with lowered breakpoints (susceptible, ≤1 mg/liter; intermediate, 2 mg/liter; resistant, ≥4 mg/liter), error rates and agreement were improved across the various methods and the rate of detection of mcr-1-positive isolates improved. These observations, taken together with recent pharmacokinetic data on optimizing target attainment for the polymyxins, suggest that more-stringent (lower) breakpoints may be reasonable, although such an approach may be limited by the inherent reliability of current testing methodologies and a lack of robust clinical correlative data, which are sorely needed.

Multi-center and multi-method evaluation of in vitro activities of ceftaroline against S. aureus

This five-site study was performed to assess the reproducibility of ceftaroline MIC and disk results for Staphylococcus aureus. Three commercial broth microdilution, three gradient diffusion and ceftaroline 5μg disk diffusion methods were compared to a reference broth microdilution method against challenge isolates (n = 41) and isolates collected at four European sites (n = 30/site). For four MIC methods (Sensititre and three gradient diffusion methods), 99.0% of consolidated MIC results were within +/− 1 dilution of the reference MIC. Categorical agreement rates based on EUCAST breakpoints for the challenge isolates were 75.6-100% and for disk testing were 78.0-92.7%. There was no clear distinction between isolates with MIC results of 1 and 2mg/L with regard to variation in MIC or molecular genotyping results. The addition of an intermediate category for isolates with MIC results of 2mg/L would help to identify these isolates as borderline susceptible/non-susceptible isolates.

Differences in potency and categorical agreement between colistin and polymyxin B when testing 15,377 clinical strains collected worldwide

Gram-negative bacilli (n=15,377) were tested against colistin (polymyxin E) and polymyxin B by a commercial broth microdilution method (Sensititre®). Among Pseudomonas aeruginosa and Acinetobacter spp., colistin and polymyxin B MIC values were within ±1 doubling dilution for >99.0% of strains. Among Klebsiella spp. and Escherichia coli, 55.0 and 53.2% of strains displayed a colistin MIC 2-fold lower than polymyxin B, but polymyxin B was slightly more potent than colistin against strains with decreased susceptibility to either polymyxin.

Influencia de la correcta identificación en la interpretación de las pruebas de sensibilidad en aislados de Aeromonas spp. productoras de bacteriemia

ObjectiveTo assess the relevance of correct identification and interpretation of susceptibility testing of Aeromonas spp. bacteremia isolates using newly developed molecular methods in comparison to previous conventional methods. Material and methodsThe study included 22 patients with bacteremia due to Aeromonas hydrophila group, microbiologically characterized using the MicroScan system. Further identification to species level was performed by mass spectrometry, and confirmed by sequencing the rpoB gene.The MIC of imipenem, cefotaxime, piperacillin-tazobactam, ciprofloxacin and cotrimoxazole was studied using a commercial broth microdilution and antibiotic gradient strips with low and high inocula. Detection of carbapenemase production was performed using the modified Hodge test, and was confirmed by amplifying the cphA gene by PCR. ResultsA total of 9 (40.9%) isolates were identified as Aeromonas hydrophila, 8 (36.4%) as Aeromonas veronii, and the remaining 5 (22.7%) isolates as Aeromonas caviae.Resistance to beta-lactams according to both the commercial microdilution and MIC gradient strips methods was: 36%-50% to imipenem; 4%-56% to cefotaxime, and 27%-56% to piperacillin/tazobactam.The agreement between results generated by the automated system and the diffusion antibiotic gradient strip was, for all 3 species, 68% for imipenem, 50% to cefotaxime, and 46% to piperacillin/tazobactam.No resistance to cotrimoxazole and ciprofloxacin was found by either of the two methods, although 22.7% of the strains were resistant to nalidixic acid. ConclusionsIt is essential to identify the isolates of Aeromonas spp. at the species level, due to the fact that beta-lactam resistance is species- and method-dependent. The high rate of resistance to beta-lactam and quinolones reduce their application as empiric treatments for invasive infection by Aeromonas ssp.

Validation of Sensititre Dry-Form Broth Microdilution Panels for Susceptibility Testing of Ceftazidime-Avibactam, a Broad-Spectrum-β-Lactamase Inhibitor Combination.

Ceftazidime-avibactam is a broad-spectrum-β-lactamase inhibitor combination in late-stage clinical development for the treatment of serious infections. In preparation for clinical microbiology laboratory use, a validation experiment was initiated to evaluate a commercial broth microdilution product (Sensititre dried MIC susceptibility system) compared to reference panels using 525 recent clinical isolates. Among 11 pathogen groups, all had Sensititre MIC/reference MIC ratios predominantly at 1 (47.5% to 97.5%), and automated and manual endpoint results did not differ. Enterobacteriaceae MIC comparisons showed a modest skewing of Sensititre MIC results toward an elevated MIC (33.9%), but the essential agreement was 98.9% with 100.0% reproducibility. In conclusion, Sensititre panels produced accurate ceftazidime-avibactam MIC results, allowing quality MIC guidance for therapy following regulatory approvals.

MRSA carrying mecC in captive mara.

ObjectivesTo characterize the staphylococcal cassette chromosome mec (SCCmec), virulence and antimicrobial susceptibility of Staphylococcus aureus ST130 isolated from mara (Dolichotis patagonum), a large rodent species native to South America and kept in captivity at Copenhagen Zoo.MethodsThe presence of mecC was confirmed by PCR in 15 S. aureus ST130 isolated from mara during a previous study. WGS was performed on two randomly selected isolates to characterize their genomes with respect to SCCmec, virulence and resistance gene content. Antimicrobial susceptibility was tested using commercial broth microdilution tests.ResultsAll the isolates belonged to spa type t528 ST130 and carried mecC. Based on WGS, mecC was 100% identical to the prototype sequence of S. aureus strain LGA251. The sequence of SCCmec type XI in the mara isolates had 23 SNPs compared with the one described in LGA251. The two sequenced strains harboured a set of virulence factors and other genomic features previously observed in ST130. Both strains carried norA as the only putative antimicrobial resistance gene in addition to mecC.ConclusionsOur findings support the notion that a genetically conserved mecC-carrying MRSA ST130 clone is widespread in a variety of unrelated hosts in Denmark. Since the mara at Copenhagen Zoo have limited contact with humans and other animal species, it remains unclear whether mara are natural hosts of ST130 or acquired this lineage from unknown sources. The broad host range of MRSA ST130 supports its designation as a generalist lineage.

Validation of a commercial dry-form broth microdilution device (Sensititre) for testing tedizolid, a new oxazolidinone.

Tedizolid, a novel oxazolidinone antibacterial with potent activity against a wide range of Gram-positive pathogens, was recently approved by regulatory authorities for the treatment of acute bacterial skin and skin structure infections. A commercial broth microdilution device (Sensititre; Thermo Fisher Scientific) was validated using 285 selected Gram-positive isolates, and the device was documented to have 100.0% essential and categorical agreement with reference MIC results and excellent MIC endpoint reproducibility.

Relationship between level of antibiotic use and resistance among Escherichia coli isolates from integrated multi-site cohorts of humans and swine

The objective of this longitudinal ecological study was to examine the relationship between the prevalence of antibiotic-resistant (AR) commensal Escherichia coli isolates from both monthly human wastewater and composite swine fecal samples and the concurrent aggregated monthly antibiotic use recorded within each host species in multi-site vertically integrated swine and human populations. In addition, human vocation (swine worker versus non-swine worker), swine production group, and season were examined as potential confounding variables. Human and swine E. coli isolates ( n = 2469 human and 2310 swine, respectively) were tested for antimicrobial susceptibility using a commercial broth microdilution system. In the human population, among swine workers the relative odds of tetracycline resistance were increased significantly for tetracycline (class) drug use at the third quartile and above of mean monthly dosage (MMD) (OR = 1.8) as compared to the referent category (non-use). The relative odds of ciprofloxacin resistance were significantly increased for ciprofloxacin use in non-swine workers (OR = 5.5) as compared to the referent (non-use). The relative odds of tetracycline resistance were increased significantly for chlortetracycline use in medicated feed for the upper tertile of MMD category (OR = 2.9) as compared to the referent category (no use) across all swine production groups. While high variability among seasonal samples over the 3-year period was observed, no common seasonal trends relating to antibiotic use and prevalence of resistance over the 3-year period were apparent. The overall effects of concurrent human and swine antibiotic use on AR E. coli levels were inconsistent and modest in this study.

Tigecycline Activity Against Isolates from Medical Centers Located in China, Hong Kong and Taiwan (2006): A SENTRY Antimicrobial Surveillance Program Report

Background: There are no published information on tigecycline potency and spectrum from isolates from Indonesia. As a component of the SENTRY Antimicrobial Surveillance Program (Asia-Pacific Region), we evaluated the activity of tigecycline tested against recent (2006) isolates from Indonesia by reference MIC methods. Methods: Non-duplicate strains were consecutively collected from three medical centres in Indonesia. All isolates were tested against tigecycline using validated commercial broth microdilution panels (TREK Diagnostics), with concurrent acceptable quality control and CLSI interpretations (M100-S18) for comparison agents. Tigecycline breakpoints published by the United States Food and Drug Administration were applied for each indicated species or genus, and the proposed/provisional Acinetobacter spp. breakpoint (≤2mg/L) per Jones et al. (2007) was applied Results: A total of 383 (307 Gram-negative and 76 Grampositive) isolates were evaluated. Tigecycline was highly active against the top 10 most frequently isolated nonpseudomonal pathogens which comprised 82% of all strains. The highest tigecycline MIC90 results (2mg/L were recorded for non-indicated species, Proteus-Providencia. P. aeruginosa was also not significantly inhibited by tigecycline (MIC90, >8mg/L; data not shown) Conclusions: Tigecycline demonstrated excellent activity against all the commonly isolated pathogens from Indonesia, including those being multidrug-resistant to other antimicrobial classes. Tigecycline shows promise for therapy of indicated, antimicrobial-resistant species in this nation and indeed, the entire Asia-Pacific region.

Evaluation of MicroScan MICroSTREP Plus Antimicrobial Susceptibility Panel for TestingStreptococcus pneumoniae

93.0%. Overall there were 11.7% minor, 0.7% major, and 0.7% very major interpretative category errors observed. The results of antibiotic susceptibility testing by Etest were similar to those obtained by the MicroScan MICroSTREP plus panel. Conclusion: The MicroScan MICroSTREP plus panel, a commercial broth microdilution method, has a comparable accuracy to CLSI broth microdilution method for the resistance testing of S. pneumonia. This panel can be used for determining susceptibilities of S. pneumoniae to a wide variety of antimicrobial agents in clinical microbiology laboratories. (Korean J Clin Microbiol 2008;11:18-22)

Prevalence of Campylobacter spp. in cattle in Finland and antimicrobial susceptibilities of bovine Campylobacter jejuni strains.

The study investigated the prevalence of Campylobacter spp. in Finnish cattle at slaughter and carcass contamination after slaughter. During the period January to December 2003, bovine rectal fecal samples (n=952) and carcass surface samples (n=948) from 12 out of 15 Finnish slaughterhouses were examined. In total, campylobacters were detected in 31.1% of fecal samples and in 3.5% of carcass surface samples. Campylobacter jejuni was isolated from 19.5%, Campylobacter coli from 2.2%, and presumptive Campylobacter hyointestinalis from 10.8% of fecal samples. Campylobacters were detected in 4.4% and 37.4% of the fecal samples examined both by direct culture and by enrichment (n=730), respectively, suggesting a low level of campylobacters in the intestinal content. A slightly increasing trend was observed in the overall prevalence of campylobacters towards the end of summer and autumn. Seventeen different serotypes were detected among the fecal C. jejuni isolates using a set of 25 commercial antisera for serotyping heat-stable antigens (Penner) of C. jejuni by passive hemagglutination. The predominant serotypes, Pen2 and Pen4-complex, were isolated from 52% of the fecal samples. Subtyping by pulsed-field gel electrophoresis (SmaI) yielded 56 and 20 subtypes out of 330 fecal and 70 carcass C. jejuni isolates, respectively. MICs of ampicillin, enrofloxacin, erythromycin, gentamicin, nalidixic acid, and oxytetracycline for 187 C. jejuni isolates were determined using a commercial broth microdilution method. Sixteen (9%) of the isolates were resistant to at least one of the antimicrobials tested. Resistance to nalidixic acid was most commonly detected (6%). No multiresistance was observed.

Commercial broth microdilution panel validation and reproducibility trials for NVP PDF-713 (LBM 415), a novel inhibitor of bacterial peptide deformylase

NVP PDF-713 (LBM 415) is a peptide deformylase inhibitor being progressed into clinical trials. Dry-form broth microdilution panels of NVP PDF-713 were compared to reference MIC panels of 552 recent clinical isolates. Most (99.2%) dry-form MIC results were within +/- 1 log(2) dilution of the reference panel MICs. Of the bacteria tested, Streptococcus pneumoniae and Haemophilus influenzae showed a bias towards higher and lower MICs, respectively. Same-day and between-day reproducibility tests showed that 98.9% and 96.7% of MIC values, respectively, were within +/- 1 log(2) dilution step, thereby demonstrating a high degree of reliability of the dry-form MIC product for clinical studies.

Validation of commercial dry-form broth microdilution panels and test reproducibility for susceptibility testing of dalbavancin, a new very long-acting glycopeptide

Results from dalbavancin dry-form commercial broth microdilution MIC panels (Sensititre, TREK Diagnostics) were compared with reference frozen-form MIC values to assure the validity and reproducibility of the extended shelf-life product. A collection of 402 organisms from four major organism groups were used in the validation trial and 10 strains for reproducibility replicate tests. A total of 98.6% commercial dalbavancin MIC results were within ±1 log 2 dilution of reference values (76.2% were identical) and reproducibility trials produced identical MIC results in 88.9–92.2% of dalbavancin MIC comparisons. These dalbavancin MIC results demonstrated the acceptable accuracy of commercially-prepared broth microdilution products for use in subsequent clinical trials.