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The eQUANT System is an automated inoculum preparation system that uses potentiometric sensing of oxidation-reduction potential changes due to pathogen metabolism to generate a 0.5 McFarland-equivalent suspension (the eMcFarland or eMcF) from positive blood culture samples that can be used for direct, qualitative in vitro susceptibility testing by the agar disk diffusion test method (Kirby-Bauer). Samples are processed directly from blood culture samples identified as positive by a continuous monitoring blood culture system and confirmed as Gram-negative rods by Gram stain. Organism identification must be confirmed by an FDA cleared device for direct testing from positive blood culture before processing samples on the eQUANT System.

Evaluation of the eQUANT System's inoculum preparation was conducted for use with agar disk diffusion susceptibility testing and performance was demonstrated for the following antimicrobial agents with Enterobacterales species, Acinetobacter species and Pseudomonas aeruginosa as identified below:

Amoxicillin/clavulanate- Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis

Ampicillin- Escherichia coli

Aztreonam- Citrobacter freundii, Enterobacter cloacae, Escherichia aerogenes, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens, and Pseudomonas aeruginosa

Cefazolin- Klebsiella pneumoniae

Cefepime- Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens, and Pseudomonas aeruginosa

Ceftriaxone- Citrobacter freundii, Enterobacter cloacae, Escherichia aerogenes, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens

Ertapenem- Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Klebsiella axytoca, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens

Gentamicin- Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Klebsiella axytoca, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens, and Pseudomonas aeruginosa

Levofloxacin- Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens, and Pseudomonas aeruginosa

Meropenem- Acinetobacter spp., Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens, and Pseudomonas aeruginosa

Piperacillin/tazobactam- Acinetobacter spp., Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Serratia marcescens, and Pseudomonas aeruginosa

Tobramycin- Citrobacter freundii, Enterobacter cloacae, Escherichia aerogenes, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus vulgaris, Serratia marcescens, and Pseudomonas aeruginosa

Susceptibility test results are intended to be used in conjunction with other clinical and laboratory findings. Standard laboratory protocols for processing positive blood cultures should be followed to ensure availability of isolates for supplemental testing as needed. Additionally, subculture of positive blood culture is necessary for the susceptibility testing of organisms present in polymicrobial samples, for testing antimicrobial agents and species not indicated for testing with the device, for epidemiologic testing, and for recovery of organisms present in microbial samples.

The eQUANT™ System is an automated system that uses potentiometric sensing of changes in oxidationreduction potential (ORP) during pathogen metabolism to prepare an organism concentration equivalent to a 0.5 McFarland (1-2e8 CFU/ml ± 0.6 log) directly from a positive blood culture. The eQUANT™ System consists of four components: the eQUANT™ Instrument, a single use eTube™ Disposable, a single use eQUANT™ Reagent tube (CAMHB with antifoam), and a workflow tray.

The eQUANT™ System processes a single positive blood culture sample at a time. Before processing on the eQUANT™ System, the positive blood culture is confirmed as Gram-negative rods by Gram stain, and a rapid FDA-cleared identification (ID) method for testing from positive blood culture is performed to confirm organism ID. Mixed cultures or organisms identified that are not included in the eQUANT™ System indications for use should not be processed on the eQUANT™ System. Positive blood cultures must be processed immediately on the eQUANT™ System or within 12 hours of blood culture bottle positivity should delays be unavoidable. Once the organism ID is confirmed, 1 mL of eQUANT™ Reagent (cation-adjusted Mueller Hinton broth (CAMHB) supplemented with antifoam (0.0015%) to reduce air bubble formation) is added to the eTube™ Disposable, followed by the addition of 34 µL of the positive blood culture. The eTube™ Disposable with diluted sample is vortexed and then placed in the eQUANT™ System for incubation.

Once inserted, the eTube™ Disposable sits in a thermal module which is heated to 37°C ± 2°C to grow the bacteria to a concentration equivalent to a 0.5 McFarland, or eMcF). The eQUANT™ Sensor located in the eTube™ Disposable is an ORP sensor consisting of two electrode components, which both come into direct contact with the diluted positive blood culture sample. The eQUANT™ ORP sensor responds to changes in the ORP during pathogen growth/metabolism. As the concentration of microorganisms in the sample increases, the growth media becomes reduced, and the voltage measured by the ORP sensor becomes more negative. With the organism ID of the tested sample and the blood culture bottle type as inputs to the system, the algorithm is applied to the real-time voltage measurements to determine the point in time at which the organism concentration reaches a level equivalent to a standard 0.5 McFarland. At the endpoint, the sample immediately starts to cool down to 15°C ± 2°C to inhibit further growth. The sample can be held for up to one (1) hour on the instrument, before being used for downstream Disk Diffusion AST testing.

Here's a breakdown of the acceptance criteria and study information for the eQUANT System, based on the provided document:

Acceptance Criteria and Device Performance

• A. baumannii: >95% CA for all bottle types assessed (100% CA).
• P. aeruginosa: >95% CA for all bottle types except BD BACTEC Aero Plus (90.5% CA, with two minor errors). The two minor error eQUANT™ zone diameters were less than 3 mm difference compared to the standard method, considered acceptable.
• Enterobacterales: >95% CA only obtained for BACT/ALERT SN (96.9% CA). Other bottle types showed 90-93% CA due to minor errors. The majority (93.8%) of error results had zone diameters ≤3 mm difference compared to the standard method, considered acceptable. 63/64 minor errors were due to a single K. pneumoniae isolate. (Table 4) |
  | Interfering Substances (eMcFarland Concentration): All eMcFarland concentrations meet 2.51e7 – 7.96e8 CFU/mL in the presence of interferents. | All resulting eMcFarland concentrations met defined acceptance criteria (2.51e7 – 7.96e8 CFU/mL). (Tables 5-6) |
  | Interfering Substances (Downstream AST): No reproducible interference observed in downstream AST testing. | No reproducible interference was observed. (Tables 5-6). High concentrations of hemoglobin (A. baumannii, P. aeruginosa) and platelets (P. aeruginosa) initially caused aborted runs. At decreased interferent concentrations, valid eMcFarlands were generated, and AST results were as expected. Minor errors in Ampicillin and Chloramphenicol were deemed acceptable due to zone diameter differences ≤ 3 mm. |
  | Carryover: No bacterial carryover between runs. | No carryover was observed, as evidenced by monomicrobial cultures and the expected organism morphology during alternating runs of E. coli and P. aeruginosa. |
  | Method Comparison (eMcFarland Concentration): ≥95% of eMcFarland colony counts fall within 2.51e7 – 7.96e8 CFU/mL. | 99.1% of PBC samples were within the expected colony count range (219/221 samples). Two samples (one A. spp., one P. aeruginosa) were outside the range, but showed no errors in Disk Diffusion results. (Table 8) |
  | Method Comparison (Disk Diffusion AST):
• Overall CA: ≥95%
• VME: ≤1%
• ME: ≤1.5%
  (for each antimicrobial agent/organism group combination) | Most antibiotic/group combinations met overall acceptance criteria.
• Exceptions to ≥95% CA: Amoxicillin/Clavulanate/Enterobacterales (94%), Cefazolin/Enterobacterales (85% - *removed from Indications for Use for E. coli and P. mirabilis due to

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