CHROMID CARBA agar (CARB) by bioMerieux SA

CHROMID® CARBA agar is a selective and differential chromogenic medium that is intended for the qualitative detection and presumptive identification of carbapenemase-producing Escherichia coli and Klebsiella pneumoniae in rectal swab specimens from patients at risk of colonization. CHROMID® CARBA agar is intended as an aid in the detection, identification of colonization and control of these bacteria in a healthcare setting.

Rectal swabs are inoculated directly onto CHROMID® CARBA agar without enrichment and results can be interpreted after incubation for 18-24 hours. Presumptive carbapenemase-producing colonies of E. coli appear pink to burgundy and those of K. pneumoniae appear blue-green or blue-grey.

Other organisms besides carbapenemase-producing E. coli and K. pneumoniae can also grow on CHROMID® CARBA agar with colonies that appear pink to burgundy or blue-grey. Sub-culture to non-selective medium is required to confirm organism identity, for antimicrobial susceptibility testing, confirmation of carbapenemase production and epidemiological typing.

A lack of growth or the absence of pink to burgundy or blue-grey colonies does not preclude the carriage of carbapenemase producing organisms.

Device Description

CHROMID® CARBA agar consists of a nutritive base combining different peptones, 3 chromogenic substrates and antibiotics. These components enable the screening and presumptive identification of E. coli: spontaneous coloration (pink to burgundy) of strains producing ß-glucuronidase (ß-GUR) and/or ß-galactosidase (ß-GAL) and K. pneumoniae: spontaneous blue-green to bluish-grey coloration of strains producing ß-glucosidase (ß-GLU) from rectal swabs.

AI/ML Overview

The document describes the regulatory approval of CHROMID® CARBA agar, a chromogenic medium for detecting carbapenemase-producing Escherichia coli and Klebsiella pneumoniae. While it specifies the device's performance, it doesn't present "acceptance criteria" in a typical table format with specific target values like "sensitivity > X%" and "specificity > Y%." Instead, it details the results of analytical and clinical studies to demonstrate the device's acceptable performance and substantial equivalence to a predicate device.

Here's an attempt to structure the information based on your request, inferring acceptance criteria from the presented results:

1. Table of Acceptance Criteria (Inferred from Study Results) and Reported Device Performance

Since explicit numerical acceptance criteria were not directly stated, they are inferred based on the observed "acceptable results" and high agreement percentages across various studies.

Acceptance Criteria Category	Inferred Acceptance Threshold (Goal)	Reported Device Performance (CHROMID® CARBA agar)
Analytical Performance
Limit of Detection (LOD)	Low CFU/mL detected for target strains.	1.5x10³ CFU/mL for K. pneumoniae ATCC® 1705™ and E. coli ATCC® 2340™.
Cross Reactivity (Specificity)	Minimal cross-reactivity with non-target organisms; Characteristic coloration for CPE.	16 CPE strains (various species and carbapenemases) grew with characteristic pink/blue-green/blue-grey colonies. Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Pseudomonas putida, and Acinetobacter baumanii grew but without characteristic coloration (colorless), indicating acceptable specificity.
Challenge Testing (Reactivity)	High recovery rate of target strains with characteristic colors.	K. pneumoniae: All 41 strains recovered with characteristic blue-green color. E. coli: 9/11 strains grew with characteristic burgundy color; 2 E. coli failed (one had intermediate MICs, the other susceptible to carbapenems).
Mixed Infection	Target organisms detectable in presence of other flora up to certain concentrations.	When competitive species were <10⁸ CFU/mL, target KPC-producing organisms grew with characteristic color. At 10⁸ CFU/mL, some competitive species inhibited or masked growth of target organisms. This indicates a practical limit to detection in heavily contaminated samples, which is a known limitation for culture media.
Incubation Time	Consistent performance within 18-24 hours.	All 10 KPC-EK strains recovered with expected colony colors after 16 hours of incubation and at each 2-hour interval up to 28 hours, supporting the 18-24 hour incubation window.
Interfering Substances	No interference with common substances.	No interference observed with 21 tested interfering substances (e.g., medical lubricants, medications, natural products).
Clinical Performance
Prospective Clinical Study: Overall PP/NP Agreement for E. coli	High PPA and NPA.	Positive Percent Agreement (PPA): Not applicable (0 positive E. coli cases in clinical study).Negative Percent Agreement (NPA): 99.7% (707/709); 95% CI 99.0-99.9%.
Prospective Clinical Study: Overall PP/NP Agreement for K. pneumoniae	High PPA and NPA.	PPA: 84.3% (43/51); 95% CI 72.0-91.8%.NPA: 97.7% (643/658); 95% CI 96.3-98.6%.
Contrived Samples: Overall PP/NP Agreement for E. coli	High PPA and NPA.	PPA: 80.0% (16/20); 95% CI 58.4-91.9%.NPA: 98.9% (188/190); 95% CI 96.2-99.7%.
Contrived Samples: Overall PP/NP Agreement for K. pneumoniae	High PPA and NPA.	PPA: 96.6% (84/87); 95% CI 90.3-98.8%.NPA: 91.1% (112/123); 95% CI 84.7-94.9%.
Reproducibility	High agreement between sites and operators.	Overall between-site reproducibility: 99.3% (894/900).
Quality Control	High agreement with expected results for QC organisms.	Overall QC test results: 99.8% (569/570) as expected. Includes 100% agreement for positive controls and 99.5% for negative control.

2. Sample Size Used for the Test Set and Data Provenance

Analytical Studies (Overall): Specific sample sizes vary per analytical test:
- Recovery Study (LOD): 2 well-characterized KPC strains.
- Cross Reactivity: 59 target and non-target organisms.
- Challenge Testing (Analytical Reactivity): 52 KPC-EK strains.
- Mixed Infection: 4 carbapenemase-producing strains in various mixtures.
- Incubation: 10 KPC-EK strains.
Clinical Studies / Method Comparison:
- Prospective Clinical Study: Total of 709 unique rectal swab specimens were included in the analysis.
  - Data Provenance: Prospectively collected rectal swabs from three external laboratories (2 in the US, 1 in Europe).
- Challenge Study (Clinical Section): 50 well-characterized isolates (11 KPC negative, 39 KPC positive) tested in saline matrix.
  - Data Provenance: One external site.
- Contrived Samples Study: Total of 210 contrived samples (simulated rectal swab matrix).
  - Data Provenance: Tested at four different sites.
- Reproducibility: 10 well-characterized isolates tested in triplicate each day for five days at three sites.

3. Number of Experts Used to Establish Ground Truth for the Test Set and Their Qualifications

The document does not explicitly state the number of experts or their specific qualifications (e.g., "radiologist with 10 years of experience") for establishing the ground truth for the test sets.
For the clinical studies, "ground truth" was established based on a combination of CDC enrichment culture method, followed by subculture, biochemical identification, carbapenem susceptibility testing, CARBA NP testing, and PCR for carbapenemase resistance markers (blaKPC, blaNDM, blaOXA-48, blaVIM, blaIMP). This indicates a highly technical and multi-faceted laboratory-based ground truth definition rather than expert visual interpretation. The performance of these reference methods themselves would implicitly rely on expert laboratory personnel and validated protocols.

4. Adjudication Method for the Test Set

The document does not describe an explicit adjudication method (like 2+1 or 3+1 consensus) for the test set used in the context of human reviewers agreeing on an outcome.
The determination of the "carbapenemase status" for ground truth in clinical studies followed a defined algorithm (Table 1), which relied on multiple laboratory tests (MIC, Carba NP, PCR). This is a rules-based, objective definition rather than an expert consensus interpretation.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No, an MRMC comparative effectiveness study was not done.
This device is a culture medium interpreted visually (colony color). The studies described are primarily analytical and clinical performance evaluations of the medium itself, not comparative studies of human reader performance with or without AI assistance. The "reader" in this context is a lab technician observing colony growth and color.

6. Standalone (Algorithm Only Without Human-in-the-Loop Performance)

This question is not directly applicable to the device. CHROMID® CARBA agar is a manual culture medium that relies on visual interpretation by a human observer (a laboratory technician/microbiologist). It is not an AI algorithm. Its performance is inherently "human-in-the-loop," as the human observes the results.

7. Type of Ground Truth Used

Expert Consensus / Reference Method based on Laboratory Techniques for Clinical Samples:
- For the clinical studies, the "ground truth" (Carbapenemase Status) was highly robust, determined by a comprehensive CDC enrichment culture method combined with:
  - Biochemical identification
  - Carbapenem susceptibility testing
  - CARBA NP testing (a phenotypic test for carbapenemase activity)
  - PCR for specific carbapenemase resistance genes (blaKPC, blaNDM, blaOXA-48, blaVIM, blaIMP).
- A specific algorithm (Table 1) was used to integrate these results to define a positive or negative carbapenemase status. This is a very strong, multi-modal, and objective form of ground truth for microbial resistance.

8. Sample Size for the Training Set

The document does not explicitly mention a separate "training set" as is common in AI/machine learning contexts. This is because the device is a chemical culture medium, not a machine learning model that undergoes a training phase. Its formulation and development (analogous to "training") would be based on scientific principles of microbiology and chromogenic media development, validated through the analytical and clinical studies described.

9. How the Ground Truth for the Training Set Was Established

As there is no distinct "training set" for an AI model, this question is not applicable. The development of the medium's formula would have relied on known biochemical properties of target organisms and carbapenemase mechanisms discovered through extensive microbiological research, which form the scientific basis for its selective and differential properties.

Summary

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Image /page/0/Picture/0 description: The image contains the logo of the U.S. Food and Drug Administration (FDA). On the left is the Department of Health & Human Services logo. To the right of that is the FDA logo, which is a blue square with the letters "FDA" in white. To the right of the blue square is the text "U.S. FOOD & DRUG ADMINISTRATION" in blue.

July 6, 2018

bioMérieux SA Asa Karlsson Sr. Regulatory Affairs Manager 376 Chemin de l'Orme Marcy l'Etoile, 69280 Fr

Re: K181092

Trade/Device Name: CHROMID CARBA agar (CARB) Regulation Number: 21 CFR 866.1700 Regulation Name: Culture medium for antimicrobial susceptibility tests Regulatory Class: Class II Product Code: JSO Dated: April 24, 2018 Received: April 25, 2018

Dear Asa Karlsson:

We have reviewed your Section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.

If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part 801 and Part 809); medical device reporting of medical device-related adverse events) (21 CFR 803); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820); and if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR 1000-1050.

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K181092

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR Part 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to http://www.fda.gov/MedicalDevices/Safety/ReportaProblem/default.htm.

For comprehensive regulatory information about mediation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/) and CDRH Learn (http://www.fda.gov/Training/CDRHLearn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (http://www.fda.gov/DICE) for more information or contact DICE by email (DICE@fda.hhs.gov) or phone (1-800-638-2041 or 301-796-7100).

Sincerely,

Ribhi Shawar -S
For

Uwe Scherf, M.Sc., Ph.D. Director Division of Microbiology Devices Office of In Vitro Diagnostics and Radiological Health Center for Devices and Radiological Health

Enclosure

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Indications for Use

510(k) Number (if known) K181092

Device Name CHROMID® CARBA agar (CARB)

Indications for Use (Describe)

A lack of growth or the absence of pink to burgundy or blue-grey colonies does not preclude the carriage of carbapenemase producing organisms.

Type of Use (Select one or both, as applicable)

☑ Prescription Use (Part 21 CFR 801 Subpart D)	□ Over-The-Counter Use (21 CFR 801 Subpart C)
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SECTION 029. 510(k) SUMMARY

510(k) SUMMARY

CHROMID® CARBA agar

A. 510(k) Submission Information:

510(k) Submission:	K181092
Submitter's Name:	bioMerieux SA
Address:	376 Chemin de l'Orme69280 Marcy l'Etoile, FRANCE
Contact Person:	Asa KarlssonSr. Regulatory Affairs Manager
Phone Number:	+33 (0)6 48 61 68 49
Email:	asa.karlsson@biomerieux.com
510(k) Summary
Date of Preparation:	June 28, 2018
B. Device Name:
Formal/Trade Name:	CHROMID® CARBA agar
Classification Name:	21 CFR 866.1700Culture Medium for Antimicrobial Susceptibility Test
Product Code	JSOCulture Media, Antimicrobial Susceptibility Test, ExcludingMueller Hinton Agar
Common Name:	CHROMID® CARBA agar (CARB)
C. Predicate Device: CHROMID® VRE agar (K091025)

D. 510(k) Summary:

Intended Use:

CHROMID® CARBA agar is a selective and differential chromogenic medium that is intended for the qualitative detection and presumptive identification of carbapenemaseproducing Escherichia coli and Klebsiella pneumoniae in rectal swab specimens from

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Traditional 510(k) Submission

patients at risk of colonization. CHROMID® CARBA agar is intended as an aid in the detection, identification of colonization and control of these bacteria in a healthcare setting.

Other organisms besides carbapenemase-producing E. coli and K. pneumoniae can also grow on CHROMID® CARBA agar with colonies that appear pink to burgundy or bluegreen to blue-grey. Sub-culture to non-selective medium is required to confirm organism identity, for antimicrobial susceptibility testing, confirmation of carbapenemase production and epidemiological typing.

A lack of growth or the absence of pink to burgundy or blue-green to blue-grey colonies does not preclude the carriage of carbapenemase producing organisms.

Indications for use:

See Intended Use

Device Description:

Substantial Equivalence:

The similarities of CHROMID® CARBA agar when compared to the predicate device are described in the following table:

Category	Predicate DevicebioMerieux SACHROMID® VRE agarK091025	Proposed DevicebioMerieux SACHROMID® CARBA agarK181092	Substantially equivalent
Similarities
Classification, andProduct code	Class II, 21 CFR 866.1700JSO	Class II, 21 CFR 866.1700JSO	Equivalent
Intended Use	CHROMID® VRE agar is aselective and differentialchromogenic medium containing8 µg/mL vancomycin, for thequalitative detection ofEnterococcus faecium and E.faecalis showing acquiredvancomycin resistance (VRE) instool specimens. CHROMID®VRE agar can be used as an aidto identify, prevent and control	CHROMID® CARBA agar is aselective and differentialchromogenic medium that isintended for the qualitativedetection and presumptiveidentification of carbapenemase-producing Escherichia coli andKlebsiella pneumoniae in rectalswab specimens from patients atrisk of colonization.CHROMID® CARBA agar is	EquivalentBoth agars are designed todetect resistancemechanisms but fordifferent antimicrobialspecies.
	Predicate Device	Proposed Device
Category	bioMerieux SA	bioMerieux SA	Substantially equivalent
	CHROMID® VRE agar	CHROMID® CARBA agar
	K091025	K181092
	VRE colonization in healthcare	intended as an aid in the
	stings.	detection, identification of
		colonization and control of these
	CHROMID® VRE agar is not	bacteria in a healthcare setting.
	intended to diagnose VREinfection nor to guide or monitor	Rectal swabs are inoculated
	treatment for infections.	directly onto CHROMID®
	Subculture to non-selective	CARBA agar without
	media (e.g., trypticase soy agar	enrichment and results can beinterpreted after incubation for
	with 5% sheep blood) is needed	18-24 hours. Presumptive
	for further identification,	carbapenemase-producing
	susceptibility testing andepidemiological typing.	colonies of E. coli appear pink to
		burgundy and those of K.
		pneumoniae appear blue-greenor blue-grey.

		Other organisms besides
		carbapenemase-producing E.coli and K. pneumoniae can also
		grow on CHROMID® CARBA
		agar with colonies that appear
		pink to burgundy or blue-green
		to blue-grey. Sub-culture to non-
		selective medium is required to
		confirm organism identity, forantimicrobial susceptibility
		testing, confirmation of
		carbapenemase production and
		epidemiological typing.
		A lack of growth or the absence
		of pink to burgundy or blue-green to blue-grey colonies does
		not preclude the carriage of
		carbapenemase producing
		organisms.
Test method	Manual, culture media	Manual, culture media	Identical
Method of	Direct inoculation of the sample	Direct inoculation of the sample	Identical
inoculation	type without enrichment.	type without enrichment.
Storage of the	2-8° C in their box until expiry	2-8° C in their box until expiry	Identical
device	date.	date.
	Outside the box, plates can be	Outside the box, plates can be
	stored for 2 weeks in the dark inthe cellophane sachet at 2-8° C.	stored for 2 weeks in the dark inthe cellophane sachet at 2-8° C.

Formula	Formula / Liter	Formula/ Liter	Equivalent
	Casein and meat peptone	Casein and meat peptone
	(bovine or porcine) ........ 18g	(bovine or porcine) ........ 13g	The formulas contain
	Heart peptone ........ 3g	Soy peptone ........ 5g	similar ingredients and have
	Corn starch ........ 1g	Carbohydrates ........ 1g
Category	Predicate DevicebioMerieux SACHROMID® VRE agarK091025	Proposed DevicebioMerieux SACHROMID® CARBA agarK181092	Substantially equivalent
	Sodium chloride...............6gAgar........................15gSelective mixture........28.8mgChromogenic mixture.....0.13gPurified water................1LFinal pH: 7.2	L-Tryptophan................0.9gPhosphate buffer .............1gNutrient mixture...............2gAgar........................18gSelective mixture............1.35gChromogenic mixture......1.23gPurified water................1LFinal pH: 7.4	a similar final pH.Both formulas can be adjusted and/or supplemented according to the performance criteria required.
Differences
Analytes	Vancomycin resistant E. faeciumand E. faecalis .	Carbapenemase-producing E. coliand K. pneumoniae .	Different target species andantimicrobial resistancephenotypes.
Specimen Types	Swabs(stools)	Swabs(rectal)	Different specimen types
Interpretation ofpositive results	Observe bacterial growth and theappearance of colonies.Positive E. faecium : Violetcolonies.Positive E. faecalis : Blue togreen colonies.	Observe bacterial growth and theappearance of colonies.Presumptive positive E. coli :Pink to burgundy colonies.Presumptive positive K.pneumoniae : Blue-green tobluish-grey colonies.	EquivalentDifferent color changesdepending on bacterialspecies provide a visualinterpretation of positiveresults.Positive results obtained onCHROMID® CARBA agarare presumptive.
Incubation timeand conditions	Incubate at 35-37°C in aerobicconditions.Examined for growth after 24 to48 hours.	Incubate at 35-37°C in aerobicconditions.Examined for growth after 18 to24 hours.	Identical.Potential extendedincubation time for thepredicate.

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CHROMID® CARBA agar Traditional 510(k) Submission

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CHROMID® CARBA agar Traditional 510(k) Submission

Both the devices use a selective mixture for the detection of resistance mechanisms and a chromogenic mixture for the presumptive identification of the bacterial species. Their formulas and method of inoculation on the agar are similar. The differences between the new device and the predicate device are related to the bacterial species and antimicrobial resistance mechanisms detected and the associated colony colors, the specimen type and incubation time. The performance data presented in this submission support a substantial equivalence

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Performance Characteristics:

Analytical Studies

The following analytical studies were conducted to evaluate the performance of the CHROMID® CARBA agar: Interfering Substances, Recovery Study (Limit of Detection), Cross Reactivity (Analytical Specificity), Challenge Testing (Analytical Reactivity), Mixed Infection and Incubation Time. All analytical performance studies demonstrated acceptable results.

Interfering Substances: No interference was observed with 21 interfering substances including Zinc Oxide, Pramocaine hydrochloride, Miconazole nitrate, K-Y Jelly, Loperamide hydrochloride, Playtex Personal wipes, Witch Hazel, Diosmectite, Talc, K-Y Liquibeads vaginal moisturizer, Vaseline, Glycerol, Phenylephrine HCl, Trojan Enz condoms, Physiological saline, Bisacodyl, Ispaghula husk, Benzocaine + Resorcinol, Ruscoside + Lidocaine hydrochloride + Prednacinolone acetonide, Hydrocortisone and Human Blood.

Recovery Study (Limit of Detection (LOD)): Two well-characterized KPC strains K. pneumoniae ATCC® 1705™ and E. coli ATCC® 2340™ were tested to determine the lowest number of CFU/mL detected on CHROMID® CARBA agar. After 18 to 24 hours of incubation, the lowest dilution for the detection (Limit of Detection (LOD)) of both strains was 1.5x103 CFU/mL.

Cross Reactivity (Analytical Specificity): To evaluate the analytical specificity of CHROMID® CARBA agar, testing was performed with high concentrations (10° CFU/mL; 1000 times the LOD) of 59 target and non-target organisms. The strains tested included bacterial and fungal species encountered in stools, CPE and strains of E. coli and K. pneumoniae that produced other carbapenemases besides KPC type enzyme. After 18 to 24 hours of incubation, growth and colony coloration were analyzed.

Sixteen CPE grew with pink to burgundy or blue-grey colonies:
Six KPC strains belonging to the following species: three C. freundii (blue-grey), one
P. rettgerii (blue-green), one E. cloacae (blue-green) and one K. aerogenes [E. aerogenes| (blue-green),
. Four strains of K. pneumoniae with a resistant mechanism other than KPC: one VIM,
one IMP, one OXA-48, one NDM (all blue-green),
. Three strains of E. coli with a resistant mechanism other than KPC: one NDM, one VIM, one IMP (all pink-to burgundy)
. Two strains of M. morganii with NDM (both blue-green),
One strain of S. marcescens with SME (blue-green).

Pseudomonas aeruginosa (VIM), Stenotrophomonas maltophilia (VIM), Pseudomonas putida and Acinetobacter baumanii (NDM) grew on CHROMID® CARBA agar but without a characteristic coloration (colorless).

See Limitations section in the package insert.

Challenge Testing (Analytical Reactivity): Fifty-two well-characterized KPC-EK strains were tested on CHROMID® CARBA agar using a calibrated inoculum at 4.5x109 CFU/mL (3 times the LOD).

After 18 to 24 hours of incubation, all the K. pneumoniae strains were recovered with characteristic blue-green color. Among the 11 E. coli studied, 9 of them grew with a

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Traditional 510(k) Submission

characteristic burgundy color. The two other E. coli failed to grow; of these, one had an MIC in the susceptible range for ertapenem and was intermediate for imipenem and meropenem and the other was susceptible to all three carbapenems tested.

Mixed Infection: Four carbapenemase-producing strains including two E. coli and two K. pneumoniae that each harbored KPC carbapenemase were tested at three times the LOD value in mixtures with other target and non-target organisms at 104 to 108 CFU/mL:

one carbapenem non-susceptible carbapenemase-negative K. pneumoniae, .
. one carbapenem non-susceptible Pseudomonas aeruginosa with VIM carbapenemase,
. one carbapenem non-susceptible E. coli with NDM carbapenemase,
one carbapenem susceptible K. pneumoniae.
one carbapenem non-susceptible Enterobacter cloacae with KPC carbapenemase •
one carbapenem non-susceptible Morganella morganii with NDM carbapenemase
. one carbapenem non-susceptible Providencia rettgeri with KPC carbapenemase

After 18 to 24 hours of incubation, the results obtained showed that when the competitive species were present at <108 CFU/mL, colonies of the four KPC producing target organisms grew with the characteristic color (either pink-burgundy for E. coli or bluegreen/blue-grey for K. pneumoniae). However, when present at 108 CFU/mL, KPCproducing E. cloacae, NDM-producing M. morganii, VIM-producing P. aeruginosa and NDM-producing E. coli inhibited or masked the growth of one or more KPC-producing target organisms. Please refer to the Limitations section of the package insert.

Incubation: Ten well-characterized isolates representing KPC-EK strains were tested every two hours between 16 and 28 hours of incubation at +35°C ± 2°C. The 10 strains were recovered with the expected colony colors after 16 hours of incubation and at each reading interval until 28 hours. The results of the study support the ability to recover carbapenemase-producing E. coli and K. pneumoniae on CHROMID® CARBA agar after incubation for 18-24 hours as stipulated in the device labeling.

Clinical Studies including Challenge, Reproducibility and Quality Control

Challenge Study: Fifty well characterized isolates were tested at one external site at two times the LOD in saline matrix.

The following strains were tested:

11 KPC negative strains: 6 K. pneumoniae and 5 E. coli,

39 KPC positive strains: 27 K. pneumoniae and 12 E. coli.

KPC positive strains included KPC-2, KPC-3 and KPC-4 gene variants.

Other resistance mechanisms were tested among the negative strains, including ESBL, AmpC and carbapenem non-susceptible carbapenemase-negative strains.

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Traditional 510(k) Submission

K. pneumoniae
CHROMID®	Expected status
CARBA	Negative	Positive	Total
Negative	23	0	23
Positive	0	27	27
Total	23	27	50

CHROMID® CARBA agar at 24 hours compared to expected status

Positive Percent Agreement 100.0% (95% CI: [87.5 - 100.0] % ) Negative Percent Agreement 100.0% (95% CI: [85.7 - 100.0] %)

E. coli
CHROMID®CARBA	Expected status
	Negative	Positive	Total
Negative	38	0	38
Positive	0	12	12
Total	38	12	50

Positive Percent Agreement 100.0% (95% CI: [75.8 - 100.0] %) Negative Percent Agreement 100.0% (95% CI: [90.8 - 100.0] %)

Reproducibility and Quality Control:

Ten well-characterized isolates of carbapenemase-producing E. coli (4) and K. pneumoniae (6) that harbored blakec were tested in a blinded fashion in triplicate each day for five days at three sites, and by two different operators at each site. Isolates were tested at approximately the LOD target level and plates were read at 24 hours. The overall between-site reproducibility was 99.3% (894/900).

Quality Control was performed with three quality control organisms tested at each study site by CHROMID® CARBA agar on each day of comparative and reproducibility testing:

Species	Strain	Expected Result	Agreement (%)
K. pneumoniae	ATCC® BAA-1705TM	Blue-green/blue-grey colonies	190/190(100)
E. coli	ATCC® BAA-2340TM	Pink-burgundy colonies	190/190(100)
K. pneumoniae	ATCC® 700603TM	No growth	189/190(99.5)

Overall, 569/570 (99.8%) of Quality Control test results for CHROMID® CARBA agar were as expected.

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CLINICAL PERFORMANCE

Method Comparison

Prospective study on fresh clinical samples:

The performance of CHROMID® CARBA agar was evaluated at three external laboratories (2 in the US, 1 in Europe) using prospectively collected rectal swabs. A total of 1099 swabs from unique subjects were initially enrolled, of which 390 were excluded from the analysis of performance due to quality control failure (343), missing data (42) or questionable data reliability (5). Results from 709 swabs were therefore included in the analysis of performance. The characteristics of all colonies growing on CHROMID® CARBA medium (pink-to-burgundy, blue-green to blue-grey, colorless, and colors other than pink-to-burgundy or blue-green to blue-grey) at 18 to 24 hours were compared to the results obtained from the CDC enrichment culture method using selective Trypticase Soy broth, followed by subculture to MacConkey agar and phenotypic and genetic characterization of isolated lactose fermenting colonies.

Isolates from both the reference method and CHROMID® CARBA agar were identified biochemically and their carbapenemase status was determined by carbapenem susceptibility and CARBA NP testing, as well as PCR for carbapenemase resistance markers (Table 1).

CarbapenemMIC a	Carba NP Test	CarbapenemasePCR b	CarbapenemaseStatus
Non-susceptible	Positive	Positive	Positive
Non-susceptible	Positive	Negative	Negative
Non-susceptible	Negative	Positive	Positive
Non-susceptible	Negative	Negative	Negative
Susceptible	Positive	Positive	Positive
Susceptible	Positive	Negative	Negative
Susceptible	Negative	Positive	Negative c
Susceptible	Negative	Negative	Negative

Table 1. Algorithm for determining carbapenemase status of isolates

a Non-susceptible: Intermediate or Resistant to one or more of the carbapenem antimicrobial agents tested (ertapenem, imipenem and meropenem)

b Multiplex PCR for blamp, blakpc, blandM, blaoxA-48 or blayM

C Phenotypic evidence of non-susceptibility to carbapenems in addition to a positive PCR result was required to establish the Carbapenemase Status as positive

The results of the study are presented in Tables 2 and 3 for carbapenemase-producing E. coli and K. pneumoniae, respectively.

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		CDC Reference Culture Method
		Positive	Negative	Total
CHROMID®CARBA agar	Positive a	0	2 c	2
	Negative b	0	707	707
	Total	0	709	709
Positive Percent Agreement		Not applicable
Negative Percent Agreement		99.7% (707/709); 95% CI 99.0-99.9%

Table 2. Detection of carbapenemase-producing E. coli in the Prospective Clinical Study

95% CI: 95% score confidence interval

a Pink-burgundy colonies
b No growth or colonies not pink-burgundy
C Colonies from 1/2 specimens confirmed as carbapenem non-susceptible, carbapenemase negative K. pneumoniae; colonies from 1/2 specimens identified as Enterococcus faecalis

		Table 3. Detection of carbapenemase-producing K. pneumoniae in the Prospective
Clinical Study
		CDC Reference Culture Method
		Positive	Negative	Total
CHROMID®	Positive a	43	15 e, f	58
	Negative b	8 c, d	643	651
CARBA agar	Total	51	658	709
Positive Percent Agreement		84.3% (43/51); 95% CI 72.0-91.8%
Negative Percent Agreement		97.7% (643/658); 95% CI 96.3-98.6%

95% CI: 95% score confidence interval

a Blue-green/blue-grey colonies
b No growth or colonies not blue-green/blue-grey
C Includes 1 specimen from which carbapenemase-positive K. pneumoniae was recovered by the Reference Method but which yielded blue-green to blue-grey colonies on CHROMID® CARBA agar that were identified biochemically as P. aeruginosa
d 8/8 isolates grew on CHROMID® CARBA agar when inoculated at approximately the LoD target level (103 CFU/mL in stool); all 8 carried blakec, were Carba NP Test positive and carbapenem non-susceptible (resistant to ertapenem, imipenem and meropenem)
e 5/15 isolates on CHROMID® CARBA agar were confirmed as carbapenem nonsusceptible K. pneumoniae that carried: 4/5 isolates were Carbapenemase Statuspositive and carried blaker and 1/5 isolates was Carbapenemase Status-negative
f 10/15 specimens produced blue-green/blue-grey colonies that were identified as Enterobacteriaceae other than K. pneumoniae (Serratia marcescens (6), Citrobacter freundii (2) and Enterobacter cloacae (2))

Analysis of contrived samples:

To supplement the prospective clinical study, testing was also performed using contrived specimens consisting of well-characterized isolates in simulated rectal swab matrix (stool diluted in saline).

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A total of 210 contrived samples inoculated with one of the following concentrations of organisms: 1x LOD, 3x LOD, 10x LOD, were included in the study. The samples were blinded and tested at four different sites.

The results of the study are summarized in Tables 4 and 5 for carbapenemase-producing E. coli and K. pneumoniae, respectively.

		Organism Identity & Carbapenemase Status
		Positive	Negative	Total
CHROMIDCARBA agar	Positive a	16	2 c	18
	Negative b	4 d	188	192
	Total	20	190	210
Positive Percent Agreement		80.0% (16/20); 58.4-91.9%
Negative Percent Agreement		98.9% (188/190); 95% CI 96.2-99.7%

Table 4. Detection of carbapenemase-producing E. coli in contrived specimens

95% CI: 95% score confidence interval

a Pink-burgundy colonies

b No growth or colonies not pink-burgundy
C 2/2 isolates were carbapenem non-susceptible E. coli (resistant to meropenem and ertapenem and an intermediate MIC for imipenem); both isolates were positive for Extended Spectrum ß-Lactamase (ESBL)
d False negative results were obtained with 4 strains of carbapenem non-susceptible E. coli that harbored blaoxa8 (2), blaNDM (1) and blavM (1) and which were spiked at target levels ranging from 1X to 10X LoD; 2/4 strains had an intermediate MIC to at least one carbapenem including 1 strain that was also susceptible to ertapenem

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		Organism Identity & Carbapenemase Status
		Positive	Negative	Total
CHROMID®CARBA agar	Positive a	84	11 c, d	95
	Negative b	3 e	112 f	115
	Total	87	123	210
Positive Percent Agreement		96.6% (84/87); 95% CI % 90.3-98.8%
Negative Percent Agreement		91.1% (112/123); 95% CI 84.7-94.9%

Table 5. Detection of carbapenemase-producing K. pneumoniae in contrived specimens

95% CI: 95% score confidence interval

a Blue-green/blue-grey colonies
b No growth or colonies not blue-green/blue-grey
C 5/11 false positive results were obtained with carbapenem non-susceptible K. pneumoniae, all of which were positive for ESBL (3) or ESBL and AmpC (2)
d 6/11 false positive results were due to Carbapenemase Status-positive species of Enterobacteriaceae other than K. pneumoniae that harbored blaxpc: E. cloacae (4), K. oxytoca (1) and K. ozaenae (1)
e 3/3 false negative results were obtained with Carbapenemase Status positive isolates at the LoD target level; the strains carried carbapenemase resistance markers as follows: bland (1), blake (1) or blaoxA-48 (1); 2/3 strains had a susceptible or intermediate MIC to at least one of the three carbapenems tested (ertapenem, imipenem or meropenem)
f 18/112 samples contained carbapenem non-susceptible strains of K. pneumoniae of which 17 were phenotypically carbapenemase negative; 11/18 were positive for ESBL and 6/18 were positive for AmpC

The clinical study which was performed under CLSI M100-S25, S26, S27 and S28, between April, 2016 through October, 2017 is also compliant to CLSI M100-S28. except the new requirement regarding the integrity check by a disk diffusion or MIC method for the QC strain ATCC® 700603™ which was not required by S26 and as such was not done. No impact on the performances is expected.

Regulation Number and Section

§ 866.1700 Culture medium for antimicrobial susceptibility tests.

(a)
Identification. A culture medium for antimicrobial susceptibility tests is a device intended for medical purposes that consists of any medium capable of supporting the growth of many of the bacterial pathogens that are subject to antimicrobial susceptibility tests. The medium should be free of components known to be antagonistic to the common agents for which susceptibility tests are performed in the treatment of disease.(b)
Classification. Class II (performance standards).