(262 days)
Not Found
No
The device description and performance studies focus on the chemical and biological properties of the agar medium and its ability to selectively grow and visually identify MRSA based on color change. There is no mention of AI, ML, image processing, or any computational analysis of the results.
No.
This device is an in vitro diagnostic (IVD) device used for the qualitative detection of MRSA from nasal colonization and skin structure infections to aid in prevention, control, and diagnosis. It is explicitly stated that it is "not intended to diagnose, guide, or monitor therapy for MRSA infections," nor is it intended to "monitor treatment for MRSA infections." Therefore, it does not provide therapeutic benefits.
Yes
The "Intended Use / Indications for Use" section explicitly states that the device is for "qualitative detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA)" and "qualitative detection of MRSA from skin structure infections," which aids in the "identification and diagnosis of MRSA infections." The performance studies and the mechanism described in the "Device Description" section (chromogenic detection of MRSA) further confirm its role in identifying a medical condition.
No
The device is a chromogenic agar medium, which is a physical substance used in laboratory testing, not a software program.
Yes, this device is an IVD (In Vitro Diagnostic).
Here's why:
- Intended Use: The intended use clearly states the device is for the "qualitative detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA)" and "qualitative detection of MRSA from skin structure infections." These are diagnostic purposes performed on biological specimens (nasal swabs and skin structure infection specimens).
- Device Description: The description details a "selective and differential chromogenic medium" used to identify MRSA based on its enzymatic activity and resulting color change. This is a typical description of an in vitro diagnostic culture medium.
- Clinical Studies: The document describes clinical studies performed to evaluate the performance of the device using patient specimens. This is a requirement for demonstrating the effectiveness of an IVD.
- Performance Metrics: Key metrics like Sensitivity and Specificity are provided, which are standard performance indicators for diagnostic tests.
- Predicate Device: A predicate device (Bio-Rad MRSA Select™) with a K number (K100589) is listed. K numbers are associated with FDA clearances for medical devices, including IVDs.
All these elements strongly indicate that the chromID™ MRSA agar is an In Vitro Diagnostic device.
N/A
Intended Use / Indications for Use
chromID™ MRSA agar is a selective and differential chromogenic medium for :
A. The qualitative detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA), to aid in the prevention and control of MRSA in healthcare settings.
The test is performed on anterior nares swab specimens from patients and healthcare workers to screen for MRSA colonization. chromID™MRSA when used to detect nasal colonization is not intended to diagnose, guide, or monitor therapy for MRSA infections, or provide results of susceptibility to methicillin.
B. The qualitative detection of MRSA from skin structure infections.
chromID™ MRSA is indicated for use in conjunction with other laboratory tests and clinical data available to aid in the identification and diagnosis of MRSA infections. Concomitant cultures for skin structure infections are necessary to recover organisms for further microbiological susceptibility testing or epidemiological typing.
A negative result does not preclude MRSA infection. chromID™MRSA is not intended to monitor treatment for MRSA · infections, or provide results of susceptibility to methicillin.
Product codes (comma separated list FDA assigned to the subject device)
JSO
Device Description
chromID™ MRSA agar consists of a rich nutritive base combining different peptones. It also contains a chromogenic substrate of α-glucosidase and a combination of several antibiotics (cefoxitin, etc.) that favor the growth and direct detection of MRSA, including hetero-resistant strains, by revealing orglucosidase activity (patent registered) through the appearance of green colonies. The α-glucosidase produced by S. aureus cleaves the chromogenic substrate, which gives a green color to the S. aureus colonies growing on the medium. The MRSA strains are identified by the presence of green colonies that result from the chromogen incorporated in the medium. The selective mixture of antibiotics inhibits most bacteria not belonging to the genus Staphylococcus, as well as yeasts.
Mentions image processing
Not Found
Mentions AI, DNN, or ML
Not Found
Input Imaging Modality
Not Found
Anatomical Site
anterior nares, skin and skin structure infections
Indicated Patient Age Range
Not Found
Intended User / Care Setting
healthcare settings / laboratory
Description of the training set, sample size, data source, and annotation protocol
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Description of the test set, sample size, data source, and annotation protocol
A total of 690 SSSI specimens were collected for the study at 4 external clinical laboratories. Three specimens were excluded because they did not meet specimen acceptance criteria. Seven specimens were removed due to protocol deviations. A total of 680 specimens were valid for comparison data analysis.
For the Reference Culture Method, all specimens were enriched in Tryptic Soy broth with 6.5% NaCl (TSB) for 24 hours. Negative broth cultures were incubated an additional 24 hours. Positive cultures were then subcultured to Tryptic Soy agar with 5% sheep blood (BAP). Colonies suggestive of Staphylococcus species were tested by Gram stain, catalase and latex aqqlutination. Staphylococcus aureus isolates were tested for resistance to oxacillin by the Cefoxitin Screen test. All colonies resistant to oxacillin by the Cefoxitin Screen test were tested for the presence of the mecA gene by PCR and by VITEK MS for species confirmation.
A positive result by Reference Culture was defined as the recovery of cefoxitin-resistant Staphylococcus aureus from the specimen. All other results, including the growth of cefoxitinsusceptible Staphylococcus aureus, growth of other species and no growth, were considered negative.
Summary of Performance Studies (study type, sample size, AUC, MRMC, standalone performance, key results)
Non-clinical (analytical) and clinical studies were performed for the chromID™ MRSA agar following the FDA Draft Guidance "Establishing the Performance Characteristics of In Vitro Diagnostic Devices for the Detection of Methicillin-Resistant Staphylococcus aureus (MRSA) for Culture Based Systems", issued June 15, 2011.
Analytical Performance
- Reproducibility: A set of ten mecA-positive or mecA-negative Staphylococcus aureus isolates were tested in triplicate each day for five days at three of the clinical study sites using multiple lots of chromID™ MRSA media. Isolates were tested at 10^3 CFU/mL and plates were read at 24 hours. The overall reproducibility rate was 100% (450/450).
- Quality Control: Two quality control organisms (Staphylococcus aureus ATCC 29213, Staphylococcus aureus ATCC 43300) were tested at each study site. The results of QC testing met the pre-defined acceptance criteria (≥ 95% agreement) when compared to expected results as determined by oxacillin MIC and mecA PCR.
- Analytical Reactivity: A challenge set composed of 80 mecA MRSA strains and 5 mecC MRSA strains was inoculated on the chromID™ MRSA medium with an inoculum equivalent to 10° CFU/mL. After 24 hours of incubation, 58/80 mecA MRSA strains and 4/5 mecC MRSA strains were detected.
- Expression of Resistance: Twenty-eight well-characterized S. aureus strains were tested with inoculum concentrations between 10^0 -10^6 CFU/mL. All low level and high level methicillin-resistant strains were detected at an inoculum of >10^0 CFU/mL. The 5 borderline oxacillin-resistant and 3 methicillin-susceptible strains did not grow.
- Mixed Infection Study: Ten MRSA strains (5 low level methicillin-resistant and 5 high level methicillin-resistant) at a concentration of 10^3 CFU/mL were inoculated with one of three non-MRSA strains (methicillin-susceptible S. aureus, methicillin-resistant coaqulase negative Staphylococcus epidermidis, and Escherichia coli) at 10^0 – 10^6 CFU/mL. The presence of these non-MRSA organisms did not negatively impact chromID™ MRSA performance.
- Recovery Study: Two well-characterized MRSA strains (ATCC® 43300™ and CDC Mu3-BR) were tested. At 24 hours the lowest dilution for detection for ATCC® 43300™ was 10^3 CFU/mL and 10^0 CFU/mL for CDC Mu3-8R.
- Cross Reactivity: 71 non-MRSA strains representing bacterial and fungal species were inoculated onto chromID™ MRSA medium at a high inoculum level (10^6 CFU/mL). After 24 hours, 44 strains did not grow and 20 strains grew colonies without green pigment. Green colonies (cross reactivity) were observed for 3 Klebsiella pneumoniae, one Enterobacter cloacae (all 4 carbapenemase producing (KPC)), and one S. pseudintermedius and 2 S. sciuri strains (all 3 oxacillin-resistant).
- Interference: Interfering substances were evaluated at physiologically or biologically relevant concentrations. No interference was observed for human blood, mucin, anticoagulants, plasma, and buffy coat. Some topical antibiotics and antiseptics interfered with MRSA detection due to their antibacterial activity.
- Incubation: The incubation times for three MRSA strains (10^3 CFU/mL) were 20 hours for two strains (ATCC 43300 and S. aureus 0611169) and 27 hours for one strain (CDC Mu3-8R).
Clinical Studies
- Study Type: Comparison of chromID™ MRSA at 24 Hours to Reference Culture Method (TSB) at 48 Hours.
- Sample Size: 680 valid specimens.
- Key Results:
- Positives by chromID™ MRSA: 166 (true positive) + 13 (false positive) = 179
- Negatives by chromID™ MRSA: 11 (false negative) + 490 (true negative) = 501
- Total Reference Culture Positive: 177
- Total Reference Culture Negative: 503
- The overall prevalence of MRSA in this study by the Reference Culture Method was 26.0% (177/680).
- The prevalence of MRSA as determined by chromID™ MRSA at 24 hours was 26.3% (179/680).
Key Metrics (Sensitivity, Specificity, PPV, NPV, etc.)
Specificity 97.4% (95% CI: [95.6-98.5])
Sensitivity 93.8% (95% CI: [89.2-96.5])
Predicate Device(s): If the device was cleared using the 510(k) pathway, identify the Predicate Device(s) K/DEN number used to claim substantial equivalence and list them here in a comma separated list exactly as they appear in the text. List the primary predicate first in the list.
Bio-Rad MRSA Select™ (K100589)
Reference Device(s): Identify the Reference Device(s) K/DEN number and list them here in a comma separated list exactly as they appear in the text.
Not Found
Predetermined Change Control Plan (PCCP) - All Relevant Information for the subject device only (e.g. presence / absence, what scope was granted / cleared under the PCCP, any restrictions, etc).
Not Found
§ 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).
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Food and Drug Administration 10903 New Hampshire Avenue Document Control Center - WO66-G609 Silver Spring, MD 20993-0002
March 11, 2016
BIOMERIEUX, INC. JEWELL COULSON SR. REGULATORY AFFAIRS SPECIALIST 595 ANGLUM RD. HAZELWOOD MO 63042
Re: K151688
Trade/Device Name: chromID™ MRSA Regulation Number: 21 CFR 866.1700 Regulation Name: Culture medium for antimicrobial susceptibility tests Regulatory Class: II Product Code: JSO Dated: February 4, 2016 Received: February 8, 2016
Dear Ms. Coulson:
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 Parts 801 and 809); medical device reporting (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.
1
If you desire specific advice for your device on our labeling regulations (21 CFR Parts 801 and 809), please contact the Division of Industry and Consumer Education at its toll-free number (800) 638 2041 or (301) 796-7100 or at its Internet address
http://www.fda.gov/MedicalDevices/Resourcesfor You/Industry/default.htm. 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 the CDRH's Office of Surveillance and Biometrics/Division of Postmarket Surveillance.
You may obtain other general information on your responsibilities under the Act from the Division of Industry and Consumer Education at its toll-free number (800) 638-2041 or (301) 796-7100 or at its Internet address
http://www.fda.gov/MedicalDevices/ResourcesforYou/Industry/default.htm.
Sincerely yours,
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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DEPARTMENT OF HEALTH AND HUMAN SERVIGES Food and Drug Administration
Indications for Use
510(k) Number (if known) K151688
Device Name
chromIDTM MRSA
Indications for Use (Describe)
chromID™ MRSA agar is a selective and differential chromogenic medium for :
A. The qualitative detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA), to aid in the prevention and control of MRSA in healthcare settings.
The test is performed on anterior nares swab specimens from patients and healthcare workers to screen for MRSA colonization. chromID™MRSA when used to detect nasal colonization is not intended to diagnose, guide, or monitor therapy for MRSA infections, or provide results of susceptibility to methicillin.
B. The qualitative detection of MRSA from skin structure infections.
chromID™ MRSA is indicated for use in conjunction with other laboratory tests and clinical data available to aid in the identification and diagnosis of MRSA infections. Concomitant cultures for skin structure infections are necessary to recover organisms for further microbiological susceptibility testing or epidemiological typing.
A negative result does not preclude MRSA infection. chromID™MRSA is not intended to monitor treatment for MRSA · infections, or provide results of susceptibility to methicillin.
| 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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Image /page/3/Picture/1 description: The image shows the logo for bioMerieux. The logo consists of the word "BIOMERIEUX" in a sans-serif font, with a stylized graphic above it. The graphic is a circle bisected by a curved line, with one half of the circle containing a series of horizontal lines.
510(k) SUMMARY
| Submitter's Name: | bioMérieux, Inc. |
|---|---|
| Address: | 595 Anglum Road |
| Hazelwood, MO 63042 | |
| Contact Person: | Jewell Coulson |
| Senior Regulatory Affairs Specialist | |
| Phone Number: | 314-731-7342 |
| Fax Number: | 314-731-8689 |
| Date of Preparation: | February 4, 2016 |
| Device : | |
| Formal/Trade Name: | chromID™ MRSA |
| Common Name: | Culture media |
| Classification | II |
| Regulation Name | Culture Media for Antimicrobial Susceptibility Tests |
| Regulation Number | 21 CFR 866.1700 |
| Product Code | JSO |
| Predicate Device: | Bio-Rad MRSA Select™ (K100589) |
| 510(k) Summary: |
Intended Use:
chromID™ MRSA agar is a selective and differential chromogenic medium for :
-
A. The qualitative detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA), to aid in the prevention and control of MRSA in healthcare settings.
The test is performed on anterior nares swab specimens from patients and healthcare workers to screen for MRSA colonization. chromID™ MRSA when used to detect nasal colonization is not intended to diagnose, guide, or monitor therapy for MRSA infections, or provide results of susceptibility to methicillin. -
B. The qualitative detection of MRSA from skin structure infections.
chromID™ MRSA is indicated for use in conjunction with other laboratory tests and clinical data available to aid in the identification and diagnosis of MRSA infections. Concomitant cultures for skin and skin structure infections are necessary to recover organisms for further microbiological susceptibility testing or epidemiological typing. A negative result does not preclude MRSA infection. chromID™ MRSA is not intended to monitor treatment for MRSA infections, or provide results of susceptibility to methicillin.
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Device Description:
chromID™ MRSA agar consists of a rich nutritive base combining different peptones. It also contains a chromogenic substrate of α-glucosidase and a combination of several antibiotics (cefoxitin, etc.) that favor the growth and direct detection of MRSA, including hetero-resistant strains, by revealing orglucosidase activity (patent registered) through the appearance of green colonies. The α-glucosidase produced by S. aureus cleaves the chromogenic substrate, which gives a green color to the S. aureus colonies growing on the medium. The MRSA strains are identified by the presence of green colonies that result from the chromogen incorporated in the medium. The selective mixture of antibiotics inhibits most bacteria not belonging to the genus Staphylococcus, as well as yeasts.
Substantial Equivalence
The similarities of ChromID™ MRSA agar when compared to the predicate device are described in the following table.
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| Device | Predicate | |
|---|---|---|
| Item | chromID™ MRSA Agar | Bio-Rad MRSASelect™ |
| Similarities | ||
| Intended Use | chromID™ MRSA agar is a selective and | |
| differential chromogenic medium for : | MRSASelect™ is a selective and | |
| differential chromogenic medium for: | ||
| A. The qualitative detection of nasal colonization | ||
| of methicillin-resistant Staphylococcus | ||
| aureus (MRSA), to aid in the prevention and | ||
| control of MRSA in healthcare settings. | ||
| The test is performed on anterior nares swab | ||
| specimens from patients and healthcare | ||
| workers to screen for MRSA colonization. | ||
| chromID™ MRSA when used to detect nasal | ||
| colonization is not intended to diagnose, | ||
| guide, or monitor therapy for MRSA | ||
| infections, or provide results of susceptibility | ||
| to methicillin. | A) The qualitative detection of nasal | |
| colonization of methicillin resistant | ||
| Staphylococcus aureus (MRSA) to aid | ||
| in the prevention and control of MRSA | ||
| infections in healthcare settings. The | ||
| test can be performed on anterior | ||
| nares specimens from patients and | ||
| healthcare workers to screen for | ||
| MRSA colonization. MRSASelect™ is | ||
| not intended to diagnose MRSA | ||
| infection nor to guide or monitor | ||
| treatment of infection. Results can be | ||
| interpreted after 18 to 28 hours | ||
| incubation. | ||
| B. The qualitative detection of MRSA from skin | ||
| and skin structure infections. | ||
| chromID™ MRSA is indicated for use in | ||
| conjunction with other laboratory tests and | ||
| clinical data available to aid in the | ||
| identification and diagnosis of MRSA | ||
| infections. Concomitant cultures for skin and | ||
| skin structure infections are necessary to | ||
| recover organisms for further microbiological | ||
| susceptibility testing, or epidemiological | ||
| typing. | ||
| A negative result does not preclude MRSA | ||
| infection. chromID™ MRSA is not intended to | ||
| monitor treatment for MRSA infections, or | ||
| provide results of susceptibility to methicillin. | B) The qualitative detection of methicillin | |
| resistant Staphylococcus aureus | ||
| (MRSA) from skin and soft-tissue | ||
| wound specimens. The | ||
| MRSASelect™ is indicated for use in | ||
| conjunction with other laboratory tests | ||
| and clinical data available to aid in the | ||
| identification and diagnosis of MRSA | ||
| from patients with skin and soft-tissue | ||
| infections. Concomitant cultures and | ||
| susceptibility testing are necessary for | ||
| all skin and soft-tissue wound | ||
| specimens. MRSASelect™ is not | ||
| intended to guide, or monitor treatment | ||
| for MRSA infection, or provides results | ||
| of susceptibility to methicillin. Results | ||
| can be interpreted after 18 to 28 hours | ||
| incubation. | ||
| Test method | Manual | Manual |
| Inoculum | Direct Specimen | Direct Specimen |
| Specimen | Anterior nares specimens | Anterior nares specimens |
| Skin and skin structure specimens | Skin and soft-tissue wound specimens |
The chromID™ MRSA agar utilizes nutrient agar medium that contains selective and differential agents and is very similar to the MRSASelect™ agar. Both devices incorporate a chromogenic substrate that is enzymatically cleaved by S. aureus and result in colored MRSA colonies. Both devices incorporate selective agents in the agar to inhibit most bacteria not belonging to the genus Staphylococcus, as well as yeasts. The significant technological difference between the two media is the type of chromogenic substrate incorporated in the media to indicate the presence of MRSA colonies. The safety and effectiveness of the chromID™ MRSA agar is not impacted by the technology differences.
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Image /page/6/Picture/1 description: The image shows the logo for bioMerieux. The logo consists of the company name in a sans-serif font, with a stylized globe above it. A curved line extends from the top of the globe, arcing over the company name. The globe is divided into two halves, one with vertical lines and the other solid.
Performance Characteristics:
Non-clinical (analytical) and clinical studies were performed for the chromID™ MRSA agar following the FDA Draft Guidance "Establishing the Performance Characteristics of In Vitro Diagnostic Devices for the Detection of Methicillin-Resistant Staphylococcus aureus (MRSA) for Culture Based Systems", issued June 15, 2011.
Analytical Performance
- Reproducibility A set of ten mecA-positive or mecA-negative Staphylococcus aureus isolates . were tested in triplicate each day for five days at three of the clinical study sites using multiple lots of chromID™ MRSA media. Isolates were tested at 103 CFU/mL and plates were read at 24 hours. The overall reproducibility rate was 100% (450/450).
- Quality Control Two quality control organisms were tested at each study site by chromlD™ ● MRSA on each day of testing. The organisms tested were:
| Staphylococcus aureus | ATCC 29213 |
|---|---|
| Staphylococcus aureus | ATCC 43300 |
The results of QC testing with chromID™ MRSA agar met the pre-defined acceptance criteria (≥ 95% agreement) when compared to expected results as determined by oxacillin MIC and mecA PCR.
- Analytical Reactivity - A challenge set composed of 80 mecA MRSA strains and 5 mecC MRSA strains was inoculated on the chromID™ MRSA medium with an inoculum equivalent to 10° CFU/mL. After 24 hours of incubation, 58/80 mecA MRSA strains and 4/5 mecC MRSA strains were detected on the chromID™ MRSA medium.
- . Expression of Resistance - Twenty-eight well-characterized S. aureus strains were tested on chromID™ MRSA (10 low level methicillin-resistant, 10 high level methicillin-resistant, 5 borderline oxacillin-resistant, and 3 methicillin-susceptible) using inoculum concentrations between 100 -10° CFU/mL. All low level and high level methicillin-resistant strains were detected at an inoculum of >10° CFU/mL. The 5 border-line oxacillin-resistant and 3 methicillin-susceptible strains did not grow, as expected, on chromID™ MRSA at inoculum concentrations as high as 10° CFU/mL.
- Mixed Infection Study Ten MRSA strains (5 low level methicillin-resistant and 5 high level ● methicillin-resistant) at a concentration of 103 CFU/mL were inoculated on chromID™ MRSA with one of three non-MRSA strains (methicillin-susceptible S. aureus, methicillin-resistant coaqulase negative Staphylococcus epidermidis, and Escherichia coli) at 10° – 10° CFU/mL to evaluate the recovery of MRSA on chromID™ MRSA media in the presence of non-target organisms. The presence of these non-MRSA organisms did not negatively impact chromID™ MRSA performance.
Recovery Study .
Two well-characterized MRSA strains (ATCC® 43300™ and CDC Mu3-BR) were tested to determine the lowest number of CFU/mL detected on chromID™ MRSA. At 24 hours the lowest dilution for detection on chromID™ MRSA for ATCC® 43300™ was 103 CFU/mL and 10° CFU/mL for CDC Mu3-8R.
- Cross Reactivity To evaluate the analytical specificity of the chromID™ MRSA media, 71 non-● MRSA strains representing bacterial and fungal species potentially encountered in skin and skin structure infections were inoculated onto chromID™ MRSA medium at a high inoculum level (10° CFU/mL). After 24 hours of incubation, 44 strains did not grow and 20 strains grew colonies without green pigment. Green colonies (cross reactivity) were observed for 3 Klebsiella
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pneumoniae and one Enterobacter cloacae strains. All 4 were carbapenemase producing (KPC). Green colonies were also observed for one S. pseudintermedius and 2 S. sciuri strains. All 3 were oxacillin-resistant strains.
- Interference Interfering substances were evaluated at physiologically or biologically relevant ● concentrations and mixed with bacterial suspensions (9:1, v:v). No interference was observed for human blood, mucin, anticoagulants, plasma, and buffy coat. Some topical antibiotics and antiseptics interfered with MRSA detection on chromID™ MRSA due to their antibacterial activity. Use of compounds containing the active ingredients listed below may have an inhibitory effect on MRSA growth that is unrelated to chromID™ MRSA medium performance: colistimethate sodium 25 MUI/100mL, bacitracin 50,000 Ul/100mL, dexamethasone 0.1g/100mL, neomycin sulfate 350,000 Ul/100mL, polymixin B sulfate 600,000 Ul/100mL, benzalkonium chloride 500mg/100mL, chlorhexidine digluconate 200mg/100mL, 1% hydrocortisone, 10% povidone iodine, 2% mupirocin, hydrogen peroxide 8 mg/g, ethanol 380 mg/g, 70% isopropyl alcohol. Benzocaine (14 g/L) may delay colony coloration or inhibit growth of MRSA on chromID™ MRSA.
- Incubation The incubation times required for three MRSA strains, at an organism concentration ● of 103 CFU/mL to produce positive chromID™ MRSA results was 20 hours for two strains (ATCC 43300 and S. aureus 0611169) and 27 hours for one strain (CDC Mu3-8R).
Clinical Studies
chromID™ MRSA was evaluated at four geographically diverse clinical sites. chromID™ MRSA performance was determined by examining the presence of green colonies on the media after 24 hours. All green colonies were tested by Gram stain, catalase and latex agglutination. All Staphylococcus aureus colonies were tested for resistance to oxacillin by the Cefoxitin Screen test (30ug). All green colonies were also tested for the presence of the mecA gene by PCR and by VITEK® MS for species confirmation.
For the Reference Culture Method, all specimens were enriched in Tryptic Soy broth with 6.5% NaCl (TSB) for 24 hours. Negative broth cultures were incubated an additional 24 hours. Positive cultures were then subcultured to Tryptic Soy agar with 5% sheep blood (BAP). Colonies suggestive of Staphylococcus species were tested by Gram stain, catalase and latex aqqlutination. Staphylococcus aureus isolates were tested for resistance to oxacillin by the Cefoxitin Screen test. All colonies resistant to oxacillin by the Cefoxitin Screen test were tested for the presence of the mecA gene by PCR and by VITEK MS for species confirmation.
A positive result by Reference Culture was defined as the recovery of cefoxitin-resistant Staphylococcus aureus from the specimen. All other results, including the growth of cefoxitinsusceptible Staphylococcus aureus, growth of other species and no growth, were considered negative.
A total of 690 SSSI specimens were collected for the study at 4 external clinical laboratories. Three specimens were excluded because they did not meet specimen acceptance criteria. Seven specimens were removed due to protocol deviations. A total of 680 specimens were valid for comparison data analysis.
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chromID™ MRSA at 24 Hours
Compared to Reference Culture Method (TSB) at 48 Hours
| | Reference Culture Method
(TSB) Result | | |
|--------------------------------|------------------------------------------|-----|-------|
| chromID™ MRSA
Result in 24h | Pos | Neg | Total |
| Pos | 166 | 13* | 179 |
| Neg | 11** | 490 | 501 |
| Total | 177 | 503 | 680 |
*13 discordant specimens (chromID™ MRSA result of MRSA positive: culture-based testing result of MRSA neqative) were observed. 5 of the 13 chromID™ MRSA positive specimens were confirmed as MRSA by Cefoxitin Screen Test. 8 cultures grew green colonies on
chromID™MRSA that were not MRSA.
**11 discordant specimens (chromID™ MRSA result of MRSA negative: culture-based testing result of MRSA positive) were observed. 6 cultures displayed no growth on chromID' MRSA. 4 cultures grew non-green MRSA colonies on chromID™ MRSA. One specimen grew green colonies on chromID™ MRSA that were not identified as MRSA.
Specificity 97.4% (95% CI: [95.6-98.5]) Sensitivity 93.8% (95% CI: [89.2-96.5])
The overall prevalence of MRSA in this study by the Reference Culture Method was 26.0% (177/680). . The prevalence of MRSA as determined by chromID™ MRSA at 24 hours was 26.3% (179/680).
Conclusion
A comparison of the intended use and the results of non-clinical performance studies support that chromID™ MRSA agar is substantially equivalent to the predicate device.