Transport is part of the result. For Chromatic CRE Agar Base Culture Media, time, temperature, oxygen exposure, and delay before inoculation determine what remains recoverable. The discussion below connects its documented role with preparation variables, controls, interpretation, and the limits of inference. Catalogue 611619 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
ChromaticTM CRE Agar Base is a chromogenic selective medium used with supplements for detection of carbapenem-resistant Enterobacteriaceae directly from clinical specimens.Carbapenems (imipenem, meropenem, ertapenem and doripenem) are the last shelter from multi-resistant Gram-negative bacterial infections. Carbapenemase is an enzyme class which can be produced by Klebsiella pneumoniae and by other organisms including Serratia spp, Enterobacter spp, Escherichia coli and Citrobacter freundii. Early detection of carbapenems resistance is essential in orderto limit the spread of these pathogens.
Method principle
Peptone mix is a source of amino acids, nitrogen, minerals, vitamins, and other factors which increases the growth of bacteria. Chromogenic and selective mix facilitates the identification of bacteria on the basis of the color and colony morphology. Agar is the solidifying agent.Supplementation with ChromaticTM CRE Supplement (ref. 81088) inhibits most of the non-Enterobacteriaceae and the carbapenem-sensitive organisms.
Formula and functional interpretation
(g/l)Peptone Mix40.0Chromogenic and Selective Mix 1.8Agar15.0Final pH 7.0 ± 0.2
Review the nutritive, selective, differential, buffering, reducing, and indicator components against the expected target and background flora. Preparation errors can change recovery, inhibition, colour development, or endpoint visibility even when incubation is correct.
Preparation and execution: controlled method points
Preparation: Suspend 56.8 g of powder in one liter of deionized or distilled water. Bring to boil and shake until completely dissolved. Sterilize at 121°C for 15 minutes. Cool up to 45-50°C. Aseptically, add the contents of 2 vials (10 ml) of ChromaticTM CRE Supplement (ref. 81088) reconstituted as directed in the instructions for use that accompany the product. Pour in Petri dishes.
Procedure: Inoculate the medium directly from faecal screening swabs, or using a sterile loop previously dipped in liquid suspension of the sample, by streaking the specimen onto the agar surface. Incubate aerobically at 37°C for 18-24h.
Translate the method into controlled worksheet fields: catalogue and lot, preparation mass or volume, water quality, pH where applicable, heating or sterilization, supplements, dispense volume, preparation date, expiry assignment, incubation atmosphere and temperature, reading window, equipment, and analyst. Record departures as deviations instead of silently normalizing them.
Quality control: what the control result protects
Challenge both sides of performance. Include a target reaction demonstrating recovery and, when relevant, a non-target or alternate reaction challenging inhibition or differentiation. Record expected and observed responses, acceptance criteria, strain and passage, lot, incubation, and disposition. A failed control blocks result interpretation until the cause is resolved.
Interpretation and confirmation pathway
K. pneumoniae produces blue-violet colonies. E. coli produces red colonies.Enterobacter spp, produces blue-green colonies. Citrobacter spp, produces blue colonies with red halo.Non-Enterobacteriaceae (if not inhibited) produce white to naturally pigmented colonies.
Record the raw observation before the conclusion: morphology or colour, growth pattern, endpoint, reaction intensity, reading time, and control response. Presumptive reactions remain presumptive. Route atypical, weak, mixed, or delayed reactions through the confirmation step in the current method.
Storage, stability, and pre-use inspection
CONDITIONS The powder is very hygroscopic, store the powder at 10-30°C, in a dry environment, in its original container tightly closed and use it before the expiry date on the label or until sings of deterioration or contamination are evident. Store prepared plates at 2-8°C away from light.WARNING AND
Receipt and storage records should reconstruct temperature exposure, lot rotation, expiry, container integrity, and time outside controlled storage. Inspect colour, clarity, fill volume, gel integrity, contamination, dehydration, and precipitate before use.
Limitations and boundaries of use
The product does not contain hazardous substances in concentrations exceeding the limits set by current legislation and therefore is notclassified as dangerous. it is nevertheless recommended to consult the safety data sheet for its correct use. The product is designed for In vitro diagnostic use and must be used only by properly trained operators.
Applicability depends on matrix, target organism, interfering flora, inoculum, validated method, and regulatory setting. Do not transfer conditions or acceptance criteria from a different matrix without verification.
Troubleshooting from evidence, not guesswork
- Poor recovery: check preparation, pH, overheating, supplement addition, inoculum, atmosphere, storage, and control performance.
- Loss of selectivity: review formulation, sterilization, expiry, inoculum burden, enrichment sequence, and incubation time.
- Weak or atypical reaction: confirm reading time and atmosphere, compare controls, document mixed growth, and follow confirmation requirements.
- Run-to-run drift: trend lot, analyst, equipment, water, preparation batch, controls, and environmental conditions.
External method context
The product should be understood as one measurement component in an antimicrobial susceptibility method. The analytical chain includes isolate purity, standardized inoculum, medium composition, antimicrobial concentration, incubation atmosphere and time, endpoint reading, and the interpretive table selected by the laboratory. A shift in any upstream variable can move an MIC or zone without a change in organism biology, which is why QC distributions and trend review are more informative than a single pass/fail control.
External laboratory-quality guidance also supports a lifecycle view: verify the method when introduced, bridge new lots against an accepted lot, trend control results, investigate nonconformities, and retain enough raw observations to reconstruct the decision. This is the practical difference between reproducing a preparation instruction and demonstrating that the resulting measurement is fit for its intended use.
EUCAST disk diffusion and quality control
EUCAST requires standardized methodology, current breakpoint tables, and routine quality control; the laboratory remains responsible for the final susceptibility report. For broth dilution, inoculum density, cation content, pH, incubation atmosphere, endpoint definition, and two-fold dilution design influence MIC reproducibility. Breakpoints are interpretive rules applied after a technically valid MIC or zone measurement; they are not properties of the product alone. Review the authoritative source.
FDA Bacteriological Analytical Manual
FDA BAM methods organize food microbiology around validated sampling, preparation, enrichment, isolation, and confirmation steps, with method applicability tied to the matrix and target organism. Sampling uncertainty, homogenization efficiency, inhibitory ingredients, dilution design, and countable range can dominate the result before the culture medium is ever inoculated; those variables belong in method verification and uncertainty review. Review the authoritative source.
WHO Laboratory Quality Management System handbook
WHO laboratory quality guidance treats document control, equipment, purchasing and inventory, process control, records, occurrence management, and continual improvement as connected parts of reliable testing. Review the authoritative source.
Technical references
- Manufacturer product documentation for catalogue 611619.
- EUCAST disk diffusion and quality control (access checked 2026-07-20).
- FDA Bacteriological Analytical Manual (access checked 2026-07-20).
- WHO Laboratory Quality Management System handbook (access checked 2026-07-20).
Bench-use checklist
- Verify product identity, catalogue number, lot, expiry, and storage history.
- Document preparation and incubation exactly as controlled in the SOP.
- Define controls and acceptance criteria before testing.
- Record raw observations, control response, reading time, and confirmation decision.
- Escalate failed controls, atypical reactions, and departures through the quality system.