A susceptibility result can shift before the organism changes. That is why Contact Slide Chrom 3 must be considered together with inoculum, atmosphere, incubation, and endpoint reading. The discussion below connects its documented role with preparation variables, controls, interpretation, and the limits of inference. Catalogue 525462 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
Contact Slide Chrom 3 is a ready-to-use device with two media solidified onto a plastic support used for the microbial monitoring of surfaces of sanitary importance and analysis of food and water samples. The chromogenic and selective medium allows the detection of E. coli and the differentiation from the other enterobacteria. The other medium is used for the isolation of S. aureus while inactivating disinfectants.
Method principle
ChromaticTM Coli Coliform is used for the detection of beta-glucuronidase-positive E. coli and coliform bacteria. Chromogenic and selective mix allows to identify microorganisms on the basis of the color and morphology of the colonies while inhibiting most of Gram-positive bacteria. Baird Parker + Neutralizing is used for the screening of staphylococci and hygiene monitoring on surfaces even in the presence of residues of disinfectants. Sodium pyruvate stimulates the growth of S. aureus while glycine and lithium chloride inhibit most organisms other than staphylococci. Egg yolk, besides being an enrichment, aids in the identification process showing the lecithinase activity. Tellurite is reduced by coagulase-positive staphylococci causing blackening of colonies.
Formula and functional interpretation
ChromaticTM Coli Coliform Side 1 (g/l) Baird Parker + Neutralizing Side 2 (g/l) Peptone 20.0 Enzymatic Digest of Casein 10.0 Yeast Extract 3.0 Beef Extract 5.0 Sodium Chloride 5.0 Yeast Extract 1.0 Chromogenic and Selective Mix 2.7 Glycine 12.0 Agar 15.0 Sodium Pyruvate 10.0 Final pH 7.2 Lithium Chloride 5.0 Egg Yolk 50.0 ml Potassium Tellurite 0.1 Neutralizing * Agar 17.0 Final pH 7.2 *Histidine, 1.0 Lecithin, 0.7 Tween 80, 5.0 Sodium Thiosulfate, 0.5*Histidine, 1.0 Lecithin, 0.7 Tween 80, 5.0 Sodium Thiosulfate, 0.5
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
Procedure: 1.Take a slide from the refrigerator and leave it at ambient temperature for about 5 minutes 2.Unscrew and extract the slide from its cylindrical container. Avoid any contact with the agar surface. 3.For surfaces monitoring, flex the cap forming a 90° angle and push for 10 seconds the slide on the surface to be examined. For examination of food and water, hold the slide by the cap and immerse it completely in a suspension of the sample. 4.Reinsert the slide into its tube, screw it tight and incubate at 35 ± 2°C for 18-24 hours. RESULTS
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
© Liofilchem - Contact Slide Chrom 3- Rev.1 / 30.10.2014 Page 1 of 2 Instructions For Use Slides are inoculated with the microbial strains indicated in the QC table. Inoculum for productivity: 50-100 CFU Inoculum for selectivity: 104-106 CFU Inoculum for specificity: 103-104 CFU Incubation conditions: 35 ± 2°C for 18-24 hours. QC Table.
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
After incubation observe the color and the morphology of the colonies growth on ChromaticTM Coli Coliform (Side 1) and interpret the results as indicated in the ID table. ID Table Microorganism Typical colony color (Side 1) E. coli Green Other coliform bacteria Mauve Other bacteria (if not inhibited) Colorless On Plate Baird Parker + Neutralizing (Side 2) Staphylococcus aureus cultivates with black shiny colonies surrounded by a clear halo.
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
AND TRANSPORT CONDITIONS 2-8°C away from light, until the expiry date on the label. However, our stability studies have shown that the transport at 18-25°C for 4 days, or at 35-39°C for 48 hours, does not alter in any way the
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 not classified as dangerous. It is nevertheless recommended to consult the safety data sheet for its correct use. The product must be used by properly trained operators only.
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 525462.
- 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.