A susceptibility result can shift before the organism changes. That is why Buffered NaCl-Peptone Solution modified pH 7.0 + NT 9 mL 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 26470 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
Buffered NaCl-Peptone Solution pH 7.0 modified + NT is used for dissolving, suspending and diluting test samples. Its composition is based on the recommendations in the Harmonized Pharmacopoeias for the microbiological examination of non-sterile products. Conforms to ISO 21149 for the detection of viable microorganisms in cosmetics, this
Method principle
Sodium phosphate and potassium phosphate are the buffering agents. Sodium chloride maintains the osmotic balance. A low peptone content provides nitrogen, vitamins, minerals and amino acids to ensure the viability of the organisms. Lecithin neutralizes quaternary ammonium compounds. Histidine inactivates aldehydes. Polysorbate (Tween 80) is a source of fatty acids and is effective against phenolic compounds and mercurial derivates. Sodium thiosulfate neutralizes halogen compounds.
Formula and functional interpretation
(g/l) Potassium Dihydrogen Phosphate 3.6 Disodium Hydrogen Phosphate Dihydrate 7.2 Sodium Chloride 4.3 Peptone 1.0 Lecithin 3.0 Histidine 1.0 Polysorbate 80 30 ml Sodium Thiosulfate 5.0 Final pH 7.0 ± 0.2 at 25°C
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: of samples which have an antimicrobial effect or which are not soluble in water.
Procedure: Dissolve or dilute the product to be examined (usually a 1 in 10 dilution is prepared) in Buffered NaCl-Peptone Solution modified pH 7.0 + NT. Use the suspensions within 2 hours or within 24 h if stored at 2-8°C.
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
The medium is inoculated with the microbial strains indicated in the QC table. Inoculum for diluent: 103-104 CFU. Incubation conditions: 22.5 ± 2.5°C for 2 hours. QC Table. Microorganism Growth on TSA Staphylococcus aureus ATCC 6538 ± 30% colonies of original count Pseudomonas aeruginosaATCC 9027 ± 30% colonies of original count Escherichia coli ATCC 8739 ± 30% colonies of original count Salmonella TyphimuriumATCC 14028 ± 30% colonies of original count Bacillus subtilis ATCC 6633 ± 30% colonies of original count Candida albicans ATCC 10231 ± 30% colonies of original count WARNING AND
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
No marked increase or decrease in original colony forming unit (CFU) count.
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
Store tubes and bottles at 10-25°C away from light. Do not use the product beyond its expiry date on the label or if product shows any evidence of contamination or any sign of deterioration.
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 is intended for professional use only and must be used 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.
FDA BAM Chapter 5: Salmonella
The current FDA BAM Salmonella workflow separates pre-enrichment, selective enrichment, selective plating, and confirmation. That sequence is scientifically important: enrichment increases target representation in a mixed matrix, selective conditions manage competing flora, and confirmation prevents a colour or colony morphology from being treated as identity. A laboratory transferring the method should verify recovery and selectivity on its own matrix classes rather than assuming that a medium performs identically across foods, water, and environmental samples. Review the authoritative source.
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.
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 26470.
- FDA BAM Chapter 5: Salmonella (access checked 2026-07-20).
- EUCAST disk diffusion and quality control (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.