For antimicrobial testing, Salmonella DIFFERENTIAL Broth Culture Media sits at the point where organism growth becomes a quantitative or categorical measurement. The discussion below connects its documented role with preparation variables, controls, interpretation, and the limits of inference. Catalogue 24135 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
Salmonella Differential Broth is a liquid medium used for the detection of Salmonella spp from faeces and other materials.
Method principle
Proteose peptone provides carbon, nitrogen, vitamins and minerals for organisms growth. Yeast extract is a source of vitamins, particularly of B-group. L-Lysine is an amino acid substrate for the enzyme decarboxylase. Xylose, lactose and sucrose are the fermentable carbohydrates. Ferric ammonium citrate and sodium thiosulfate are the indicators of hydrogen sulfide production under alkaline conditions. Phenol red is the pH indicator. Phosphates act as buffer. Tergitol 4 is the selective agent inhibiting all Gram-positive bacteria and moulds as well as numerous Gram-negative bacteria including Proteus, Providencia and Pseudomonas spp.
Formula and functional interpretation
(g/l)Proteose Peptone2.0Yeast Extract3.0L-Lysine5.0Xylose3.75Lactose7.5Sucrose7.5Ferric Ammonium Citrate0.2Sodium Thiosulfate0.2Phenol Red0.08Sodium Dihydrogen Phosphate0.3Disodium Hydrogen Phosphate 1.3Tergitol 44.6 mlFinal pH 7.4 ± 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
Procedure: Process the specimen as appropriate. Inoculate Salmonella Differential Broth. Incubate at 35 ± 2°C for 18-24 h.Note: Avoid delay between sample collection and inoculation to not affect the test result.
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
1.Control of general characteristics, label and print2.Sterility control7 days at 22 ± 2°C, in aerobiosis7 days at 35 ± 2°C, in aerobiosis3.Microbiological controlInoculum for productivity: ≤100 CFUInoculum for selectivity: >103 CFUIncubation Conditions: 35 ± 2°C for 18-24 hMicroorganismGrowthColourBlackeningSalmonella TyphimuriumATCC 14028GoodRedPositiveEscherichia coli ATCC 25922Partially inhibitedYellowNegativeProteus mirabilisATCC 12453Inhibited------Staphylococcus aureusATCC 25923Inhibited------TABLE OF SYMBOLS Batch code In vitro DiagnosticMedical Device Manufacturer Use by Fragile,
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
Development of a red colour indicates the presence of Salmonella spp that may be made even more evident by the formation of a black precipitate. Non-Salmonella species are either inhibited or produce a colour change of the medium to yellow.Subculture to a selective agar plate such as XLD Agar (ref. 10056) for isolation and further analysis.
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
10-25°C away from light, until the expiry date on the label or until signs of deterioration or contamination are evident.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.
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 24135.
- 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.