A susceptibility result can shift before the organism changes. That is why Baird Parker AGAR + RPF (RT) Culture Media 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 10999 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
Baird Parker Agar + RPF is a selective medium used for isolating coagulase-positive staphylococci in foods and other materials, as recommended in ISO 6888-2.
Method principle
Pancreatic digest of casein and meat extract provide amino acids, carbon, nitrogen, vitamins and minerals. Yeast extract is a source of vitamins, particularly of B-group. Sodium pyruvate stimulates the growth of S. aureus without destroying the selectivity. Glycine and lithium chloride have inhibitory action for organisms other than S. aureus. Bovine fibrinogen, rabbit plasma and trypsin inhibitor are the substrates which enable the detection of coagulase activity: the presence of rabbit plasma together with bovine fibrinogen leads to
Formula and functional interpretation
(g/l)Pancreatic Digest of Casein10.0Meat Extract 5.0Yeast Extract 1.0L-Glycine12.0Sodium Pyruvate10.0Lithium Chloride 5.0Agar17.0Bovine Fibrinogen 5.0Rabbit Plasma - EDTA25 mlTrypsin Inhibitor 0.025Potassium Tellurite 0.025Final pH 7.2 ± 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: Prepare the sample suspension and further decimal dilutions in Maximum Recovery Diluent (ref. 20071). Transfer, by means of a sterile pipette, 0.1 ml of the test sample if liquid or of the initial suspension in the case of other products, to a plate of Baird Parker Agar + RPF.Repeat the
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: 50-100 CFUInoculum for selectivity: 104-106 CFUInoculum for specificity: 103-104 CFUIncubation Conditions: 24-48 hours at 37 ± 1°C, in aerobiosisMicroorganismGrowthColony colourOpacity haloStaphylococcus aureusWDCM 00034GoodBlack - greyYesEscherichia coliWDCM 00013Inhibited------Staphylococcus saprophyticusWDCM 00159GoodBlack - greyNoStaphylococcus epidermidisWDCM 00036GoodBlack - greyNoTABLE OF SYMBOLS
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
Typical colonies of S. aureus are black or grey, shining and convex, surrounded by a zone of clearing of the medium. After 24 hours incubation an opalescent ring immediately in contact with the colonies may appear in this clear zone.
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. Eliminate if 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 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.
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 10999.
- 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.