For antimicrobial testing, ANTIBIOTIC TEST - Device for the evaluation of residual antimicrobial 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 80350 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
ANTIBIOTIC TEST is a device constituted by particular paper discs impregnated with living spores of Bacillus subtilis ATCC 6633 and with a dry culture medium. This device is indicated for the evaluation of residual antimicrobial power in urines, milk and other biological fluids. KIT CONTENTEach kit contains:•2 cartridges with 25 discs each, impregnated with living spores of Bacillus subtilis ATCC 6633 and with a dry culture medium;•50 plastic tubes.
Method principle
OF THE METHODThe paper disk contains living spores of Bacillus subtilis ATCC 6633 and a culture medium with triphenyl- tetrazolium- chloride (TTC). Spores and mediumare released into solution after the addition of the liquid sample to examine (urine, milk or other biological fluid). Substances endowed with antimicrobial activity, eventually present in the liquid sample, inhibit Bacillus subtilis spores development, so that liquid in the tube does not change its colour. In the caseof lack of substances with antimicrobial activity, Bacillus subtilis spores sprout.
Preparation and execution: controlled method points
Procedure: 1.Take the cartridge containing the disks from the refrigerator and allow it to reach room temperature. 2.Take a disk of Antibiotic Test from the cartridge and put it into a tube.3.Add 0.2 mL of urine, milk or other biological fluid to test.4.Cap the tube and incubate at 36 ± 1 °C for 24 hours.5.Observe for development of a red colour after 8-12-24 hours.
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
Each batch of ANTIBIOTIC TEST is submitted to
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
OF THE RESULTSThe development of a red color in the tube of the sample indicates the absence of antimicrobial substances or their presence at a lower concentration than sensitive limit of the methods.The absence of a red colour in the tube indicates the presence of antimicrobial substances in the sample at a higher concentration than sensitive limit of the method.
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
OF THE SAMPLESIn order to perform the test on urine use the same sample of the urinoculture. For collection of milk or other biological fluids, follow the instructions suggested for culture tests on these samples.Store the samples at 2-8 °C before use.
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
Results obtained with ANTIBIOTIC TEST are qualitative.
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 80350.
- 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.