For antimicrobial testing, DRIGALSKI Lactose Agar 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 10018 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
Drigalski Lactose Agar is a medium used for the isolation and differentiation of Enterobacteriaceae and non- fermenting gram-negative bacilli (NFGNB), including Acinetobacter baumannii, from clinical specimens.
Method principle
Peptone and meat extract provide of amino acids, nitrogen, carbon, minerals and vitamins for organisms growth. Yeast extract is a source of vitamins of group B. Sodium thiosulfate, desoxycholate and crystal violet suppress the growth of gram-positive bacteria. Lactose is the fermentable carbohydrate. Bromothymol blue is the pH indicator. Agar is the solidifying agent.
Preparation and execution: controlled method points
Procedure: Inoculate the medium by spreading the sample over the agar surface to obtain well isolated colonies. Incubate plates inverted, aerobically at 35 ± 2°C for 18-24 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
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
Lactose fermenters, such as E. coli, Klebsiella and Enterobacter, produce acid forming yellow colonies surrounded by yellow medium. Non-fermenters, such as Proteus, Providencia, Hafnia, Salmonella, Serratia, Alcaligenes, Pseudomonas and Acinetobacter, cultivate with blue-grey to greenish colonies surrounded by blue to blue-green medium. Additional biochemical or immunological tests may be required for confirmation.
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
The powder is very hygroscopic, store the powder at 10-30°C, in a dry environment, in its original container tightly closed. Store bottles and prepared plates 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. Avoid quick temperature shifts of plated medium to prevent condensation.
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
For in vitro diagnostic use. For professional use only. Operators must be trained and have certain experience in the laboratory methods. Please read the instructions carefully before using this product. Reliability of assay results cannot be guaranteed if there are any deviations from the instructions in this document. Consult the Safety Data Sheet (SDS) for information regarding hazards and safe handling practices.
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 10018.
- 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.