For antimicrobial testing, Legionella AGAR (GVPC) (RT) 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 10998 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
Legionella Agar (GVPC) is a selective medium used for primary isolation of Legionella spp from water samples. This medium conforms to the recommendations of ISO 11731 and ISO 11731-2 for examination of all kinds of environmental samples including potable, industrial and natural waters and associated materials as well.
Method principle
Yeast extract provides amino acids, nitrogen, carbon, vitamins and minerals. Activated charcoal decomposes hydrogen peroxide, a metabolic product toxic to Legionella spp, and may also collect carbon dioxide and modify surface tension. ACES buffer (N-2- acetamido-2-aminoethane sulfonic acid) and potassium hydroxide maintain the proper pH for optimal growth. Alpha-ketoglutarate, cysteine and ferric pirophosphate are incorporated to satisfy the specific nutritional requirements of Legionella species. Agar is the solidifying agent. Glycine, vancomycin and polymyxin B inhibit or suppress most non-target bacterial species, both Gram-positive and Gram-negative, including common contaminants such as enterococci, coliform, and Pseudomonas spp, while cycloheximide suppresses the growth of yeasts and moulds.
Formula and functional interpretation
(g/l) Yeast Extract 10.0 Charcoal Activated 2.0 ACES Buffer 10.0 Potassium Hydroxyde 2.8 α-Ketoglutarate 1.0 Ferric Pyrophosphate 0.25 L-Cysteine 0.4 Agar 13.0 Glycine 3.0 Vancomycin 0.001 Polymyxin B 80000 IU Cycloheximide 0.08 Final pH 6.9 ± 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
Procedure: According to ISO 11731, perform direct analysis if the number of Legionella is expected to exceed 105 per liter. Otherwise, samples need to be concentrated by membrane filtration or by centrifugation prior to culture. To reduce the growth of unwanted bacteria, two portions of sample, concentrated or not, are treated either with heat or acid. A third portion is left without any further treatment. For liquid samples, inoculate by spreading 0.1 to 0.5 ml of the test over the agar surface, or filter 10 to 1000 ml of water sample before placing the membrane onto the agar. Incubate at 36 ± 2°C for up to 10 days in humidified atmosphere (air with 2.5% CO2 can be beneficial for the growth of some Legionella but is not essential). Regarding sample transport and
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 productivity: 50-100 CFU. Inoculum for selectivity: 104-106 CFU. Incubation conditions: 36 ± 2°C for up to 10 days in humidified atmosphere. QC Table. Microorganism Growth Legionella pneumophila WDCM 00107 Good Legionella anisa WDCM 00106 Good Enterococcus faecalis WDCM 00087 Inhibited Pseudomonas aeruginosa WDCM 00025 Inhibited Escherichia coli WDCM 00013 Inhibited 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
Examine for growth and fluorescence under long-wave UV light on at least two occasions during the incubation period starting from the third day. Colonies of Legionella on black media or black membrane are often white-grey-blue-purple in colour, but can be brown, pink, lime-green or deep-red. They are smooth with an entire edge and exhibit a characteristic ground-glass
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
, analysis should begin as soon as possible after the sample has been taken, preferably on the same day. Samples should be protected from heat and sunlight, kept between 6-20°C and transported to the laboratory within 24 hours of collection.
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.
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 10998.
- 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.