A susceptibility result can shift before the organism changes. That is why Fraser Broth Base 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 610375 is discussed as a laboratory measurement component; implementation should follow the laboratory SOP and validated reference method.
Analytical scope and method role
Fraser Broth Base is a liquid medium used with supplements for the selective enrichment of L monocytogenes and Listeria spp from food, animal feeding and environmental samples in the area of food production and food handling.This medium is completed after the addition of one of the following supplements: •Half Fraser Supplement (ref. 81043)•Fraser Supplement (ref. 81046)Both supplements consist of a Vial A containing Acriflavine and Nalidixic acid and of a Vial B with Ammonium Iron(III) Citrate.
Method principle
Enzymatic digest of animal tissues, enzymatic digest of casein and meat extract provide nitrogen, vitamins, minerals and amino acids for organisms growth. Yeast extract is a source of vitamins, particularly of B-group. Sodium chloride maintains the osmotic balance of the medium and in a so high concentration inhibits enterococci. Potassium and sodium phosphates act as buffer system. Aesculin is hydrolyzed by all Listeria species to aesculetin. Lithium chloride is inhibitory for the accompanying flora. Ferric ions provided by ammonium iron(III) citrate will react with aesculetin producing a blackening of the medium. Acriflavine and nalidixic acid are selective agents.
Formula and functional interpretation
(g/l)Enzymatic Digest of Animal Tissues 5.0Enzymatic Digest of Casein 5.0Meat Extract 5.0Yeast Extract 5.0Sodium Chloride 20.0Disodium Phosphate, anhydrous 9.6*Potassium Dihydrogen Phosphate 1.35Aesculin 1.0Lithium Chloride 3.0Final pH 7.2 ± 0.2 at 25°C*Equivalent to 12.0 g of Disodium Hydrogen Phosphate, dihydrate.
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
Preparation: Suspend 55 g of powder in 1 liter of deionized or distilled water. Bring to boil and shake until completely dissolved. Sterilize at 121°C for 15 minutes. Cool up to 45-50°C. Aseptically, add rehydrated content of 2 vials A (10 ml) and of 2 vials B (10 ml) taken from the selected supplement.
Procedure: 1.Add sample to Half Fraser Broth to prepare a 10-fold dilution (w/v or v/v). Skip directly to step 3 for the enumeration method described in ISO 11290-2.For the detection method in ISO 11290-1, incubate at 30 ± 1°C for 25 ± 1 h. 2.Transfer 0.1 ml of the primary enrichment culture into 10 ml of Fraser Broth. Incubate at 37 ± 1°C for 24 ± 2 h. 3.From the enrichment cultures or from the initial suspension (depending on the method used) surface inoculate onto O.A. Listeria Agar (ref. 10620). Incubate at 37 ± 1°C for 24 ± 2 h and for an additional 24 ± 2 h. 4.Following 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.Microbiological controlSupplement: Half Fraser SupplementIncubation Conditions: 30 ± 1°C / 25 ± 1 hInoculum for productivity: ≤100 CFUMicroorganismSpecificationListeria monocytogenes serovar 4b + Escherichia coli + Enterococcus faecalisWDCM 00021WDCM 00013WDCM 00009Blackening of the medium,>10 colonies on O.A.
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
A blackening of Half Fraser Broth and Fraser Broth can be observed after incubation. Blue-green colonies with or without halo on O.A. Listeria Agar are considered presumptive Listeria spp. Typical colonies of L. monocytogenes are surrounded by an opaque halo. For the enumeration method count all colonies presumed to be L. monocytogenes and/or Listeria spp.For confirmation, subculture onto appropriate non-selective agar, e.g. Blood Agar, Nutrient Agar, TSYEA (ref. 10432). Then, carry out confirmation tests including a positive and negative control.
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
CONDITIONS The powder is very hygroscopic, store the powder at 10-30°C, in a dry environment, in its original container tightly closed and use it before the expiry date on the label or until signs of deterioration or contamination are evident. Store prepared medium at 2-8°C away from light.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 professional use only and must be used by properly trained operators. LIOFILCHEM S.r.l.Via Scozia, Zona Ind.le - 64026, Roseto degli Abruzzi (TE) - ITALYTel +39 0858930745 Fax +39 0858930330 www.liofilchem.com TECHNICAL SHEETTS 610375Rev.1 / 23.11.2018Page 2 of 3
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 10: Detection of Listeria monocytogenes
FDA's Listeria method places selective enrichment and plating inside a staged detection workflow and requires confirmation of suspect isolates. The broader lesson is that injured or low-level cells, competing flora, and matrix carryover can affect apparent recovery; verification should therefore include stressed target cells, representative backgrounds, and a defined confirmation pathway. 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 610375.
- FDA BAM Chapter 10: Detection of Listeria monocytogenes (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.