V5, 09/06/2015 Definition of a no growth food and what factors are considered to determine a growth / no growth food? Including micro niches and significance of delayed growth. Philip Bronstein (FSIS) Robert Buchanan (UMD) Leon Gorris (Unilever) Marcel Zwietering (WUR) Workshop Evaluation of Risk Factors for Foodborne Listeriosis, 16-18 June 2015 1
A. Definition of a no growth food B. What factors are considered to determine a growth / no growth food? - Including micro niches and significance of delayed growth. 2
Global level: Codex Alimentarius - Listeria in RTE standard 1 1 http://www.codexalimentarius.org/download/standards/10740/cxg_061e.pdf 3
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Are these clear and appropriate criteria for growth: - Scientifically? - Practically? 10
Are these clear and appropriate criteria for Lm growth (Scientifically? Practically?) Growth is: an increase in Lm levels that is greater than an average of 0.5 log CFU/g for at least the expected shelf life under reasonably foreseeable conditions of distribution, storage and use Why 0.5 log CFU/g?: Explanation: this is twice the estimated standard deviation (i.e. 0.25 log) associated with the experimental enumeration using viable counting/plate counts Context: rule of thumb/accepted practice Question: can it me an average of a set of measurements (e.g. n = 3) or should a defined set of measurements all be below 0.5 log CFU/g (taking the rule of thumb limit as 2x a SD-value already includes an average, i.e. the SD-value). Shelf-life queries Definition mentions a specified storage temperature? But temp fluctuations should be considered Can it be foreseen shelf-life as a minimum or should there be a margin/buffer (e.g. a period longer than foreseen shelf-life; worst-case conditions?) 11
A. Definition of a no-growth food Regulatory status Codex criteria for growth/no growth have been formally implemented in Canada 1 and Australia 2, and informally in the European Union 3. Non-mandatory guidance on acceptable Lm limits in US 4 1 http://www.hc-sc.gc.ca/fn-an/legislation/pol/policy_listeria_monocytogenes_2011-eng.php 2 http://www.foodstandards.gov.au/code/microbiollimits/pages/criteria-for-listeria-monocytogenes-in-ready-to-eat-foods.aspx 3 http://ec.europa.eu/food/food/biosafety/salmonella/microbio_en.htm 4 http://www.fda.gov/food/guidanceregulation/guidancedocumentsregulatoryinformation/foodprocessinghaccp/ucm073110.htm 12
Guidance formally issued: Canada // draft guidance developed in European Union 13
EU_RL_Lm (2014) http://eur-lex.europa.eu/legal-content/en/txt/pdf/?uri=celex:32005r2073&from=en EU_RL_Lm (2013) http://ec.europa.eu/food/food/biosafety/salmonella/docs/translation_guidance_lm_en.pdf http://ec.europa.eu/food/food/biosafety/salmonella/docs/technical_guidance_listeria_en.pdf 14
EU_RL_Lm (2013) Guidance Document on Listeria monocytogenes shelf-life studies for ready-to-eat foods To categorize food; based on Codex criterion: No growth when δ 0.5 log 10 cfu/g, Growth when δ > 0.5 log 10 cfu/g, 15
Useful guidance for FBOs and governments Test at least 3 different batches of the same product. Perform microbial challenge tests with a mixture of at least 3 strains to account for variations in growth among the strains. Among the selected strains one must be a reference strain (ATCC, NCTC, CIP or equivalent). The other strains must be isolated from the same or a similar food matrix. Before the implementation of the challenge test, conduct prior trials to determine the time necessary to reach the stationary phase. Subculture each strain in a medium (e.g. Tryptone Soy Broth (TSB) or Brain Heart Infusion (BHI)) and at a temperature (37 C) favourable to optimal growth of Listeria monocytogenes, for a sufficient time for the organism to reach the beginning of the stationary phase. Target the contamination level at 50 cfu/g, which should not exceed 100 cfu/g. The inoculation must be as effective as possible at simulating natural contamination conditions and maintaining the intrinsic properties of the foodstuff. In order to minimise changes to the physical-chemical properties, the inoculum should not exceed 1% of the volume of the test unit, EURL Lm 2008; V2 of technical guidance document for conducting shelf-life studies on Lm in RTE foods 16
The storage (incubation) conditions applied during challenge testing must comply with the conditions at which the product is most likely to be subjected in normal use, until its final consumption. This should include the typical temperature range at which the product is to be transported, distributed and stored. Storage time and temperature(s) used to determine product shelf-life has (have) to be properly justified and documented by the FBO. - When the FBO has its own data on the two first stages of the cold chain (from manufacturing to retail, storage at retail), the use of this information is preferred (in particular for exported products). - If no FBO data is available, Table 3 has to be followed. EURL Lm 2014, V3 technical guidance document for conducting shelf-life studies on Listeria monocytogenes in ready-to-eat foods 17
Calculation of growth potential. - The growth potential is the difference between the median of results at the end of the challenge test and the median of results at the beginning. - For each batch, the standard deviation (due to measurement uncertainty and contamination heterogeneity) between the log10-results at "day 0 should be 0.5 log10 cfu/g; otherwise the challenge test is not acceptable. - For each batch, the growth potential is calculated and the highest value obtained amongst all tested batches is retained. EURL Lm 2014, V3 technical guidance document for conducting shelf-life studies on Listeria monocytogenes in ready-to-eat foods 18
EU_RL_Lm (2013) Guidance Document on Listeria monocytogenes shelflife studies for readyto-eat foods To categorize food; based on Codex criterion: No growth when δ 0.5 log 10 cfu/g, Growth when δ > 0.5 log 10 cfu/g, Guidance on establishing safe shelf-life Using durability and challenge tests Considering historic data, PM, risk assessment etc. Assessing growth potential (growth rate; level at end shelf-life, etc..) 19
A. Definition of a no-growth food Recommendations To confirm that the Codex criteria for growth/no growth are an appropriate basis for separating foods that support Lm from those that do not. To provide practical guidance to government and industry on the validation of no-growth foods To consider also providing practical guidance to government and industry on the assessment of safe shelf-life for growth foods To include the recommendations (after discussion and work done during the workshop) in the white paper 20
A. Definition of a no growth food B. What factors are considered to determine a growth / no growth food? - Including micro niches and significance of delayed growth. 21
B. What factors are considered to determine a growth / no growth food? Referenced also f.i. in Health Canada (2011). Policy on Listeria monocytogenes in Ready-to-Eat Foods. FD-FSNP 0071 22
EU_RL_Lm (2013) Guidance Document on Listeria monocytogenes shelf-life studies for ready-to-eat foods (also: table 1 in EU_RL_Lm, 2014) 23
Impact of micro niches? - Food rheology/structures for instance can lead to physico-chemical factors controlling Lm growth to be inhomogeneous or inconsistent in time/space. - Bacteria grow at interfaces (particulate/fluid; oil/water; etc). - Microbial activity can change intrinsic factors (e.g. ph, a w ) locally. In theory, this could lead to micro-niches where Lm cells may locally experience less stringent control or more stringent control; both events could potentially compromise establishing correctly whether a food is no growth There is no overview of epidemiological evidence or scientific literature specifically documenting the impact of micro-niches for Lm in RTE foods However, the possible presence in foods of micro-niches needs to be considered in establishing whether a food is no growth Depending on the factors affected, practical solutions may be found to avoid micro-niches or to add/change controlling factors Validation of appropriate product/process design is through durability and challenge testing 24
Significance of delayed growth? - The growth rate 1 and the lag-phase of growth of Lm can vary between strains. - Microbial activity can change intrinsic factors (e.g. ph, aw) locally. - Temperature fluctuations over time/space influence lag-phase/growth-rate The possible impact of underestimating growth (y/n; potential) needs to be considered in establishing whether a food is no growth Validation of appropriate product/process design is through durability and challenge testing under realistic conditions (f.i. under controlled, dynamic conditions; fast track testing not advisable) It is appropriate to validate for different strains or using cocktails of strains, considering, for instance availability of strains isolated from the same or similar food with comparable Lm growth controlling factors availability of reference Lm strains with documented short lag-phases relative to the relevant Lm growth controlling factors 1. Aryani et al., 2015. Quantifying strain variability in modelling growth of Listeria monocytogenes. IJFM, 208: 19-29 25
What factors are considered to determine a growth / no growth food? Including micro niches and significance of delayed growth. Recommendations To provide practical guidance to government and industry on the physico-chemical factors that individually or in combination determine no growth - Giving examples of key factors and synergies (cannot be exhaustive; different formats can be considered) - Illustrating methods/approaches for validation - Stressing need to consider micro niches and delayed growth in validation of no growth ; suggesting approaches To include the recommendations (after discussion and work done during the workshop) in the white paper 26