Evaluating Escherichia coli contamination in bivalve mollusks using the impedance method: a comparison with most probable number analyses and correlation with environmental parameters

Submitted: 19 December 2022
Accepted: 16 February 2023
Published: 8 June 2023
Abstract Views: 1317
PDF: 236
Publisher's note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.


The application of an electrochemical (impedance) tool for monitoring Escherichia coli contamination in shellfish was evaluated after 13 months of observation. The primary aim of the present study was to compare the standard most probable number (MPN) and µ-trac 4200 (log imped/100 g) for the assessment of E. coli contamination (log MPN/100 g) in non-depurated bivalve mollusks (BM) from five sampling areas of the Veneto-Emilian coast (Italy) (118 samples). The secondary aim was to evaluate the correlation between E. coli concentrations in BM and environmental factors on a large data set (690). The methods showed a moderate, positive correlation (0.60 and 0.69 Pearson and Spearman coefficients, respectively; P<0.01) in Ruditapes philippinarum. The McNemar test indicated analogous sample classification between methods, and the impedance method overestimated the most contaminated class (P=0.03; >4,600 MPN/100 g). The results highlighted the suitability of the impedance method for a faster evaluation and routine use especially in clams, while in Mytilus it seemed less effective. Different models built by multivariate permutational variance analysis and multinomial logistic regression selected the suitable environmental features able to predict the E. coli load. Overall, salinity and season affected the E. coli contamination, whereas locally it was mainly influenced by hydrometry and salinity. The application of the impedance method coupled with environmental data analysis could help purification phase management to adhere to legal limits and could represent an advantage for local control authorities to define actions, considering extreme meteorological events' effects as a proactive reaction to climate change.

Campos CJA, Kershaw SR, Lee RJ, 2013. Environmental influences on fecal indicator organisms in coastal waters and their accumulation in bivalve shellfish. Estuar Coast 36:834-53. DOI: https://doi.org/10.1007/s12237-013-9599-y

Colaiuda V, Di Giacinto F, Lombardi A, Ippoliti C, Giansante C, Latini M, Mascilongo G, Di Renzo L, Berti M, Conte A, Ferri N, Verdecchia M, Tomassetti B, 2021. Evaluating the impact of hydrometeorological conditions on E. coli concentration in farmed mussels and clams: experience in Central Italy. J Water Health 19:512-33. DOI: https://doi.org/10.2166/wh.2021.203

Consorzio di Bonifica Delta del Po, 2014. The Po delta lagoons. Ed. Consorzio di Bonifica Delta del Po, Taglio di Po (Italy).

Dupont J, Dumont F, Menanteau C, Pommepuy M, 2004. Calibration of the impedance method for rapid quantitative estimation of Escherichia coli in live marine bivalve mollusks. J Appl Microbiol 96:894-902. DOI: https://doi.org/10.1111/j.1365-2672.2004.02218.x

Dupont J, Martial C, Cédric K, Lardeux AL, Roulex J, Menanteau C, Dumont F, Auffray E, 2010. Validation of an impedance method as an alternative to the European reference method for rapid enumeration of Escherichia coli in live bivalve molluscs. ICMSS, 14-19 Juin 2009, Nantes.

EUFOMA 2021. The EU fish market. 2021 Edition. Available from: https://www.eumofa.eu/documents/20178/477018/EN_The+EU+fish+market_2021.pdf/27a6d912-a758-6065-c973-c1146ac93d30?t=1636964632989.

European Commission, 2003. Guidance document number 5. Transitional and coastal waters. Typology, reference conditons and classification systems. Luxemburg: Office for official publications of the European communities. European Parliament, 10 2000. EU Water Framework Directive 2000/60/EC.

European Commission, 2004. Regulation of the European Parliament and of the Council of 29 April 2004 laying down specific hygiene rules for on the hygiene of foodstuffs, 853/2004/CE. In: Official Journal, L 139/55, 30/04/2004.

European Commission, 2005. Commission regulation of 15 November 2005 on microbiological criteria for foodstuffs, 2073/2005. In: Official Journal, L 338/1, 22/12/2005.

European Commission, 2015. Commission regulation of 8 December 2015 amending Annex II to Regulation (EC) No 854/2004 of the European Parliament and of the Council laying down specific rules for the organisation of official controls on products of animal origin intended for human consumption as regards certain requirements for live bivalve molluscs, echinoderms, tunicates and marine gastropods and annex I to regulation (EC) No 2073/2005 on microbiological criteria for foodstuffs. In: Official Journal, L 323/2, 9/12/2015.

European Commission, 2019. Implementing regulation (EU) laying down uniform practical arrangements for the performance of official controls on products of animal origin intended for human consumption in accordance with regulation (EU) 2017/625 of the European Parliament and of the Council and amending Commission Regulation (EC) No 2074/2005 as regards official controls. In: Official Journal, L 131/51, 17/05/2019.

Holcomb DA, Stewart JR, 2020. Microbial indicators of fecal pollution: recent progress and challenges in assessing water quality. Curr Environ Heal Reports 7:311-24. DOI: https://doi.org/10.1007/s40572-020-00278-1

Ifremer, 2014. Enumeration of Escherichia coli in live bivalve molluscan shellfish by the direct impedance technique using the BacTrac 4300. Series Analyser, 1. Available from: https://www.iss.it/documents/5430402/0/E+coli_enumeration-BacTrac_impedance_+technique_v1.pdf/8d4555fe-c8ba-8c4a-5b7a-86cfe134c986?t=1623946878855.

ISO, 2015. Microbiology of the food chain - horizontal method for the enumeration of ß-glucuronidase-positive Escherichia coli - part 3: detection and most probable number technique using 5-bromo-4-chloro-3-indolyl - ß - glucuronide. Norm ISO/FDIS 16649-3:2015. Geneva: International Organization for Standardization Publications.

IZS Umbria, 2023. Depurazione dei molluschi bivalvi: principi e aspetti pratici. Available from: http://www.izsum.it/files%5CDownload%5C83%5C13508%5CDepurazione.pdf.

Maicu F, De Pascalis, F, Ferrarin C, Umgiesser G, 2018. Hydrodynamics of the Po river-delta-sea system. J Geophys Res Oceans 123:6349-72. DOI: https://doi.org/10.1029/2017JC013601

MIPAAF, 2014. Piano strategio per l’acquacoltura in Italia 2014-2020. Available from: https://www.politicheagricole.it/flex/cm/pages/ServeAttachment.php/L/IT/D/b%252F1%252Ff%252FD.428bdb5bca0aa9cf42e1/P/BLOB%3AID%3D8752/E/pdf.

Pigłowski M, 2019. Pathogenic and non-pathogenic microorganisms in the rapid alert system for food and feed. Int J Environ Res Public Health 16:477. DOI: https://doi.org/10.3390/ijerph16030477

Saingam P, Li B, Yan T, 2020. Fecal indicator bacteria, direct pathogen detection, and microbial community analysis provide different microbiological water quality assessment of a tropical urban marine estuary. Water Res 185:116280. DOI: https://doi.org/10.1016/j.watres.2020.116280

Tabanelli G, Montanari C, Gardini A, Maffei M, Prioli C, Gardini F, 2017. Environmental factors affecting Escherichia coli concentrations in striped venus clam (Chamelea gallina L.) harvested in the North Adriatic sea. J Food Prot 80:1429-35. DOI: https://doi.org/10.4315/0362-028X.JFP-17-058

Walker DI, Younger A, Stockley L, Baker-Austin C, 2018. Escherichia coli testing and enumeration in live bivalve shellfish – present methods and future directions. Food Microbiol 73:29-38. DOI: https://doi.org/10.1016/j.fm.2017.12.006

Currò S, Fasolato L, Balzan S, Biziato G, Paesanti F, Bargelloni L, Cardazzo B, Novelli E. Evaluating <i>Escherichia coli</i> contamination in bivalve mollusks using the impedance method: a comparison with most probable number analyses and correlation with environmental parameters. Ital J Food Safety [Internet]. 2023 Jun. 8 [cited 2024 Jun. 13];12(2). Available from: https://www.pagepressjournals.org/ijfs/article/view/11103


Download data is not yet available.