OHEJP-RaDAR-D-JRP3-3.4 Scientific report on a model of AMR exposure through shellfish consumption

Kyrre Kausrud, Jurgen Chardon, Guido Correia Carreira, Clazien de Vos, Catherine McCarthy, Arno Swart, Annemarie Käsbohrer

Introduction

Antimicrobial resistant (AMR) bacteria in seafood represent a potential risk for humans by two main mechanisms, either clonal transfer of resistant bacteria or by horizontal gene transfer (HGT) of mobile genetic elements (MGE) to previously susceptible pathogens.  

            The emergence of successful multi drug resistant (MDR) variants of Escherichia coli and Klebsiella pneumoniae, belonging to certain clonal lineages, has contributed to the rapid global spread of ESBLs and carbapenemases [1]. These clones are considered “global hig hrisk clones” and have an excellent ability to colonize human hosts, disseminate and cause infections, with E. coli Sequence type (ST) 131 and K. pneumoniae ST258 as pertinent examples [2].  To be better equipped for the emerging AMR challenge, a thorough investigation of transmission routes and reservoirs is needed, WHO underlines the knowledge gap on the food chain in transmission of AMR bacteria, and AMR bacteria from seafood has been identified by EFSA as an issue for monitoring [3]. 

            Extended spectrum beta lactamase (ESBL)-producing E. coli is one of several emerging AMR microbes which have been detected in blue mussels. The origin of such resistances may be both from human or animal sources contaminating seawater. The filtration rate of blue mussels is temperature dependent, but at 15 ̊C it may exceed 120 litres of water per day [4]. They thus constitutes potential hot spots for accumulating pathogenic and antimicrobial resistant bacteria from the marine environment. If ESBL organisms accumulated from the environment survive heat treatment, AMR genetic elements can be transferred to the human microbial community. Thereby, these may be transferred to other bacteria's including pathogens.

            The potential for blue mussels to be a significant source of ESBL - producing E. coli to humans is unknown. Blue mussels typically undergo heat treatment before consumption, and commercial produced blue mussels have a food safety regulation limit of 230 E. coli/100g for direct human consumption (854/2004/EC, 2004), demanding that shellfish with higher E. coli concentrations be moved to cleaner water until the concentration falls below this level. As E. coli is an indicator of faecal contamination makes it useful as an indicator of pathogens which spreads this way, but this limit might not be enough to avoid ESBL-producing E. coli being transferred to humans from mussels/ shellfish. In addition, consumption of wild-harvested mussels occurs in many coastal areas, particular during vacation times.  

            The heat treatment performed by the consumer is traditionally kept to a minimum (until the shell opens), so there is a need for public knowledge of the potential for survival of both E. coli and ESBL-producing E. coli in such a food matrix. There exists little knowledge about the persistence of viable ESBL producing E. coli in different food matrixes where only light heat treatment are performed before consumption, but both the maximum obtained temperature within the mussel as well as the duration of certain temperatures will likely have an impact on bacterial survival, determining the amount of remaining viable from the original contamination. 

            The aim of this study was therefore to assess the survival of ESBL-producing E. coli in heat-treated (cooked) blue mussels following different heat treatment regimes,  and to develop a corresponding exposure model and tool for risk assessment and guideline development. To achieve this, we conducted experiments inoculating live shellfish with E. coli as an indicator for ESBL-producing E. coli to avoid unacceptable contamination risks, and used ESBL in controlled heat treatment experiments comparing it to E. coli to verify their role as an indicator and accumulate additional data on heat inactivation.