Fishery and aquaculture products increasingly represent an important food source for the world population. The intensification of aquaculture guided an increase in the use of antimicrobials in this sector as well. The aquatic environment represents a link among humans, animals and environmental antibiotic resistance. The rising problem of antibiotic resistance leads to the need for the identification of indicator bacteria and the development of monitoring methods, which are poorly standardized for the aquatic environment. Aeromonas spp., a ubiquitous bacterium in aquatic environments, is among the possible candidates as bacterial indicator. The goals of this study were to: (i) evaluate the antibiotic-resistance profile of different antimicrobial classes in Aeromonas spp. collected from seafood sold in superstores of central Italy; (ii) propose possible epidemiological cut-offs for the genus Aeromonas and evaluate its effectiveness as a possible bacterial indicator for monitoring antibiotic resistance in seafood. The results obtained revealed a high presence of Aeromonas spp. in seafood categories, highlighting its candidature as a bacterial indicator. The presence of isolates resistant to some of the tested antibiotics has been described, even if in rare occasion. This data raises concerns about the food safety of seafood for consumption, which may represent a risk for public health and consumers. In this study, we described the epidemiological cut-offs which agree with the literature, representing a contribution to the definition of reliable epidemiological cut-offs for the genus Aeromonas spp.

This study assessed Escherichia coli as an indicator of antimicrobial resistance (AMR) in retail seafood, integrating microbiological and genomic analyses within a One Health perspective. Overall, E. coli was cultured from 55 (13%) of 422 raw samples from seven seafood categories commonly consumed in Italy. E. coli was detected across multiple seafood types, but particularly in bivalves (23%) and crustaceans (20%). Because these species can accumulate or acquire faecal contaminants from the aquatic environment or along the post-harvest chain, they represent relevant matrices for AMR monitoring. In parallel, we investigated the presence of Extended-β-Lactamase ESBL-, AmpC- and carbapenemase-producing Enterobacteriaceae. Cefotaxime-resistant E. coli isolates were identified at low but relevant frequencies, especially in bivalves, and were characterised phenotypically and by whole-genome sequencing. Most isolates carried clinically important ESBL or AmpC genes, more frequently blaCTX-M-15, often on contigs predicted as plasmid-associated, indicating their potential for horizontal spread. An ESBL-producing Atlantibacter hermannii harbouring blaCTX-M-55 was also recovered from frozen shrimps. Additional AmpC-producing Enterobacteriaceae, including Citrobacter and Enterobacter species, were detected in a subset of samples.Overall, our findings support the suitability of E. coli as an AMR indicator organism for retail bivalves and crustaceans. The detection of ESBL-producing strains, carrying important plasmid-borne resistance determinants, highlights the need to strengthen AMR surveillance in these seafood commodities.

OBJECTIVES:We aimed to characterise the genomic features of two multidrug-resistant (MDR) isolates from retail seafood samples. METHODS:Antimicrobial susceptibility was determined by minimum inhibitory concentration (MIC) tests. Genome sequences were obtained by hybrid sequences of short and long. RESULTS:The two MDR (ampicillin, cefotaxime, ciprofloxacin, ceftazidime, nalidixic acid, gentamicin, tetracycline, sulfamethoxazole, cefoxitin, and trimethoprim) Enterobacter hormaechei (E. hormaechei) isolates belonged to ST114. Nineteen antibiotic resistance genes (ARGs), including mcr-9, were identified in the genomes. The mcr-9 and other resistance determinants were on an IncHI2 plasmid. Sequence analysis showed mutations in genes implicated in colistin resistance, of which a non-conservative one was present in the qseB. Virulence genes of T6SS or involved in motility were identified in both genomes. Comparison of mcr-9 plasmids allowed us to identify similar plasmids in the isolates from Italy and in the five best hits of the PLSDB database, with some regions of difference in the MDR region. A genome cluster analysis grouped our isolates into the same clade of ST114 E. hormaechei isolated from humans in Guadeloupe in 2018 and Switzerland in 2019, most of which harboured an IncHI2 replicon but not the mcr-9 gene. CONCLUSIONS:The finding of MDR E. hormaechei in seafood, carrying the mcr-9 and other resistance determinants on IncHI2 plasmids, enhances our understanding of antimicrobial resistance (AMR) and highlights the importance of gaining more data on the occurrence and circulation of AMR and ARGs in aquatic environments, in order to better understand sources, transmission routes, and evolution of AMR mechanisms.

The detection of tetrodotoxins (TTXs) in European shellfish led the European Union to request a risk assessment from the European Food Safety Authority (EFSA). EFSA set a reference limit of 44 µg TTX equivalents kg−1 and called for more data on TTX occurrence, especially in gastropods, which can accumulate in TTXs but remain poorly studied. Recently, preliminary monitoring has revealed the recurrent presence of TTXs in mussels in three areas along the North–Central Adriatic coast of Italy, while research on non-bivalve organisms has not yet been carried out. This study presents a preliminary survey, conducted from January 2023 to March 2025, on the presence of TTXs in gastropods, echinoderms, and arthropods collected from this area. A method in Hydrophilic Interaction Liquid Chromatography coupled with tandem Mass Spectrometry (HILIC-MS/MS) for detecting TTXs in bivalve mollusks was first tested through an international proficiency test, then optimized for the other invertebrates, the object of this study. TTX levels in all gastropods and arthropod samples were undetectable, while traces (~5 µg kg−1) were found in one echinoderm sample (Paracentrotus lividus), marking the first reported occurrence of TTX in this species. Sea urchins are widely consumed in Italy; therefore, this finding is of particular importance from a public health perspective and deserves further investigation. Some gastropod genera or species sampled (e.g., Nassarius, Rapana venosa) have been identified as TTX carriers in other regions; therefore, the negative results obtained in this study may be related to seasonal or geographic variability. These results provide valuable data to EFSA’s call for monitoring emerging risks, particularly as climate change may increase TTX prevalence in European waters as well as worldwide.

Arcobacter spp. has been recognized as an emerging pathogen and a potential zoonotic agent, with the three species A. butzleri, A. cryaerophilus, A. skirrowii causing the majority of human and animal infections. Despite its widely recognized presence in the food chain, Arcobacter spp. is not mandatorily investigated in food items and related environments, leading to epidemiological underestimation in the food chain and consequently in clinical setting. Here we describe a new approach, involving culture, real-time PCR, mPCR and MALDI-TOF, for the detection of the three above-mentioned Arcobacter species.Results indicated that the integrated approach performed with high sensitivity and efficiency, although some features of the matrices, such as pH, could influence the outcome. However, the method could be suitable for the routine analysis of different food matrices, in order to increase the diagnostic capacity of laboratories involved in monitoring zoonotic agents in the food and veterinary field.

Background/Objectives: Due to the rising problem of antimicrobial resistance, there is increasing attention in the scientific community towards alternative approaches to combat Antimicrobial-Resistant (AMR) pathogens that do not involve the use of antibiotics. In this regard, the European Medicines Agency (EMA) and the European Food Safety Authority (EFSA) have promoted experimentation with predatory bacteria to fight antibiotic resistance. With the aim of identifying predatory bacteria suitable for the control of antibiotic-resistant bacteria, in this work we isolated a strain of Halobacteriovorax from an estuarine aquatic environment using a CTX-M-producing E. coli strain as prey and characterized it with respect to optimal physico-chemical parameters for growth and predation. Furthermore, we studied its predatory capacity against other E. coli strains and Multi-Drug-Resistant (MDR) Salmonella. Finally, we conducted challenge experiments to evaluate the growth of predator and prey over time. Methods: The Halobacteriovorax strain, designated HE7, was identified by 16S rRNA analysis. To isolate Halobacteriovorax and to evaluate its predatory ability towards different preys, the double-layer agar plating technique was applied. Results: HE7 showed in vitro predatory activity against all MDR strains of E. coli and Salmonella tested. In the 107 predator/103 prey and 107 predator/107 prey challenges, HE7 after 6 h achieved the total killing and a reduction of about 6 logs in the prey, respectively, maintaining this effect for up to 24 h. Conclusions: The results of this study highlight that HE7, but more generally Halobacteriovorax, could find application both alone and in an integrated context of antimicrobial strategies as an alternative to antibiotics.

It is known that the consumption of edible lamellibranch mollusks (ELMs), undercooked or raw, is a vehicle for the oral transmission of viral and bacterial pathogens. The ELMs most frequently fished/cultivated and consumed in Italy are Mytilus galloprovincialis and Chamelea gallina. The aim of this project was to standardize the cooking conditions of M. galloprovincialis and C. gallina, reproducible in a domestic environment, to obtain food in which the microbiological risk was eliminated but, at the same time, preserved the original organoleptic characteristics. The results showed that for C. gallina and M. galloprovincialis, cooking for 2 minutes after opening all shells, according to a method suitable for home application, is sufficient to eliminate the microbiological risk.

Seafood is a crucial global food source, but its role as a reservoir for antibiotic-resistant pathogens is concerning. This study focuses on the prevalence of antibiotic resistance in retail seafood, using Enterococcus spp. as an indicator. Seven categories of raw seafood were collected from retail markets in Central Italy. Out of 422 samples, 288 tested positive for Enterococcus spp., resulting in a prevalence rate of 68.25% (CI95%: 63.66%-72.51%). The most common species were E. faecalis (48%) and E. faecium (17.4%). Enterococcus spp. was most frequently found in cephalopods, salmon, bivalves, and crustaceans than in sea bass and bream. The odds of Enterococcus spp. recovery were higher in frozen than in fresh samples, while there was no difference between farm-raised and wild-caught seafood. A subset of 102 isolates was selected for antibiotic resistance testing, showing the highest resistance rates to quinupristin/dalfopristin (52.94%) and tetracycline (27.45%). Over 70% of isolates were multidrug-resistant. Additionally, strains resistant to vancomycin and oxazolidinones, two last-resort antimicrobials, were detected. Vancomycin resistance was observed in E. casseliflavus and E. gallinarum, which are naturally resistant due to the vanC chromosomal cluster. The optrA gene, responsible for resistance to oxazolidinones and phenicols, was found in E. thailandicus and E. faecium, where it was located on to a transferable plasmid. In conclusion, this study confirms the widespread presence of Enterococcus spp. in retail seafood. The detection of multi-resistant isolates and resistance to last-resort antimicrobials highlights significant human health risks, stressing the importance of including Enterococcus spp. in seafood antibiotic resistance surveillance.

The spread of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is a major public health issue. Bivalves are filter-feeder animals capable of bioaccumulating the microorganisms present in water. This physiological characteristic makes them both good indicators of environmental contamination and possible carriers of pathogenic bacteria, including those resistant to antimicrobials. The aim of this study was to investigate the occurrence of ESBL-producing E. coli in clams (n = 308) collected from harvesting areas of the Central Adriatic Sea between 2018 and 2019. ESBL- /class C β-lactamase (AmpC)- producing E. coli and Escherichia spp. were isolated by streaking over the surface of MacConkey agar plates supplemented with cefotaxime enriched broths of the initial shellfish suspension. E. coli and Escherichia spp. resistant to cefotaxime were screened for ESBL production by using the double disk synergy test. Susceptibility to different antimicrobials and confirmation of ESBL-production were determined by the minimum inhibitory concentration (MIC) test. Isolates were further characterized by whole genome sequencing (WGS) and bioinformatic analysis of genomes with different tools. Overall, ESBL-producing E. coli were isolated from 3% of the samples. Of 13 ESBL- and ESBL−/AmpC-producing Escherichia spp. (n = 11 E. coli, n = 1 E. marmotae, n = 1 E. ruysiae) isolates, 13 were resistant to ampicillin and cefotaxime, 9 to sulfamethoxazole, 6 to tetracycline and nalidixic acid, 4 to trimethoprim, and 3 to ceftazidime, cefoxitin, ciprofloxacin, and chloramphenicol. Moreover, the majority (8/11) of the ESBL-producing E. coli isolates were multidrug-resistant. WGS showed that the isolates predominantly carried the blaCTX-M-15 gene (3/11) and blaCTX-M-14 and blaCTX-M-1 (2/11 each). The AmpC β-lactamase CMY-2 was found in two isolates. Phylogroup A was the most prevalent (5/11), followed by phylogroups D (4/11), F (1/11), and B2 (1/11). Ten different sequence types (STs) were identified. Occurrence at sampling sites ranged between 0 and 27%. To identify associations between the occurrence of ESBL-producing E. coli and E. coli levels, samples were divided into two groups, with E. coli at >230 MPN/100 g and E. coli at ≤230 MPN/100 g. ESBL-producing E. coli isolates were significantly more commonly recovered in samples with higher E. coli levels (14%) than in those with lower levels of E. coli (2%). Moreover, the majority (3/4) of the potentially pathogenic strains were isolated in samples with higher E. coli levels. These findings provided evidence for the bacterial indicator of fecal contamination, E. coli, as an index organism for ESBL-producing E. coli isolates in bivalves.

The recovery and characterization of a multidrug-resistant, KPC-3-producing Klebsiella michiganensis that was obtained from Venus clam samples is reported in this study. A whole-genome sequencing (WGS) analysis using Illumina and Nanopore technologies of the K. michiganensis 23999A2 isolate revealed that the strain belonged to the new sequence type 382 (ST382) and carried seven plasmid replicon sequences, including four IncF type plasmids (FII, FIIY, FIIk, and FIB), one IncHI1 plasmid, and two Col plasmids. The FIB and FIIk plasmids showed high homology to each other and to multireplicon pKpQIL-like plasmids that are found in epidemic KPC-K. pneumoniae clones worldwide. The strain carried multiple beta-lactamase genes on the IncF plasmids: bla(OXA-9) and bla(TEM-1A) on FIB, bla(KPC-3) inserted in a Tn4401a on FIIK, and bla(SHV-12) on FIIY. The IncHI1-ST11 harbored no resistance gene. The curing of the strain caused the loss of all of the bla genes and a rearrangement of the IncF plasmids. Conjugal transfer of the bla(OXA-9), bla(TEM-1A) and bla(KPC-3) genes occurred at a frequency of 5x10(-7), using K. quasipneumoniae as a recipient, and all of the bla genes were transferred through a pKpQIL that originated from the recombination of the FIB and FIIk plasmids of the donor. A comparison with 31 K. michiganensis genomes that are available in the NCBI database showed that the closest phylogenetic relatives of K. michiganensis 23999A2 are an environmental isolate from soil in South Korea and a clinical isolate from human sputum in Japan. Finally, a pan-genome analysis showed a large accessory genome of the strain as well as the great genomic plasticity of the K. michiganensis species. IMPORTANCE Klebsiella michiganensis is an emerging nosocomial pathogen, and, so far, few studies describe isolates of clinical origin in the environment. This study contributes to the understanding of how the dissemination of carbapenem-resistance outside the hospital setting may be related to the circulation of pKpQIL-like plasmids that are derived from epidemic Klebsiella pneumoniae strains. The recovery of a carbapenem-resistant isolate in clams is of great concern, as bivalves could represent vehicles of transmission of pathogens and resistance genes to humans via the food chain. The study demonstrates the plasticity of K. michiganensis genome, which is probably useful to multiple environment adaptation and to the evolution of the species.

The Arcobacter genus comprises a group of bacteria widely distributed in different habitats that can be spread throughout the food chain. Fluoroquinolones and aminoglycosides represent the most common antimicrobial agents used for the treatment of Arcobacter infections. However, the increasing trend of the antimicrobial resistance of this pathogen leads to treatment failures. Moreover, the test implementation and interpretation are hindered by the lack of reference protocols and standard interpretive criteria. The purpose of our study was to assess the antibiotic resistance pattern of 17 A. butzleri strains isolated in Central Italy from fresh vegetables, sushi, chicken breast, and clinical human samples to provide new and updated information about the antimicrobial resistance epidemiology of this species. Antimicrobial susceptibility testing was carried out by the European Committee on Antimicrobial Susceptibility Testing (EUCAST)'s disc diffusion method. All the strains were multidrug resistant, with 100% resistance to tetracyclines and cefotaxime (third generation cephalosporins). Some differences were noticed among the strains, according to the isolation source (clinical isolates, food of animal origin, or fresh vegetables), with a higher sensitivity to streptomycin detected only in the strains isolated from fresh vegetables. Our data, together with other epidemiological information at the national or European Union (EU) level, may contribute to developing homogeneous breakpoints. However, the high prevalence of resistance to a wide range of antimicrobial classes makes this microorganism a threat to human health and suggests that its monitoring should be considered by authorities designated for food safety.

The aim of the present study was to evaluate Vibrio parahaemolyticus occurrences in bivalve molluscs harvested from Sardinian coastal environments between 2013 and 2015. The prevalence of pathogenic V. parahaemolyticus isolates is based on the detection of the two major virulence genes thermostable direct hemolysin (tdh) and thermolabile hemolysin (trh) To assess changes between 2011 and 2018 in the prevalence of V. parahaemolyticus in bivalve molluscs, we compared our results with those of previous investigations. In total, 2,933 samples were collected: 1,079 in 2013, 1,288 in 2014, and 566 in 2015. The mean prevalence of V. parahaemolyticus in shellfish was 3.5% in 2013, 1.7% in 2014, and 3.5% in 2015. The highest percentage of positive samples in 2013 and 2014 was observed in clams (3.5% and 2.7%, respectively), whereas in 2015, it was reported in oysters (15.1%). By comparing the sampling period of 2011-2014 with that of 2015-2018, an increase in the prevalence of V. parahaemolyticus was observed in shellfish (p < 0.05). In parallel, 208 potentially enteropathogenic V. parahaemolyticus strains were identified through the years 2011-2018 and, in particular, 10 trh+ and six tdh+ isolates. Our present study provides information regarding trends of V. parahaemolyticus occurrences in bivalve molluscs harvested from Sardinian coastal environments between 2011 and 2018 suggesting that the prevalence varies depending on the sampling period and shellfish species.

Background: The presence of carbapenemase-producing bacteria (CPB) in animal hosts and along the food chain may result in the development of reservoirs for human infections. Several CPB strains isolated from animals have been reported, suggesting that transmission and dissemination of the corresponding genes between humans and animals may occur. Animal and food samples have complex backgrounds that hinder the detection of CPB present in low concentrations by standard detection procedures. Methods: We evaluated the possibility of detecting blaKPC, blaVIM, and blaOXA-48-like carbapenemases in 286 animal and food samples (faeces from farm and companion animals, raw meat, bivalve molluscs) by culture-based and standard molecular methods and by ddPCR. Results: The proposed ddPCR managed to detect the target genes, also in samples resulting negative to standard methods. While the presence of blaKPC and blaVIM was detected in few samples (~3%), one third of the samples (n = 94/283) carried different variants of blaOXA-48-like genes. Conclusion: A specific and sensitive method such as ddPCR could be suitable to evaluate the current veterinarian and environmental situation and to assess the dynamic transmission and persistence of CPB between animals and humans and vice versa.

EDITORIAL article Front. Microbiol., 07 March 2022 | https://doi.org/10.3389/fmicb.2022.863038

Bivalves are filter-feeding animals able to accumulate contaminants and microorganisms, either of marine or terrestrial origin. The aim of this study was to describe the prevalence of antimicrobial resistance (AMR) in bacterial isolates from bivalves using a systematic review of the literature. Comprehensive searches of MEDLINE, EMBASE, and Web of Science were carried out, based upon a registered protocol (PROSPERO), and following the preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) guidelines. The methodological quality of the included studies was assessed using a modified Hoy checklist. Meta-analyses of prevalence were carried out using random-effects models. In total, 103 articles were selected from 1,280 records and were included in the final analysis. The studies were from Asia (n = 54), Europe (n = 27), South and North America (n = 10 and n = 6, respectively), Africa (n = 2), Oceania (n = 1), and multicentre and intercontinental (n = 3). The meta-analysis of multiple antibiotic resistance (MAR) index revealed Aeromonas spp. as the genus with the highest prevalence of AMR (37%), followed by Vibrio spp. (34%), Salmonella spp. (18%), and Escherichia coli (15%). Resistance to third/fourth/fifth generation cephalosporins and fluoroquinolones, two highest priority, critically important antimicrobials (HPCIA), was recorded in approximately 10% of E. coli isolates. Resistance to carbapenems was very low (<2%) in Salmonella spp. and in E. coli, but was found in 5% of Vibrio spp. and in more than a third of Aeromonas spp. isolates. In aquatic bacteria, resistance to carbapenems was higher in Asian than in European isolates. Our study shows the presence of antibiotic resistant bacteria (ARB), including bacteria resistant to HPCIA, in marine bivalves, posing a risk for consumers.

Tetrodotoxins (TTXs), potent neurotoxins, have become an increasing concern in Europe in recent decades, especially because of their presence in mollusks. The European Food Safety Authority published a Scientific Opinion setting a recommended threshold for TTX in mollusks of 44 µg equivalent kg−1 and calling all member states to contribute to an effort to gather data in order to produce a more exhaustive risk assessment. The objective of this work was to assess TTX levels in wild and farmed mussels (Mytilus galloprovincialis) harvested in 2018–2019 along the coastal area of the Marche region in the Central Adriatic Sea (Italy). The presence of Vibrio spp. carrying the non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) genes, which are suspected to be involved in TTX biosynthesis, was also investigated. Out of 158 mussel samples analyzed by hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry (HILIC-MS/MS), 11 (7%) contained the toxins at detectable levels (8–26 µg kg−1) and 3 (2%) contained levels above the EFSA safety threshold (61–76 µg kg−1). Contaminated mussels were all harvested from natural beds in spring or summer. Of the 2019 samples, 70% of them contained V. alginolyticus strains with the NRPS and/or PKS genes. None of the strains containing NRPS and/or PKS genes showed detectable levels of TTXs. TTXs in mussels are not yet a threat in the Marche region nor in Europe, but further investigations are surely needed.

This research aimed to study the abundance and molecular diversity of Vibrio parahaemolyticus-specific Halobacteriovorax strains isolated from seawater of the Adriatic Sea and the relationship between predator and prey abundances. Moreover, predator efficiency of the Halobacteriovorax isolates toward V. parahaemolyticus and Vibrio cholerae non-O1/O139 strains was tested. V. parahaemolyticus NCTC 10885 was used as primary host for the isolation of Halobacteriovorax from seawater by the plaque assay. Molecular identification was performed by PCR detection of a fragment of the 16S rRNA gene of the Halobacteriovoraceae family members. Moreover, 700 bp PCR products were sequenced and compared between them and to clones described for other sampling sites. Vibrio counts were performed on TCBS agar from 100 ml of filtered water samples and presumptive colonies were confirmed by standard methods. Predatory efficiency of Halobacteriovorax isolates was tested by monitoring abilities of 3-day enrichments to form clear lytic halos on a lawn of Vibrio preys, by the plaque assay. Out of 12 seawater samples monthly collected from June 2017 to May 2018, 10 were positive for V. parahaemolyticus specific Halobacteriovorax with counts ranging from 4 to 1.4 × 103 PFU per 7.5 ml. No significant relationship was found between Halobacteriovorax and Vibrio abundances. The 16SrRNA sequences of our Halobacteriovorax strains, one for each positive sample, were divided into three lineages. Within the lineages, some sequences had 100% similarity. Sequence similarity between lineages was always <94.5% suggesting that they may therefore well belong to three different species. All Halobacteriovorax isolates had the ability to prey all tested Vibrio strains. Additional research is necessary to assess whether stable strains of Halobacteriovorax are present in the Adriatic Sea and to understand the mechanisms by which Halobacteriovorax may modulate the abundance of V. parahaemolyticus and other vibrios in a complex marine ecosystem.

Summary Bdellovibrio bacteriovorus is a predator micro‐organism towards other Gram‐negative bacteria. We tested B. bacteriovorus to control Escherichia coli growth on chicken slices and canned beef. Moreover, we analysed B. bacteriovorus's lytic ability on eight toxigenic or multidrug‐resistant E. coli strains. In chicken slices, the predator induced the highest prey reduction (4.3 log) respect to control at 6 h. In canned beef, the predator induced the highest prey reduction (2.1 log) respect to control at 6 h. Moreover, B. bacteriovorus showed lytic ability towards all tested E. coli strains. B. bacteriovorus could control E. coli and other pathogenic and spoilage bacteria in those meat‐based foods that have a shelf life <10 days. It could integrate modified atmosphere packaging (MAP) to prolong the shelf life and improve the safety of pre‐packed fresh meat, meat preparations and meat products. In future applications on meat‐based foods, B. bacteriovorus could also minimise the use of additives.

This study evaluated the application of a Halobacteriovorax isolated from water of the Adriatic Sea (Italy) in controlling V. parahaemolyticus in mussels (Mytilus galloprovincialis). Two 72 h laboratory-scale V. parahaemolyticus decontamination experiments of mussels were performed. The test microcosm of experiment 1 was prepared using predator/prey free mussels experimentally contaminated with Halobacteriovorax/ V. parahaemolyticus at a ratio of 10(3) PFU/10(5) CFU per ml, while that of experiment 2 using mussels naturally harbouring Halobacteriovorax that were experimentally contaminated with 10(5) CFU per ml of V. parahaemolyticus. For experiment 1, was also tested a control microcosm only contaminated with 10(5 )CFU per ml of V. parahaemolyticus.. Double layer agar plating and pour plate techniques were used to enumerate Halobacteriovorax and V. parahaemolyticus, respectively. 16 S rRNA analysis was used to identify Halobacteriovorax. For both experiments in the test microcosm the concentration of prey remained at the same level as that experimentally added, i.e. 5 log for the entire analysis period. In experiment 1, V. parahaemolyticus counts in mussels were significantly lower in the test microcosm than the control with the maximum difference of 2.2 log at 24 h. Results demonstrate that Halobacteriovorax can modulate V. parahaemolyticus level in the mussels. The public impact of V. parahaemolyticus in bivalves is relevant and current decontamination processes are not always effective. Halobacteriovorax is a suitable candidate in the development of a biological approach to the purification of V. parahaemolyticus in mussels.