• Antimicrobial activity of natural compounds against listeria spp. and their effects on sensory attributes in salmon (Salmo salar) and cod (Gadus morhua)

      Pedrós-Garrido, Selene; Clemente, Isabel; Calanche, J. B.; Condón-Abanto, Santiago; Beltrán, J. A.; Lyng, J. G.; Brunton, N.; Bolton, Declan; Whyte, Paul; Department of Agriculture, Food and the Marine; et al. (Elsevier, 2019-07-15)
      The application of natural preservatives on fresh fish has potential to extend shelf-life. In the present study, 8 essential oils (EOs) (lemon, lemongrass, lime, garlic, onion, oregano, thyme and rosemary) and 3 organic acids (OAs) (ascorbic, citric and lactic) were evaluated. The antimicrobial activity of these compounds was tested in-vitro against four confirmed Listeria spp. isolated from retail skin-packed salmon and cod. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were established for each compound. Then, a sensory evaluation was performed by a panel of ‘expert assessors’ on cooked fish treated with all of the OAs and any 4 EOs with a MIC <0.8%. A series of descriptors were assigned to characterize the combination of each compound with cooked salmon or cod. The highest antimicrobial effect against all Listeria spp. was observed for lactic acid (0.31–2.5%), but treatment with this compound resulted in the development of organoleptically unacceptable changes in salmon or cod. The most acceptable OAs for salmon and cod were ascorbic acid (1.25%) and citric acid (0.63%) respectively, which were shown to enhance certain organoleptic characteristics. The most effective EO against all Listeria strains evaluated was oregano oil (0.2%) and it was considered suitable as a treatment for salmon. In contrast, none of the EOs tested was organoleptically acceptable in combination with cod because of their strong odours and flavours that masked the fresh attributes associated with this fish.
    • Effect of applying crust-freezing after skin-packaging on the natural microflora of Atlantic salmon (Salmo salar) during storage at low temperatures

      Pedrós-Garrido, S.; Condón-Abanto, S.; Calanche, J.B.; Beltrán, J.A.; Lyng, J.G.; Bolton, Declan; Brunton, Nigel; Whyte, P.; Department of Agriculture, Food and the Marine; 13F458 (Teagasc, 2021-03-26)
      The aim of the present study was to evaluate the effect of crust-freezing (CF) on fresh salmon fillets in skin-packaging during storage at −2.0°C. After CF, all treated samples and untreated controls were stored in a refrigerated cabinet for 20 d. Sampling was carried out at days 0, 2, 6, 8, 10, 14 and 20 in order to analyse total volatile basic nitrogen (TVB-N) and levels of mesophilic and psychrophilic viable counts (MVC and PVC). Enterobacteriaceae (ENT), lactic acid bacteria (LAB), H2S-producing bacteria (SPB) and Pseudomonas spp. (PSE). No significant differences in TVB-N were found between samples except for those taken on day 20 where TVB-N levels of CF samples were lower than controls. Our results suggest that ENT might be the limiting microbial group to determine the end of shelf-life. Thus, if this group is used as an indicator of acceptability, the shelf-life of salmon can be extended from 8 to 20 d when skin-packed and then treated with CF.
    • Genetic characterisation of a subset of Campylobacter jejuni isolates from clinical and poultry sources in Ireland

      Truccollo, Brendha; Whyte, Paul; Burgess, Catherine; Bolton, Declan; Teagasc; 0028 (Public Library of Science (PLoS), 2021-03-09)
      Campylobacter spp. is a significant and prevalent public health hazard globally. Campylobacter jejuni is the most frequently recovered species from human cases and poultry are considered the most important reservoir for its transmission to humans. In this study, 30 Campylobacter jejuni isolates were selected from clinical (n = 15) and broiler (n = 15) sources from a larger cohort, based on source, virulence, and antimicrobial resistance profiles. The objective of this study was to further characterise the genomes of these isolates including MLST types, population structure, pan-genome, as well as virulence and antimicrobial resistance determinants. A total of 18 sequence types and 12 clonal complexes were identified. The most common clonal complex was ST-45, which was found in both clinical and broiler samples. We characterised the biological functions that were associated with the core and accessory genomes of the isolates in this study. No significant difference in the prevalence of virulence or antimicrobial resistance determinants was observed between clinical and broiler isolates, although genes associated with severe illness such as neuABC, wlaN and cstIII were only detected in clinical isolates. The ubiquity of virulence factors associated with motility, invasion and cytolethal distending toxin (CDT) synthesis in both clinical and broiler C. jejuni genomes and genetic similarities between groups of broiler and clinical C. jejuni reaffirm that C. jejuni from poultry remains a significant threat to public health.
    • A preliminary study of Salmonella spp., Listeria monocytogenes, Escherichia coli O157, Enterococcus faecalis and Clostridium spp. in Irish cattle

      Russell, L.; Galindo, C.P.; Whyte, P.; Bolton, Declan; Department of Agriculture, Food and the Marine; Teagasc Walsh Scholarship Programme; 14/SF/487; 2014239 (Teagasc, 2021-06-03)
      Although Salmonella spp., Escherichia coli O157, Listeria monocytogenes, Enterococcus faecalis and Clostridium spp. present a significant food safety and/or spoilage issue for the beef sector, there are limited data on their prevalence in Irish cattle. The objectives of this preliminary study were to investigate the distribution (percentage of farms positive) of Salmonella spp., E. coli O157, L. monocytogenes, E. faecalis and Clostridium spp. and the overall prevalence (%) of these bacteria in cattle on a small cohort of Irish beef farms. A total of 121 fresh bovine faecal samples were obtained on 10 randomly selected beef farms in the Northeast of Ireland and tested for the target pathogens using standard culture-based methods. Presumptive positives were confirmed using previously published polymerase chain reaction (PCR) methods. Salmonella were not detected in any of the samples. E. coli O157, L. monocytogenes, E. faecalis and Clostridium spp. were present on 50%, 40%, 100% and 100% of farms, respectively, with overall (all farms) prevalence rates in cattle of 9%, 8.2%, 61.9% and 87.6%, respectively. This study suggests that E. coli O157 may be more prevalent than previously thought and L. monocytogenes, E. faecalis and Clostridium spp. are widespread in Irish beef animals.