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Dry-cured ham is a highly appreciated meat product. During the ripening, moulds grow on its surface such as Penicillium nordicum and Aspergillus westerdijkiae producers of ochratoxin A (OTA). This mycotoxin poses a risk to consumers that must be controlled. The aim of this work is to evaluate the effectiveness of Debaryomyces hansenii and Staphylococcus xylosus isolated from dry-cured ham as a combined biocontrol culture (BCA) to reduce the OTA produced by one strain of A. westerdijkiae and two strain of P. nordicum, and to assess the metabolomic changes they cause. Each mould was inoculated alone and in combination with BCA on dry-cured ham for 14 days at 20 °C. OTA and total metabolites were analysed in a mass spectrometer Orbitrap Q- Exactive Plus. The Compound Discoverer software, in-house Python-based software and the Metaboanalyst software were used for metabolite analysis. BCA reduced the OTA of A. westerdijkiae, P. nordicum 15 and P. nordicum 856 by 78 %, 99 % and 65 % respectively. BCA caused changes in their metabolome, mainly in the phenylalanine metabolism pathway altering compounds such as Phenylacetaldehyde, Phenylpyruvate or trans-2-hydroxycinnamate, the synthesis of phenylalanine, tyrosine, and tryptophan altering compounds such as 4-hydroxyphenylpyruvate or L-tryptophan, and in the synthesis of oxylipins derived from the linoleic acid metabolism such as 13-OxoODE, 9(S)-HODE or 9(10)-EpOME., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Staphylococcus xylosus ( S. xylosus ) has become an emerging opportunistic pathogen due to its strong biofilm formation ability. Simultaneously, the biofilm of bacteria plays an important role in antibiotic resistance and chronic infection. Here, we confirmed that rutin can effectively inhibit biofilm formation in S. xylosus , of which the inhibition mechanism involves its ability to interact with imidazole glycerol phosphate dehydratase (IGPD), a key enzyme in the process of biofilm formation. We designed experiments to target IGPD and inhibited its activities against S. xylosus . Our results indicated that the activity of IGPD and the amount of histidine decreased significantly under the condition of 0.8 mg/ml rutin. Moreover, the expression of IGPD mRNA ( hisB ) and IGPD protein was significantly down-regulated. Meanwhile, the results from molecular dynamic simulation and Bio-layer interferometry (BLI) technique showed that rutin could bind to IGPD strongly. Additionally, in vivo studies demonstrated that rutin treatment reduced inflammation and protect mice from acute mastitis caused by S. xylosus . In summary, our findings provide new insights into the treatment of biofilm mediated persistent infections and chronic bacterial infections. It could be helpful to design next generation antibiotics to against resistant bacteria., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Qu, Cui, Xing, Zou, Huang, Wang, Wu, Bello-Onaghise, Yuan and Li.)

Toxigenic moulds can develop on the surface of dry-cured meat products during ripening due to their ecological conditions, which constitutes a risk for consumers. A promising strategy to control this hazard is the use of antifungal microorganisms usually found in these foods. However, to date, the effectiveness of gram-positive catalase-positive cocci (GCC+) has not been explored. The aim of this work was to select GCC+ isolates with antifungal activity to study its effectiveness in a dry-cured ham model system at the environmental conditions reached during the ripening. Forty-five strains of GCC+ were evaluated and the isolate Staphylococcus xylosus Sx8 was selected to assess its efficacy at two different concentrations (10 6 and 10 4 cfu/mL) against Penicillium nordicum , Aspergillus flavus , Aspergillus parasiticus, and Penicillium griseofulvum at 15, 20, and 25 °C. The results showed that the inoculation of 10 6 cfu/mL of S. xylosus completely inhibited the growth of most fungi. In addition, in the presence of this strain at 10 4 cfu/mL, a significant reduction in fungal growth and mycotoxins production was observed at the three temperatures studied. In conclusion, S. xylosus Sx8 possesses great potential as a biological agent to control toxigenic moulds in dry-cured meat products., Competing Interests: The authors declare no conflict of interest.

The presence of determinants of resistance to antibiotics can constitute a possible safety hazard in coagulase-negative staphylococci (CNS), which are widely present in food of animal origin. Among CNS, S. xylosus is a species frequently isolated from fermented meat products. Resistance to tetracycline was found to be one of the most distributed resistances occurring in S. xylosus strains isolated from fermented sausages. We evaluated the transfer of tetracycline resistance in vitro and in situ between S. xylosus strains. We selected three strains isolated from dry fermented sausages, resistant to tetracycline but not to minocycline, their resistance occurring by a mechanism of active efflux encoded by the tetK gene. Only one strain was able to transfer its tetracycline resistance to a recipient strain initially susceptible and plasmid-free using a filter mating procedure. Transfer of tetracycline resistance was observed at very low frequencies of 3.4 × 10 -9 per recipient. To further investigate the transferability of this tetracycline resistance, the donor and recipient strains were tested in pilot-scale fermented sausage production. This transfer was possible but at a low rate, 1.4 × 10 -7 , and only under conditions of a high inoculation level of 10 8  CFU/g of meat. The tetK gene is located on a small mobilizable plasmid close to Staphylococcus aureus pT181 plasmid. In conclusion, the transfer of tetracycline resistance between strains of S. xylosus is possible, but at a really low frequency in vitro and in situ in fermented sausages. Even if this represents a very moderate risk, it should be taken into account as required by the European approach of Qualified Presumption of Safety (QPS) and AFSSA safety recommendations, advising that strains used as starter cultures should not carry any transferable antibiotic resistance.

Staphylococcus xylosus ( S. xylosus ) is an AT-rich and coagulase-negative Staphylococcus (CNS). It is normally regarded as non-pathogenic, however, recent studies have demonstrated that it is related to human opportunistic infections and bovine mastitis. In addition, S. xylosus strains have the ability to form biofilm. Biofilms are also involved in chronic infections and antibiotic resistance, there are only a few reports about cefquinome inhibiting S. xylosus biofilm formation and the protein targets of cefquinome. In our study, we found that sub-MICs of cefquinome were sufficient to inhibit biofilm formation. To investigate the potential protein targets of cefquinome, we used iTRAQ for the analyses of cells at two different conditions: 1/2-MIC (0.125 μg/mL) cefquinome treatment and no treatment. Using iTRAQ technique and KEGG database analysis, we found that proteins differently expression in histidine metabolism pathway may play a role in the process by which 1/2-MIC (0.125 μg/mL) cefquinome inhibits S. xylosus biofilm formation. Interestingly, we found a sharply down-regulated enzyme [A0A068E9J3 imidazoleglycerol-phosphate dehydratase (IGPD)] involved in histidine metabolism pathway in cefquinome-treated cells. We demonstrated the important role of IGPD in sub-MICs cefquinome inhibiting biofilm formation of S. xylosus by gene ( hisB ) knockout, IGPD enzyme activity and histidine content assays. Thus, our data sheds light on important role of histidine metabolism in S. xylosus biofilm formation; especially, IGPD involved in histidine metabolism might play a crucial role in sub-MICs cefquinome inhibition of biofilm formation of S. xylosus , and we propose IGPD as an attractive protein target of cefquinome.