Aims The aim of this study was to characterize Staphylococcusaureus isolates of food origin (dairy and meat products, pastries and sandwiches) determining the carriage in enterotoxin genes and the antimicrobial resistance pheno/genotypes. Methods and results A total of 300 food samples were collected and analysed for the detection of S. aureus. The presence of enterotoxin genes was investigated by multiplex PCRs. Resistance of isolates to 11 antimicrobials was determined using disc diffusion method and molecular characterization of methicillin‐resistant S. aureus was carried out by spa typing and multilocus sequence typing. Overall, 51 out of 300 samples (17%) were contaminated with S. aureus, and 104 isolates were recovered. In all, 65 of these isolates (62·5%) harboured one or more genes encoding for staphylococcal enterotoxins, being seg and sei the most observed genes. The highest resistance profile was ascribed to penicillin G (95·19%). Five isolates were methicillin‐resistant (MRSA) harbouring the mecA gene. All MRSA isolates belonged to the sequence type ST5 and to two different spa types (t450 and t688); the MRSA‐t450 isolate carried the scn gene (specific marker of the immune evasion cluster system), but the four MRSA‐t688 isolates were scn negative. The MRSA isolates carried enterotoxin genes but were negative for the genes of the Panton Valentine leukocidine (lukF/S‐PV). Conclusion The presence of enterotoxigenic S. aureus isolates, including MRSA, in food samples can represent a risk for public health. Significance and Impact of this Study This work describes the molecular characteristics of MRSA strains isolated from foods in Algeria and it can contribute to an extended database concerning the S. aureus isolated from food origin.

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Staphylococcus aureus is a major human pathogen and an important cause of livestock infections. More than 20 staphylococcal enterotoxins with emetic activity can be produced by specific strains responsible for staphylococcal food poisoning, one of the most common food-borne diseases. Whole genome sequencing provides a comprehensive view of the genome structure and gene content that have largely been applied in outbreak investigations and genomic comparisons. In this study, six enterotoxigenic S. aureus strains were characterised using a combination of molecular, phenotypical and computational methods. The genomes were analysed for the presence of virulence factors (VFs), where we identified 110 genes and classified them into five categories: adherence (n = 31), exoenzymes (n = 28), genes involved in host immune system evasion (n = 7); iron uptake regulatory system (n = 8); secretion machinery factors and toxins’ genes (n = 36), and 39 genes coding for transcriptional regulators related to staphylococcal VFs. Each group of VFs revealed correlations among the six enterotoxigenic strains, and further analysis revealed their accessory genomic content, including mobile genetic elements. The plasmids pLUH02 and pSK67 were detected in the strain ProNaCC1 and ProNaCC7, respectively, carrying out the genes sed, ser, and selj. The genes carried out by prophages were detected in the strain ProNaCC2 (see), ProNaCC4, and ProNaCC7 (both positive for sea). The strain ProNaCC5 resulted positive for the genes seg, sei, sem, sen, seo grouped in an exotoxin gene cluster, and the strain ProNaCC6 resulted positive for seh, a transposon-associated gene. The six strains were used for the production of naturally contaminated cheeses which were tested with the European Screening Method for staphylococcal enterotoxins. The results obtained from the analysis of toxins produced in cheese, combined with the genomic features represent a portrait of the strains that can be used for the production of staphylococcal enterotoxin-positive cheese as reference material.

Please note two corrections to the above article.The L. monocytogenes strain mentioned in the first sentence of the first paragraph of the Materials and Methods section should have been noted as 10 and was isolated from cheese, not cold-smoked salmon as published.

The control of pathogenic bacteria present in foods, as well as scientific data concerning their behavior, are closely linked to analytical methods used and the way they are implemented. To assess the capacity of the laboratories to conduct correctly microbiological analyses, national and international proficiency testing schemes are organized. To set up these inter-laboratory studies (ILS), it is necessary to prepare artificially contaminated samples, which contamination level is sufficiently stable regarding their transportation conditions to the participating laboratories.In this context, we tested several procedures to maintain the concentration of Listeria monocytogenes and coagulasepositive staphylococci in milk samples: freezing temperature and addition of bacteriostatic agents at refrigeration temperatures, such as nystatin, boric acid, sodium azide, the lactoperoxidase system, or a boric acid mixture. Through this study we selected preservation procedures, which could be used to stabilize the contamination level of artificially contaminated milk samples during transportation without preventing the growth of the target bacteria during the analysis and after the initial dilution step. Boric acid mixture and boric acid were found to be effective in stabilizing the contamination level of Staphylococcus aureus in milk samples, whereas freezing, a boric acid mixture, and boric acid were suitable for milk samples containing L. monocytogenes, depending on the samples' contamination rate.