Antibacterial efficacy of chemically and plant-synthesized zinc oxide nanocomposite against Staphylococcus aureus and Escherichia coli inoculated in Tilapia fillet

Aims@#Edible coatings developed from biodegradable materials such as starch and zinc oxide nanoparticles (ZnO-NPS) are efficient antimicrobials that could be used as a food additive to reduce the bacterial load on the food surface. Therefore, this study was aimed to examine the effect of chemical and green synthesized ZnO-NPS with different concentrations on the survival of Escherichia coli and Staphylococcus aureus in fish fillets during chilling storage at 4 ± 1°C.@*Methodology and results@#ZnO-NPS were chemically prepared by mixing zinc acetate dihydrate with sodium hydroxide. Lavandula officinalis was used for the green synthesis of ZnO-NPS. The sterile biodegradable coating containing 2 and 5% of both chemically and green synthesized ZnO-NPS were made using starch, gelatin, xanthan gum and glycerol. Different bacterial cocktail strains of both E. coli and S. aureus were inoculated onto Tilapia fillet samples. The coating solution with different antimicrobials was aseptically spread in Tilapia fillets and examined periodically within two days intervals for the survival of S. aureus and E. coli during chilling at 4 ± 1 °C. Both chemically and plantsynthesized ZnO-NPS reduced the growth of both S. aureus and E. coli by about 3.7 log10 CFU/cm2 of Tilapia fillet. The incorporation of L. officinalis increased the antibacterial activity of ZnO-NPS. Staphylococcus aureus was more sensitive than E. coli for both chemically and plant-synthesized ZnO-NPS. Moreover, zinc oxide biodegradable coating extended the shelf-life of chilled Tilapia fillets by about 4 days.@*Conclusion, significance and impact of study@#The results of the current study demonstrated the incorporation of L. officinalis into ZnO-NPS biodegradable coating which may be promising in reducing microbial growth on food surfaces.

Genetic virulence of biofilm-forming Salmonella recovered from chicken sausages and nuggets

Aims@#Salmonella is one of the most common foodborne illnesses worldwide. Poultry meat and products are the main sources of human infection. Therefore, the main objective of the current study was to assess the genetic virulence of biofilm-forming Salmonella isolated from chicken sausage and nuggets.@*Methodology and results@#Isolation of Salmonella was carried out using XLD agar; suspected colonies were identified biochemically and then serotyped using the Kauffman-White scheme for detection of somatic (O) and flagellar (H) antigens. Congo red (CR) medium was used for the assessment of biofilm formation of the isolated strains. The invasion gene (invA), the heat-labile Salmonella enterotoxin gene (stn), plasmid-encoded fimbriae (pefA) genes, the protein effectors sopB, sopD and biofilm genes in six Salmonella isolates were investigated using mPCR, following QIAamp® DNA Mini Kit instructions and 1.5% agarose gel electrophoreses. Salmonella was detected in 12%, 8% and 4% of the examined frozen packaged raw chicken sausage, frozen packaged raw chicken nuggets and ready-to-eat sausage. The isolated strains were S. Typhimurium, S. Enteritidis, S. Essen and S. Montevideo. Moreover, mPCR indicated the presence of biofilm gene (csgD gene), stn, sopB and sopD virulence genes in all isolated strains (100%); however, pefA gene failed to be detected.@*Conclusion, significance and impact of study@#The current findings showed that every Salmonella isolate examined was capable of creating biofilm at room temperature. As a result, these isolates are more likely to persist on abiotic surfaces, which raises the danger of cross-contamination and foodborne outbreaks.