نشریه بهداشت مواد غذایی
سال دوازدهم شماره 1 (پیاپی 45، بهار 1401)

Listeria monocytogenes is a foodborne pathogen the cause of listeriosis that has long-term survival due to biofilm formation. This study aimed to investigate the efficacy of nisin 102 IU/ml, nisin encapsulated with chitosan and sodium alginate on biofilm formation and changing the expression level of genes related to biofilm formation in L. monocytogenes. L. monocytogenes ATCC 19115 (serotype 4b) was treated by nisin 102 IU/ml and microencapsulated nisin with chitosan and sodium alginate solutions. The effectiveness of nisin on cell survival was estimated by calculating the optical absorbance. After proving the presence of prfA, sigB, and agrA genes, the effect of 102 IU/ml nisin dilution on L. monocytogenes biofilm was investigated by the microtiter plate method. The expression level of prfA, sigB, and agrA genes was analyzed using real-time PCR methods (qRT-PCR). The inhibition rate of biofilm formation in L. monocytogenes by nisin 102 IU/ml was 57% at 37°C and pH 5.5. The maximum inhibition of biofilm formation was related to the simultaneous use of nisin 102 IU/ml with chitosan and sodium alginate at 37°C and pH 5.5. Nisin microencapsulated with chitosan and sodium alginate can increase its effectiveness in preventing the biofilm formation of L. monocytogenes to 76% (p<0.0001). Nisin 102 IU/ml decreased the expression level of prfA, sigB, and agrA by -2.313, -2.808, and -1.453-fold compared to the control (p<0.0001). Nisin only had significant inhibitory activity against L. monocytogenes biofilm. Nisin microencapsulated with chitosan and sodium alginate had high efficacy in preventing the biofilm formation of L. monocytogenes.

Pseudomonas are among psychrophilic bacteria and have been reported in various studies as the predominant spoilage bacterial in slaughter carcass. The aim of this study was to track Pseudomonas spp. from different stages of the slaughter line, slaughterhouse environment and equipment and drop in the packaging. Characteristics such as pigment production, movement pattern and biofilm formation capability of the isolates were also determined. For this purpose, 108 samples were sampled from three industrial poultry slaughterhouses in Tabriz. According to the results, the highest contamination was detected in the samples of the floors, abdominal cavity of carcass and drip samples, respectively. The lowest contamination was observed in the samples related to drinking water, live chicken breast swab and scalder, respectively. The average movement of the Swimming type was significantly (p ≤ 0.001) higher than the two types of Swarming and Twitching movements. And in terms of pigment production, the dominant color was green. Moreover, most of the isolates were able to form biofilms and about 30% of the isolates had moderate and strong ability to produce biofilms. In conclusion, most of the Pseudomonas spp. contamination occurs through different parts of the slaughter line and also the equipment and environment of the slaughterhouse. Due to the biofilm production capacity of Pseudomonas isolates, the issue of proper and more effective washing and disinfection of the slaughter line and equipment is of particular importance.

As natural antioxidants and antimicrobials, essential oils (EOs) have been increasingly used to control foodborne pathogens. However, the application of EO in the food industry is limited due to low water solubility, intensive flavor, and high volatility. Therefore, to enhance water dispersion and prevent EO from degradation, nanoemulsions may be an alternative. In this study, two types of thyme essential oil (TEO) nanoemulsions, with distilled water (NEO) and with cinnamon aqueous extract (NEOC), were prepared. The physical, antimicrobial and antioxidant properties of TEO extracts and nanoemulsions were determined. The results showed that the mean particle size and PDI index of NEOC and NEO were 728.2 and 162.4 nm and 0.19 and 0.30, respectively. Polyphenolic compounds of aqueous extract of cinnamon, TEO, NEO and NEOC were in the range of 33.4 to 10.9 mg gallic acid equivalent/g. The antioxidant activity (DPPH) was in the range of 16.3 to 66.4%. Phenolic compounds and DPPH, TEO and NEOC were the highest. Also, the antimicrobial effects of NEO and NEOC against Staphylococcus aureus and Salmonella Typhimurium were significantly higher than TEO and cinnamon aqueous extract. The lowest values of MIC and MBC were first related to NEOC and then to NEO, which indicates the greater sensitivity of the studied microorganisms to nanoemulsions. According to the results, the highest antimicrobial and antioxidant activity was related to NEOC nanoemulsion. Therefore, it can be used in food products to prevent food poisoning and to treat diseases caused by S. aureus and S. Typhimurium.

Diarrheal strains of Escherichia coli (DEC) are common pathogens that cause acute intestinal diseases in humans through the consumption of contaminated food. The present study was conducted on 240 samples including strudel, pizza, sandwiches, and salad. E. coli was isolated by conventional culture tests and confirmed by PCR (using uidA gene). Out of 240 samples, 123 isolates (51.25%) were found positive as E. coli. Amongst 103 isolates (42.9%) contained no pathogenic genes. 11 isolates (4.6%) were identified as EPEC, 5 isolates (2%) as EHEC, 2 isolates (0.8%) as EAEC. ETEC and EIEC were not detected in any of the samples. Due to the contamination of ready-to-eat food samples with intestinal pathogenic pathotypes, continuous monitoring of the field of ready-to-eat food is suggested.

Improper use of antibiotics, and the subsequent residues in raw animal products such as milk, can directly or indirectly cause health problems in human communities such as allergic reactions and reduce the effectiveness of antibiotic treatments. The aim of the present study was to determine the residual levels of tylosin, gentamicin, and neomycin in milk and ice cream distributed across Tehran. A total of 125 samples, including raw milk, pasteurized and sterilized milk, traditional and pasteurized ice cream. The samples were randomly obtained from retail centers in Tehran from July to September 2019. The residual levels of tylosin, gentamicin, and neomycin were determined using high-performance liquid chromatography (HPLC) method. Of the samples, tylosin, gentamicin, and neomycin were detected in 94.4%, 92.2%, and 96.6%, respectively. The highest tylosin residues in raw milk and ice cream samples was 26.72 ± 1.55 and 26.01 ± 1.55 μg/l, respectively. The highest gentamicin residues in raw milk and ice cream samples were 28.15 ± 1.29 and 28.8 ± 1.29 μg/l, respectively. The highest neomycin residues in raw milk and traditional ice cream samples were 33.46 ± 1.95 and 34.7 ±1.95 μg/l, respectively. According to the Iranian National Standard, in all tested samples the residual antibiotics were below the standard approval limit. Since most samples contained antibiotic residues, continuous monitoring of milk samples for antibiotic residues is recommended.

This study aimed to investigate the antioxidant and antimicrobial properties of Echinacea purpurea, which is used as an antiseptic, immune system booster, antimicrobial, antioxidant and anti-poisoning herbaceous plant. Antioxidant and antimicrobial properties, total phenolic compounds and DPPH radical scavenging of the extract were measured. Antimicrobial properties of the extract were assessed using well-diffusion method. The components of the extract were identified using gas chromatography-mass spectrometry (GC MS). The data were analyzed using SPSS and Duncan's statistical test. The plant extract showed high level of phenolic compounds. The DPPH radical scavenging of the extract was tested at concentrations of 0.22, 0.25, 0.27, 0.31, 0.35, 0.41, 0.50 g/ml. The concentration of IC50 indicated sufficient inhibitory potential of the extract. The diameter (means ± SD) of the growth inhibition zone for Staphylococcus aureus, Escherichia coli and Aspergillus niger was estimated at 4.67 ± 1.24, 3.11 ± 0.84 and 1.78 ± 0.89 mm, respectively. Based on well-diffusion assay, S. aureus was found more sensitive than E. coli, and E. coli was more sensitive than A. niger. Using the gas chromatography-mass spectrometry, 81.38% of the total extract compounds were identified. Important components of the extract consisted of germacrene D (21.67%), paracetamol (5.53%), Bernoulli (4.58%), respectively. The results showed that Echinacea extract had excellent antioxidant and antimicrobial effects.