مجله میکروب شناسی مواد غذایی
سال دهم شماره 3 (پاییز 1402)

Fungal toxins (mycotoxins) are a group of secondary metabolites of fungi that have different mutagenic, carcinogenic, estrogenic or acute toxicity effects. Among the types of fungal toxins, aflatoxins are known as a potential cause of liver cancer and affect the body's immune system. Aflatoxin M1 is found in the milk of animals fed with feed contaminated with aflatoxin B1. This study was conducted with the aim of determining the presence and amount of aflatoxin M1 in pasteurized curd and dry curd consumed in the cities of Isfahan province in Iran. In this research, the amount of aflatoxin M1 in pasteurized curd and dry traditional curd was investigated, and for this purpose, ELISA method was used. According to the obtained results, the average minimum and maximum concentration of aflatoxin M1 in dry curd samples is 0.210±0.020 ppb and 0.66±0.02 ppb, respectively. Also, the average minimum and maximum concentration of aflatoxin M1 in pasteurized curd samples is 0.2±0.02 ppb and 0.65±0.02 ppb, respectively. The analysis of the obtained results showed that 30% of the samples studied in this research had pollution exceeding the permissible limit. Considering the high consumption of curd and other dairy products in our country, more attention should be paid to the control and monitoring of dairy production and consumption.

Natural honey is a proper substrate to isolate probiotic bacteria. Characterization of probiotic and antifungal properties of microorganisms isolated from food ecosystems such as natural honey that have been less studied is an interesting task. In the present study, after molecular identification of a predominant lactic acid bacterium (LAB) isolated from the natural honey, its probiotic properties and antifungal effect were investigated. Then, the antibacterial (spot method) and antifungal (overlay method) activities of the LAB isolate were evaluated against some foodborne microorganisms. Sequencing results of the PCR products led to the identification of Enterococcus faecium. Survival rate of the isolate in simulated gastrointestinal conditions was equal to 20.68%, and its antibacterial and antifungal effects on Salmonella enterica and Aspergillus niger were also 31.06 and 32.35% inhibition, which were significantly (P<0.05) higher than the other foodborne indicators studied. Furthermore, the isolate had a proper antibiotic resistance profile, and it had no hemolytic activity. Auto-aggregation ability of the isolate was also equal to 32.34%, and its co-aggregation with Escherichia coli, S. enterica, Listeria monocytogenes and Bacillus cereus was 34.29, 21.35, 15.58 and 14.98%, respectively. Based on the results, it can be concluded that the E. faecium isolated from honey can be used as probiotic and/or protective culture in food industry.

Melissa officinalis is a medicinal plant with high antimicrobial properties. The present study was performed to evaluate the antimicrobial effects of Melissa officinalis essential oil on food-borne bacteria. Melissa officinalis aerial parts were prepared and after approval by experts used to prepare essential oils. The diameter of the growth inhibition zone of Listeria monocytogenes, Salmonella typhimurium, Escherichia coli and Staphylococcus aureus was assessed using disk diffusion and compared with antibiotics. The minimum inhibitory concentration (MIC) and the minimum bacterial concentration (MBC) of Melissa officinalis essential oil were evaluated on the target bacteria. Citronellal (14.4%) and Caryophyllene oxide (11%) were the most important compounds identified in Melissa officinalis essential oil. The diameter of the growth inhibition zone of the bacteria against Melissa officinalis essential oil ranged from 3.93±0.42 to 15.23±1.17 mm. Application of 4 mg/ml concentration of Melissa officinalis essential oil caused the largest diameter of the growth inhibition zone of Staphylococcus aureus (14.70±0.27 mm), Escherichia coli (10.33±0.29 mm) and Salmonella typhimurium (10.18±0.52 mm). The antimicrobial effects of Melissa officinalis essential oil were dose-dependent (P <0.05). The lowest and highest levels of MIC and MBC of Melissa officinalis essential oil were obtained for Staphylococcus aureus (1.25 and 2.5, respectively) and Salmonella typhimurium (10 and 20, respectively). The diameter of the growth inhibition zone of bacteria treated with Melissa officinalis essential oil was higher than that of many antibiotics, but lower than that of vancomycin. Melissa officinalis essential oil can be used as a substance with antimicrobial properties, especially in food films.

Probiotics are living cellular components that have beneficial effects on the host in a certain number when they enter the gastrointestinal tract. The aim of this study was to produce and evaluate the effects of the probiotic bacterium Lactobacillus acidophilus, which expresses the peach's peptide Tachyplesin I, on the growth of Salmonella. The recombinant plasmid pNZ8148- Tachyplesin containing the Tachyplesin gene was introduced into E. coli by heat shock and then purified. The recombinant vector containing the tachiplicin gene was then inserted into Lactobacillus acidophilus by electroporation method and screened by chloramphenicol antibiotic and PCR. Then, the inhibitory effect of engineered Lactobacillus acidophilus on the growth of Salmonella was investigated and compared with antibiotic discs..After confirmation of the entry of plasmid pNZ8148-Tachyplesin into Lactobacillus acidophilus, it had an inhibitory effect on the growth of Salmonella pathogenic bacterium as the diameter of the growth inhibition zone created on Salmonella was acceptable under the influence of engineered Lactobacillus. After comparing the diameter of the auras of ampicillin, chloramphenicol and tetracycline antibiotic disks with engineered lactobacillus and performing statistical analysis, no significant difference was reported. Considering that the presence of Tachyplesin gene in Lactobacillus acidophilus was confirmed, the resulting growth inhibition zone around Salmonella indicates that the expression and secretion of Tachyplesin gene in Lactobacillus has an antibiotic-like effect on Salmonella.

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a significant pathogen to induce food poisoning in humans. This bacterium possesses the ability to produce heat-resistant enterotoxins. This investigation examined the prevalence, antibiotic resistance patterns, and frequency of enterotoxin coding genes in MRSAisolates obtained from ready-to-eat foods. One hundred and twenty-five samples of ready-to-eat food were collected and transported to the laboratory on ice. Staphylococcus aureus was isolated using microbial culture, and MRSAisolates were confirmed using cefoxitin and oxacillin discs. The antibiotic resistance patterns and frequency of enterotoxin coding genes were determined through disc diffusion and PCR methods, respectively. The prevalence of MRSAwas 68.42%, 66.66%, 62.5%, and 28.57% in pounded kebab, grilled chicken, hamburger, and sausage samples, respectively. Methicillin-resistant Staphylococcus aureus strains exhibited the highest resistance to penicillin (100%), doxycycline (80.64%), tetracycline (77.41%), and erythromycin (70.96%). The isolates exhibited the lowest resistance against vancomycin and rifampin (22.58%). The prevalence of enterotoxin genes, SEA and SEG, was reported as 58.06% and 61.29%, respectively. The simultaneous presence of multiple enterotoxin coding genes and resistance to various antibiotics in MRSAstrains isolated from ready-to-eat food samples highlights a significant health concern within this food category. Preventing the indiscriminate use of antibiotics can mitigate the risk of methicillin-resistant enterotoxin-producing Staphylococcus aureus in ready-to-eat foods.

The aim of the present study is to investigate the antioxidant and antimicrobial properties of hydro alcoholic and aqueous extracts of grape seed varieties on Gram-positive and Gram-negative microorganisms isolated from poultry meat. 94 poultry meat samples including chicken, quail, turkey and ostrich were randomly collected from sales centers of Isfahan province. Microorganisms were identified by biochemical tests. Aqueous and hydro alcoholic extracts of grape seeds of black alfi, black gohari, black shahani, Rish-Baba, Shasat-arus and Rooster tail varieties were prepared by soaking method. Antimicrobial properties of hydro alcoholic and aqueous extracts of grape seeds were investigated by disk diffusion and MIC (minimum inhibitory concentration) methods. The antioxidant property of the extracts was evaluated by DPPH method and the IC50 value was calculated. The phenolic compounds present in aqueous and hydro alcoholic extracts of grape seeds were measured by high-performance liquid chromatography. The frequency of Arcobacter butzleri, Campylobacter jejuni, Listeria monocytogenes and Staphylococcus aureus was 11.45%, 17.70%, 1.04% and 16.66%, respectively. The antimicrobial effect of aqueous and alcoholic extracts of grape seed was higher on gram positive bacteria in both methods. Alcoholic extracts had more antimicrobial effect than aqueous extracts, Rish-Baba grape showed the most antimicrobial effect. The highest percentage of DPPH in hydro alcoholic extracts is related to black alfi and Rish-Baba grape seed extracts, and in aqueous extracts of black alfi and black shahani grape seeds.

With the increase in the amount of food production, the need for maintenance is felt in order to deliver healthy and high-quality food to consumers. Today, extensive research has been done in relation to the use of natural antimicrobial compounds to deal with pathogens of food origin, and it has been determined that these compounds are a suitable alternative to chemical antimicrobial compounds. Plant essential oils have good antimicrobial properties due to the presence of polyphenolic compounds. Meat is the main source of protein of animal origin, which is considered one of the most perishable foods due to its abundant nutrients. Nowadays, the use of food coatings containing natural antimicrobial and antioxidant agents, including plant essential oils, is one of the new methods of preservation, which has a good potential to prevent pathogenic microorganisms and also increase the shelf life. They have the shelf life of meat products and are able to increase the shelf life and preserve the natural appearance of meat and meat products. It is interesting to note that active films containing essential oils provide an environmentally friendly solution in the meat industry. In general, active food packaging has shown a suitable technology for improving meat quality and reducing waste in the food industry. This study was conducted with the aim of investigating the antimicrobial effects of different plant essential oils and their synergistic effects in meat preservation.

One of the characteristics of lactobacilli is their ability to produce biosurfactant compounds. In this research, the biosurfactant of Lactobacillus acidophilus and Lactobacillus casei was used to evaluate the antimicrobial and anti-biofilm potential against four pathogenic bacteria including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumannii.

Biosurfactant extraction was done from Lactobacillus acidophilus and Lactobacillus casei, using the method of determining the minimum growth inhibitory concentration (MIC) was used to determine the antimicrobial potential. Also, the micro titer plate method was used to measure the anti-biofilm potential and the type of biofilm of each strain was determined in the presence of Lactobacillus acidophilus and Lactobacillus casei biosurfactant in different concentrations.

Determination of the minimum inhibitory concentration (MIC) for pathogen strains, the highest percentage was observed at the concentration of 125 and 250 mg/ml. The anti-biofilm effect of biosurfactant has been used in the approximate concentrations of 62.5 mg/ml, 125 mg/ml and 250 mg/ml. Determination of antibiotic sensitivity showed the results of sensitive, semi-sensitive and resistant states, but the results obtained for Acinetobacter baumannii shows resistance to all antibiotic discs.

The biosurfactant isolated from Lactobacillus acidophilus and Lactobacillus casei had antibacterial properties against pathogenic bacteria, also the biosurfactant of Lactobacilli showed that it has anti-biofilm capability.