مجله میکروب شناسی مواد غذایی
سال هفتم شماره 4 (زمستان 1399)

Due to the increasing demand for the high quality of meat products, long shelf life, and minimum processing, therefore, this study aimed to evaluate the antimicrobial activity of the two standard strains Lactobacillus delbrukii subspp delbrukii )PTCC 1333( and Lactobacillus fermentum (PTCC 1744) on the most common isolated bacteria from meat. In this study, 50 meat samples including red meat, minced meat, and fish were purchased from different areas of Shiraz city. The samples were transferred to the lab and cultivated in Nutrient Broth as well as blood agar. Then the isolates were purified and the most common isolates identified using biochemical tests. The inhibitory activity of the two strains lactobacillus supernatant against the most common isolates was investigated by the good diffusion agar method. As well as to prevent the inhibitory effects of organic acids and H2O2, the supernatant was treated with sodium hydroxide and catalase enzyme. Finally, the most common isolates were identified by PCR molecular technique. Common bacteria were reported by the molecular test as Escherichia coli (16.6%), Enterobacter cloacae (16.6%), Hafnia alvei (50%), and Aeromonas salmonicida (16.6%). The greatest effect of lactic acid bacteria on Escherichia coli, Hafnia alvei, and Aeromonas salmonicida was observed. Among the two standard strains of lactobacillus, Lactobacillus delbrukii has a greater effect on isolated bacteria. The supernatant of the two lactobacilli, without neutralizing with Sodium Hydroxide and catalase, had antimicrobial activity against the most common isolates.

This study was aimed to study the effects of virkon S on microbial load indices of poultry meat and internal organs. 180 broiler chicks were divided into three equal groups. The first and second groups received 250 g and 500 g of virkon S per 1000 liters of water for 10 consecutive days, from 31 days to 41 days, respectively, and the third group received no combination in the water. To evaluate the effect of virkon S on the population of Escherichia coli flora on meat, heart, and liver, poultry were sampled from these organs at the end of 42 days and their microbial status was evaluated by culture and enumeration of E. coli. The results showed that virkon S at concentrations of 250 and 500 g per 1000 liters of drinking water for 10 days could reduce E. coli population and microbial load of meat, heart, and liver of poultry, significantly. Therefore, according to the findings of this study, the use of virkon S in broiler chickens' drinking water can improve the hygienic quality of poultry meat.

In recent years, the incidence of foodborne illnesses has caused considerable concern among the population. Despite advanced mechanisms in health and inspection during food production, microorganisms are potential hazards during food processing, packaging, transportation, storage, and distribution. To reduce the economic loss and life-threatening diseases, and also diminish the adverse effects of chemical preservatives on foods and the increased resistance of microorganisms to antibiotics, the application of natural antimicrobial compounds that have detrimental and inhibitory effects on the pathogenic agents has been considered by researchers. Bacteriocins produced by lactic acid bacteria such as nisin, lacticin 3147, pediocin PA-1, pediocin AcH, and enterocin A and B are natural antimicrobial additives. Researchers face limitations when using bacteriocins such as inappropriate distribution in the food matrix, lack of inhibition in gram-negative bacteria and yeast, inefficiency in the neutral and alkaline pH range, and inactivation at high temperatures. To address these problems, processed bacteriocins such as microencapsulated nisin are used instead of free nisin. Also, bacteriocins are applied in combination with other processes such as active packaging, high hydrostatic pressures, pulsed electric fields, gentle heat treatments, and lactoperoxidase system. In this study, first, the bacteriocins in terms of their structure and mechanism of action are reviewed and then the use of bacteriocins in foods as natural preservatives is discussed.

The detrimental effects of chemical preservatives and the tendency of consumers to use foods without preservatives or with natural preservatives have increased the use of natural antimicrobial compounds, including plant essential oils and extracts in food industries. Considering the numerous antimicrobial properties of Caraway (Bunium persicum Boiss) and the assumption that its use in lactic cheese increases the shelf life of a product with an acceptable aroma and flavor, in this study the effects of essential oil and alcoholic extract of Caraway on the growth of Staphylococcus aureus, Listeria monocytogenes, E. coli O157, Aspergillus flavus, and Aspergillus niger as well as total counts of mold and yeast were evaluated. Also, its effect on total counts of LABs and sensory properties of cheese was studied. Results showed that this plant was able to delay microbial growth. Caraway showed a more inhibitory effect on the studied microbes in lactic cheese and the antimicrobial activity of the essential oil was higher than the extract so that at the end of storage samples containing 1% essential oil had the lowest count of the target microbes. Comparison of the effect of essential oil and extract on the growth of the studied microbes showed that the Caraway had more effect on the growth control of Aspergillus flavus and Escherichia coli O157in lactic cheese. In the case of lactic acid bacteria, as the shelf life increased, the number of bacteria decreased in the cheese, and decreasing was greater in the control samples.

Escherichia coli O157:H7 is one of the most important enteric pathogenic strains that is usually transmitted to humans through contaminated water and food. These strains cause hemorrhagic colitis, HUS syndrome, cytopenic purpura thrombosis, and, in some cases, death. The main repository of these bacteria is ruminants. The aim of this study was genetic classification (genotyping) of isolates of this strain isolated from raw meat and poultry by RAPD-PCR method. 344 samples of ruminants and poultry were collected from fresh meat supply centers in Isfahan and Shahrekord. Genetic classification of O157:H7 isolates was performed by the RAPD-PCR method. Of 344 raw meat samples studied, 202 Escherichia coli isolates (58.7%) were isolated. The rate of O157: H7 strain was 17.8% (36 samples). Genetic classification of Escherichia coli O157:H7 isolates showed 9 different profiles among these 36 isolates and found an affinity of 43.7 to 100% among the isolates. This study showed high molecular similarity between E. coli O157: H7 strains isolated from different animals in Isfahan and Shahrekord. It was also found that RAPD-PCR is a simple, fast, and inexpensive method for describing the genetic diversity of different E. coli strains including strain O157:H7.

Based on the increasing prevalence of type 2 diabetes, the present study aimed to investigate the effect of Lactobacillus isolated from dairy products on blood glucose in diabetic rats. Isolation and characterization of Lactobacillus from dairy products were performed using biochemical and molecular tests. In this study, treatment was performed on 49 male Wistar rats with a mean age of approximately 6 to 8 weeks. Rats were divided into 7 groups of 7 each. In the intervention group, Lactobacillus ruteri and Lactobacillus plantarum were used. At the end of 4 weeks, weight changes and blood glucose levels of the rats were compared to the positive and negative controls. Statistical analysis was performed using SPSS software, chi-square test, or Fisher's exact test for comparison of variables. The results showed that during one month the mice were exposed to Lactobacillus bacteria had the highest weight in the fourth week and the lowest weight in the first week of the study. A significant decrease in blood glucose level was observed in the groups consuming L. plantarum and L. ruteri. The present study showed that intervention of Lactobacillus without altering diet or specific diet in rats can significantly decrease blood sugar in the bacterial group. Considering the effect of the studied bacteria on blood glucose reduction, it can be claimed that Lactobacillus can be suggested as an adjunctive treatment in patients with type 2 diabetes.

Aflatoxins are mycotoxins produced by some the fungi species such as Aspergillus and Penicillium of which Aflatoxin B1 is one of the most potent hepatic carcinogens in animal species. Wheat, flour, and bread are some of the most consumed foodstuffs and nutritious environments for the growth of mycotoxin-producing molds. According to the position of flour production factory of Kiar city and long duration of stay of wheat in its warehouses, this study aimed to study the aflatoxin B1 levels in the wheat and flour of this factory and the baked bread of them. In this study, 27 wheats, flour, and bread samples (9 samples of each) were collected and prepared from the Kiar flour factory and the concentration of aflatoxin B1 of samples was determined by High-Performance Liquid Chromatography (HPLC). The results showed that the aflatoxin B1 levels in wheat, flour, and baked bread were lower than the national standard limit, so those foodstuffs are not polluted by aflatoxin B1. Also, the aflatoxin B1 levels of wheat samples are higher than bread samples and the aflatoxin B1 levels of flour samples are higher than bread samples, therefore that toxin decreases efficiently during yeast production and heat of baking. On the other hand, due to the strong linear correlation between aflatoxin B1 levels in wheat, flour, and bread, an increase of the toxin in wheat causing the increase of the toxin in flour and bread; so reducing the production of aflatoxin in wheat using control of the temperature and humidity in wheat silages more effectively resulting in a further reduction of aflatoxin in flour and bread. As a result, it is recommended to monitor the wheat warehouses in terms of ventilation, flour production for preparing a variety of food products and bake the ingredients at the optimum temperature.

Fish and other aquatic animals, directly and indirectly, can be contaminated with Listeria monocytogenes and consequently, fish and their products are considered a carrier for this bacterium. The present study investigated the contamination of farmed rainbow trout and common carp with this bacterium as well as the phylogenetics of the isolates. A total of 50 samples of farmed fish were obtained from local fish supply centers in Shahrekord City from July to September 2018. Based on the molecular experiments, 18 (36%) of the 50 studied samples were contaminated with L. monocytogenes as 26% and 10% of the isolates were found in trout and carp, respectively. From 18 isolates, 12 samples (66.66%) belonged to serotype 4b, one belonged to serotype 1/2a and the other 5 samples belonged to serotype 1/2b. According to the results of the present study and regarding the importance of the bacteria in terms of public health, continuous and accurate hygienic monitoring seems to be necessary.