مجله میکروب شناسی مواد غذایی
سال سوم شماره 4 (زمستان 1395)

Pigment production from microorganisms is more advantageous than other biological resources such as plants. To date, a research on the effect of chemical mutagens on the production of carotenoid pigments from Micrococcus roseus has not been done. Hence, the aim of this study was to optimize the production of carotenoid pigments from M. roseus treated with sodium azide. Carotenoid production from M. roseus was significantly increased at the presence of sodium azide mutagen. However, the production of total carotenoid (TC) and biomass dried weight (BDW) from M. roseus was reduced at the presence of high concentrations of sodium azide and high effect duration of sodium azide. Concentration of sodium azide and its treatment duration time had the greatest effect on the pigment production from M. roseus under treatment with sodium azide. Sodium azide concentration of 94.95 µg/L, treatment duration of 13.23 min, incubation temperature of 25.91 °C, and incubation time of 87.87 h were found as the optimum condition for the production pigment from M. roseus under treatment with sodium azide. At this optimum conditions, amount of responses was measured 7.61 mg/L and 8.36 g/L for TC and BDW, respectively.

Verotoxigenic Escherichia coli (VTEC) or Shigatoxin producing Escherichia coli (STEC) is an important pathogenic E. coli that can cause diarrhea or hemorrhagic colitis in humans. Hemorrhagic colitis occasionally progresses to hemolytic uremic syndrome (HUS), an important cause of acute renal failure in children and morbidity and mortality in adults. In the elderly, the case fatality rate for HUS can be as high as 50%. Escherichia. coli O157:H7 has been recognized as a cause of this syndrome since the 1980s. The reservoirs for STEC O157:H7 are ruminants, particularly cattle and sheep, which are infected asymptomatically and shed the organism in feces. Other animals such as rabbits, pigs and poultry can also carry this organism. Infections with STEC in other serogroups, including members of O26, O91, O103, O104, O111, O113, O117, O118, O121, O128 and O145, are increasingly recognized as causes of hemorrhagic colitis and HUS. Humans acquire STEC by direct contact with animal carriers, their feces, and contaminated soil or water, or via the ingestion of underdone ground beef, other animal products, and contaminated vegetables and fruits. Thorough cooking of raw meats, pasteurization of milk, treatment of private water supplies, and the avoidance of cross-contamination from raw meats or cattle feces to other foods are the most effective ways of preventing STEC infections. Generally, the detection of STEC is laborious, and currently there are no simple, inexpensive methods available for routine isolation of all STEC strains.

Yogurt is one of the most popular types of fermented milk almost all over the world particularly the Middle East. However, due to poor sanitary conditions of milking and storage, improper heat treatment, and secondary contamination, milk is a good media for transmission of a broad range of pathogens. The aim of this study was to examine health and chemical properties of artisanal yogurt produced by nomads. Samples were collected from nomadic regions in Khorasan-e-Razavi Province. The viable count of coliform, E.coli, coagulase-positive staphylococci (Staphylococcus aureus), yeast and molds, lactic acid bacteria and chemical properties (pH, acidity, fat and total solid) were determined. Most probable number (MPN) technique showed that only one yogurt sample prepared with raw milk exposed to low heat treatment (40 °C) was contaminated with 2/4 × 102 CFU/g coliform and was E. coli positive. No Staphylococcus aureus were found in all examined samples. High counts of Yeast and molds in some samples revealed unsatisfactory sanitary conditions during fermentation and post production. PH of yogurt samples was in the range of 3.8 - 4.3 and the acidity was between 1.3 – 2%. The fat content of yogurt samples was varied between 0.5 to 45%. It is concluded that above mentioned products were considered containing health risks. Authorities should pay more attention and supervision focused on improving health conditions for production of such dairy product. This survey is the first reported case about production of a yogurt with raw milk in Iran.

Cronobacter sakazakii is one of the main pathogens that transmitted by feeding infants by contaminated infant formula and baby-food. This bacterium is one of the major causes of mortality, digestive diseases and meningitis in newborns. This study was performed in order to detect microbiological and molecular contamination by Cronobacter sakazakii and study antibiotic resistance pattern of bacterial isolates. Two hundred samples of infant formula and baby food from deferent brands were collected and after microbial detection, bacteria’s isolates were detected, using PCR method. Then antibiotic resistance pattern of isolates were evaluated using disk diffusion method. Three samples from total 100 baby food (3%) and 5 samples from total 100 infant formula (5%) had Cronobacter sakazaki infection. A, B and C brands from infant formula and A, D brands from baby food were contaminated with Cronobacter sakazakii. B and C brands from infant formula (10% each of them) and A brand from baby food (8%) were infected with Cronobacter sakazakii. Isolates from Cronobacter sakazakii which isolate from infant formula and baby food demonstrated most Sensitivity to ciprofloxacin (20.38), meropenem (19.83) and imipenem (19.63) and most resistance to amoxicillin, ampicillin, tigecycline, ticarcillin, aztreonam and ceftazidime. Careful inspection on the raw material quality of infant formula and baby food as well as, exact supervision on production procedure, sanitation in addition to use natural antimicrobial can reduce Prevalence rate of this bacteria.

Various ways to increase the duration used for food storage, among whom radiation can be used as an effective way to retard spoilage in food in particular is concerned with the origin of the fish. In this study 50 grass carp (Grass carp) (Ctenopharyngodon idella) (mean weight 1-1.5 kg) for gamma irradiation with cobalt-60 source by doses of zero, 1.5, 2.5 and 3.5 kGy chosen and then change microbial load and total volatile nitrogen in the days 1, 7 and 14 were evaluated under the conditions of storage in refrigerator. These research results demonstrate the significant decline in aerobic mesophilic bacteria and T.V.N in the irradiated samples in comparison with non-irradiated samples. In this study, given that the dose of 3.5 kGy dose caused a significant decrease in comparison with other (standard range) T.V.N values and aerobic mesophilic bacteria was in the refrigerator until the seventh day. Therefore, in Grass carp using it (3.5kGy) as the best dose to prevent corruption is recommended in seventh days.

Each year, large amount of pistachio by-product (PBP) was produced after the processing of fresh pistachio. PBP has suitable nutritional value and is used as a feed stuff in animal nutrition. The objective of this study was to determine the microbial contamination and concentration of aflatoxin in PBP. The samples of PBP were collected from two types of processing system (traditional and industrial), three stage of pistachio harvesting, and three different intervals time of picking up the skin (1-2 hours, 5-6 hours and ≥13 hours). All samples were dried under the sun and then were milled. All of the samples were cultured in a sterile culture and total mould, Aspergillus moulds and Coliform, and E.coli bacteria were counted. The concentration of total aflatoxin was measured by HPLC via extraction. Results showed that the means of microbial population of total moulds, Aspergillus moulds and Coliforms, and E.coli bacteria count were 21000, 3892, 3094 and 1.1 CFU/g, respectively, that were below a critical level to interfere in animal nutrition. Although microbial population were different in sampling area (P

Application of natural preservatives to protect foods from microbial spoilage and to control the occurrence of foodborne pathogens has become an important issue worldwide. The aim of this study was to investigate the inhibitory effect of Basil (Ocimum basilicum L.) essence of Staphylococcus aureus, Escherichia coli and Rhodotorula rubra. The basil essence was extracted by hydro-distillation using Clevenger apparatus. The components of the essence was analyzed by GC/MS. Afterwards, using micro-dilution method the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) for S. aureus, E. coli and R. rubra was estimated. Based on results, 43 various components were detected in basil essence, namely benzene (20.97%), E-citral (12.845%), Z-citral (6.137%), methyl chavicol (7.68%) and thymol (7.79%). MIC and MBC for was 0.25 mg/ml for E. coli and R. rubra, meanwhile it was estimated at 0.5 mg/ml for S. aureus. Taking into account the various components of basil essence as well as their antimicrobial properties, it was concluded that, with considering the natural properties of each food type, basil essence can be used as a food preservative.

In this study, antibacterial effects of methanol extracts of red Onions with the scientific name; Allium cepa L.by the method of determining of MIC and MBC andthen perform antibiotic susceptibility test by the agar disk diffusion method onthe standard strains of some bacteria in terms of food hygiene and were compared with the effects of some antibiotics.Results showed that the highest inhibitory effect was on Yersinia enterocolitica and Clostridium perfrigenes (MIC=62.5µg/mL) and the lowest same effect was on Staphylococcos aureus(MIC=500µg/mL).As well as the most bactericidal effect was on Yersinia enterocolitica (MBC=62.5µg/mL) and the lowest same effect was on Staphylococcos aureus (MBC=1000µg/mL).Also the results ofantibiogram tests indicated that the onions, methanol extracts have optimum antibacterial effect to the effects of the Vancomycin and Nalidixic acid as standard antibiotics and the greatest impact of this terms submitted on Clostridium perfrigenes(gram-positive bacteria) and Yersinia enterocolitica(gram-negative bacteria) thatstatistically; in the range of p