مقالات رزومه دکتر محمدباقر حبیبی نجفی

Cronobacter sakazakii is an opportunistic pathogen, which has been linked to the contamination of powdered infant formula, and associated with outbreaks leading to fatalities in neonatal intensive care units. Few studies have explored the direct interaction between probiotics and C. sakazakii. In this study, the effect of a Lactiplantibacillus plantarum strain (M17) along with the standard strain Lactobacillus plantarum (ATCC 8014) and the well-characterized probiotic strain Lactobacillus rhamnosus GG on the adhesion of C. sakazakii to intestinal epithelial cells was analyzed.

Acid and bile tolerance of M17 was evaluated in the presence of pepsin and pancreatin. L-arginine hydrolysis was investigated using an arginine-including medium. Auto-aggregation and co-aggregation assays were performed by absorbance measurement. Minimum inhibitory concentrations of the antimicrobials recommended by the European Food Safety Authority were established. Total lactic acid and the ratio of D/L lactate isomers were determined with a Megazyme enzymatic kit. The ability of the isolate to produce biogenic amines was tested by qualitative and quantitative monitoring. Hemolysis was assessed phenotypically on MRS agar enriched with sheep blood. The strain was tested for its capability to adhere to mucin and Caco-2 cells. The antagonistic effects of the strain against C. sakazakii were further evaluated in vitro on mucin and cultured Caco-2 cells. The LAB strain was added simultaneously with, before, and after C. sakazakii to Caco-2 cells for competition, exclusion and displacement assays, respectively. Data analysis was performed in R using one-way analysis of variance, and the experimental groups were compared with the controls using Tukey’s test. P values <0.05 were considered statistically significant.

There was no significant difference in the survival rate of M17 and L. plantarum ATCC 8014 at pH = 4. After 2 h of incubation at pH = 2.5, the survival rate of L. plantarum ATCC 8014 was estimated to be higher than strain M17, but this difference was not significant. After 4 hours of incubation at pH = 8, M17 showed a higher survival rate than L. plantarum ATCC 8014, and this difference was significant after transfer from pH = 4. These results confirm the appropriate viability of M17 in the gastrointestinal tract. Both M17 and L. plantarum ATCC 8014 developed the color yellow in the L-arginine hydrolysis assay, which confirms the safety of these strains. The percentage of auto-aggregation for M17, L. plantarum ATCC 8014, and Lactobacillus rhamnosus LGG was estimated at 24.38, 25.28, and 32 after 6 hours, respectively, and no statistically significant difference between the two isolates were noticed. Given the auto-aggregation and co-aggregation parameters of M17, this strain may constitute a defense mechanism against C. sakazakii. Strain M17 showed resistance to kanamycin and clindamycin antibiotics. With intrinsic resistance, the risk of transferring resistance genes is not only speculative, but practically impossible. Intrinsic resistance of lactic acid bacteria may be considered desirable because it ensures their survival when the host is treated with antibiotics. Both D and L isomers of lactic acid were produced by the studied strains. In humans, D(-)-lactic acidosis is a rare metabolic complication that has only been reported in individuals with short bowel syndrome). Clinical studies have shown that the consumption of probiotic bacteria producing D(-)-lactic acid is safe for children and does not cause a long-term increase in blood D(-)-lactic acid. The reference L. plantarum strain and M17 did not produce biogenic amine precursors, and had no ß-hemolytic activity. Mucin adhesion assay exhibited that M17 has less adhesion (12.10 ± 1.14 %) than L. plantarum ATCC 8014 (13.33 ± 2.30 %) and LGG (15.93 ± 2.06 %) although these differences were not statistically significant. However, the amount of adhesion for the positive control sample Escherichia coli K12 (25.19 ± 4.40 %) was significantly higher than those of the other strains. Compared to the positive control, M17 had a significantly lower adhesion rate (6.8 ± 1.41) to CaCo-2 cells. This value was estimated at 13.77 ± 3.53 % for the reference strain and 21.6 ± 7.54 % for Lactobacillus fermentum PCC (positive control). In antagonistic assays, M17 was able to reduce the adhesion of C. sakazakii to mucin and CaCo-2 cells in all three methods of exclusion/inhibition, competition and displacement. Statistical analysis of the results does not show a significant difference between M17 and LGG. Therefore, the performance of M17 is similar to that of the standard probiotic LGG.

Lactic acid bacteria with acceptable ability to adhere to epithelial cells can be suitable for colonization in the intestine. They can act as a barrier to fight pathogens through various competitive mechanisms, such as co-aggregation with pathogens and adhesion. The M17 strain has an acceptable immune profile and probiotic properties because it shows an acceptable antagonistic activity against C. sakazakii invasion.

Folate is a term used for a set of compounds with similar biological activities. Folate (polyglutamates) naturally contains all forms of vitamins in this family. In other words, folic acid is a form of folate that is oxidized, this compound is stable and can be absorbed by humans (monoglutamate)[1]. There are several methods for measuring folate, but due to the fact that in this study, the production of extracellular folate (Quatrofolate) was examined, so the microbial assay method was used as the main method. Lactobacillus. Rhamnosus (ATCC7469), which is used as a sensing organism. [2,3] This method can also measure all forms of folate. In this study, 47 medical strains isolated from traditional dairy products were Special Khorasan. traditional yogurt (12 strains of Streptococcus.thermophilus and 15 strains of Lactobacillus delbrueckii subsp. Bulgaricus, 13 strains of Lactobacillus delbrueckii subsp. Lactis, 3 strains of Lactobacillus helveticus) were studied. The results of this evaluation showed that both strains (25 and 26) of Lactobacillus delbrueckii subsp. Bulgaricus produced significant high folate concentrations (133.23 μg / mL and 102.34 μg / mL), as well as K73 strain of Streptococcus.thermophilus, strain 73 from the strains of  Lactobacillus delbrueckii subsp. Lactis and strain No.87 from the three strains of Lactobacillus helveticus (90.29 μg / mL, μg / mL39.71, μg / mL 17.94), were also able to produce high amounts of quatrofolate. According to this study, it was found that the examined previously isolated strains have a potential ability to produce extracellular folate, and the microbial assay method for measuring a sensitive vitamin such as folate in all its forms is considered an efficient and accurate method.

There are increasing concerns about transmission of some enteric viruses which are closely related to human-pathogenic strains via animals and their products, contaminated water and foods. Therefore, the use of appropriate processing methods to control these viruses is essential. The aim of this study was to assess the survival of enteric viruses in cheese processing. The role of fat content of cheese (1.5, 2.5 and 3.2%), MS2 bacteriophage spiked levels (100, 102, 104 and 106) in separation of enteric viruses in curd and whey in the press process, the effect of chemical parameters(acidity and pH) on the exchange of enteric viruses in cheese and salt water in processing time were evaluated. MS2 survival was studied by double layer agar and data were assessed in complete randomized design in triplicates. According to the results, it was concluded that MS2 bacteriophage had the maximum survival in whey at fat content of 3.2% and spiked level of 6 log10in which it was 4/67 based on the logarithmic scale. Also, the maximum survival in curd was at fat content of 3.2%. In brine process, the most survival of bacteriophages in cheese and whey was at fatcontent of 3.2% and spiked level of 6 log10. In general, MS2 bacteriophage had the most survival in brine than curd.

One of the most important factors in producing yogurt is choosing the right starter. Native isolates of any country are among the genetic resources of that country, which play a major role in the production and development of the organoleptic properties of fermented products. Therefore, it seems necessary to study the industrial applications of native isolates. In this study, the production of yogurt was investigated by using native starter isolates from traditional Khorasan yogurts and its comparison with yogurts produced with two types of commercial starters.  

Six strains of Streptococcus thermophilus and three strains of Lactobacillus delbrueckii subsp. Bulgaricus isolated from traditional Khorasan yogurts were selected. The proteolytic activity of Streptococcus thermophilus strains was determined according to the method of Erkus et al(2012) and the proteolytic activity of Lactobacillus delbrueckii subsp. Bulgaricus was determined according to the method of Nespolo et al.(2010). Milk acidification activity byall examined strains was evaluated according to the method of Erkus et al.(2012). The production property of gamma-aminobutyric acid of native isolates was also evaluated using the method of Lacroix et al. (2013). Yogurt was produced using commercial starters and native isolates. Acidity and pH were measured according to Iranian National Standard No. 2852. Synersis of yogurt samples was measured using centrifugation according to Çelik (2007) method. In order to measure textural properties, a combination of backward extrusion techniques and Texture Profile Analysis (TPA) was used (Yang et al, 2010). Sensory characteristics of yogurt samples were evaluated by 20 panelists using five-point hedonic scale. This study was conducted based on factorial experiment using a completely randomized design. Statistical analysis of data was performed using Minitab Statistical Software (version 17) and ANOVA. Comparison of means was performed using Tukey’s test at the significant level (p < 0.05).  

The results of proteolytic activity of Lactobacillus delbrueckii subsp. Bulgaricus showed that the L3 code was weaker than the other two strains. All Streptococcus thermophilus strains were positive protease. All Streptococcus thermophilus strains of the study decreased the pH of the milk to 4.6 in less than five hours, and Streptococcus thermophilus strain S6 code, as the fastest acid producer, decreased the pH of the milk to 4.6within 3 and half hours (Figure 2). The results of GABA production showed that among the streptococcus thermophilus strains, S1, S5 and S6 codes had distinct blue discoloration. Among the Lactobacillus strains, except the L3 strain, two other strains produced green color. Of the 18 samples of the yoghurt, S5L2 and S2L2 samples showed the highest decrease in pH and increased in acidity compared to other samples after being stored refrigerated overnight (P <0.05). The other samples had the same pH and acidity changes as the control samples after overnight refrigeration. The results show the ability of yogurt producion by native starters to compete with those produced by commercial starters in terms of technological characteristics. Thus, samples with codes S2L2, S3L1, S3L2, and S1L1 showed less Synersis of   yogurt than commercial starters. This decrease in the Synersis of yogurt might due to the possibility of exopolysaccharide production by these strains. Textural characteristics of yogurt samples were the hardness of the samples in the range of 3 to 4 N, which was significantly different (P <0.05). The lowest hardness was observed for the S3L3, which can be attributed to the poor proteolytic activity of the strain. L3, S6L2, S3L2 and S2L2 had the highest   hardness compared to other compounds and control samples (P <0.05). This differences in the hardness of the samples can be attributed to the possible production of some metabolites by the strains. There was no statistically significant difference in the adhesion properties of the samples (p <0.05). Considering the sensory evaluation scores, it was found that in all respects, S3L3 had the lowest score among the other samples (P <0.05). This was in good correlation with the results of the textural properties of the test. Therefore, this compound was eliminated compared to the control samples. Finally, considering the proteolytic behavior of the strains and the ability to produce acid and GABA, as well as the sensory, rheological and physicochemical properties of 18 samples in comparison to the two control samples, Streptococcus thermophilus strains with codes S4, S2, S5, S1, S6, and Lactobacillus delbrueckii subsp. Bulgaricus strains with codes L1 and L2 have the potential to be used as commercial starters in the form of compounds S1L1, S2L2, S5L1, S6L2, S4L2.

Several factors are considered during production of yogurt, among which selecting the accurate starter and or adjunct culture is one of the most important factors. This study was aimed to measure the degree of proteolysis, ACE-inhibitory, microbial and antioxidant activity of yogurt produced by a commercial starter supplemented with native co-cultures isolated from traditional yogurts during a 20-days of storage. All treatments were also compared with the commercial culture as control. Initially, five strains of Lactobacillus lactis, two strains of Lactobacillus helveticus, one strain of Lactobacillus delbrueckii, one strain of Pedicucus pentosaseus and one strain of Vissella sibaria used to inoculate into 40 yogurt samples in a completely randomized factorial design with two replications. The samples were kept at 5 ˚C for 20 days and investigated for their physicochemical properties (pH and acidity), degree of proteolysis, ACE-inhibitory, microbial antioxidant activity. The results of statistical analyses showed that application of native co-cultures was significantly increased the degree of proteolysis, ACE-inhibitory, and antioxidant activity of the samples. Our findings showed that, yogurt inoculated with the native strains of Lactobacillus lactis had the highest scores for ACE-inhibitory and antioxidant activity. In all co-cultures, ACE-inhibitory (47%) and antioxidant activity (58%) exhibited a positive correlation with proteolysis. Our results show that co-cultures greatly affect the ACE-inhibitory and antioxidant activity, which can be used in the production of functional food stuffs.

Production of butter from yogurt is a traditional way practiced in many rural regions in Iran. The objective of this study was to isolate and identify the lactic acid bacteria strains with capability of Cholesterol reduction in order to be used as starter in industrial butter production. 10 samples of Iranian traditional butter were collected from local farms across the country. Isolates were identified as LAB based on their Gram reaction, morphology and catalase test in MRS, M17 and MRS with L-Cysteine hydrochloride and L-Mupirocin media. Strains showing high ability of cholesterol reduction and tolerated to bile and acid were then identified by molecular techniques. Finally, the selected strains were used in the formulation of industrial butter production. According to the results of probiotic properties tests, 10 strains showing high ability of cholesterol reduction and tolerated to bile and acid were identified by molecular techniques. The results indicated that 4 isolates belonged to Enterococcus durans, 4 isolates to Lactobacillus, 1 isolate to Pediococcus and 1 isolate to Neoscardovia. Lactobacillus brevis M-4386 4358, Pediococcus pentosaceus M-4384 4336, Neoscardovia arbecensis M-4391 4378 and Lactobacillus pentosus M-4390 4377 were selected to produce industrial butters from cream. The strains used have led to significant changes in the cholesterol content of all samples, and in all samples, cholesterol content was lower than the control. The highest level of cholesterol reduction was achieved in the butter sample prepared by Lactobacillus pentosus M-4390 4377.

Accumulation of polyethylene (PE) wastes has become a major environmental problem. The objective of this research was to assess the potential for microbial degradation of sun-treated low-density PE as a natural way to eliminate PE wastes in semi-industrial condition. Low-density polyethylene (LDPE) films were exposed to one month of sun radiation treatment and then cultured with two PE-degrading bacteria (Sphigobacterium moltivorum IRN11 and Delftia tsuruhatensis IRN27) in aerobic bioreactors over 100 days. Weight loss percentage of the PE and the culture pH were measured. Also, Changes in the chemical structure of the LDPE were assessed by FT-IR and surface erosion and microbial layer formation by bacterial activity was observed by Scanning Electron Microscopy. Partial increases in the culture pH were recorded during the incubation period. The weight loss percentage for T-LDPE samples cultured with Sphigobacterium moltivorum IRN11 and Delftia tsuruhatensis IRN27 was 3.31%±0.013 and 3.98%±0.025 in TLDPE samples, respectively, and functional carbonyl-groups in the TLDPE samples decreased significantly due to bacterial hydrolysis. SEM images showed the different microbial layer formation on sun-treated low-density polyethylene (T-LDPE) for both bacteria. Our results suggest that exposure of LDPE to sun radiation had a significant effect on biodegradation of Ld-PE films and that the two bacteria tested were able to enhance the biodegradation the T-LDPE.

The complex composition of the essential oils and the variety of chemical structures of their constituents are responsible of a wide range of biological activities many of which are of increasing interest in the field of foodstuff preservation (Romanazzi et al. 2012). Regarding that higher amount of EOs are required for food preservation, their application can negatively influence taste or odor. To avoid this unwanted side effect, several EOs can be combined. On the other hand the synergistic possible effect produced by the combination of plant essential oils was referred as an efficient strategy to combat microbial development(Wagner. 2011). The main purpose of this study was to evaluate the antifugal synergistic effect of combination of some essential oils including thyme, cinnamon, rosemary and marjoram aginst apple rot fungi during posthrvest storage. In this experiment, chemical composition of the essential oils was analyzed by gas chromatography. For evaluation of antifungal activity based on MIC, against Alternaria alternanta, Penicillium expansum and Botrytis cinerea, an agar dilution method was used. EOs interactions were assessed using a checkerboard microdilution method. The evaluated concentrations were in the range of 5 dilutions below the MIC to twice the MIC. For the double combinations, a two-dimensional checkerboard with twofold dilutions of each EOs was used (six double combinations). The maximum antifungal activity was demonstrated by thyme oil which showed MIC values 1250 μg/mL for A. alternanta and P.expansum and 625 μg/mL for B. cinerea .Cinnamon oil with MIC values1250 μg/mL against A. alternanta and B. cinerea and 2500 μg/mL against P.expansum displayed more inhibitory effects than rosemary and marjoram essential oils. In antifungal synergy testing, some double combinations (thyme/rosemary, thyme/cinnamon and cinnamon/marjoram) were found to be synergistic (FICi≤0. 5). The in vivo assay also demonstrated considerable inhibitory effects of EO combination treatments. Results from artificial wounding of trated apple indicated that double combination of thyme/cinnamon (156, 312 μg/mL) has more inhibitory effect than single EO treatments. Although the major components of thyme and cinnamon (especially thymol, carvacrol and cinnamaldehyde) are very important for their antifungal activity, other less-active compounds in rosemary and marjoram (such as α–Pinene, 1.8-cineole, Terpinene-4-ol and γ-Terpinene) play a significant role, as they can strengthen the effects of major components, though synergistic effects have also been observed

The increasing microbial resistance to existing antibiotics has increased the interest in novel antimicrobial compounds. Antimicrobial peptides (AMPs) represent an attractive alternative to classical antibiotics. Lasioglossins are a group of peptides with antimicrobial activity. The inhibitory effects of a recombinant synthetic Lasioglossin, Lasioglossin ɪɪɪ, on five food pathogens (Staphylococcus aureus, Salmonella typhimurium, Enterococcus faecalis, Listeria monocytogenes and Escherichia coli) and its cytotoxicity on the normal cell line was investigated in vitro. The findings showed great antimicrobial function of the peptide. Minimum inhibition concentration and minimum bactericidal concentration of Lasioglossin ɪɪɪ on the pathogens were the range of 3.851-8.625 and 7.703-15.406, respectively. Results indicated Staphylococcus aureus showed the highest sensitivity to Lasioglossin ɪɪɪ. The Lassioglossin demonstrated cytotoxic effect on human embryonic kidney cells in higher concentration (1652 µg/ml) in comparison to MIC and MBC values. The results indicate that this peptide can be competed with common antibiotics in terms of the bactericidal properties.

The purpose of this study was to investigate the effect of different extracting conditions on antioxidant and antimicrobial activity of pimpinella affinis. Samples were extracted by using maceration, ultrasonic assisted method (UAE) and supercritical fluid extraction (SFE). Extraction yield and total phenolic compounds (TPC) of extracts were measured and the antioxidant activity of were analyzed in terms of four concentration (500, 1000, 1500 and 2000 ppm) using DPPH free radical scavenging and betacaroten:linoleate assays. The phenolic compounds fractions were determined using LC-MS system. TPC of extracts ranged between 1502.25 to 1836.69 mg GA/100g E. The results showed that SFE and UAE have highest extraction yield and TPC respectively. The UAE extract has highest antioxidant activity in DPPH free radical scavenging method. Clorogenic acid (13.54%) was the most compound of extract. The results of this study suggest that pimpinella extract due to have phenolic compound have antioxidant and antimicrobial activity and it can be good alternative for synthetic antioxidants.

Lactic acid bacteria, a group of non-spore forming gram-positive microorganisms, in the form of cocci or bacilli which produce lactic acid as a major product of the carbohydrate fermentation. These bacteria produce several compounds such as bacteriocins that exhibit anti bacterial activity against pathogenic and spoilage bacteria which lead to increase the safety and shelf life of food. Lactic acid bacteria especially species of the genus Lactobacillus are an indispensable part of intestinal microbiota in human and animals and were found in most probiotic products. The aim of this study was to isolate and identify the lactobacillus strains from microbiota of six samples of traditional Motal cheese. In order to achieve this objective, out of 180 strains of lactic acid bacteria from Motal cheese, 19 isolates using biochemical confirmed tests were selected as the genus of Lactobacillus, using PCR amplification of 16s rRNA gene sequences methods. Finally,Lactobacillus brevis, Lactobacillus plantarum, Lactobacillus casei and lactobacillus buchneri were found to be 13, 4, 1 and 1 isolates respectively. Determination the potential technological and probiotic characteristics of all isolates in order to introduce their appropriate application are underway.

Biodegradable edible zein microfibers were prepared using acetic acid as solvent. Uniform and beadfree zein fibers could be obtained by changing the solution concentration, the electrospinning voltage, the solution feed rate and the distance between needle tip and collector. The solution concentration at three levels: 22, 26 and 30 w/v %, the electrospinning voltage at three levels: 10, 20 and 30 kV, the solution feed rate at three levels: 4, 8 and 12 ml/h and the distance between needle tip and collector at three levels: 10, 15 and 20 cm were studied. Central composite design (CCD) was utilized to study the effect of electrospinning parameters of zein solution and the data were analyzed using response surface methodology (RSM). According to results of this research, the solution concentration had significant influence (P

In this study¡ the effect of prebiotic compounds (Inulin and wheat fibers) and fat (0%¡ 2% and 3.5%) on viability of Lactobacillus casei in symbiotic yogurt¡ its physicochemical properties¡ proteolysis¡ inhibition of angiotensin I-converting enzyme (ACE- inhibitory) and antioxidant activity during 21 days storage at 5±1 ºC was investigated. According to the results¡ adding prebiotic compounds significantly increased water holding capacity¡ proteolysis and ACE inhibitory of all treatments (P

There is a global interest to study lactic acid bacteria (LAB) of artisanal fermented products like yoghurt for improving or replacing current strains used in commercial starter cultures. In this work, five traditional yoghurt samples were collected from different areas of Khorasan-e-Razavi. Grouping and identification of isolates were carried out on the basis of physiological and biochemical tests (nonmolecular),as well as ARDRA technique and sequencing (molecular methods). Totally, 71 isolates including 33 Streptococcus thermophilus, 30 Lactobacillus delbrueckii (subsp. Bulgaricus and lactis), were identified as dominant strains in all yoghurt samples. Also 8 other isolates belonging to Lactobacillus helveticus, Pediococcus pentosaceus and Weissella cibaria were observed. Results of this research show the diversity of LAB population in collected samples.

One of the most important aspects of food preservation is controlling the growth of microorganisms, which if overlooked it leads to uncontrolled growth of microorganisms associated with food spoilage and food poisoning. Microbial contamination of foods is important because of pathogens are capable to transfer to foods during the processing, distribution, and storage. Escherichia coli and Bacillus cereus can cause spoilage in food; intake food contains plenty of bacteria and toxic. Therefore it is important to eliminate or control these bacteria safely. Ultraviolet (UV) radiation is considered as non-ionizing radiation and the first time in 1940 was used as a method for infection elimination in air. This approach nowadays is widely used for controlling microbial growth and as disinfection in food industry. Wavelength range of ultraviolet radiation is approximately 328-210 nm. The beam is naturally present in the sunlight. The bactericidal effect of UV irradiation depends on the type of bacteria, the distance, and dose of radiation. The most cytotoxic effect of UV irradiation is obtained at the wavelength of 260 nm, which corresponds to the intense absorption of energy by organic bases in the nucleic acid. UV irradiation causes radicals generation, which subsequently attack the nucleic acid and develop mutations in their genomes and gene transcription and translation processes. In this study, the antibacterial effect of different exposure times of ultraviolet radiation on the growth of E. coli and B. cereus was evaluated.

All media used in this study was procured from Merck Company. Ultraviolet device (Camag, USA) was used at wavelength of 254 nm, Nr= 29000, Amp= 0.25. B. cereus isolation: 1 mL of different dilutions of rice (0.1, 0.01, and 0.001) was transferred to Brain-heart infusion (BHI) and it was incubated at 32 °C for 24 h. A loop containing the bacteria was then transferred to Mannitol Egg Yolk Polymyxin (MYP) agar and it was incubated at 35 °C for 24 h. B. cereus produce big and round colonies, with a halo around the colonies. Starch test was carried out as confirming test for B. cereus colonies. Briefly, some colonies of B. cereus were added to test tube with sterile distilled water containing starch and a few drops of lugol. Development of blue color indicates the presence of B. cereus due to starch hydrolysis. E. coli isolation: E. coli was isolated from raw milk following the method described by Kargar et al. (2005). Briefly, raw milk was first homogenized; 0.1 ml of each dilution of homogenized raw milk was inoculated on Escherichia coli broth medium containing 20 mg novobiocin. E. coli was then isolated after transferring the former media on EMB specific culture and incubation at 36 °C for 24 h. After confirming colonies by Durham tube and complementary tests, pure cultures were obtained from them by streak-plate method. UV irradiation: A loop of E. coli colonies was transferred to nutrient broth and it was treated with UV beam (254 nm) at three times (40, 60, and 80 s). After preparing dilution of 0.0001 for each of the treatments and incubating for 24 h, survival curve was plotted. These operations were also carried out on B. ceruse colonies. A control sample also was considered for each examined bacterium.

Rate of Bacillus cereus growth was reduced under UV radiation. As it is shown, Death curve of E. coli, E. coli count was decreased by increasing the time of UV radiation, so that count of this bacteria reached to about zero after UV radiation for 80 s. However, reduction of B. cereus count was less than E. coli count at same wavelength (254 nm) and time of irradiation. This revealed that B. cereus have more resistance to UV radiation compared to E. coli. These results were consistent to observation of Sharp (1940) who evaluate the effects of UV light on bacteria suspended in air and reported that required energy for air sterilization containing B. cereus is more than twice the energy is needed to eliminate E. coli. UV light more penetrates to cell wall of Gram-negative bacteria compared to Gram-positive bacteria due to having a small amount of peptidoglycan in the cell wall and caused mutations in regulating genes of transcription and translation.

The efficiency of the two main processes of cell is reduced in the presence of UV irradiation and leads to growth reduction and death. The more resistance of B. cereus can be for several reasons, such as having a thicker cell wall compared to E. coli, and the capability to produce spore, and the capability to proofing mutations.