فصلنامه دنیای میکروب ها
سال پنجم شماره 3 (پیاپی 13، پاییز و زمستان 1391)

Botulism is a food poisoning problem in which the transmission of neuromuscular stimuli is disrupted due to the activity of botulinum neurotoxins (BoNT) produced by Clostridium botulinum. The botulinum neurotoxins are the most known toxic substances that cause flaccid paralysis due to preventing the release of the neurotransmitter acetylcholine at neuromuscular junctions. The aim of this study was cloning the heavy chain (HC) domain of Clostridium botulinum neurotoxin gene in E. coli as a gene vaccine candidate. In this study, the heavy chain of neurotoxin of Clostridium botulinum was fully amplified based on PCR and the specific primers. DNA fragment of heavy chain of neurotoxin gene was cloned by T/A cloning technique in PCR 8/GW/TOPO vector and the clone was transformed into E. coli. Cloning of 2530 bp of neurotoxin was confirmed by PCR. The results of next step showed that the heavy chain of Clostridium botulinum neurotoxin was successfully cloned in       E. coli . Final confirmation of construct was done by BamHI and HindIII restriction enzymes. According to the results, the amplified gene can be used as a target for gene vaccines against botulism in the future.

Many bacteria utilize quorum sensing mechanism in order to coordinate their vital functions such as survival, motility, production of biofilm, pathogenicity factors, etc. Interfering with the complicated cell-to-cell communication system paralyses bacterial calls to perform their different indigenous functions like pathogenicity. In this study interfering effects of two distinguished plant extracts, whitetop and dill, on bacterial quorum sensing of Chromobacterium violaceum CV026 was evaluated. Whitetop and dill plant species were collected from the surrounding agricultural areas and commercial fields of Urmia City. The collected plants were extracted using three organic solvents, 96% ethanol, n-hexane and methanol. The Antimicrobial susceptibility and anti-quorum sensing bioassays were then performed to find out their bactericidal property and depletion of violacein, respectively. Furthermore, the assays regarding pathogenicity suppression using anti-quorum sensing activity and acyl homoserine lactone induction through Pectobacterium carotovorum subsp. carotovorum strain were carried out. Based on the results, both of the plant extracts possess meaningful anti-QS activities; however, the proportion of the activity in whitetop was fewer than dill. Furthermore, the aforementioned plant extracts had bactericidal activity in which whitetop had more proportion in comparison to dill. Due to decrease in the production level of violacein by CV026 as a result of the anti-quorum sensing activity of whitetop and dill extracts, application of the extracts can be considered as an appropriate approach for controlling bacterial pathogens without developing resistance.

Most Enterohemorrhagic E. coli O157:H7 strains are able to adhere to Vero cell line tightly and produce shiga toxin. The aim of this study was to develop a probiotic in vitro model for protection against E. coli O157:H7.

This study was performed experimentally on probiotic Bifidobacterium and shigatoxinogen E.coli O157:H7 in Vero cell line monolayers. The probiotic bacterium first was grown in MRS media and then was transferred into the vero cell line-containing wells. After incubation, the cells were first exposed to three different treatments (pure stx1, stx2, a mix of stx1and stx2) and then were treated with E. coli O157:H7 bacterial culture. After 24 h incubation at 37° C in CO2 incubator, the cell changes were observed by invert microscope.

The vero cell lines pre-treated with probiotic bacterium responded differently to the doses of used Shiga-toxin and E. coli O157:H7. When the cells were treated with only toxin or E. coli O157:H7, there was a intensive amounts of cell cytotoxicity. However, pre-treatment with prebiotic bacterium decrease significantly the toxicity caused by E. coli O157:H7. The survival rates of the Vero cells treated with probiotic ranged between 80% and 100% compared with controls.  

Based on the results of this study, the probiotic bacteria and the supernatant prepared from their culture decrease the cell toxicity effects of shiga-toxin and E. coli O157:H7. Therefore, the probiotic bacteria can be used as an alive vaccine in food industry in order to prevent and treatment of infections.

Today hydrocarbon pollution is the most important environmental problem. Biological methods can play an important role in removing these contaminants to the environment. This study was aimed to isolate aliphatic compounds degrading bacteria and identify the best degrading strain. Sampling of waste oil depot took in the city of Kerman, Tehran and hydrocarbon-contaminated soils. Alkane degrading bacteria were isolated by using enrichment Bushnel-Hass medium containing hexadecane (as source carbon). In order to identify superior strains, a part of 16SrDNA gene was amplified by PCR and then sequenced. Also, the presence of alkane’s hydroxylase gene in these strains was confirmed by using specific primers. A total of fifteen alakne degrading bacteria were isolated which 8 strains were selected as superior strains. These strains belonged to the genus of Rhodococcus jostii,Stenotrophomonas maltophilia strain M2, Achromobacter piechaudii, Tsukamurell atyrosinosolvens, Pseudomonas fluorescens, Rhodococcus erythropolis,Stenotrophomonas maltophilia strain Q1, Pseudomonas aeruginosa. In this study, the highest growth rate of strians was in concentrations 2.5 percent of hexadecane and the lowest was found in 7 percent. Also, all of the strains have alkane hydroxylase gene. Our results indicated that threre is a high diversity of degradative bacteria in Iran ecosystem and their ability to degrade petroleum wastewater. So, with a proper management of these bacteria can be used to minimize pollution caused by waste oil industries.

Rhizoctonia canker, caused by Rhizoctonia solani, is found in growing potato fields. Since there is no commercial resistance cultivar, the tubers are sterilized with systemic fungicides. However, because of environmental damages, scientist attempts to replace the chemical agent with the most environmentally friendly compounds. This study was aimed to evaluate antifungal activity of five medical herbs against Rhizoctonia solani. The study aimed to investigate antifungal effects of five native plants (Satureja bachtiarica, Zataria Multifera, Achillea millefolium, Ziziphora clinopodioides and Thymus daenensis) on Rhizoctonia canker. After collection of the plants from Chaharmahal and Bakhtiari Province, they were cleaned (washing and drying) and extracted by ethanol 80%. The antifungal activity was then evaluated using disc diffusion method. The most of extractions showed desirable antifungal effects against Rhizoctonia solani. The widest (18.93 mm) and narrowest (6.66 mm) inhibition hallows were observed when Rhizoctonia solani were exposed to the disks containing extracts of Zataria Multifera and Ziziphora clinopodioides, respectively. According to the results, the extracts isolated from the aforementioned plants are able to inhibit the growth of pathogenic Rhizoctonia solani.

Nowadays, Shrimp culture has been prevailed in most of tropical countries; however, a variety of diseases have currently affected the business worldwide. Infectious bacterial agents are the most significant hygienic problems observed in the cultured shrimps . This study was aimed to isolate and identify microflora of farm ponds and western white shrimp gastrointestinal tract (Litopenaeus vannamei) in the Bushehr Province farm ponds and their survey as probiotic. The shrimp and pond water samples were collected from 10 farm ponds (located at Bushehr Province). After transferring the samples to laboratory, the shrimp samples were autopsied to access to their intestinal microflora. The isolated bacteria were identified based on biochemical tests, morphology and Biolog software. Antibacterial activities of the isolates against 6 common pathogenic bacteria in shrimps were then investigated using well diffusion and disk diffusion methods. Overall, 12 bacterial genera were isolated from the farm ponds and shrimp gastrointestinal tract. The majority of bacterial species most abundantly isolated were Bacillus, Vibrio and Pseudomonas. Among the isolated bacteria, Bacillus, Micrococcus and Corynebacterium showed the most antibacterial activity against evaluated pathogenic bacteria. Almost all the isolated bacteria from shrimp gastrointestinal tract were found in farm ponds as well. The bacterium Bacillus sp., for instance, is able to inhibit the growth of pathogens through secreting antimicrobial products.