Aim and Background: Paraffins are high molecular weight hydrocarbons and in the reservoir, under high- temperature/pressure conditions remain in a state of equilibrium. However, as the crude oil is pumped out to the surface, temperature and pressure are reduced. Below the cloud point, the paraffinic hydrocarbons precipitate out of the crude oil and form deposits on the oil production systems. This problems are usually mitigated by thermal fluid treatments, pigging or using chemicals and solvents.While most of these remedies are in use, they have certain disadvantages.Moreover, these remedial options are expensive. A microbial intervention to prevent paraffin deposition, is a non hazardous and economically viable approach. This investigation was aimed at finding a bacterial strain that being able to effectively degrade tetracosane .

Materials and Methods :Soil samples were collected from oil contaminated soil near Tehran refinery. Samples were transferred into 40 ml sterile mineral salts medium containing tetracosane as the sole source of carbon and energy. By a multi step enrichment and screening technique a bacterium was isolated and by morphological characteristics, biochemical tests and phylogenetic methods, it was identified as the Mycobacterium genus.

Results: This strain was able to use tetracosane as the sole source of carbon and energy. Our results showed the selected strain grow well in pH range of 4-9 and temperature range of 30 - 40 °C with optimal growth at 35°C, had an acceptable growth at 5% NaCl and was able to degrade 80 percent of the tetracosane within 24 days.

Conclusion: According to the rate of tetracosane decomposition by this bacteria under conditions listed , its application can be profitable in preventing paraffin deposition. Further investigation in physical model is required to confirm the ability of the strain in wax deposit mitigation from oil wells.

Aim and back ground: In recent years the threat of acquisition of antibiotics resistance caused by over use of antibiotics is growing. The purpose of this study was to survey the pattern of antibiotic resistance and evaluate of Multi-drug resistance Escherichia coli and analyze the plasmid profile of these clinical strains.

Materials and Methods: This study was performed on 83 clinical Escherichia coli, obtained from four hospital (imam Khomeini, Alborz, Kasra, qaem) and two private laboratories (Razi and Kavosh), of Karaj city. Isolates were identified as Escherichia coli based on standard biochemical tests. The isolates were screened for Antimicrobial susceptibility test by 20 antibiotics using Kirby-Bauer disk diffusion method. Plasmid profiles of these isolates have been analyzed by alkaline lysis method.

Result: Antibiotic resistance pattern were observed as follows: Nitrofurantoin 8.4%, Tetracycline 63.8%, Amoxicillin 83%, Ofloxacin 30%, Levofloxacin 30%, Co-trimoxazole 59%, Amikacin 18%, Imipenem 25.3%, Choloramphenicol 16.9%, Cephalexin 61.4%, Gentamycin 28.2%, Norfloxacin 33.7%, Nalidixic acid 56.6%, Cephalothin 48.2%, Ciprofloxacin 32.5%, Ceftazidime 27.7%, Ceftriaxone 37.3%, Ceftizoxime 16.9%, Cefotaxime 38.5%, Amoxycillin/Clavulanic acid 68.7%. Of 83 isolates 92.77% (77) isolates were resistance to more than two unrelated drugs. Of 83 isolates, 65 isolates, (78.3%) showed the presence of plasmid.

Conclusion: The results of this study indicate a growing resistance pattern to the first line antibiotics, prescribed for urinary tract infection. High presence of plasmids in these strains, play an important role in multidrug resistance in these bacteria.