Jundishapur Journal of Microbiology
Volume:6 Issue: 3, May 2013

Analysis and applications of lesser known underutilized seed oils are important, since there is little or no information on their composition and uses, most of them are discarded as waste every year. The present work reports the antibacterial activities of diethanolamides (nonionic surfactant) and sulphated diethanolamide (anionic surfactant) synthesized from the seed oil of Citrullus lanatus. Diethanolamide biosurfactant was produced from the oil via transamidation reaction using sodium methoxide as catalyst while the diethanolamide was sulphated using chlorosulphonic acid. The conversion of the oil to the biosurfactants was monitored using FTIR spectrophotometer. The iodine and saponification values of Citrullus lanatus oil were 118.50 ± 0.80 g iodine/100g and 199.10 ± 2.40 mgKOH/g respectively. Linoleic acid (56.9 %) was reported to be the most abundant fatty acid in Citrullus lanatus oil. The biosurfactants inhibited the growth of organisms such as Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumonia and Escherichia coli with diethanolamide biosurfactant exhibiting better antibacterial activity than sulphated diethanolamide.

One of the most important causes of complications and mortality in medical centers are nosocomial infections. Disinfection of hospital surfaces is essential element for ensuring that infectious agents are not transmitted to patients. Alcoholbased and chlorine-based disinfectants have unfavorable properties. Given that the antimicrobial effect of heavy metals such as silver is recognized as a viable option for eliminating bacteria, the exploration of nanotechnology in this context has been described in this study. Nanotechnology uses both science and technology to produce new materials with nano-scales. The effect of silver nanoparticles on some common hospital bacteria has been studied in this research. Patients and We have selected nine patient's metal file covers and following sterilizing, we have infected them with one of these bacteria; Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus. Then, the infected surfaces have been disinfected with different dilutions of silver nanoparticles. Sampling and culturing has done following four specific intervals. Afterwards, the colonies that developed have been counted and compared. All of the three dilutions of silver nanoparticles could bring the colony count out of 7.5x106 to less than 100 which indicate more than a 99 percent reduction. No remarkable difference of the three dilutions of disinfectants was observed in reducing the colony count in 5,15, 30 and 60 minute disinfection intervals (P value > 0.05). The effect of constant dilution of silver nanoparticles on the reduction of organisms varied in response to the time of disinfection (P value < 0. 05). Silver nanoparticles had appropriate effects in all three types of dilutions and allowing for a more protracted contact time has given significantly better results.

Acinetobacter species, specially, Acinetobacter baumannii, is known, as an important opportunistic pathogen, with a variety of infections such as pneumonia, bacteraemia, meningitis, urinary tract, skin and soft tissue infections, associated with high mortality. High prevalence of multidrug resistance in A. baumannii, limits our therapeutic choices in the treatment of infections caused by this bacterium. The current study aimed to determine in vitro activity of tigecycline and colistin against clinical isolates of MDR A. baumannii, from patients admitted in ICUs Tehran hospitals. This study was conducted from March 2009 to November 2010, on a total of 91 Acinetobacter species isolated from clinical specimens in ICUs. All isolates were subjected to PCR to detect blaOXA-51 like gene that is unique to A. baumannii. The antimicrobial susceptibility for 13 different antibiotics was tested. A. baumannii (blaOXA-51-like gene) was detected in 84 (92.30%) isolates.Resistance rates in A. baumannii, were found to be for Imipenem 50 (59.52%), Gentamicin 65 (77.38%), Ciprofloxacin 81 (96.42%), Amikacin 44 (52.38%), Cefotaxime 81 (96.42%), Cefepime 69 (82.14%), Ceftazidim 81 (96.42%), Meropenem 74 (88.09%), Trimethoprim - sulfamethoxazole 78 (92.85%), Aztreonam 82 (97.61%), Colistin and Polymyxin-B 0%. No interpretive criteria have been approved for tigecycline against Acinetobacter spp. so; the results were interpreted by the criteria recommended by Jones, and US FDA for Enterobacteriaceae. Resistance rates for tigecycline were 3 (3.57%) (Jones criteria) and 19 (22.61%) (FDA criteria). It is clear that new antimicrobials are needed to treat MDR A. baumannii. Polymyxins and tigecycline are among the few antibiotics available to treat infections with these bacteria but little was known about the antimicrobial activity of these agents. The Present study provided valuable information about the effects of the above mentioned drugs that can be used for health policy. It should be noted that there is a need for regular surveillance of bacterial resistance to these antimicrobial agents.

Bedsore is one of the major problems in all the societies as patients are confined to bed. Due to antibiotic resistant strains being a significant obstacle for cure, many plants and herbs are being used by researchers as medicinal compounds. The investigation of synergistic effect of cellulose biopolymer and Papaver macrostomum extract on bedsores bacterial community. Acetobacter xylinum PTTC 1734 was cultured in Schramm-Hestrin (SH) medium and incubated at 30°C for 24-48 hours. NaOH treatment and absolute ethanol were used to extract cellulose biopolymer and plant antimicrobial substance, respectively. The Biopolymer structure was scanned by a Scanning electron microscope (SEM). Antimicrobial activities, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) of these extracts were all determined separately. The effective concentration of each extract's alone, combined, and synergistic effects were evaluated. Biopolymer absorption efficiency was assayed as the absorbent bed. Pesudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus were the dominate bacteria isolated from bedsore samples. Antimicrobial effects of cellulose, P. macrostomum extract, and the combination of both were determined on the isolated bacteria as 1, 10, and 15 mm respectively. 100-1000μl/mL of flower ethanol extract concentrations of P. macrostomum indicated the maximum effect on mixed bedsore's bacteria rather than leaf and mixed extraction. Concentrations 500 1000μl/mL decreased the bacterial bedsore's growth and completely inhibited it. 3.5g/L of cellulose biopolymer was obtained from A. xylinum broth culture medium. Scanning electron microscopy analysis confirmed the branched structure of this polymer. Cellulose absorption efficiency was evaluated to be 14.5ml/g in this investigation. Because of high-absorbance of bio-cellulose, combined plant extraction with this biopolymer caused a decrease in the growth of bedsore microorganisms with the minimum extract concentration, 100μl. Combination of bio-cellulose and P. macrostomum flower ethanol extract can be used for patients who suffer from bedsore lesions in concentration 0.1% of MBCs. Furthermore, clinical studies are needed to confirm the efficiency of in vivo application.

Light and photosensitizers affectthe survival of bacteria in natural environments. Also light and photosensitizers are used for disinfection of materials such as blood, blood products, and water. The present study was aimed toinvestigate the effect of different wavelengths of visible light and UV-A on the synthesis of some oxidative stress enzymes of Escherichia coli (E. coli) in seawater. Seawater were filtered by using Whatmann No:1 filter paper, followed by sterilization in the autoclave. The E. coli W3110 strain was grown at 37 oC, centrifuged, and transferred in seawater, then methylene blue was added to the seawater samples, with the exception of control samples. The seawater samples were incubated with white, blue, green, red, and UV-A light sources. Cell extracts were prepared by sonication, and then catalase, superoxide dismutase (SOD), glutathion peroxidase(GP),and glucose-6- phosphate dehydrogenase(G-6-PD) activities were measured. It was found that in all studied wavelengths with or without Methylene Blue (MB), the level of all studied enzymes decreased remarkably when compared to dark controls. It was observed that the synthesis level of SOD, glutathione peroxidase GP, and glucose 6 phosphate dehydrogenase G-6-PD in E. coli decreased significantly in red light with respect to white, blue, and green light in seawater, to which methylene blue was added. In E. coli the decrease was 13% of G-6-PD expression, 10% of GP expression, and 17% of SOD expression in red light with MB after 16-hour incubation in seawater; however, these enzymes decreased to 45%, 84%,and 71% in white light, 33%, 47%, and 54% in blue light, 53%, 53%,and 64% in green light at the same incubation hours, respectively. Also, the enzyme acitivity in red light without MB did not show a significant difference when compared to other light sources. It was shown in the present study that red light among visible light sources has a crucial effect in decreasing the oxidative stress enzymes in seawater containing MB.

One disadvantage of expressing heterologous proteins in Escherichia coli is that the proteins are frequently expressed as insoluble inclusion bodies. To avoid this problem, heterologous proteins are typically expressed as a fusion protein. Maltose binding protein (MBP) is one of the widely used partners for production of recombinant fusion proteins in E. coli. MBP is among the most effective solubility enhancers. In addition, MBP can be used as an affinity tag for purification of recombinant proteins on a column of amylose resin. The purpose of this study was to investigate the use of rice flour, a natural source of amylose, for purification of MBP fusion proteins. MBP and a fusion protein of MBP and avian influenza virus nucleoprotein (MBP-NP) were expressed in E. coli and subjected to purification by rice flour and a commercial amylose resin. The purified proteins were analyzed by SDS-PAGE. The results indicated that MBP and MBP NP, both were successfully purified by rice flour. Rice flour can be used for purification of MBP fusion proteins. Although the efficiency of purification by rice flour is less than amylose resin, however, the yield is sufficient to obtain a quantity of protein required for research purposes.

Mycobacterium tuberculosis has the ability to invade type II alveolar epithelial cells. As a result, the associations between invasion of alveolar epithelial cells and pathogenesis of lung infection seem strong. The current study aimed to evaluate the presence of M. tuberculosis in patients with lung cancer. Patients and This cross-sectional study was performed on samples collected from 380 patients with lung cancer who referred to two state-run hospitals in Mashhad, Iran. Microscopic and cultural methods were utilized to assess the presence of M. tuberculosis in the patients` specimens. The subjects included 252 (66.3%) males and 128 (33.7%) females. Based on cultural and microscopic methods, M. tuberculosis infection was observed in twenty six (6.8%) of cases. Results of the current study showed the high prevalence of M. tuberculosis among the patients with lung cancer; therefore, it seems that continuous surveillance is essential to monitor the M. tuberculosis in the patients with lung cancer.

Helicobacter pylori is responsible for one of the most common human infections and is a major risk factor for stomach ulcer disease and gastric cancer. H. pylori infection has been reported to be associated with generation and development of coronary artery disease (CAD). Moreover, diabetic patients positive for H. pylori infection showed a higher prevalence of CAD compared to H. pylori-negative patients. The main association between H. pylori infection and CAD seems to be generation of chronic low-grade inflammation. The current study aimed toinvestigate H. pylori’s capability to induce low-grade inflammation in the host; therefore H. pylori was compared to Escherichia coli E. coli in its ability to activate neutrophils. Furthermore, H. pylori’s capability to induce apoptosis in peripheral blood lymphocytes was studied. Peripheral blood neutrophils were treated with bacterial cells and the expression of the integrin CD11b that is critical for neutrophils adhesion, migration, and immune functions was assessed by flow cytometry. Additionally, peripheral blood lymphocytes were treated with H. pylori or E. coli then bacterial-induced apoptosis was examined by Annexin-V and Propidium Iodide (PI) staining. The obtained data showed that C 11b expression on cells treated with H. pylori was significantly lower than cells treated with E. coli. Furthermore, H. pylori induced apoptosis in lymphocytes significantly more than E. coli. Diminished neutrophilic activation along with enhanced lymphocytic apoptosis could explain enhanced predisposition to CAD through induced chronic low-grade inflammation.

Brucellosis is the most common global zoonosis and an important public health problem in many parts of the world including Iran. Diagnosis of brucellosis is frequently difficult to establish and conventional methods are not always successful in identifying the organisms. Rapid detection of Brucella species by an automated blood culture system and Polymerase Chain Reaction (PCR) may lead to an earlier diagnosis and may improve patient management. The current study aimed to evaluate PCR technique as a diagnostic tool for brucellosis in comparison to conventional bacteriological techniques. A total of 50 patients suspected to have brucellosis were included in this study. All patients presented clinical signs compatible with brucellosis. Diagnosis was established by detecting a titer equal to or greater than 1:160 by the standard tube agglutination (STA) method. Blood samples and sera from the patients were tested by culture using BACTEC 9050 system and PCR using primer set to amplify a 223 bp region with in the gene coding for a 31 KD Brucella antigen. Eleven 22%) whole blood samples and 17 (34%) serum samples out of 50 had positive PCR and 7 (14%) patients had Brucella species grown in their cultures. Out of 43 blood culture negative samples, 10 (23.3 %) were positive with the serum PCR versus in 4(9.3 %) with whole blood PCR. The results suggest that the serum PCR assay is rapid and easy to perform and highly sensitive and specific, and it may therefore be considered a useful tool for diagnosis of human brucellosis.

Although the number of infectious diseases has sharply decreased in last few decades, parasitic diseases persist in developing countries. On the other hand, chronic psychiatric patients tend to have low self-control, poor personal hygiene, long term institutionalization and extremely low self-care should be monitored for parasitic diseases since psychosocial conditions can contribute to an affinity for infectious diseases. The aim of study was to investigate intestinal parasites in chronic psychiatric patients. Patients and In this cross-sectional study, all chronic psychiatric patients from Sina Hospital of Shahre-Kord University of Medical Sciences were recruited from April to November 2010. From each patient, 3 stool samples were collected every other day. Samples were transferred to Department of Parasitology of Faculty of Medicine and were examined by wet direct smear, Ziehl-Neelsen and Rayan blue trichrome stains. Direct smear was examined microscopically by performing a standard direct smear using normal saline (0.85%) and Iodine solution (Lugol). Stools were stained by Ziehl-Neelsen and Rayan blue trichrome in order to investigate Cryptosporidium and Microsporidia respectively. Forty-seven patients (72%) were male and 18 (28%) were female.The minimum time of institution was 2 months and the longest period of incarceration was 152 months. The mean of hospitalization duration was 94.7 months. Forty-four cases (68%) of participants were infected with intestinal parasites.The most frequent parasites were Blastocystis hominis in 15 cases (23%) followed by Microsporidia in 12 cases (18.5%), Giardia lamblia in 7 cases (11%), Isospora in 5 cases (8%) and Cryptosporidium in 4 cases 6.2%), respectively. Opportunistic protozoan parasites such as Microsporidia, Isospora and Cryptosporidium should be considered as a potential pathogen in this setting and more health care should be given to this specific group.

Toluene is a cyclic aromatic hydrocarbon which is widely used as an industrial feedstock and as a solvent. It is one of the major parts of pollution in oil-contaminated environments. The main aim of this study was to isolate and characterize a Bacterium with high potential application in toluene bioremediation. To isolate a toluene-degrading Bacterium, several seawater and wastewater samples were added to toluene-containing basal salt media (BSM). The isolate was identified by morphological features, biochemical tests, and molecular characterization. Also, physiological characteristics of the isolated strain were determined. The isolate represented the capability of growing on toluene under both aerobic and anaerobic conditions. Moreover, this Bacterium could also use different toxic compounds as the sole sources of carbon and energy. Sequence analysis of 16S rDNA showed that the isolated strain was closely related to Uncultured Bacterium clone A1-E3_M13R 98%) and was submitted as Bacterium Ex-DG74 in NCBI. Bacterium Ex-DG74 showed a tolerance to organic solvent and saline conditions as it could grow in the medium containing over 15% toluene (v/v) and NaCl (w/v), and degraded 79% and 45% of toluene (1% (v/v)) in aerobic and anaerobic conditions, respectively. In this investigation we succeeded to isolate a novel toluene-degrading Bacterium from wastewater. This isolated strain could be considered as a biological material for the toluene bioremediation.

Brucellosis is prevalent in the Mediterranean basin, the Indian subcontinent, the Arabian peninsula, and in parts of Central Asia, Africa, Central and South America. However it continues to be one of the major health problems in developing countries, including Turkey. The current study aimed to determine the incidence of brucellosis, which is previewed to be very common in the northeastern region of Turkey, in order to emphasize the problem. Seroprevalence of brucellosis was examined in sera of 2913 patients who referred to Igdır State Hospital between February and December of the year 2010 by Standard Tube Agglutination Test method. Results were statistically evaluated using chi-square trend analysis method. Significantly high level (1/40 dilution) of specific antibodies were detected in 525 (18 %) patient sera (P = 0.111). We hope that Turkey will be one of the brucellosis-free countries in near future with highlights from the current and further studies.

Hepatitis C virus (HCV) is the main cause of infection that has the potential to cause chronic liver disease. Injecting drug users (IDUs) have a key role in HCV transmission in Iran. Knowledge of the distribution of various genotypes is essential for successful future research and control strategies. The aim of this study was to identify HCV genotypes among chronic infected injecting drug users (IDUs) in Tehran, Iran. Patients and In this cross sectional study, we investigated HCV genotypes among 36 plasma samples from HCV infected IDUs (35 male and 1female, mean age: 33.67, and age range 20-62 years), referred to Research Center of Iranian Blood Transfusion Organization(IBTO) in Tehran from December 2008 to March 2009.HCV Genotyping was performed using type-specific primers. Genotypes 3a, 1a and 1b were found in 58.3 %, 25% and 16.7 % patients, respectively. Our study demonstrated the high prevalence of genotype 3a among injecting drug users, which is also found in Europe and United states.

Toxoplasma gondii is a worldwide parasite which infects animals and human. Infections with this zoonotic parasite are acquired mostly by consumption of undercooked or raw meat, which contains tissue cysts. The current study was conducted to determine the seroprevalence of Toxoplasma infection in farm animals in southern Iran. Sera were obtained from 346 farm animals including 80 cows, 33 dogs, 35 horses, 95 sheep, 90 goats, 9 turkeys and 4 geese and evaluated by Modified Agglutination Test (MAT) to detect anti Toxoplasma antibodies. Anti-Toxoplasma antibodies were detected in sera of 121 out of 346 (34.9%) animals. The highest rate of infection (55%) was found in the cattle, followed by dogs (51.5%), horses (40%), sheep (29.5%), goats 18.8%) and turkeys (11.1%). No antibody was detected in any sera of 4 geese. Most of animals (86%) had antibody titer of 1:20. Males consisted 34.3% and females 40% of seropositive animals but the difference was not statistically significant (P > 0.05). Correlation between age of animals and Toxoplasma infection was also insignificant (P > 0.05). High seroprevalence of toxoplasmosis observed in this region indicates that farm animals may play a major role in transmitting the infection to human through consumption of undercooked meats.

Pseudomonas aeruginosa possesses a polar flagellum made up of flagellar subunits, which are encoded by fliC gene. Flagella have important roles in the motility, chemotaxis, and establishment of P. aeruginosa in the acute phase of infections. The inhibition of flagellar expression may be a promising therapeutic approach to prevent the pathogenesis. The gene-silencing effect of siRNA may be useful for this strategy. The current study investigated the efficacy of siRNA on the expression of flagellin, because it is an important protein in the initial stages of P. aeruginosa infections. The current research designed and synthesized 21 bp siRNA duplexes against P. aeruginosa flagella. Quantitative RT–PCR was performed to determine whether the siRNAs inhibit the expression of the flagellin mRNA in vitro. The efficacy of siRNA was determined by the motility test and in a murine model of hematogenous pulmonary infection. In quantitative RT–PCR,it was shown that the siRNA significantly inhibited the expression of the flagella mRNA. FilC gene knockdown by the siRNA resulted in a significant decrease in the expression of the flagellar mRNA in the siRNA group as compared with that of the control (P < 0.05). In the motility test,the motility was inhibited in the siRNA group more effectively than in the control group. In the murine infection model, a significant decrease in the number of viable bacteria was detected in the siRNA group when compared with the control (7.87 ± 0.54 in the former versus 4.69 ± 0.35 log cfu/mL in the latter mean ± SD, P < 0.05). The development of delivery systems into bacteria with an efficacy compatible to that in human use could be a key for the potential utility of siRNA for the prophylaxis and treatment of P. aeruginosa-induced hematogenous pulmonary infections in humans.

Giardia lamblia is an enteric protozoan parasite, which infects human and a wide range of vertebrate hosts. The aim of this study was to investigate genotypes of G. lamblia from children fecal samples in Ahvaz, South West of Iran by PCR-RFLP method. Fecal samples were collected from 58 children who were positive for G. lamblia. DNA extractions were performed by QIAamp Stool Mini Kit. DNA were evaluated by semi nested PCR-RFLP assay, targeting the glutamate dehydrogenase (gdh) gene, which was used to distinguish within and between genotypes A and B. Fifty samples (86%) were confirmed by semi-nested PCR. Genotype analysis among 50 isolates indicated 5 (10%) and 8 (16%) assemblages AII and B, respectively. Mixed Infections with both assemblages AII and B were also detected in 37 (74%) cases. Current study indicated the molecular characterization of G. lamblia in southwest of Iran. Postulated sources of contamination by accidental discharge of sewage effluent and faecal contamination from animals may contribute to this high rate of mixed infection in the current study. Further studies are needed to underestand the source and route of infection better.

Listeria monocytogenes causes listeriosis characterized by encephalitis, septicaemia, and abortion or stillbirth. Its traditional diagnosis is based on serological responses, whileseveral molecular methods have been developed for safer and more rapid, sensitive, and accurate detection.The epidemiology, prevalence, shedding routes, and antibiotic resistance properties of L. monocytogenes are essentially unknown in various animals species. The present study was performed to study the shedding routes, and antibiotic resistance properties of L. monocytogenes isolated from milk, feces, urine, and vaginal secretion of bovine, ovine, caprine, buffalo, and camel in Iran. A total of 596 milk, 619 feces, 443 vaginal swab, and 522 urine samples were collected from various animal species. Samples were examined by culture, conventional and real-time PCR for evaluating the presence of L. monocytogenes. Finally antimicrobial resistance properties were studied using the simple disc diffusion method. The culture method showed that 186 of 2180 samples (8.53%) had positive results for L. monocytogenes. In total,61 (10.23%) milk, 40 (6.46%) feces, 43 (9.7%) vaginal swab, and 48 (9.19%) urine samples had positive results for L. monocytogenes using conventional PCR. After the Light Cycler real-time PCR it was recognized that 69 (11.57%) milk, 48 (7.75%) feces, 53 (11.96%) vaginal swab and 57 (10.91%) urine samples hadpositive results for the presence of L. monocytogenes. The sensitivity and specificity of conventional and real-time PCR were 94% and 99.1%, and 100% and 97.9%, respectively. L. monocytogenes had the highest shedding in bovine milk (10.83%), ovine urine (16.98%), caprine feces (14.38%), buffalo milk (11.11%), and camel vaginal secretion (15.18%). Antibiotic resistance to tetracycline (71.3%) was the highest, while the resistance to nitrofurantoin (5.72%) had the lowest frequency. Shedding of L. monocytogenes in different animal species, and different samples are different. Due to antibiotic resistance, especially in L. monocytogenes, veterinarians should pay more attention to prescribe antibiotics. We recommend using the real-time PCR for safe, sensitive, and rapid detection of L. monocytogenes in clinical samples, and using the disk diffusion methods to prescribe suitable antibiotics.

Pneumocystis jirovecii (formerly known as P. carinii) is one of the most opportunistic agents, which frequently leads to hospitalization and death in immunocompromised patients, especially in HIV-infected individuals. The current study is the first report on the rate of the infection in Iranian HIV-infected individuals. Patients and We used two nested PCR and PCR RFLP assays to amplify mt LSU rRNA and DHPS genes in 126 samples obtained from the respiratory systems of Iranian HIV-patients with CD4 count < 200 cells/μL, who were referred to two Research Centers from August 2010 to March 2011. In the group of studied patients, 112 were male 88.9%). The mean age of the patients was 35.12 ± 9.75 years. Median CD4 T cell count of the patients was 93 cells/μL. Thirty nine patients (31%) were hospitalized, and 24 patients (18.9%) tested positive for Mycobacterium tuberculosis. In spite of receiving Pneumocystis pneumonia prophylaxis and highly active anti-retroviral therapy, P. jirovecii was detected in 15 samples (11.9%). Just one patient (0.8%) was co-infected with Mycobaterium tuberculosis. The mortality rate due to Pneumocystis pneumonia (PCP) was 26.6%. None of the isolates showed any mutation in codons 55 and 57, which are associated with resistance to sulfa/sulfon drugs. The sequencing results showed that the genetic patterns of Iranian isolates were similar to Indian and Spanish isolates (99% identity). The study indicated that the rate of P. jirovecii infection is similar to those reported from Asian, Indian and African countries. The similarity of the genetic pattern between Iranian and Indian isolates is probably due to their close geographical proximity.

Listeria monocytogenes has been isolated from various foods and environments in temperate areas, tropical countries and different parts of Iran. The bacterium as a psychrotrophic organism is capable of growth at refrigeration temperatures. The current study was conducted to determine the incidence of Listeria spp. on the surfaces of domestic refrigerators in Ahvaz city as a tropic area, to provide insights in to true burden of, and the risks posed by the bacterium in domestic refrigeration systems. During December 2009 – June 2010, 180 refrigerators located at student accommodations and private homes in Ahvaz, were sampled for the presence of Listeria spp. The temperature of each refrigerator was measured and owners were asked to fill out a questionnaire regarding the method of cleaning. All samples were tested by culture in Listeria enrichment broth (LEB), Oxford agar and PALCAM agar using standard methods. Suspected colonies were identified by biochemical tests. L. monocytogenes was present in 1 domestic refrigerator out of the 180 investigated (0.5 %) and L. innocua was also isolated from 2 refrigerators (1.2%). It was demonstrated that a significant number of the investigated refrigerators were operating at a temperature that can compromise the safety of the foods stored inside them. Also, most owners used mixture of water and dishwasher and some of them used water alone to clean their refrigerators. Although the incidence of L. monocytogenes in domestic refrigerators in Ahvaz is low contamination of the stored food in refrigerator by the bacterium is still a concern. Two of the isolated Listeria were from student accommodations. It was found that most of the refrigerators used in student accommodations in comparison to private homes, were not cleaned in low frequency and had higher temperature.