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The genus Pseudomonas consists of more than 120 species that are ubiquitous in moist environments such as water and soil ecosystems and are pathogenic to animals and humans. Within the genus of Pseudomonas, P. aeruginosa is most frequently associated with human infections. The bacterium is regarded as an opportunistic pathogen, primarily causing nosocomial infections in immunocompromised patients. The existing knowledge regarding the pathogenesis of P. aeruginosa has mainly been obtained through studying clinical isolates; particularly those involved in causing chronic lung infection in cystic fibrosis patients. Nosocomial infections commonly associated with P. aeruginosa include ventilator-associated pneumonia, catheter-associated urinary tract infections, wound infections in severe burn patients and septicaemia with their pathogenesis shown to be multifactorial. The bacterium is also capable of producing a number of toxins via the type III secretion system, as well as secreting enzymes and proteins including elastase, phospholipase C and siderophores. However, P. aeruginosa is also a waterborne pathogen, commonly found in environmental waters as well as in other sources such as sewage treatment plants. The public health implication of these bacteria whilst in the environment has not been fully investigated. Here we review our present knowledge about the pathogenesis of P. aeruginosa in clinical settings and the environment. 

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Shot hole caused by Wilsonomyces carpophilus is one of the main constraints to prune fruit production in Iran particularly in Khorasan Razavi province. It causes foliage shot hole in spring and early summer; fruit-spotting and cankers on limbs and twigs during autumn rains. The fungus was isolated from the lesions of twigs and was purified on PDA. The pathogenicity and virulence on detached twigs of stone fruit tree species was examined in vitro. Virulence of the pathogen as measured by lesion length was significantly different among the different host species, showing the nectarine as the most susceptible species. In contrast to other hosts, sour cherry did not show any canker on shoots or twigs and disease progress was just as tissue colonization by the fungus hyphae. However, other species such as prune, cherry, apricot and almond did not show significant differences. The results of bud and shoot evaluations indicated that the fungus overwinters as hyphae and conidia in buds, and in the form of hyphae as well as thick-walled globular chlamydospores in twigs. Additionally, viability of recovered conidia ranged from 33 to 90% throughout the dormant season. A better understanding of disease cycle and survival mode of the fungus will help to manage and prevent the disease.

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Background: Escherichia coli (E. coli) strains are among predominant agents causing nosocomial and community acquired infections. The majority of strains encode numerous virulence factors including fimbrial adhesions, secretory proteins and toxins, siderophores, and capsule. This study aimed to investigate the prevalence rate of virulence encoding genes and carbapenem resistance-encoding genes among imipenem-resistant E. coli isolates collected from patients hospitalized in Tehran, Iran.
Materials and Methods: In this cross-sectional study (April 2015-December 2017), 50 non-duplicated carbapenem-resistant E. coli isolates were collected from clinical specimens (stool, urine, blood, and wound) of hospitalized patients in three hospitals in Tehran, Iran. The antibiotic susceptibility profile was determined against 15 antibiotics on Mueller Hinton Agar (MHA) as per CLSI guidelines version 2016. The PCR was used to detect virulence and antibiotic resistance encoding genes.
Results: From a total of 50 carbapenem-resistant E. coli isolates, the highest resistance rate was observed to ceftazidime (100%), tetracycline (88%), amoxicillin (100%), sulfonamide (60%), and the least resistance rate was observed against amikacin (14%), gentamicin (22%), and fosfomycin (0%). The genes mediating resistance were as follows: beta-lactams OXA-48 (8%), IMP (16%), VIM (0%), NDM-1 (0%),  fosA3 (0%), quinolones (qnrA 48%), and colistin mcr-1(0%). Furthermore, the prevalence rates of of fimA, hlyA, cnf1, vat, pic, crl, and papH were 88, 36, 28, 10, 12, 54, and 88%, respectively.
Conclusion: In this study, all imipenem-resistant E. coli isolates were susceptible to fosfomycin, and all were  fosA3 negative. Among carbapenemase genes, IMP and OXA-48 type enzymes associated with higher MIC levels (8 to 32 µg.mL^-1) were detected. In this study, data suggest the role of these carbapenemases in resistance to carbapenems. Furthermore, the presence of multiple drug resistant strains encoding adhesive and secretory virulence factors is a concern for the infections treatment. 

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Effects of three nutritional levels of beet root molasses, cheese permeate, wheat bran extract, rice bran extract and Sabouraud^,s Dextrose Broth (SDB) were evaluated for blastospore production by two isolates of Beauveria bassiana sensu lato. at an interval of 24 h for seven days. Depending on the isolate, maximum blastospore production was obtained in 12% rice bran extract and 20% cheese permeates on the 7^th day. Both isolates produced the fewest blastospores in 4% cheese permeate. Virulence of blastospores, produced in liquid media containing beet root molasses, permeate, wheat bran extract and SDB (as control), on third instar larvae of brown tail moth Euproctis chrysorrhoea indicated that there were no significant differences among these nutritional media for either one of the isolates. Considering blastospore quantity and quality in terms of virulence and local accessibility, cheese permeate was found to be the best medium for mass production of B. bassiana blastospores.  

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Aims: Mycoplasma synoviae, as one of the main pathogens of birds, causes a lot of economic losses to the poultry industry. This study aimed to identify M. synoviae strains in clinical samples by PCR and culture methods.
Materials & Methods: A total of 135 samples were randomly collected from the respiratory tracts of female broilers in industrial poultry farms in Kerman, Iran during the first six months of 2016. Samples were cultured on Frey and PPLO broth media. Then PCR method was performed to identify Mycoplasma genus and synoviae species. Finally, multiplex PCR was performed to determine the prevalence of P1, P30, and P116 virulence genes.
Findings: In this study, 17 (32%) out of 53 poultry samples were positive for the presence of Mycoplasma genus by culture method, whereas according to the PCR results, 25 (47%) out of 53 samples were confirmed as Mycoplasma genus, among which 13 samples (25%) were identified as M. synoviae species. Among the strains confirmed as M. synoviae, the prevalence rate of P1, P30, and P116 genes was 7 (53.8%), 6 46.1%), and 5 (38.46%), respectively.
Conclusion: According to the PCR and culture methods results, the prevalence of M.  synoviae strains was high in industrial poultry farms, Kerman, Iran. The PCR results revealed a higher prevalence rate for this bacterium, suggesting that this method may be more reliable than culture method.

 

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Fusarium oxysporum f. sp. lycopersici (Fol) is the causal agent of vascular wilt in tomato, an important plant disease in Iran. Four monogenic resistance genes in tomato are used for identification of races of Fol and their corresponding avirulence genes Avr1, Avr2 and Avr3 were identified in pathogen one of which, Avr2, is f.sp. specific. Hence they can serve as reliable markers for racial identity and f.sp discrimination. These markers have been used for strains from other countries except Iran. Furthermore, a point mutation in Avr3 can lead to enhanced virulence of Fol on a susceptible tomato cultivar. To identify forma specialis and racial identity, Avr genes were studied in a collection of Iranian strains. Results revealed that PCR assay is very efficient in distinguishing between non-pathogenic and low virulence strains and in the vast majority of strains, avirulence genotype was consistent with Fol race1. Furthermore, to determine whether allelic variation of Avr3 could separate strains of different degrees of virulence, Avr3 wassequenced in Fol strains with high and low virulence. The resultsrevealed that allelicvariation of Avr3 was not correlated with degree of virulence in Iranian strains.
 

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Backgrounds: Listeria monocytogenes is an opportunistic pathogen causing listeriosis, its pathogenicity is due to the presence of virulence factors including InlA, InlB, PlcA, PlcB, ActA, Iap, and Hly. The purpose of this study was to evaluate the formation of biofilm and its association with serotypes and virulence factors in L. monocytogenes isolates.
Material and Methods: In this study, 51 L. monocytogenes isolates were collected from blood, urine, feces, placenta, rectum, and vagina samples as well as livestock and food samples. Biofilm production was measured using microtiter plate assay, and virulence genes were identified by PCR method.
Findings: Out of 51 isolates, 27 (52.9%) were non-biofilm producers, 17 (33.3%) were weak biofilm producers, four (7.8%) were medium biofilm producers, and three (5.9%) were strong biofilm producers. According to this study results, different L. monocytogenes strains could form biofilm with various intensities. The actA, flaA, inlJ, inlA, and plcB genes were observed in all the isolates. The frequency of the hlyA, plcA, iap, inlB, and inlC genes among the isolates was 90.2, 94.1, 98, 88.2, and 82.4%, respectively. There was no significant correlation between the presence/absence of virulence genes in biofilm producing and non-biofilm forming isolates, except for the inlC and iap genes, which showed a significant correlation with the ability to form biofilm.
Conclusion: Due to the high prevalence rate of biofilm formation among the isolates and the importance of biofilm production in medical surfaces and food industries, eradication of biofilm-forming isolates is important.
 

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Backgrounds: In recent years, Enterococcus species have emerged as a leading cause of nosocomial infections worldwide. The aim of this study was to determine the virulence biomarkers and antibiotic resistance profiles of Enterococcus spp. collected from a main tertiary teaching hospital in Bandar Abbas, Iran.
Materials & Methods: A total of 71 Enterococcus were isolated from clinical specimens of patients in different wards of a hospital. Enterococcus spp. were verified by detecting ddl gene using PCR-based method. Virulence-encoding genes including gelE and cylA were detected using PCR. Antibiotic resistance was assessed using the disk diffusion assay, and vancomycin resistance was identified using the E-test method.
Findings: Among Enterococcus isolates, 50 and 21 isolates were identified as E. faecalis and E. faecium, respectively. Most of the Enterococcus species were isolated from urine, followed by wound samples. The most prevalent virulence genes among E. faecalis isolates were cylA (60%) and gelE (30%); also, 19 and 14% of E. faecium isolates were positive for cylA and gelE genes, respectively. Many isolates of E. faecalis (84%) and E. faecium (76%) were resistant to one or more antibiotics and showed high resistance to gentamicin and ciprofloxacin.
Conclusion: This study revealed a high prevalence of ciprofloxacin and gentamicin resistance and a high frequency of virulence genes among E. faecalis isolates. Due to the high prevalence of MDR Enterococcus strains, control measures are necessary to prevent the emergence and transmission of these strains in different hospital wards.
 

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Backgrounds: This study was done to evaluate the distribution of virulence-associated genes and antibiotic resistance in avian colibacillosis-causing Escherichia coli (E. coli) isolates.
Materials & Methods: In this study, 122 E. coli strains isolated from colibacillosis-suspected chickens in commercial broiler poultry farms (Guilan province, Iran) were examined for the presence of 12 virulence genes (hlyF, iroN, iss, iutA, ompT, astA, tra, sfa-foc, papC, fimH, cvi/cva, and Tia) using polymerase chain reaction (PCR). Antimicrobial susceptibility assessment was performed for the isolates using disc diffusion method against 19 antibiotics.
Findings: The fimH, iut, tra, iss, iroN, hly, and ompT genes were detected as the most prevalent genes among colibacillosis-causing isolates (more than 70%), while sfa-foc (S fimbriae and F1C fimbriae subunits) had the lowest frequency among colibacillosis-causing E. coli isolates (3.28%).
Conclusion: Virulence-associated genes were frequently detected in avian pathogenic E. coli strains. These findings could help better understand the pathogenicity potential of E. coli in poultry. Preventative measures are necessary to reduce food and environmental contamination with avian E. coli strains.

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Backgrounds: Diabetic patients are at risk of developing serious foot infections with methicillin-resistant Staphylococcus aureus (MRSA) strains, which are associated with high morbidity and mortality. This study aimed to investigate the frequency of different prophage types and virulence factors among MRSA strains isolated from patients with diabetic foot infections (DFIs) in a referral hospital in Tehran, Iran during 2019 and 2020.
Materials & Methods: A total of 238 S. aureus isolates were collected and confirmed using specific primers. The presence of staphylococcal enterotoxins (sea-seq) and hlb, sak, eta, etb, and tsst-1 genes among MRSA isolates was tested using separate polymerase chain reaction (PCR) assays. Also, multiplex PCR was employed for prophage typing of MRSA isolates.
Findings: A total of 73 (31%) isolates were confirmed as MRSA, among which four prophage types and 13 different prophage patterns were identified, and prophage type SGF and prophage pattern 7 consisting of SGB, SGF, SGFa, and SGFb types were the dominant ones. Also, 11 enterotoxin-encoding genes and four virulence factor genes were detected among the isolates. All MRSA isolates were positive for sea, sek, seq, and hlb genes. Moreover, out of 12 different enterotoxin patterns, most MRSA isolates were classified into enterotoxin pattern 1, harboring three enterotoxin genes (sea, sek, and seq).
Conclusion: This study results indicated the presence of different prophage types and virulence factor genes among MRSA strains isolated from DFI patients, which enable them to produce a variety of diseases.

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Anthracnose disease caused by Ophiognomonia leptostyla, is the most important and widespread fungal disease on Juglans regia. Walnut disease symptomatic samples were collected from different provinces of Iran, during 2015–2016. Fungal isolates were identified based on ITS-rDNA sequence data. Variance analysis of colony growth rate (mm/day) and acervulus density on medium, was significant. Acervulus density on medium was strongly correlated with colony growth rate. The Max acervulus density was 60% and > 80% for Hamedan and Mazandaran isolates respectively. The virulence of six selected isolates was examined on cv. Chandler. Virulence indices including spot diameter, disease severity, spot area average and logistic infection rate except spot number index, could successfully detect significant differences among isolates. SA-SE1 isolate from Mazandaran showed significantly the most virulence indices: disease severity (%), spot area and logistic infection rate. For the other five isolates, four significant levels in all virulence indices were observed. In summary after this isolate, other isolates including TA-ZY21, LA-SY21, U94-SR1, HA-GH22 and MA-K1 were placed in the next steps of virulence ranking. There was insignificant correlation between colony growth rate and disease severity. However, the acervulus density and disease severity were significantly correlated implying the importance of acervular conidial inoculum in secondary disease cycle progress. Disease severity was strongly correlated with number of spots, spot diameter and logistic infection rate. Disease severity was also negatively correlated with Mid-time (time to progress 50%). Moreover, there was positive relationship between logistic infection rate and three traits: number of spots, spot diameter and spot area average. This study was the first of the disease virulence components on cv. Chandler in Iran.
 

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Background: Pathogenic Escherichia coli (E. coli) is usually known as the principal agent of hospital-acquired infections, particularly those related to urinary tract infections (UTIs). The purpose of tThis study aimedwas to determine ESBL (extended-spectrum B-lactamase) production and quinolone resistance (qnr) genes in cytotoxic necrotizing factor 1 (CNF-1)- producing E. coli isolatesd from UTIs in Iraq.
Materials & Methods: A total of 996 E. coli isolates were obtained from UTIs infections in two general hospitals in Hillah, Babylon, Iraq (during 2014-2022), and 100 uropathogenic E. coli (UPEC) were cnf-1 gene carriers. ESBL production was evaluated using the double-disk synergy -test. The qnr genes were detected using polymerase chain reaction (PCR).
Findings: Nalidixic acid and chloramphenicol resistance wasincluded 70% and 30%, respectively. ESBL production was observed among 46% of cnf-1 -carriers isolates. The qnrA, qnrB, and qnrS genes were detected in 18%, 21%, and 11% of the isolates, respectively. ESBL-producing isolates mainly carried the qnrB gene and showedhad the highest resistance levels to quinolones. Major risk factors of pathogenic E. coli isolation included older age (68%, p= 0.031), previous hospitalization (76%, p= 0.021), and urinary catheter (83%, p= 0.018).
Conclusion: Although the prevalenceexistence of the cnf-1 gene was not high among UPEC isolates, its prevalencerate was high among quinolone-resistant and ESBL-producing isolates. The cContinuous investigation of virulence and resistance genes is essential tfor monitoring and controlling the infections and facilitate their control. ItMore investigation is necessary to determine the virulence  traits factors and resistance genes among UPEC in Iraq and to take in timely measures action to hinder the spread of resistance genes from spreading to other nosocomial isolates.
 

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In the present study, the cuticle-degrading enzymes production potential of five native Beauveria bassiana (TV, OZ, UN, DV and DE) isolates was investigated in the presence of cuticles from Eurygaster integriceps, Ephestia kuehniella and Zophobas morio. Furthermore, histopathology of infected insects by B. bassiana was studied. The level of cuticle degrading enzymes was the highest and lowest for TV (as the most virulent isolate) and DE (as the weakest isolate), respectively. E. integriceps nymphs as the most sensitive host produced the highest level of cuticle degrading enzymes (Pr2, exochitinase, and lipase) while Z. morio as the most resistant host, produced the lowest level of hydrolytic enzymes. According to histopathological study, the fungal isolate could not penetrate into Z. morio cuticle, as no mycelia or hyphae were observed in its tissues after inoculation, while fungal bodies were detected in microscopic slides of the other two insects. Overall, the chemical and topographical structure of insect cuticle had a substantial effect on the virulence of entomopathogenic fungus. Production of enzymes including proteases (especially Pr2), chitinase (N-acetyl-glucosaminidase), and lipases was positively related to virulence of fungus isolates. It can be concluded that not only the hydrolytic activity of B. bassiana isolates, but also host cuticle composition determine the pathogenesis and virulence cascade in fungus-insect interactions.

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Fusarium oxysporum f. sp. albedinis (Foa) is a soil borne fungus causing the most serious disease of date palm (Phoenix dactylifera L.) called “Bayoud”. In the present study, five medicinal plants from the Algerian Sahara (Southwest of Algeria): Limoniastrum feei (aerial part, roots), Launeae arborescens (Batt.) Murb. (aerial part, roots), Fredolia aretioides Moq. et Coss. (aerial part, roots), Asteriscus graveolens (Forsk) (leaves, stems) and Acacia raddiana (leaves, bark), were used to evaluate their extracts for antifungal activity against Foa. Two parts from each plant were used for extraction by four solvents: methanol, ethyl acetate, dichloromethane and hexane. The antifungal test was conducted using disc diffusion technique and relative virulence (RV) test (on potato tuber tissue). For both tests, four extract quantities were used (200, 400, 800 and 1,600g). The relative virulence was presented as necrotic tissue weight (mg) of potato tuber tissue. Among all solvents, methanol had the best extraction yield (mean: 6.35%, minimum: 2.27%, maximum: 9.80%). The highest frequency of antifungal effect on Foa was presented by ethyl acetate extracts (32.50% of detectable effect). The best effect was observed for ethyl acetate extract of Limoniastrum feei (aerial part). The virulence test showed a decrease in RV up to 30% for ethyl acetate extract of Launea arborescens aerial part. The increase in RV was observed mostly for hexanic extract from Fredolia aretioides reflecting its high toxicity compared to the other extracts.

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Objective: The aim of the this study was to investigate the prevalence of toxB, paa, lpf and iha adhesion genes in enteropathogenic Escherichia coli (EPEC) isolates lacking in two important adhesion factors, the eaeA and bfpA genes. Methods: We examined a total of 70 serologically confirmed EPEC (eaeA^-, bfpA^-) isolates. DNA from the isolates was extracted by the phenol-chloroform method. toxB, paa, lpf and iha adhesion genes in the EPEC isolates were detected by polymerase chain reaction. Data were analyzed by SPSS software and statistical analysis using the chi square test. P-values less than 0.05 were considered significant. Results: PCR was positive for the toxB gene in 2 (2.85%), paa in 3 (4.28%), lpf in 32 (45.71%) and iha in 15 (21.42%) of the 70 strains. Statistically, none of the toxB, paa, and lpf genes were associated with diarrhea. However, the iha gene showed a weak significant relation to diarrhea (P=0.11). Conclusion: The main mechanism of pathogenicity for EPEC is attachment and effacement. Therefore, EPEC (eaeA^-, bfpA^-) should have another adhesin factor, which should be investigated. EPEC strains (eaeA-, bfpA-) that possess the lpf gene are common. Further investigations of the virulence properties of these strains are necessary in order to elucidate the role of these virulence factors in diarrhea among Iranian children.

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Beauveria bassiana (Balsamo) Vuillemin is an important natural regulator of insect populations. Identification of a suitable molecular marker for detecting a virulent phenotype on a target pest would be useful in screening for effective isolates against the pest. Nine isolates of B. bassiana were tested for their virulence to adults of Tribolium castaneum (Herbst) in laboratory bioassay with 1×10⁸ conidia mL^-1. DNA markers provide more detailed genomic information.DNA fingerprints were generated by RAPD markers. Fungal DNA was extracted by CTAB. Twelve random oligonucleotide primers were used for amplification. After bioassay, three arbitrary categories of isolates were chosen i.e. isolates that caused > 45%, 45-30% and < 30% mortality, and were classified as highly (H), moderately (M), and less (L) virulent isolates based on average mortality, respectively. Also, based on LT₅₀ values, three arbitrary categories were chosen i.e. isolates with < 80 h, 80-100 h and > 100 h LT₅₀ values, and were classified as highly (H), moderately (M), and less (L) virulent isolates, respectively. The results of bioassay showed that isolates IRAN 440C and DEBI 004 were the causative agents of mycoses with the highest and lowest lethal effect, respectively. The lowest LT₅₀ value was related to DEBI 014. Cluster analysis of the RAPD data showed four clusters according to similarity, following cluster analysis using the Jaccard similarity coefficient and clustering was done using un-weighted pair group method with arithmetic (UPGMA). The results showed that there was genetic diversity between these isolates, but the groups based on virulence rating and LT₅₀ values did not match with the RAPD clusters completely.

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Objective: Candida albicans (C. albicans) is an opportunistic yeast that can lead to pathogenesis in immunocompromised individuals and under suitable conditions. Medicinal plants ingredients such as camphor can reduce the expressions of genes involved in virulence of the fungi through their antifungal properties. The products of INT1 and EFG1 are implicated in inducing filamentous growth and adhesion of C. albicans to the host tissues. Both of these characteristics are very important in its virulence. The present study focuses on the evaluation of the effects of camphor on INT1 and EFG1 expressions at three time points of treatment (24, 48, and 72 hours) via real-time PCR. Methods: We prepared serial dilutions of camphor (1, 2, 4, 8, 16, 32, 64, 128, 256, and 512 mg/ml) and co-cultured them with 1.5×10³ cells/ml of a C. albicans ATCC 10231 suspension for 48 hours at 35⁰C. Next, we determined the MIC50/90 and MFC. C. albicans cells were treated with the MIC50 concentration of camphor for 24, 48, and 72 hours. RNA from C. albicans was extractedbefore and after treatment, back translated into cDNA, and analyzed with real-time PCR. Results:MIC50, MIC90 and MFC of camphor were determined at 16 mg/ml, 32 mg/ml and 64 mg/ml, respectively. Evaluation of gene expression changes in yeast showed that camphor reduced the INT1 gene expression about 87% at 24 hours, 97% at 48 hours, and 86% at 72 hours after treatment compared to the untreated sample. EFG1 expression reduced about 58% at 24 hours, 93% at 48 hours, and 49% at 72 hours after treatment with camphor. Conclusion: In recent years, advancements have been seen in herbalism due to the increased drug resistance and adverse effects of chemical drugs. These plants may efficiently act as antifungal agents. The results of this study have shown that the use of camphor can significantly reduce the expression of virulence genes INT1 and EFG1 in C. albicans.

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Vibrio cholerae is one of the important human pathogens that is transmitted through contaminated water and food. In Qom province, due to special weather conditions, diseases caused by Vibrio cholerae are endemic. The aim of this study was the prevalence of Vibrio cholerae in water and vegetables of Qom province and the presence of two virulence genes, hlyA and toxR. During two years (2020-2021), 120 samples of agricultural water (70) and vegetables (50) in Qom province were collected. The samples were cultured on specific media. Suspicious colonies were evaluated by Gram staining and biochemical tests and the serotype Vibrio cholerae was identified by serology test. Finally, Then, the presence of virulence genes was investigated by PCR method and also the antibiotic resistance pattern by disk diffusion method was evaluated in the isolates.  Vibrio cholera bacteria were isolated from 17 samples (16.14%), all of which were Non-O1. The rate of contamination of water and vegetables was 28.14% (10 cases) and 14.00% (7 cases), respectively. In molecular evaluation, the abundance of virulence genes including: toxR (88.32%), rtxA (58.82%), hlyA (47.05%), chxA (5.88%), and 100% of isolates did not have ctxA, ace and tcpA genes. The most antibiotic resistance is related to ampicillin and amoxicillin (34.29%), followed by cefuroxime (17.46%), imipenem (11.76%), and cefoxitin and trimethoprim-sulfamethoxazole (5.88%). The results of this study showed that Vibrio cholerae Non-O1 is present in water and vegetables of Qom province, and as an important source of disease for humans therefore, continuous health monitoring of water and vegetables and proper disinfection of these foods is very important.

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Possible influence of 3 abiotic environmental factors (temperature, nitrogen salt, and benzimidazole) on wheat resistance to Puccinia triticina was studied. Under the effect of these factors, statistically significant decrease in the rust development was revealed for 6 wheat varieties. Specific changes of virulence in 6 pathogen monopustule isolates under the effect of those factors were revealed with high frequencies. Subjected to a particular factor, we observed an absolute coincidence of the infection types of seedlings infected with rust pathogen clones multiplied in the absence of this factor, and infection types of leaves, incubated in the absence of the factor, but infected with isolates, multiplied in the presence of this factor. Six subpopulations of the pathogen representing mixture of genotypes virulent to 2 wheat varieties under certain conditions were created. We did not find significant differences in two disease development indexes (number of pustules and uredospores’ number in pustule) in seedlings affected by a factor and infected with subpopulations multiplied in the absence of the factor, and disease development indexes in leaves not subjected to the factor but inoculated with subpopulations multiplied in the presence of this factor. According to the results, the influence of studied factors on expression of specific (vertical) and non-specific (horizontal) wheat seedling resistance to rust was not revealed. Obviously, significant decrease in the rust development under the effect of studied environmental factors is primarily (if not only) related to their influence on the pathogen virulence and aggressiveness.