نشریه تازه ها در میکروب شناسی دامپزشکی
سال ششم شماره 1 (بهار و تابستان 1402)

Aeromonas hydrophila bacteria is an opportunistic bacterium that can reduce the use of chemical and synthetic drugs by using medicinal plants to inhibit its growth in food. Considering the antibacterial properties of three plants, Yarrow, Lavender and Thyme, this study was conducted with the aim of investigating the antibacterial and synergistic effects of these three plants against Aeromonas hydrophila bacteria. In this study, Aeromonas hydrophila bacteria was first prepared from fish samples and confirmed by biochemical and PCR methods. Then extraction was done by maceration method and the sensitivity of isolated bacteria was checked by disk diffusion method in Mueller Hinton culture medium. Also, the minimum inhibitory concentration of medicinal plants was investigated. According to the results, the prevalence of Aeromonas hydrophila bacteria was 5%. The isolated bacteria were resistant to all the investigated antibiotics. The lowest inhibitory concentration and the lowest lethal concentration were related to the yarrow plant, which shows its stronger antibacterial effects than the other two plants. The highest lethality concentration was reported for lavender plant, and this difference was statistically significant compared to other two plants (p<0.05). In general, tracking the prevalence of these pathogens in aquatic animals, along with investigating the prevalence of drug resistance and using alternative treatments such as the use of medicinal plants with antimicrobial properties that can overcome drug resistance and prevent the further spread of these factors in the aquaculture industry It seems necessary.

Leptospirosis is a common disease between humans and animals that can survive in swimming pools, rivers, surface waters, moist soils, swamps, and hot weather. Leptospirosis can be transmitted to humans directly through contact with the urine of most rodents (rats, foxes, raccoons, etc.) by scratches or minor injuries, or indirectly through contaminated water and soil. Considering that the cultivation and growth of this bacterium is time-consuming, the use of surface plasmon resonance sensors using metamaterial structure is a suitable method for rapid diagnosis of this disease. Ordinary, leptospirosis bacteria can be detected by urine. In this article, we apply five rodent urine samples as the sensing material in the designed biosensor. In the proposed structure, gold metal has been chosen as a plasmonic metal due to its resistant against air oxidation. To check the sensitivity of this device and the results, we find absorption curves and analyze them in terms of sensitivity, detection accuracy, and quality factor. The results show that this sensor can detect leptospirosis bacteria with a sensitivity of 1315nm/RIU and a figure of merit (FOM) of 63RIU-1.

Subclinical mastitis is one of the common problems of dairy farms, which leads to a decrease in production and economic damage to the farmers. Identification of the pathogens causing subclinical mastitis in each region is necessary to prevent and control this problem. The aim of this study was to investigate the molecular prevalence of Staphylococcus aureus bacteria in subclinical mastitis cows in dairy farms of Neyshabur city. A total of 500 milking cows from 13 dairy farms located in different parts of Neyshabur city were included in the study. Milk samples were taken from all quarters and checked for subclinical mastitis using the California mastitis test. Milk samples were taken from the quarters that were positive in the California mastitis test, and evaluated for contamination with Staphylococcus aureus using polymerase chain reaction. Out of 500 dairy cows studied (2000 quarters), 94 (18.8%) had subclinical mastitis, and Staphylococcus aureus infection was detected in 8 cows (8 quarter). Based on the results of this study, the occurrence rate of subclinical mastitis as well as the prevalence of Staphylococcus aureus among subclinical mastitis cows in dairy farms of Neyshabur city is low.

Genetic fingerprinting of Escherichia coli strains in one habitat can significantly help our understanding of genetic diversity and circulation in different hosts. In this study, 48 stool samples were collected from 24 healthy zoo animal species in Kerman zoo by sterile swab. After the isolation of Escherichia coli, the strains were genetically fingerprinted by the ERIC-PCR method, and the bond patterns obtained from electrophoresis were calibrated and analyzed with Gel Quest software. In the next step, the similarity of ERIC templates was determined by drawing a phylogenetic tree by Cluster Viz software using the UPGMA algorithm. In this method, 22 clones were identified with a ≥95% similarity cutoff; The ERIC pattern of pigeon isolates had 100% similarity with a peacock isolate, and the ERIC pattern of ostrich isolates had 100% similarity with one peacock isolate. The isolates of horned chicken, casco, and one isolate of the tawny owl were grouped together with 100% similarity in terms of ERIC pattern. Also, camel isolates and one isolate from a tawny owl showed 100% similarity in the ERIC pattern. Considering that several strains isolated from different hosts with different species had 100% similarity in the ERIC pattern, it can be concluded that due to the proximity of different animal species in the same habitat such as a zoo, these strains circulated among different animals.

Chemical preservatives have harmful effects on human health, for this reason, natural compounds such as essential oils (EOs) are being considered as alternatives. Salinity stress (SS) is one of the important environmental stress that affects EOs components and its properties. The purpose of this research is to evaluate the antibacterial effect of basil (Ocimum baslicum L.) EO obtained under SS. salinity at 5 levels including control (0.3 dc/m), 1.5, 3, 5 and 8 ds/m was applied to basil plant in greenhouse conditions. Leaf weight and EO yield, also the EO components were evaluated. Also, antibacterial properties of EO by agar-well diffusion and microdilution method were evaluated against Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, Escherichia coli, Pseudomonas aerogenes and Salmonella enterica. Increasing the salinity stress up to 0.8 ds/m level, decreased the yield of leaf weight per plant (up to 142.2%) and increased the amount of EO content (up to 54.1%). Also, with the increase in SS level, some compounds such as linalool (4.8%) and germacrene (44.2%) increased, and eugenol (40.8%) and α-cadinol (34.7%) components decreased. Basil EOs showed antimicrobial effect against the target bacteria at all salinity levels. This characteristic was influenced by the type of bacteria and salinity level. Bacillus cereus was the most resistant and Salmonella enterica the most sensitive bacteria against the antimicrobial effects of basil EO. An increase in the antibacterial power of EOs was observed at salinity levels ≥ 0.3 dc/m, which can be considered for more effective use against pathogenic bacteria.

Brucellosis is a common disease between humans and animals with global distribution and an increasing trend. The control of brucellosis in humans depends on the control of the animal disease. Although there is no approved vaccine for brucellosis in humans, many efforts have been made to develop vaccines with high efficiency and low side effects for animals. Live attenuated vaccines are cheaper and more effective than other vaccines, but they can increase antibiotic resistance, interfere with serological diagnostic tests, and increase virulence in animals. Vaccination of animals with commercially available vaccines may cause disease and, in some cases, have low efficacy.  Vaccines containing recombinant protein or their coding DNA can be suitable alternatives to the conventional vaccines, because they can reduce unwanted side effects. Choosing the suitable antigen that stimulates the immune system is very important in the preparation of these vaccines. In the present study, by observing the new recombinant vaccines that are made based on recombinant proteins and DNA, it has been tried to clarify their strengths and weaknesses and the new perspective of vaccination against brucellosis. There is currently no approved vaccine for brucellosis in humans. In addition, the control of brucellosis in humans depends on the control of the animal disease. This review article searches Google scholar, PubMed, and SID databases for new research on recombinant protein and DNA vaccines against brucellosis until 2021. Considering the advantages and disadvantages of common and new brucellosis vaccines, recombinant and DNA vaccines, after conducting the research stages in large animals, can be a suitable approach to prevent the progress of brucellosis.

Antibiotic therapy of bacterial diseases has some side effects including antibiotic resistance. There is need to investigate new and natural antibacterial agents because of various side effects of antibiotics. According to antibacterial effects, essential oils (EOs) are suitable alternatives. Escherichia coli, Staphylococcus aureus and Streptococcus agalactiae cause various diseases in human and animals. Also, these three bacteria are major bovine mastitis-causing bacteria. So, this study investigated antibacterial activity of Mentha piperita (peppermint) and Mentha pulegium (pennyroyal) essential oils in comparison with lincospectin, gentamicin and amoxicillin/clavulanate antibiotics on these bacteria. Gas chromatography/mass spectrometry was used for the analysis of EOs. Antibacterial effects of the EOs on bacteria were evaluated with minimum bactericidal concentration (MBC), minimum inhibitory concentration (MIC), disk diffusion method, and time- kill assay in tryptic soy broth (TSB). Major components of peppermint EO were carvone (63.02%) and limonene (24.48%), and those of pennyroyal EO were pulegone (48.16%), eucalyptol (14.57%). According to MIC and MBC results, the antibacterial activity of peppermint was the same or higher than lincospectin and pennyroyal effect on Streptococcus agalactiae was higher than lincospectin. The inhibition zone of peppermint and pennyroyal had no significant difference with gentamycin but the effects of two EOs against the other two bacteria were lower than gentamycin and amoxicillin/clavulanate. Sub-MIC concentrations of oils decreased Escherichia coli count at 24 h. Generally, the essential oil of peppermint and pennyroyal had a significant antibacterial effect and the effect of peppermint was higher than pennyroyal.

Chicken meat, as one of the most important sources of protein in the world, shows a high rate of contamination with Escherichia coli, which can widely spread antibiotic resistance. The aim of this study was to investigate the resistance to colistin and aminoglycosides in E. coli isolated from broilers. In this study, during 2021, a total of 122 E. coli isolates were collected from the heart and liver of 20- to 45-day-old chickens with clinical signs of colibacillosis. Aminoglycosides and colistin resistant strains were identified by disk diffusion and MIC determination, respectively. Subsequently, the presence of mcr-1, mcr-2, mcr-3, aph (3′)-IIa, aac (3) -IIa and ant (3″)-Ia genes in the isolates was analyzed by PCR. Out of 122 isolates, 35 isolates (28.68%) were resistant to neomycin sulfate and 1 isolate (0.82%) was resistant to gentamicin. All isolates were sensitive to amikacin, tobramycin and streptomycin and 5 isolates (4.10%) were resistant to the colistin. In the detection of mcr genes by PCR method, none of the studied genes were identified, but aph (3′) -IIa, aac (3) -IIa and ant (3″)-Ia genes were detected in 25.41%, 23.77% and 36.88% of isolates respectively. The results of this study indicate a decrease in the sensitivity of poultry isolated E. coli to aminoglycosides and colistin. The spread of such resistant isolates is a serious warning about the reduction in treatment choices of colibacillosis and indicates the risk of transmission of resistance genes to the human microbial flora.

Aquatics, including fish, have always been one of the most perishable protein sources. For increasing storage time of the resource there are several ways including radiation.  The effect of gamma irradiation was investigated on the microbial load and total volatile nitrogen of fish meat rainbow trout (Oncorhynchus mykiss). At the beginning of these experiment, the fish meat is irradiated by 1.5, 2.5 and 3.5 KGry radiation doses and subsequently transferred to the refrigerator at 4°C. During the first, seventh and fourteenth days after irradiation (after transfer to the refrigerator) the total amount of bacteria and total volatile nitrogen was investigated. The results indicated a greatly reduction of amount of bacterial load and total volatile nitrogen by the use of various doses of gamma irradiation. Among the irradiated doses, 3.5 KGry showed the greatest decrease in these parameters, but considering that there was not huge difference between 2.5 and 3.5 KGry in the reduction, thus 2.5 KGry gamma irradiation is selected as a suitable dose for rainbow trout irradiation and subsequent storage in the refrigerator.

Mastitis, which is caused by inflammation of the mammary gland, is the most common and costly disease that affects dairy cows around the world. Treatment of mastitis during lactation is not recommended due to the risks of milk contamination with antibiotics in lactating cows. In this research, (Pulegium Mentha) plant was used to treat subclinical mastitis in Holstein cows. For this purpose, 50 Holstein cows with subclinical mastitis with an average age of 4.5 years and in the middle of the lactation stage with an average production of 20±2.7 were selected. The research was conducted in the form of a completely randomized design with two treatments and twenty-five repetitions, which treatments were: 1- control (no injection of Oji essential oil into the breast area) 2- injection of Oji essential oil into the breast area. The results of the present study showed that the injection of Oji essential oil into the mammary gland improved the average amount of milk production, reduced somatic cells, and increased the percentage of protein, fat and lactose in cows' milk (P<0.05). However, there was no significant difference between the Oji treatment and the control in terms of total elimination of intramammary infections. In general, the results of the study showed that Oji essential oil can be used in the treatment of subclinical mastitis in cows.