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KEYWORDS ABSTRACTBrucella melitensis; Brucella abortus; Persister cell; TA systems; Real-time PCR Scan to discover online Background & Objective: Persister cells are defined as a subpopulation of bacteria that are capable of reducing their metabolism and switching to dormancy in stress conditions. Persister cells formation has been attributed to numerous mechanisms, including stringent response and Toxin-Antitoxin (TA) systems. This study aimed to investigate the hypothetical role of TA systems in persister cells formation of Brucella strains by evaluating toxins of type II TA systems (RelE, Fic, Brn T, cogT) expression.Methods: Brucella strains treated with a lethal dose of gentamicin and ampicillin and to determine the number of surviving cells, bacterial colonies were counted at different time intervals. The role of TA systems in persister cell formation was then determined by toxin expression levels using qRT-PCR method. Results:Our results showed the viability of persister cells after 7 h. The results of relative qRT-PCR showed higher levels of toxin gene expression due to stress conditions, suggesting the possible role of TA systems in persister cells formation and antibiotics tolerance. Conclusion:The results of this study showed that considering the importance of persistence and the tolerance to antibiotics, further studies on persister cells formation and related genes such as the TA system genes in Brucella strains might help us to identify the precise mechanisms leading to persister cells formation. Main Subjects:Microbiology

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Objective Klebsiella pneumoniae is a gram-negative pathogen common cause of nosocomial infections. Colistin is a last resort antibiotic to treat infections caused by K. pneumoniae. In recent years, the resistance rate to colistin has increased in K. pneumoniae. This study evaluated the prevalence of colistin resistance of K. pneumoniae isolates in Iran using a systematic review and meta-analysis. Method A systematic search was performed for relevant articles until August 2021 in the following database: PubMed, Scopus, SID and Google Scholar. The pooled prevalence of colistin resistance in clinical K. pneumoniae isolates analyzed using Comprehensive Meta-Analysis Software (CMA). Results Finally, 19 articles with appropriate criteria were included in the meta-analysis. Our results showed 6.9% of the pooled prevalence of colistin resistance in clinical K. pneumoniae isolates in Iran. The results of subgroup analysis demonstrated increase resistance of colistin from 4.8%; (95% CI 1.5–13.9%) in 2013–2018 to 8.2%; (95% CI 3.4–18.6%), in 2019–2021. Also, the results of our study showed a strong association between the carbapenem producing K. pneumoniae and increased resistance to colistin. Conclusions This study showed a high prevalence of colistin resistance in K. pneumoniae isolates. It is recommended that regular evaluation be performed to control colistin resistance.

Objective: Persistence is a subpopulation of bacteria that can tolerate high doses of antibiotics by undergoing a period of dormancy. This study aimed to investigate the hypothetical role of toxin/antitoxin systems in persister cell formation of Klebsiella pneumoniae ATCC 13883 by evaluating toxins of type II toxin/antitoxin systems expression. Methods: To determine the number of surviving cells, bacterial colonies were counted at 1, 3, 5, 7, and 24 h after treated with a lethal dose of kanamycin. The role of toxin/antitoxin systems in persister cell formation was then determined by toxins of type II toxin/antitoxin systems (relE1, relE2, hipA, vapC, and doc) expression levels using real-time PCR. Results: Our results showed the viability of persister cells after 5 h. The results of relative real-time PCR showed higher levels of toxin gene expression due to stress conditions, suggesting the possible role of toxin/antitoxin systems in persister cell formation and antibiotic tolerance. Conclusion: Considering the importance of persistence and the tolerance to antibiotics, further studies on persister cell formation and related genes such as the toxin/antitoxin system genes might help us to identify the precise mechanisms leading to persister cell formation.

Persister cells are a subpopulation of bacteria with the ability of survival when exposed to lethal doses of antibiotics, and are responsible for antibiotic therapy failure and infection recurrences. In this study, we investigated persister cell formation and the role of nisin in combination with antibiotics in reducing persistence in Listeria monocytogenes. We also examined the expression of toxin-antitoxin (TA) systems in persister cells of L. monocytogenes to gain a better understanding of the effect of TA systems on persister cell formation. To induce persistence, L. monocytogenes were exposed to high doses of different antibiotics over a period of 24 hr, and the expression levels of TA system was genes were measured 5 hr after the addition of antibiotics by the quantitative reverse transcription-polymerase chain reaction (qRT-PCR) method. To investigate the effect of nisin, L. monocytogenes was exposed to a combination of nisin and antibiotics. According to our results, L. monocytogenes was highly capable of persister cell formation, and the combination of nisin and antibiotics resulted in reduced persistence. qRT-PCR results showed a significant increase in GNAT/RHH expression among the studied systems. Overall, our results demonstrated the potential of the combination of nisin and antibiotics in reducing persister cell formation, and emphasized the role of the GNAT/RHH system in bacterial persistence.

Background Endocarditis caused by Brucella infection is one of this infection's complications, including a high mortality rate. However, studies on the prevalence of this complication have been limited to some case reports. This study investigated the prevalence of Brucella endocarditis globally using a systematic review and meta‐analysis. Methods PubMed, Scopus, and Web of Science databases were searched using appropriate keywords until September 2022. All studies reporting the prevalence of endocarditis in patients with brucellosis were included in this current study. To investigate the pooled prevalence of Brucella endocarditis, random model was used in comprehensive meta‐analysis software. Results A total of 25 studies met the inclusion criteria and were included in the systematic review and meta‐analysis. The prevalence of Brucella endocarditis was 1.3%, and the death rate was 26.5%. The results did not show a significant difference in the prevalence of this complication in different regions. Conclusion According to this study's results, the prevalence of Brucella endocarditis is low, but it includes a large percentage of the deaths of affected patients. To complete our understanding of this complication and its management, more research should be done to investigate the effect of other factors, such as age and gender.