Resistance to Chlorhexidine and Benzalkonium Chloride in E. Coli ST131, A. Baumannii, and P. Aeruginosa Isolates.

BACKGROUND: The goal was to assess the antimicrobial efficacy of two commonly used biocides, chlorhexidine, and benzalkonium chloride, against MDR isolates of Pseudomonas aeruginosa, Acinetobacter baumannii, and Escherichia coli ST131, as well as the prevalence of resistance genes. METHODS: MIC of chlorhexidine and benzalkonium chloride and their effects on both the planktonic phase and biofilm were determined. Finally, the presence of genes responsible for resistance to quaternary ammonium compounds was investigated by PCR. RESULTS: No significant relationship was observed between the presence of resistance genes and different concentrations of quaternary ammonium compounds (benzalkonium chloride). There was no association between biofilm formation and the presence of resistance genes. CONCLUSIONS: Chlorhexidine digluconate and benzalkonium chloride at appropriate concentrations could prevent biofilm formation.

Investigating the role of Bacillus subtilis type II toxin-antitoxin system in drought stress survival.

Toxin-antitoxin (TA) systems, present in plasmids and bacterial chromosomes, are widespread in bacteria such as Bacillus subtilis and are known to be involved in growth regulation, bacterial tolerance to environmental stress conditions as well as biofilm formation. The aim of the current study was to investigate the role of TA systems in drought condition stress in B. subtilis isolates. The presence of TA systems including mazF/mazE and yobQ/yobR in B. subtilis (strain 168) was investigated using the polymerase chain reaction (PCR) method. TA system expression at 438 and 548 g/L of ethylene glycol concentrations was evaluated using real-time PCR method and sigB gene was used as internal control. The expression rate (fold change) of mazF toxin gene treated with 438 and 548 g/L of ethylene glycol was 6 and 8.4, respectively. This indicates an increase in the expression of this toxin in drought stress condition. Also, the fold change of mazE antitoxin in the treatment with 438 and 548 g/L of ethylene glycol was 8.6 and 5, respectively. While yobQ/yobR showed a decrease in expression in 438 and 548 g/L of ethylene glycol concentrations. So that the highest expression reduction (8.3) was observed for yobQ gene at the concentration of 548 g/L of ethylene glycol. Results of this study revealed the significant role of B. subtilis TA systems in drought stress which can be considered as the resistance mechanism of this bacterium under stress conditions.

Characterization of bacteriocins produced by Lactobacillus species against adhesion and invasion of Listeria monocytogenes isolated from different samples.

BACKGROUND: Listeria monocytogenes is an important difficult to control and eradicate foodborne pathogen due to its resistance properties to extreme conditions. Bacteriocins produced by lactic acid bacteria (LAB) can be considered as natural alternatives for safety and quality of foods, since these molecules offer antimicrobial activity against other bacteria. METHODS: In this study, Lacticaseibacillus casei, Lactiplantibacillus plantarum, and L. monocytogenes isolates were first characterized by phenotypical tests and 16S rRNA gene using PCR. Then, six types of bacteriocins produced by Lactobacilli strains were identified using molecular tests. The ability of these strains to compete with L. monocytogenes for adhesion and invasion to HT-29 cells was evaluated through colony count and MTT assay. Finally, the level of bacteriocins expression was assessed using qRT-PCR. RESULTS: L. monocytogenes strains were categorized from A1 to A8 based on the source of isolation. In the adhesion assay, L. casei + L. monocytogenes isolated from milk and Lpb plantarum + L. monocytogenes isolated from feces presented the maximum adherence values. Further, Lpb plantarum + L. monocytogenes isolated from blood invaded to HT-29 cell line at the highest level. Eventually, L. casei + Lpb plantarum + L. monocytogenes isolated from placenta revealed more expression levels in comparison with other groups. CONCLUSION: These results suggest a practical approach to classifying bacteriocins into functional groups that could be used for identifying the best mixture of bacteriocins for usage against L. monocytogenes.

The expression of type II TA system genes following persister cell formation in Pseudomonas aeruginosa isolates in the exponential and stationary phases.

Failure of infection therapy in the presence of antibiotics has become a major problem which has been mostly attributed to the ability of bacterial persister cell formation. Bacteria use various mechanisms to form persister cells in different phases, among which is the toxin-antitoxin (TA) systems. This study aimed at investigating the expression of type II TA system genes under the stress of ciprofloxacin and colistin antibiotics in the exponential and stationary phases. To determine the effects of ciprofloxacin and colistin on persister cell formation in the exponential and stationary phases of Pseudomonas aeruginosa strains, colony counting was performed at different time intervals in the presence of fivefold MIC of ciprofloxacin and colistin. In addition, the expression of relBE, Xre-COG5654, vapBC, and Xre-GNAT genes in P. aeruginosa isolates was assessed 3.5 h after antibiotic treatment in the exponential and stationary phases using qRT-PCR. Our results indicated the presence of persister phenotype of P. aeruginosa strains in the presence of fivefold MIC of ciprofloxacin and colistin compared to the control after 3.5 h of incubation in the exponential and stationary phases. Also, the number of persister cells in the stationary phase was higher than that of the exponential phase. According to the results of qRT-PCR, ciprofloxacin and colistin may induce persister cells by increasing the expression of type II TA systems in stationary and exponential phases. Ciprofloxacin and colistin may increase the formation of persister cells by affecting the expression of type II TA systems.

Association of perturbation of oral bacterial with incident of Alzheimer's disease: A pilot study.

OBJECTIVE: This case-control study was designed to compare the composition of the predominant oral bacterial microbiome in Alzheimer's disease (AD) and control group. SUBJECT: A total of 30 adult participants (15 AD and 15 healthy individuals) were entered in this study. The composition of oral bacterial microbiome was examined by quantitative real-time polymerase chain reaction (qPCR) using bacterial 16S rDNA gene. The levels of systemic inflammatory cytokines in both groups were assessed using enzyme-linked immunosorbent assays (ELISA). RESULTS: The loads of Porphyromonas gingivalis, Fusobacterium nucleatum, and Prevotella intermedia were significantly more abundant in the AD compared to the control group (p < 0.05). Although Aggregatibacter actinomycetemcomitans and Streptococcus mutans were relatively frequent in the AD group, no significance difference was observed in their copy number between two groups. Although the concentrations of IL-1, IL-6, and TNF-α were higher in the AD group, there was a significant difference in their levels between the two groups (p < 0.05). Finally, there was a significant relationship between increased number of pathogenic bacteria in oral microbiome and higher concentration of cytokines in patient's blood. CONCLUSION: Our knowledge of oral microbiome and its exact association with AD is rather limited; our study showed a significant association between changes in oral microbiome bacteria, increased inflammatory cytokines, and AD.

Distribution and expression of virulence genes (hlyA, sat) and genotyping of Escherichia coli O25b/ST131 by multi-locus variable number tandem repeat analysis in Tehran, Iran.

Escherichia coli ST131 is a pandemic clone with high antibiotic resistance, and it is a major causative agent of urinary tract infection (UTI) and bloodstream infections. This study evaluated the distribution and expression of virulence genes and genotyping of E. coli O25b/ST131 by Multi-locus variable number tandem repeat analysis (MLVA) method among UTI in patients at Tehran hospitals, Iran.A total of 107 E. coli isolates were collected from UTI patients. Polymerase chain reaction (PCR) amplification of the pabB gene was used to identify E. coli O25b/ST131 and the prevalence of sat and hlyA virulence genes was also analyzed. The microtiter method quantified biofilm formation ability in E. coli O25b/ST131. The Real-Time PCR (qRT-PCR) was performed to evaluate the expression of sat and hlyA genes. Finally, MLVA was performed for E. coli O25b/ST131 genotyping by targeting seven tandem repeats. SPSS-16 software was used for statistical analysis. Molecular study showed that 71% of isolates carried the pabB gene and were considered E. coli O25b/ST131 strains. Also, 45.8% and 17.8% of isolates carried sat and hlyA genes, respectively. The 57.9% isolates had biofilm formation ability. Expression of the studied virulence genes showed an increase in strong biofilm producing E. coli O25b/ST131 strains. A total of 76 (100%) E. coli O25b/ST131 strains were typed by the MLVA method.High prevalence of E. coli O25b/ST131 isolates in UTI patients can be a serious warning to the treatment due to the high antibiotic resistance rate, expression of virulence genes, and biofilm formation.

The expression of type II TA system genes following exposure to the sub-inhibitory concentration of gentamicin and acid stress in Brucella spp.

BACKGROUND: Brucellosis is one of the most common diseases that afflicts both humans and animals. Bacteria react to stress conditions using different mechanisms one of which is Toxin-Antitoxin (TA) systems. It is believed that the Toxin-Antitoxin (TA) systems have a key role in the chronicity of the disease. This study investigated the expression of TA system genes under acid and antibiotic stresses in Brucella spp. METHODS: Fifty Brucella isolates (17 isolated from animals and 31 isolated from human specimens, and two standard strains) were analyzed using PCR (using two pairs of primers). Then, to determine the effects of sub-MIC of gentamicin on bacterial survival and growth, colony forming unit was quantitated and turbidity was assessed following the treatment of Brucella spp, with ½ MIC of gentamicin at different time intervals. Furthermore, the colony forming unit of Brucella spp, was assessed under acid stress (pH = 5.5) compared to the control (pH = 7.6). Moreover, the expression of TA system genes in Brucella spp, was evaluated 1 h after treatment using qRT-PCR method. RESULTS: A total of 50 isolates, including 41 (82%) Brucella melitensis and 7 (14%) Brucella abortus with two standard strains Brucella melitensis (16 M) and Brucella abortus (B19) were investigated. Our results revealed the reduced growth of Brucella spp. in the presence of sub-MIC of gentamicin compared to the control. Furthermore, according to the results of qRT-PCR assay, gentamicin could increase the expression of TA system genes. Also, results of qRT-PCR showed that under acid stress, the expression of TA system gene COGT/COGAT decreased compared to the control. CONCLUSION: Although the exact role of the TA systems in response to stress is still unclear, our study provided information on the effect of the type II TA systems under the acid and antibiotic stress conditions. However, further studies are still required.

Identification of an intestinal microbiota signature associated with hospitalized patients with diarrhea.

As an important global health challenge, diarrhea kills nearly two million people each year. Postinfectious irritable bowel syndrome (IBS) usually manifests itself as the diarrhea-predominant subtype. Small intestinal bacterial overgrowth has been observed more frequently in patients with IBS compared to healthy controls. However, the pathophysiology of IBS is not fully understood, and based on recent evidences, altered gut microbiota is involved in the pathogenesis of IBS. Therefore, we aimed to compare the microbiome in hospitalized patients with diarrhea and healthy individuals. Thirty patients and 10 healthy controls were included into this case-control study. Microbial count was performed using quantitative real-time polymerase chain reaction method using bacterial 16S rRNA gene. Clostridium cluster IV and Bacteroides were significantly more frequent in the patients compared with the healthy individuals (p = 0.02 and 0.023, respectively). However, the quantity of Enterococcus and Bifidobacterium groups were significantly higher in healthy controls than in diarrheal group (p = 0.000076 and 0.001, respectively). The results showed that the number of bacteria in all bacterial groups was significantly different between healthy individuals and diabetic group, whereas the difference between the healthy group and IBS was not significant for Bifidobacterium group. The findings of this study outlined the relationship between diarrhea, IBS, and diabetes disease and bacterial composition. It could be concluded that modifying the bacterial composition by probiotics can be helpful in the control and management of the mentioned disease.

Prevalence of proline racemase/ hydroxyproline epimerase gene in human brucella isolates in Iran.

Background: Human brucellosis is a zoonotic disease caused by Brucella melitensis, Brucella abortus, and Brucella suis. Brucella causes a chronic disease, which subverts the immune defense system of their hosts. In this study, the prevalence of an important Brucella virulence determinant, prpA, which can modulate immune response, was determined in human isolates. Methods: Polymerase chain reaction (PCR) assay was standardized and applied to 37 isolates obtained from patient's specimens. Primers for prpA gene were designed and evaluated using bioinformatic tools. DNA sequencing was performed for further verification. Results: In the 37 Brucella isolates (31 Brucella melitensis and 6 Brucella abortus), 32 (86.4%) carried prpA gene. Conclusion: Presence of prpA gene in most isolates indicates the high prevalence of this gene among Iranian isolates and emphasizes its role in pathogenicity of this organism.

Prevalence of antibiotic resistance in Salmonella Typhimurium isolates originating from Iran: a systematic review and meta-analysis.

Objective: Antibiotic resistance in Salmonella represents a significant global public health concern. Among various serovars, Salmonella enterica serovar Typhimurium is prevalent in multiple countries. This study aims to conduct a systematic review and meta-analysis to evaluate the pattern of antibiotic resistance in S. Typhimurium isolates from diverse sources in Iran. Methods: We conducted a comprehensive and systematic search for relevant articles until December 2023 in the following databases: PubMed, Scopus, Web of Science, and SID. The collected data were analyzed using Stata software version 17. Results: Eighteen studies examined the pattern of antibiotic resistance in S. Typhimurium for various antibiotics in Iran. Piperacillin and tetracycline exhibited the highest resistance rates, at 79 and 60% respectively, while cefixime and ceftriaxone had the lowest resistance rates at 0%. Conclusion: Our findings indicate a high level of antibiotic resistance among the studied antibiotics. This high level of antibiotic resistance raises concerns and underscores the necessity for monitoring the use of antibiotics. Moreover, resistance to these antibiotics was more prevalent in samples isolated from animals compared to other sources. This highlights the importance of animal screening to detect the presence of drug-resistant isolates, with the ultimate goal of reducing antibiotic resistance and preventing the transmission of resistant strains to humans.

Risk Factors Associated with Human Brucellosis: A Systematic Review and Meta-Analysis.

Background: Brucellosis is a zoonosis disease that can affect humans and a wide range of domestic and wild animals. Susceptibility to brucellosis in humans can be related to various factors, such as nutritional and occupational factors. This study evaluated factors related to brucellosis and identified influential risk factors for human infection. Methods: We performed a systematic literature review and meta-analysis of studies in PubMed, Web of Science, and Scopus. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were used to measure the strength of the association between some potential factors and the risk of brucellosis. Results: From 277 initial studies, 19 case-control studies were included in this review. Significant risk factors for brucellosis included occupation (OR 3.31, 95% CI 1.68-6.55), having aborted animals (OR 4.16, 95% CI 2.03-8.50), consumption of meat (OR 2.17, 95% CI 1.44-3.36), unpasteurized milk (OR 3.86, 95% CI 1.81-8.23), and raw cheese (OR 4.20, 95% CI 1.63-10.85). Conclusion: The results of this study advance the understanding of the etiology of brucellosis. In this meta-analysis, we found the association of different environmental factors with the risk of brucellosis. Additional high-quality prospective studies are needed to determine whether these factors cause brucellosis and to identify other factors.

Prevalence of antibiotic resistance in clinical isolates of Mycobacterium kansasii: a systematic review and meta-analysis.

INTRODUCTION: The prevalence of diseases caused by non-tuberculous mycobacteria (NTM), including M. kansasii, is increasing, necessitating further information to guide prevention, control, and treatment strategies. AREAS COVERED: A comprehensive analysis of articles published until February 2023 was conducted on PubMed, Web of Science, and Scopus databases to investigate antibiotic resistance in M. kansasii species. Stata software version 17 was employed for all analyses. EXPERT OPINION: A total of 1647 articles were obtained through database search. After removing duplicates and unrelated studies, 17 cross-sectional studies that examined the breakpoints proposed by CLSI were included. The rates of resistance of M. kansasii to various antibiotics were as follows: clarithromycin (0%), rifampin (1%), amikacin (0%), ciprofloxacin (14%), linezolid (0%), moxifloxacin (0%), rifabutin (1%), doxycycline (96%), and SXT (49%). Our findings underscore the importance of managing and monitoring the use of these antibiotics, as well as the need for further studies to elucidate the exact mechanism of M. kansasii resistance to these antibiotics.

Upregulation of pmrA, pmrB, pmrC, phoQ, phoP, and arnT genes contributing to resistance to colistin in superbug Klebsiella pneumoniae isolates from human clinical samples in Tehran, Iran.

Background: Antibiotic resistance in Klebsiella pneumoniae isolates, particularly resistance to colistin, has become a growing concern. This study seeks to investigate the upregulation of specific genes (pmrA, pmrB, pmrC, phoQ, phoP, and arnT) that contribute to colistin resistance in K. pneumoniae isolates collected from human clinical samples in Tehran, Iran. Methods: Thirty eight K. pneumoniae isolates were obtained and subjected to antibiotic susceptibility testing, as well as evaluation for phenotypic AmpC and ESBL production according to CLSI guidelines. The investigation of antibiotic resistance genes was conducted using polymerase chain reaction (PCR), whereas the quantification of colistin resistance related genes expressions was performed via Real-Time PCR. Results: The highest and lowest antibiotics resistance were observed for cefotaxime 33 (86.8%) and minocycline 8 (21.1%), respectively. Twenty-four (63.2%) and 31 (81.6%) isolates carried AmpC and ESBLs, respectively. Also, antibiotic resistance genes containing blaNDM, blaIMP, blaVIM, blaSHV, blaTEM, blaCTXM, qnrA, qnrB, qnrS, and aac(6')-Ib were detected in K. pneumoniae isolates. Only 5 (13.1%) isolates were resistant to colistin and the MIC range of these isolates was between 4 and 64 µg ml-1. Upregulation of the pmrA, pmrB, pmrC, phoQ, phoP, and arnT genes was observed in colistin-resistant isolates. The colistin-resistant isolates were found to possess a simultaneous presence of ESBLs, AmpC, fluoroquinolone, aminoglycoside, and carbapenem resistant genes. Conclusions: This study reveals escalating antibiotic resistance in K. pneumoniae, with notable coexistence of various resistance traits, emphasizing the need for vigilant surveillance and innovative interventions.

Secondary Klebsiella pneumoniae infection in patients with COVID-19: A systematic review.

This study aims to investigate the development of secondary bacterial infection and risk factors associated with it in critical COVID-19 patients, and to identify the most common pathogen groups in them. All the cohort studies were retrieved from Scopus, Google Scholar, Web of Science, and MEDLINE from the inception of COVID-19 to 2022 for the following keywords: 'Klebsiella" AND "COVID-19". The most common comorbidities among the patients with COVID-19 were respiratory disease (33.62%), obesity (28.99%), and heart disease or cardiovascular disease (16.31%). We report 42.91% rate of Klebsiella spp co-infection in ICU admission patients, mostly related to K. pneumonia (26.81%), K. aerogenes (9.4%), and K. oxytoca (6.7%). The overall incidence of bacterial infection in hospitalized COVID-19 patients is estimated at 15.5% and in 32.5% of cases of co-infection patients deceased. The threat of carbapenem-resistant K. pneumoniae infections in patients with COVID-19 is imminent, therefore rational antibiotic therapy based on antibiotic sensitivity test should be implemented.

Prevalence of Brucella endocarditis: A systematic review and meta-analysis.

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.

Potential antibacterial activity and healing effect of topical administration of bone marrow and adipose mesenchymal stem cells encapsulated in collagen-fibrin hydrogel scaffold on full-thickness burn wound infection caused by Pseudomonas aeruginosa.

Burns injuries are prone to hospital-acquired infections, and Pseudomonas aeruginosa is one of the most common causes of mortality and morbidity in patients with burn injuries. Thus, this study aimed to analyze the effects of topical treatment with bone marrow (BM-MSC) and adipose mesenchymal stem cells (AD-MSC) encapsulated in collagen and fibrin scaffolds in a Balb/c model of burn wound infection. Extraction of stem cells from adipose and bone marrow tissue of rats was performed and cells were characterized using standard methods. Then, collagen, fibrin and collagen-fibrin scaffolds were constructed and the extracted cells were encapsulated in all three scaffolds. Then, 3rd degree burn was induced in mice and 1.5 × 108 (CFU/ml) of P. aeruginosa was introduced to the burn wound. Subsequently, after 24 h of inducing wound infection, encapsulated MSCs were introduced as dressings to burn wound infection and microbial load as well as rate of wound infection healing was measured. The results of this study showed that the use of BM-MSC and AD-MSC encapsulated in collagen-fibrin scaffold reduced the bacteria load down to 54 and 21 CFU/gr, respectively (P < 0.05). Moreover, BM-MSC and AD-MSC encapsulated in collagen-fibrin showed 80% and 75% wound healing, respectively (P < 0.05). Also, we found no significant between cell origin and healing. Encapsulation of MSCs into collagen-fibrin scaffolds could be effective not only against P. aeruginosa infection, but also healing and regeneration of burn wound.

Passive immunization with anti- chimeric protein PilQ/PilA -DSL region IgY does not protect against mortality associated with Pseudomonas aeruginosa sepsis in a rabbit model.

BACKGROUND: Pseudomonas aeruginosa sepsis is associated with unacceptably high mortality and, for many of those who survive, long-term morbidity. The aims of this study were to production of IgY against chimeric protein pilQ-pilA-DSL region and killed- whole cell Pseudomonas aeruginosa O1 (PAO1) strain and their efficacy for immunoprophylaxis of sepsis caused by P. aeruginosa in a rabbit model. METHODS: Specific IgY was obtained by immunization of hens. The purity of IgY was determined by SDS-PAGE analysis. The effect of IgY on growth and hydrophobicity of P. aeruginosa were performed through time-kill assay and microbial adhesion to hydrocarbons test (MATH), respectively. The efficacy of specific IgYs was examined against P. aeruginosa sepsis in a rabbit model. The rabbits were monitored for 72 h to record physiological characters and survival. Hematologic factors, C-reactive protein, pro-inflammatory cytokines, and bacterial count from blood and solid organs were measured, periodically. RESULTS: We found that the growth inhibitory effect of the anti- killed whole cell IgY was higher than anti-pilQ-pilA IgY (P < 0.001). The hydrophobicity effect of PAO1 increased when bacteria were opsonized by anti- killed whole cell IgY while the hydrophobicity activity was decreased following incubation of PAO1 with anti-pilQ-pilA IgY in a broth medium (P < 0.001). Following intravenous (IV) administration of produced IgYs, no significant difference was observed in the survival, decrease in inflammatory mediators and clinical symptoms between the groups 48h post infection (P > 0.05). Moreover, no considerable decrease was observed in the bacterial load of blood, lungs and kidneys in rabbits treated with specific IgYs and control groups (P > 0.05). No bacteria were found in the spleen and liver samples from infected rabbits. CONCLUSION: Although produced IgYs had a good immunoreactivity, IV immunization of IgYs was not protective against P. aeruginosa sepsis in the rabbit model. Further studies are needed to assess the immune response and decreasing mortality rate using the rabbit sepsis model.

Combination of Antibiotics-Nisin Reduces the Formation of Persister Cell in Listeria monocytogenes.

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.

Persister cells formation and expression of type II Toxin-Antitoxin system genes in Brucella melitensis (16M) and Brucella abortus (B19).

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.

How Phages Overcome the Challenges of Drug Resistant Bacteria in Clinical Infections.

Nowadays the most important problem in the treatment of bacterial infections is the appearance of MDR (multidrug-resistant), XDR (extensively drug-resistant) and PDR (pan drug-resistant) bacteria and the scarce prospects of producing new antibiotics. There is renewed interest in revisiting the use of bacteriophage to treat bacterial infections. The practice of phage therapy, the application of phages to treat bacterial infections, has been around for approximately a century. Phage therapy relies on using lytic bacteriophages and purified phage lytic proteins for treatment and lysis of bacteria at the site of infection. Current research indicates that phage therapy has the potential to be used as an alternative to antibiotic treatments. It is noteworthy that, whether phages are used on their own or combined with antibiotics, phages are still a promising agent to replace antibiotics. So, this review focuses on an understanding of challenges of MDR, XDR, and PDR bacteria and phages mechanism for treating bacterial infections and the most recent studies on potential phages, cocktails of phages, and enzymes of lytic phages in fighting these resistant bacteria.