Salmonella enterica serovar Typhimurium BaeSR two-component system positively regulates sodA in response to ciprofloxacin

Antimicrobial drug resistant features of Mycobacterium tuberculosis associated with treatment failure

Tuberculosis stands as a prominent cause of mortality in developing countries. The treatment of tuberculosis involves a complex procedure requiring the administration of a panel of at least four antimicrobial drugs for the duration of six months. The occurrence of treatment failure after the completion of a standard treatment course presents a serious medical problem. The purpose of this study was to evaluate antimicrobial drug resistant features of Mycobacterium tuberculosis associated with treatment failure. Additionally, it aimed to evaluate the effectiveness of second line drugs such as amikacin, linezolid, moxifloxacin, and the efflux pump inhibitor verapamil against M. tuberculosis isolates associated with treatment failure. We monitored 1200 tuberculosis patients who visited TB centres in Lahore and found that 64 of them were not cured after six months of treatment. Among the M. tuberculosis isolates recovered from the sputum of these 64 patients, 46 (71.9%) isolates were simultaneously resistant to rifampicin and isoniazid (MDR), and 30 (46.9%) isolates were resistant to pyrazinamide, Resistance to amikacin was detected in 17 (26,5%) isolates whereas resistance to moxifloxacin and linezolid was detected in 1 (1.5%) and 2 (3.1%) isolates respectively. Among MDR isolates, the additional resistance to pyrazinamide, amikacin, and linezolid was detected in 15(23.4%), 4(2.6%) and 1(1.56%) isolates respectively. One isolate simultaneously resistant to rifampicin, isoniazid, amikacin, pyrazinamide, and linezolid was also identified. In our investigations, the most frequently mutated amino acid in the treatment failure group was Serine 315 in katG. Three novel mutations were detected at codons 99, 149 and 154 in pncA which were associated with pyrazinamide resistance. The effect of verapamil on the minimum inhibitory concentration of isoniazid and rifampicin was observed in drug susceptible isolates but not in drug resistant isolates. Rifampicin and isoniazid enhanced the transcription of the efflux pump gene rv1258 in drug susceptible isolates collected from the treatment failure patients. Our findings emphasize a high prevalence of MDR isolates linked primarily to drug exposure. Moreover, the use of amikacin as a second line drug may not be the most suitable choice in such cases.

Impact of Salmonella genome rearrangement on gene expression

In addition to nucleotide variation, many bacteria also undergo changes at a much larger scale via rearrangement of their genome structure (GS) around long repeat sequences. These rearrangements result in genome fragments shifting position and/or orientation in the genome without necessarily affecting the underlying nucleotide sequence. To date, scalable techniques have not been applied to GS identification, so it remains unclear how extensive this variation is and the extent of its impact upon gene expression. However, the emergence of multiplexed, long-read sequencing overcomes the scale problem, as reads of several thousand bases are routinely produced that can span long repeat sequences to identify the flanking chromosomal DNA, allowing GS identification. Genome rearrangements were generated in Salmonella enterica serovar Typhi through long-term culture at ambient temperature. Colonies with rearrangements were identified via long-range PCR and subjected to long-read nanopore sequencing to confirm genome variation. Four rearrangements were investigated for differential gene expression using transcriptomics. All isolates with changes in genome arrangement relative to the parent strain were accompanied by changes in gene expression. Rearrangements with similar fragment movements demonstrated similar changes in gene expression. The most extreme rearrangement caused a large imbalance between the origin and terminus of replication and was associated with differential gene expression as a factor of distance moved toward or away from the origin of replication. Genome structure variation may provide a mechanism through which bacteria can quickly adapt to new environments and warrants routine assessment alongside traditional nucleotide-level measures of variation.

Quantitative phosphoproteomics reveals the effect of baeSR and acrB genes on protein phosphorylation in Salmonella enterica serovar Typhimurium

The BaeSR two-component system and the AcrB efflux pump are closely associated with Salmonella resistance to antibiotics. However, the relationship between the two-component system, efflux pumps and protein phosphorylation of Salmonella is poorly understood. In this study, S. typhimurium ciprofloxacin-resistant strain CR, baeSR gene deletion strain CR^ΔbaeSR, acrB gene deletion strain CR^ΔacrB, and double gene deletion strain CR^{ΔbaeSRΔacrB} were used to explore phosphorylated proteins with significant difference, based on non-marker, quantitative phosphorylation modified proteomics technique. Consequently, 363 phosphosites of 213 phosphoproteins were identified in the four strains. More than 70% of the phosphosites were serine phosphorylation. In the CR^ΔbaeSR/CR, CR^ΔacrB/CR and CR^{ΔbaeSRΔacrB}/CR comparison groups, 36, 37 and 49 phosphosites were significantly altered, respectively. Bioinformatic analysis revealed that the main enrichment pathways of these differentially phosphorylated proteins were metabolic pathways, biosynthesis of antibiotics, phosphotransferase system (PTS), ABC transporters, and lipopolysaccharide biosynthesis. Furthermore, 21 differentially phosphorylated proteins were identified to be associated with antibiotic resistance. These results suggest that the BaeSR two-component system and the AcrB efflux pump affect the phosphorylation of proteins in S. typhimurium and may influence the drug resistance and virulence of S. typhimurium by affecting protein phosphorylation, providing a new idea to explore the mechanism of drug resistance in Salmonella.

Adaptation and compensation in a bacterial gene regulatory network evolving under antibiotic selection

Gene regulatory networks allow organisms to generate coordinated responses to environmental challenges. In bacteria, regulatory networks are re-wired and re-purposed during evolution, though the relationship between selection pressures and evolutionary change is poorly understood. In this study, we discover that the early evolutionary response of Escherichia coli to the antibiotic trimethoprim involves derepression of PhoPQ signaling, an Mg²⁺-sensitive two-component system, by inactivation of the MgrB feedback-regulatory protein. We report that derepression of PhoPQ confers trimethoprim-tolerance to E. coli by hitherto unrecognized transcriptional upregulation of dihydrofolate reductase (DHFR), target of trimethoprim. As a result, mutations in mgrB precede and facilitate the evolution of drug resistance. Using laboratory evolution, genome sequencing, and mutation re-construction, we show that populations of E. coli challenged with trimethoprim are faced with the evolutionary ‘choice’ of transitioning from tolerant to resistant by mutations in DHFR, or compensating for the fitness costs of PhoPQ derepression by inactivating the RpoS sigma factor, itself a PhoPQ-target. Outcomes at this evolutionary branch-point are determined by the strength of antibiotic selection, such that high pressures favor resistance, while low pressures favor cost compensation. Our results relate evolutionary changes in bacterial gene regulatory networks to strength of selection and provide mechanistic evidence to substantiate this link.

Polymyxins, the last-resort antibiotics: Mode of action, resistance emergence, and potential solutions

Infections caused by multi-drug resistant (MDR) bacterial pathogens are a leading cause of mortality and morbidity across the world. Indiscriminate use of broad-spectrum antibiotics has seriously affected this situation. With the diminishing discovery of novel antibiotics, new treatment methods are urgently required to combat MDR pathogens. Polymyxins, the cationic lipopeptide antibiotics, discovered more than half a century ago, are considered to be the last-line of antibiotics available at the moment. This antibiotic shows a great bactericidal effect against Gram-negative bacteria. Polymyxins primarily target the bacterial membrane and disrupt them, causing lethality. Because of their membrane interacting mode of action, polymyxins cause nephrotoxicity and neurotoxicity in humans, limiting their usability. However, recent modifications in their chemical structure have been able to reduce the toxic effects. The development of better dosing regimens has also helped in getting better clinical outcomes in the infections caused by MDR pathogens. Since the mid-1990s the use of polymyxins has increased manifold in clinical settings, resulting in the emergence of polymyxin-resistant strains. The risk posed by the polymyxin-resistant nosocomial pathogens such as the Enterobacteriaceae group, Pseudomonas aeruginosa, and Acinetobacter baumannii, etc. is very serious considering these pathogens are resistant to almost all available antibacterial drugs. In this review article, the mode of action of the polymyxins and the genetic regulatory mechanism responsible for the emergence of resistance are discussed. Specifically, this review aims to update our current understanding in the field and suggest possible solutions that can be pursued for future antibiotic development. As polymyxins primarily target the bacterial membranes, resistance to polymyxins arises primarily by the modification of the lipopolysaccharides (LPS) in the outer membrane (OM). The LPS modification pathways are largely regulated by the bacterial two-component signal transduction (TCS) systems. Therefore, targeting or modulating the TCS signalling mechanisms can be pursued as an alternative to treat the infections caused by polymyxin-resistant MDR pathogens. In this review article, this aspect is also highlighted.

The role of two-component regulatory systems in environmental sensing and virulence in Salmonella

Adaptation to environments with constant fluctuations imposes challenges that are only overcome with sophisticated strategies that allow bacteria to perceive environmental conditions and develop an appropriate response. The gastrointestinal environment is a complex ecosystem that is home to trillions of microorganisms. Termed microbiota, this microbial ensemble plays important roles in host health and provides colonization resistance against pathogens, although pathogens have evolved strategies to circumvent this barrier. Among the strategies used by bacteria to monitor their environment, one of the most important are the sensing and signalling machineries of two-component systems (TCSs), which play relevant roles in the behaviour of all bacteria. Salmonella enterica is no exception, and here we present our current understanding of how this important human pathogen uses TCSs as an integral part of its lifestyle. We describe important aspects of these systems, such as the stimuli and responses involved, the processes regulated, and their roles in virulence. We also dissect the genomic organization of histidine kinases and response regulators, as well as the input and output domains for each TCS. Lastly, we explore how these systems may be promising targets for the development of antivirulence therapeutics to combat antibiotic-resistant infections.

Polymyxins, the last-resort antibiotics: Mode of action, resistance emergence, and potential solutions

Infections caused by multi-drug resistant (MDR) bacterial pathogens are a leading cause of mortality and morbidity across the world. Indiscriminate use of broad-spectrum antibiotics has seriously affected this situation. With the diminishing discovery of novel antibiotics, new treatment methods are urgently required to combat MDR pathogens. Polymyxins, the cationic lipopeptide antibiotics, discovered more than half a century ago, are considered to be the last-line of antibiotics available at the moment. This antibiotic shows a great bactericidal effect against Gram-negative bacteria. Polymyxins primarily target the bacterial membrane and disrupt them, causing lethality. Because of their membrane interacting mode of action, polymyxins cause nephrotoxicity and neurotoxicity in humans, limiting their usability. However, recent modifications in their chemical structure have been able to reduce the toxic effects. The development of better dosing regimens has also helped in getting better clinical outcomes in the infections caused by MDR pathogens. Since the mid1990s the use of polymyxins has increased manifold in clinical settings, resulting in the emergence of polymyxin-resistant strains. The risk posed by the polymyxin-resistant nosocomial pathogens such as the Enterobacteriaceae group, Pseudomonas aeruginosa, and Acinetobacter baumannii, etc. is very serious considering these pathogens are resistant to almost all available antibacterial drugs. In this review article, the mode of action of the polymyxins and the genetic regulatory mechanism responsible for the emergence of resistance are discussed. Specifically, this review aims to update our current understanding in the field and suggest possible solutions that can be pursued for future antibiotic development. As polymyxins primarily target the bacterial membranes, resistance to polymyxins arises primarily by the modification of the lipopolysaccharides (LPS) in the outer membrane (OM). The LPS modification pathways are largely regulated by the bacterial two-component signal transduction (TCS) systems. Therefore, targeting or modulating the TCS signalling mechanisms can be pursued as an alternative to treat the infections caused by polymyxin-resistant MDR pathogens. In this review article, this aspect is also highlighted.

Genomic Variation and Arsenic Tolerance Emerged as Niche Specific Adaptations by Different Exiguobacterium Strains Isolated From the Extreme Salar de Huasco Environment in Chilean - Altiplano

Polyextremophilic bacteria can thrive in environments with multiple stressors such as the Salar de Huasco (SH). Microbial communities in SH are exposed to low atmospheric pressure, high UV radiation, wide temperature ranges, salinity gradient and the presence of toxic compounds such as arsenic (As). In this work we focus on arsenic stress as one of the main adverse factors in SH and bacteria that belong to the Exiguobacterium genus due to their plasticity and ubiquity. Therefore, our aim was to shed light on the effect of niche conditions pressure (particularly arsenic), on the adaptation and divergence (at genotypic and phenotypic levels) of Exiguobacterium strains from five different SH sites. Also, to capture greater diversity in this genus, we use as outgroup five As(III) sensitive strains isolated from Easter Island (Chile) and The Great Salt Lake (United States). For this, samples were obtained from five different SH sites under an arsenic gradient (9 to 321 mg/kg: sediment) and isolated and sequenced the genomes of 14 Exiguobacterium strains, which had different arsenic tolerance levels. Then, we used comparative genomic analysis to assess the genomic divergence of these strains and their association with phenotypic differences such as arsenic tolerance levels and the ability to resist poly-stress. Phylogenetic analysis showed that SH strains share a common ancestor. Consequently, populations were separated and structured in different SH microenvironments, giving rise to multiple coexisting lineages. Hence, this genotypic variability is also evidenced by the COG (Clusters of Orthologous Groups) composition and the size of their accessory genomes. Interestingly, these observations correlate with physiological traits such as growth patterns, gene expression, and enzyme activity related to arsenic response and/or tolerance. Therefore, Exiguobacterium strains from SH are adapted to physiologically overcome the contrasting environmental conditions, like the arsenic present in their habitat.

The Bacteriology and Its Virulence Factors in Neonatal Infections: Threats to Child Survival Strategies

BACKGROUND

Neonatal infection refers to the infection of the newborn during the first twenty-eight days of life. It is one of the causes of infant morbidity and mortality worldwide. The aim of the study is to determine the relative contribution of the different pathogens to the overall disease burden. It will also determine the mechanisms of virulence of these pathogens that cause neonatal infections at Chukwuemeka Odumegwu Ojukwu University Teaching Hospital (COOUTH), Awka.

METHODS

Biological samples were collected from 30 neonates admitted at the special care baby unit (SCBU) of COOUTH and cultured using selective media and nutrient agar. The isolates were identified using microbiological and biochemical tests. The antibiogram study was determined using Kirby-Bauer disc diffusion method on Mueller Hinton Agar. Several methods previously reported in literature were used for the characterization of the virulence factors.

RESULTS

From the 30 blood samples collected, Pseudomonas spp. (19.7%), Escherichia coli (23%), Salmonella spp. (24.6%), and Staphylococcus aureus (32.8%) were isolated. Male to female ratio of study population was 1.5: 1. The isolates were 100 % resistant to ticarcillin, cephalothin, ceftazidime, and cefuroxime but appreciably susceptible to only levofloxacin (88.85%). They were moderately susceptible to ceftriaxone/sulbactam (39.05%) and azithromycin (26.46%). Common virulence factors identified among the isolates (up to 90 %) were hemolysin, biofilm formation, and acid resistance. Less common virulence factors were proteases (50 %), deoxyribonucleases (50 %), enterotoxins (63%), and lipopolysaccharide (70%). The virulence factors were found mostly among the S. aureus isolates.

CONCLUSIONS

Pseudomonas spp., Escherichia coli, Salmonella spp., and Staphylococcus aureus were implicated in neonatal infections in the center and most of them were resistant to conventional antibiotics. The organisms showed marked virulence and multidrug resistance properties. Levofloxacin, a fluoroquinolone, had superior activity on the isolates compared to other antibiotics used in the study.

Is Cr(III) toxic to bacteria: toxicity studies using Bacillus subtilis and Escherichia coli as model organism

The objective of this work is to detect the mode of damage caused by Cr(III), one of the widely used industrial pollutant on Bacillus subtilis-industrial strain 168 and Escherichia coli MTCC 40. Bioassays are very sensitive, precise, economical and rapid for detecting early stages of pollution. The detrimental effect of trivalent chromium becomes clear from the growth profile and growth inhibition studies. Mode of action of damage by trivalent chromium in bacterial model was found to be oxidative, as chromium is one of the redox active metals. The generation of reactive oxygen species (ROS) resulted in membrane damage which in turn had a detrimental effect on the membrane proteins as well as the DNA. The structural changes in the SEM and AFM images clearly reveals the damage caused by Cr(III) to the test bacterial models. Trivalent chromium causes greater DNA, protein and membrane damage in case of E. coli than B. subtilis. Membrane damage caused by ROS becomes evident from the production of Thiobarbituric acid reactive substances (TBARs) as the mechanism of killing followed by DNA damage and the production of elevated levels of stress proteins known as extracellular cellular proteins.

AdeR protein regulates adeABC expression by binding to a direct-repeat motif in the intercistronic spacer

Overexpression of the efflux pump AdeABC is associated with tigecycline resistance of multi-drug resistant Acinetobacter baumannii (MDRAB). A two-component regulatory system, sensor AdeS and regulator AdeR proteins regulate the pump. However, the detailed mechanism of the AdeR protein to enhance the expression of adeABC operon is not well defined. We illustrated the biological characteristics of AdeR proteins by comparing a mutant AdeR protein of a tigecycline resistant MDRAB to the wild AdeR protein. By analyzing a series of deletion constructs, a minimal gene cassette of the intercistronic spacer DNA fragment specifically bound with the adeR protein and resulted in band shifting in electrophoresis mobility shifting assays (EMSA). A conserve direct repeat motif was observed in the intercistronic spacer DNA. We demonstrated the AdeR protein was a direct-repeat-binding protein. Two common residue mutations on the AdeR proteins of tigecycline resistant MDRAB isolates could reduce their binding affinity with the intercistronic spacer. The free intercistronic spacer may then more efficiently support the read-through of the adeABC operon during the co-transcriptional translation in tigecycline resistant MDRAB isolates.

CysB-dependent upregulation of the Salmonella Typhimurium cysJIH operon in response to antimicrobial compounds that induce oxidative stress

It has been proposed that some antibiotics exert additional damage through reactive oxygen species (ROS) production. Since H₂S protects neurons and cardiac muscle from oxidative stress, it has been hypothesized that bacterial H₂S might, similarly, be a cellular protector against antibiotics. In Enterobacteriaceae, H₂S can be produced by the cysJIH pathway, which uses sulfate as the sulfur source. CysB, in turn, is a positive regulator of cysJIH. At present, the role of S. Typhimurium cysJIH operon in the protection to reactive oxygen species (ROS) induced by antimicrobial compounds remains to be elucidated. In this work, we evaluated the role of cysJIH and cysB in ROS accumulation, superoxide dismutase (SOD) activity, reduced thiol accumulation, and H₂S accumulation in S. Typhimurium, cultured in either sulfate or cysteine as the sole sulfur source. Furthermore, we assessed the effects of the addition of ceftriaxone (CEF) and menadione (MEN) in these same parameters. In sulfate as the sole sulfur source, we found that the cysJIH operon and the cysB gene were required to full growth in minimal media, independently on the addition of CEF or MEN. Most importantly, both cysJIH and cysB contributed to diminish ROS levels, increase the SOD activity, increase the reduced thiols, and increase the H₂S levels in presence of CEF or MEN. Moreover, the cysJIH operon exhibited a CysB-dependent upregulation in presence of these two antimicrobials compounds. On the other hand, when cysteine was used as the sole sulfur source, we found that cysJIH operon was completely negligible, were only cysB exhibited similar phenotypes than the described for sulfate as sulfur source. Unexpectedly, CysB downregulated cysJIH operon when cysteine was used instead of sulfate, suggesting a complex regulation of this system.

Bacterial histidine kinases as novel antibacterial drug targets

Bacterial histidine kinases (HKs) are promising targets for novel antibacterials. Bacterial HKs are part of bacterial two-component systems (TCSs), the main signal transduction pathways in bacteria, regulating various processes including virulence, secretion systems and antibiotic resistance. In this review, we discuss the biological importance of TCSs and bacterial HKs for the discovery of novel antibacterials, as well as published TCS and HK inhibitors that can be used as a starting point for structure-based approaches to develop novel antibacterials.

Structure-to-function relationships of bacterial translocator protein (TSPO): a focus on Pseudomonas

The translocator protein (TSPO), which was previously designated as the peripheral-type benzodiazepine receptor, is a 3.5 billion year-old evolutionarily conserved protein expressed by most Eukarya, Archae and Bacteria, but its organization and functions differ remarkably. By taking advantage of the genomic data available on TSPO, we focused on bacterial TSPO and attempted to define functions of TSPO in Pseudomonas via in silico approaches. A tspo ortholog has been identified in several fluorescent Pseudomonas. This protein presents putative binding motifs for cholesterol and PK 11195, which is a specific drug ligand of mitochondrial TSPO. While it is a common surface distribution, the sense of insertion and membrane localization differ between α- and γ-proteobacteria. Experimental published data and STRING analysis of common TSPO partners in fluorescent Pseudomonas indicate a potential role of TSPO in the oxidative stress response, iron homeostasis and virulence expression. In these bacteria, TSPO could also take part in signal transduction and in the preservation of membrane integrity.

Complete proteome of a quinolone-resistant Salmonella Typhimurium phage type DT104B clinical strain

Salmonellosis is one of the most common and widely distributed foodborne diseases. The emergence of Salmonella strains that are resistant to a variety of antimicrobials is a serious global public health concern. Salmonella enterica serovar Typhimurium definitive phage type 104 (DT104) is one of these emerging epidemic multidrug resistant strains. Here we collate information from the diverse and comprehensive range of experiments on Salmonella proteomes that have been published. We then present a new study of the proteome of the quinolone-resistant Se20 strain (phage type DT104B), recovered after ciprofloxacin treatment and compared it to the proteome of reference strain SL1344. A total of 186 and 219 protein spots were recovered from Se20 and SL1344 protein extracts, respectively, after two-dimensional gel electrophoresis. The signatures of 94% of the protein spots were successfully identified through matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). Three antimicrobial resistance related proteins, whose genes were previously detected by polymerase chain reaction (PCR), were identified in the clinical strain. The presence of these proteins, dihydropteroate synthase type-2 (sul2 gene), aminoglycoside resistance protein A (strA gene) and aminoglycoside 6'-N-acetyltransferase type Ib-cr4 (aac(6')-Ib-cr4 gene), was confirmed in the DT104B clinical strain. The aac(6')-Ib-cr4 gene is responsible for plasmid-mediated aminoglycoside and quinolone resistance. This is a preliminary analysis of the proteome of these two S. Typhimurium strains and further work is being developed to better understand how antimicrobial resistance is developing in this pathogen.