Cysteine auxotrophy drives reduced susceptibility to quinolones and paraquat by inducing the expression of efflux-pump systems and detoxifying enzymes in S. Typhimurium

Cellulase exhibited a therapeutic potential to inhibit Salmonella enterica serovar Typhi biofilm by targeting multiple regulatory proteins of biofilm

Biofilm-mediated Salmonella enterica serovar Typhi (Salmonella Ser. Typhi) infections are a growing global health issue due to the formation of antibiotic resistance. The study aimed to discover some of the druggable target proteins of Salmonella Ser. Typhi biofilm and antibiofilm enzyme to prevent Salmonella Ser. Typhi biofilm-mediated infection. Enzymatic therapy has demonstrated effective therapeutic results against bacterial infections due to its specificity and high binding capacity to the target. Therefore, this study focused on the computational interaction between the cellulase enzyme and Salmonella Ser. Typhi biofilm targets proteins with help of the various computational experiments such as ADMET (absorption, distribution, metabolism, excretion, and toxicity), protein-protein interactions, MMGBSA, etc. Further, in vitro validations of the typhoidal biofilm and cellulose presence in Salmonella Ser. Typhi biofilm was conducted using Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy, and Raman analysis. Additionally, a minimum biofilm inhibitory concentration assay for cellulase was conducted and find out the optimized cellulase concentration which showed its inhibitory effect on the Salmonella Ser. Typhi. The cellulase antibiofilm effect was analyzed with the help of SEM analysis. Further, the cellulose content in Salmonella Ser. Typhi was quantified before and after treatment of cellulase enzyme. As a result, 58.82 % cellulose content was decreased due to cellulase treatment in Salmonella Ser. Typhi. From the seven selected typhoidal biofilm regulatory proteins of Salmonella Ser. Typhi, we identified only five potential druggable targets: BcsA, CsgE, OmpR, CsgF, and CsgD. The BcsA protein is responsible for cellulose production in Salmonella Ser. Typhi biofilm. Consequently, cellulose worked as a fascinating drug target in Salmonella Ser. Typhi biofilm. Therefore, we used cellulase as a potential antibiofilm enzyme for target-based disruption of biofilm. The cellulase showed a high binding affinity with all five identified target proteins [BcsA(-205.62 kcal/mol) > CsgE(-108.20 kcal/mol) > OmpR(-107.58 kcal/mol) > CsgF(-73.74 kcal/mol) > CsgD(-66.61 kcal/mol)] in the protein-protein interaction analysis. Our computational analysis suggests that the cellulase enzyme may be used as a potential antibiofilm enzyme against Salmonella Ser. Typhi biofilm.

Biological Effects of Quinolones: A Family of Broad-Spectrum Antimicrobial Agents

Broad antibacterial spectrum, high oral bioavailability and excellent tissue penetration combined with safety and few, yet rare, unwanted effects, have made the quinolones class of antimicrobials one of the most used in inpatients and outpatients. Initially discovered during the search for improved chloroquine-derivative molecules with increased anti-malarial activity, today the quinolones, intended as antimicrobials, comprehend four generations that progressively have been extending antimicrobial spectrum and clinical use. The quinolone class of antimicrobials exerts its antimicrobial actions through inhibiting DNA gyrase and Topoisomerase IV that in turn inhibits synthesis of DNA and RNA. Good distribution through different tissues and organs to treat Gram-positive and Gram-negative bacteria have made quinolones a good choice to treat disease in both humans and animals. The extensive use of quinolones, in both human health and in the veterinary field, has induced a rise of resistance and menace with leaving the quinolones family ineffective to treat infections. This review revises the evolution of quinolones structures, biological activity, and the clinical importance of this evolving family. Next, updated information regarding the mechanism of antimicrobial activity is revised. The veterinary use of quinolones in animal productions is also considered for its environmental role in spreading resistance. Finally, considerations for the use of quinolones in human and veterinary medicine are discussed.

Inhibitory Concentrations of Ciprofloxacin Induce an Adaptive Response Promoting the Intracellular Survival of Salmonella enterica Serovar Typhimurium

Antimicrobial resistance (AMR) is a pressing global health crisis, which has been fueled by the sustained use of certain classes of antimicrobials, including fluoroquinolones. While the genetic mutations responsible for decreased fluoroquinolone (ciprofloxacin) susceptibility are known, the implications of ciprofloxacin exposure on bacterial growth, survival, and interactions with host cells are not well described. Aiming to understand the influence of inhibitory concentrations of ciprofloxacin in vitro, we subjected three clinical isolates of Salmonella enterica serovar Typhimurium to differing concentrations of ciprofloxacin, dependent on their MICs, and assessed the impact on bacterial growth, morphology, and transcription. We further investigated the differential morphology and transcription that occurred following ciprofloxacin exposure and measured the ability of ciprofloxacin-treated bacteria to invade and replicate in host cells. We found that ciprofloxacin-exposed S. Typhimurium is able to recover from inhibitory concentrations of ciprofloxacin and that the drug induces specific morphological and transcriptional signatures associated with the bacterial SOS response, DNA repair, and intracellular survival. In addition, ciprofloxacin-treated S. Typhimurium has increased capacity for intracellular replication in comparison to that of untreated organisms. These data suggest that S. Typhimurium undergoes an adaptive response under ciprofloxacin perturbation that promotes cellular survival, a consequence that may justify more measured use of ciprofloxacin for Salmonella infections. The combination of multiple experimental approaches provides new insights into the collateral effects that ciprofloxacin and other antimicrobials have on invasive bacterial pathogens. IMPORTANCE Antimicrobial resistance is a critical concern in global health. In particular, there is rising resistance to fluoroquinolones, such as ciprofloxacin, a first-line antimicrobial for many Gram-negative pathogens. We investigated the adaptive response of clinical isolates of Salmonella enterica serovar Typhimurium to ciprofloxacin, finding that the bacteria adapt in short timespans to high concentrations of ciprofloxacin in a way that promotes intracellular survival during early infection. Importantly, by studying three clinically relevant isolates, we were able to show that individual isolates respond differently to ciprofloxacin and that for each isolate, there was a heterogeneous response under ciprofloxacin treatment. The heterogeneity that arises from ciprofloxacin exposure may drive survival and proliferation of Salmonella during treatment and lead to drug resistance.

Investigational Studies on a Hit Compound Cyclopropane-Carboxylic Acid Derivative Targeting O-Acetylserine Sulfhydrylase as a Colistin Adjuvant

Antibacterial adjuvants are of great significance, since they allow the therapeutic dose of conventional antibiotics to be lowered and reduce the insurgence of antibiotic resistance. Herein, we report that an O-acetylserine sulfhydrylase (OASS) inhibitor can be used as a colistin adjuvant to treat infections caused by Gram-positive and Gram-negative pathogens. A compound that binds OASS with a nM dissociation constant was tested as an adjuvant of colistin against six critical pathogens responsible for infections spreading worldwide, Escherichia coli, Salmonella enterica serovar Typhimurium, Klebisiella pneumoniae, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Staphylococcus pseudintermedius. The compound showed promising synergistic or additive activities against all of them. Knockout experiments confirmed the intracellular target engagement supporting the proposed mechanism of action. Moreover, compound toxicity was evaluated by means of its hemolytic activity against sheep defibrinated blood cells, showing a good safety profile. The 3D structure of the compound in complex with OASS was determined at 1.2 Å resolution by macromolecular crystallography, providing for the first time structural insights about the nature of the interaction between the enzyme and this class of competitive inhibitors. Our results provide a robust proof of principle supporting OASS as a potential nonessential antibacterial target to develop a new class of adjuvants and the structural basis for further structure-activity relationship studies.

Low Dose Infection of Hens in Lay with Salmonella enterica Serovar Enteritidis from Different Genomic Clades

Salmonella enterica serovar Enteritidis is the leading cause of salmonellosis in people, and modeling of infections in chickens is used to identify intervention strategies. A review of 80 manuscripts encompassing 119 experiments indicated that the mean dose of infection was 10⁸ CFU per bird. Experiments of less than 10⁶ CFU were primarily conducted in immature birds. To address a lack of information on the impact of low dosages on the hen at lay, two experiments were conducted in triplicate. Experiment A addressed issues associated with vaccination; thus, hens were infected intramuscularly at 10³, 10⁵, and 10⁷ CFU. For Experiment B, which was focused more on colonization and invasion, hens were infected orally with 5 × 10³ CFU with 4 strains from different genomic clades. Samples from liver, spleen, ovarian pedicle, and paired ceca in both experiments were cultured 5, 6, 7, and 8 days postinfection. Eggshell microbiome taxa were assessed in Experiment B. Results indicated that dosages of 10³ CFU in both experiments produced enough positive samples to be used within models. The intramuscular route resulted in approximately twice as many positive samples as the oral route. The kinetics of infection appeared to differ between low and high dosages suggestive of a J-curve response. These results could impact risk assessments if the hen at lay has a nonlinear response to infectious dose.

De-repression of the smvA efflux system arises in clinical isolates of Proteus mirabilis and reduces susceptibility to chlorhexidine and other biocides

Proteus mirabilis is a common pathogen of the catheterised urinary tract and often described as intrinsically resistant to the biocide chlorhexidine (CHD). Here we demonstrate that de-repression of the smvA efflux system has occurred in clinical isolates of P. mirabilis and reduces susceptibility to CHD and other cationic biocides. Compared to other isolates examined, P. mirabilis RS47 exhibited a significantly higher CHD MIC (≥512 μg/ml) and significantly greater expression of smvA. Comparison of the RS47 smvA and cognate smvR repressor with sequences from other isolates, indicated that RS47 encodes an inactivated smvR. Complementation of RS47 with a functional smvR from isolate RS50a (which exhibited the lowest smvA expression and lowest CHD MIC) reduced smvA expression by ∼59-fold, and markedly lowered the MIC of CHD and other cationic biocides. Although complementation of RS47 did not reduce MICs to concentrations observed in isolate RS50a, the significantly lower polymyxin B MIC of RS50a indicated that differences in LPS structure are also a factor in P. mirabilis CHD susceptibility. To determine if exposure to CHD can select for mutations in smvR, clinical isolates with the lowest CHD MICs were adapted to grow at increasing concentrations of CHD up to 512 μg/ml. Analysis of the smvR in adapted populations indicated that mutations predicted to inactivate smvR occurred following CHD exposure in some isolates. Collectively, our data show that smvA de-repression contributes to reduced biocide susceptibility in P. mirabilis, but differences in LPS structure between strains are also likely to be an important factor.