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The recombinant production of Pseudomonas aeruginosa exotoxin A (ETA), a critical component for immunotoxin development, remains hindered by its complex disulfide bond architecture, cytotoxicity, and aggregation propensity. Despite recent advancements in strain engineering, a systematic, data-driven approach integrating high-throughput screening with machine learning for ETA optimization has remained largely unexplored. We implemented a combinatorial optimization platform, screening 12 engineered E. coli strains across a matrix of four induction temperatures, three chaperone systems, and four redox-modulating additives. A high-throughput fluorescence-based solubility reporter was developed for rapid screening of 576 unique conditions, followed by training of an XGBoost machine learning model to predict soluble yield. The model was validated using 5-fold cross-validation with hyperparameter optimization to mitigate overfitting. Statistical analyses included one-way ANOVA with Tukey post-hoc test, Pearson correlation, and multiple regression. The disulfide-competent strain SHuffle T7, induced at 12°C with co-expression of the DnaKJE/GroEL chaperone system and supplementation with 2 mM oxidized glutathione, yielded 3.24 ± 0.4 mg/L of soluble, enzymatically active ETA. This represents a 15-fold improvement over conventional BL21(DE3) systems (F (11,24) = 45.32, p < 0.0001). Structural validation via redox-sensitive PAGE and nano-LC-MS/MS confirmed native disulfide pairing. The trained machine learning model demonstrated high predictive accuracy (R² = 0.92, RMSE = 0.24 mg/L) with consistent performance across cross-validation folds (average R² = 0.91 ± 0.02), and identified cytoplasmic redox potential and translational rate as the primary determinants of soluble expression. We present an integrated platform that synergizes experimental high-throughput screening with predictive machine learning to overcome the challenge of ETA production. While validation on additional protein targets is needed to fully establish generalizability, this work establishes an optimized, scalable protocol for therapeutic-grade ETA and provides a transferable computational framework for the rational optimization of other complex, disulfide-rich proteins.

To trace evolution of Panton-Valentine leucocidin-positive clonal complex 398 methicillin-resistant Staphylococcus aureus (MRSA) in the Czech Republic, we tested 103 MRSA isolates from humans. Five (4.9%) were Panton-Valentine leucocidin-positive clonal complex 398, sequence types 1232 and 9181. Spread to the Czech Republic may result from travel to or from other countries.

Necrotizing pneumonia induced by Panton-Valentine leukocidin-secreting Staphylococcus aureus is a rare but life-threatening infection that has been described in patients after they had influenza. We report a fatal case of this superinfection in a young adult who had coronavirus disease.

Extracellular protein toxins contribute to the pathogenesis of a wide variety of Staphylococcus aureus infections. The present study investigated the effects that cell-wall active antibiotics and protein-synthesis inhibitors have on transcription and translation of genes for Panton-Valentine leukocidin, alpha-hemolysin, and toxic-shock syndrome toxin 1, in both methicillin-sensitive and methicillin-resistant S. aureus Subinhibitory concentrations of nafcillin induced and prolonged mRNA for Panton-Valentine leukocidin, alpha-toxin, and toxic-shock syndrome toxin 1 and increased toxin production. In contrast, clindamycin and linezolid markedly suppressed translation, but not transcription, of toxin genes. These results suggest (1) that protein-synthesis inhibition is an important consideration in the selection of antimicrobial agents to treat serious infections caused by toxin-producing gram-positive pathogens and (2) that, by inducing and enhancing toxin production, inadvertent use of beta-lactam antibiotics to treat methicillin-resistant S. aureus infections may contribute to worse outcomes

Background Mixed infection with influenza A virus (IAV) and Staphylococcus aureus ( S. aureus ) is a serious concern in children. S. aureus , particularly Panton-Valentine Leucocidin (PVL)-producing strains, is a known cause of severe, necrotizing complications. We reported three cases of severe necrotizing pneumonia caused by PVL-positive S. aureus and IAV infection from March to April in 2023. Case presentation Three previously healthy children presented with acute onset of high fever and dyspnea following IAV infection. Microbiological workup confirmed mixed infection with PVL-positive S. aureus (two methicillin-resistant, one methicillin-sensitive). Radiographic findings included necrotizing pneumonia, atelectasis and pleural effusion in all patients. All three developed necrotizing laryngotracheobronchitis, and one case was complicated by plastic bronchitis. All required intensive care unit admission, with two needing mechanical ventilation. The mainstay of successful management involved a combination of oseltamivir, linezolid, glucocorticoids, therapeutic bronchoscopy, and closed thoracic drainage. Conclusion This study firstly documented successful treatment of three cases of severe necrotizing laryngotracheobronchitis and necrotizing pneumonia caused by PVL-positive S. aureus and IAV infection. Clinicians should raise awareness of this mixed infection in children with sudden clinical worsening after influenza to provide timely and effective treatment to decrease mortality.

Purpose Misdiagnosis or delayed diagnosis of paravertebral and/or iliopsoas abscess (PVIPA) has been frequently reported to be associated with unfavorable prognosis. We aimed to develop a scoring algorithm that can easily and accurately identify patients at greater risk for PVIPA among individuals with community-onset bloodstream infections. Methods In a multicenter, retrospective cohort study, the score was developed with the first four study years and validated with the remaining two years. Applying logistic regression, the score values of prediction determinants were derived from the adjusted odds ratios (AOR). The performance of the scoring algorithm was assessed with the receiver operating characteristic (ROC) curve. Results In the derivation (3869 patients) and validation (1608) cohorts, patients with PVIPA accounted for 1.7% and 1.4%, respectively. In the derivation cohort, five independent predictors of PVIPA were recognized using multivariable analyses: time-to-defervescence > 5 days (AOR, 7.00; 2 points), Panton-Valentine Leukocidin (PVL)-producing Staphylococcus aureus (AOR, 5.98; 2 points), intravenous drug users (AOR, 2.60; 1 points), and comorbid hemato-oncology (AOR, 0.41; -1 point) or liver cirrhosis (AOR, 2.56; 1 points). In the derivation and validation cohorts, areas under ROC curves (95% confidence intervals) of the prediction algorithm are 0.83 (0.77–0.88) and 0.85 (0.80–0.90), and a cutoff score of + 2 represents sensitivity of 83.3% and 95.7%, specificity of 68.6% and 67.7%, positive predictive values of 4.4% and 4.1%, and negative predictive values of 99.6% and 99.9%, respectively. Conclusions Of a scoring algorithm with substantial sensitivity and specificity in predicting PVIPA, PVL-producing S. aureus and Time-to-defervescence > 5 days were crucial determinants.

The current pandemic of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infections is caused by several genetically unrelated clones. Here, we analyzed virulence of globally occurring CA-MRSA strains in a rabbit skin infection model. We used rabbits because neutrophils from this animal species have relatively high sensitivity to Panton-Valentine leukocidin (PVL), a toxin epidemiologically correlated with many CA-MRSA infections. Virulence in the rabbit model correlated with in vitro neutrophil lysis and transcript levels of phenol-soluble modulin a and a-toxin, but not PVL genes. Furthermore, abscesses caused by USA300 and its PVL-negative progenitor USA500 were comparatively large and similar in size, suggesting that PVL has played a limited role in the evolution of USA300 virulence in the context of skin infections. Our study indicates a major but not exclusive impact of virulence on the epidemiological success of USA300 and other CA-MRSA strains and emphasizes the importance of core genome-encoded toxins in CA-MRSA skin infections.

The pathogenicity of staphylococcus aureus is dependent largely upon its ability to secrete a number of virulence factors, therefore, anti-virulence strategy to combat S. aureus-mediated infections is now gaining great interest. It is widely recognized that some plant essential oils could affect the production of staphylococcal exotoxins when used at subinhibitory concentrations. Perilla [Perilla frutescens (L.) Britton], a natural medicine found in eastern Asia, is primarily used as both a medicinal and culinary herb. Its essential oil (perilla oil) has been previously demonstrated to be active against S. aureus. However, there are no data on the influence of perilla oil on the production of S. aureus exotoxins. A broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) of perilla oil against S. aureus strains. Hemolysis, tumour necrosis factor (TNF) release, Western blot, and real-time RT-PCR assays were performed to evaluate the effects of subinhibitory concentrations of perilla oil on exotoxins production in S. aureus. The data presented here show that perilla oil dose-dependently decreased the production of α-toxin, enterotoxins A and B (the major staphylococcal enterotoxins), and toxic shock syndrome toxin 1 (TSST-1) in both methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). The production of α-toxin, SEA, SEB, and TSST-1 in S. aureus was decreased by perilla oil. These data suggest that perilla oil may be useful for the treatment of S. aureus infections when used in combination with β-lactam antibiotics, which can increase exotoxins production by S. aureus at subinhibitory concentrations. Furthermore, perilla oil could be rationally applied in food systems as a novel food preservative both to inhibit the growth of S. aureus and to repress the production of exotoxins, particularly staphylococcal enterotoxins.

Aggregatibacter actinomycetemcomitans leukotoxin (LtxA) is a major virulence factor that kills leukocytes permitting it’s escape from host immune surveillance. A . actinomycetemcomitans strains can produce high or low levels of toxin. Genetic differences reside in the “so called JP2” ltxA promoter region. These hyper-leukotoxin producing strains with the 530 bp deletion have been studied in detail. However, regions contained within the 530 bp deletion that could be responsible for modulation of leukotoxin production have not been defined. Here, we report, for the first time, on regions within the 530 bp that are responsible for high-levels of ltx A expression. We constructed a deletion of 530 bps in a primate isolate of A . actinomycetemcomitans , which produced leukotoxin equivalent to the JP2 strain. We then constructed sequential deletions in regions that span the 530 bps. Results indicated that expression of the ltxA transcript was reduced by a potential transcriptional terminator in promoter region 298 to 397 with a ΔG = −7.9 kcal/mol. We also confirmed previous findings that transcriptional fusion between the orf X region and ltx C increased ltx A expression. In conclusion, we constructed a hyper-leukotoxin producing A . actinomycetemcomitans strain and identified a terminator located in the promoter region extending from 298–397 that alters ltx A expression.

Background. The predominant genetic background of community-associated methicillin-resistant Staphylococcus aureus has transitioned from USA400 to USA300 in most US communities. The explanation for this shift is unclear. We hypothesized that USA300 must be more pathogenic—specifically, that USA300 would have increased virulence when compared with USA400 in an animal model. Methods. Rats were inoculated intratracheally with 1 of 6 S. aureus isolates from the USA300 and USA400 backgrounds. We assessed mortality, in vivo bacterial growth, and histopathology. We assessed the in vitro expression of capsule and of selected genes believed to be important in virulence in S. aureus, including agr, saeRS, sarA, α-toxin (hla), and Panton-Valentine leukocidin (pvl). Results. USA300 isolates were more lethal, produced more severe pneumonia, and had higher in vivo bacterial density in the lung than did USA400 isolates. In vitro expression of agr, saeRS, sarA, hla, and pvl were greater in USA300 isolates. USA300 isolates were unencapsulated, whereas 2 of 3 USA400 isolates produced capsule. Conclusions. USA300 isolates were more virulent than USA400 isolates in a model of necrotizing pneumonia. The explanation for this is unclear, but it likely results from increased expression of S. aureus regulatory systems (e.g., agr, saeRS, and sarA) and the resultant upregulation of key virulence factors including α-toxin and PVL.