The NLRP6 Inflammasome Recognizes Lipoteichoic Acid and Regulates Gram-Positive Pathogen Infection.

The activator and composition of the NLRP6 inflammasome remain poorly understood. We find that lipoteichoic acid (LTA), a molecule produced by Gram-positive bacteria, binds and activates NLRP6. In response to cytosolic LTA or infection with Listeria monocytogenes, NLRP6 recruited caspase-11 and caspase-1 via the adaptor ASC. NLRP6 activation by LTA induced processing of caspase-11, which promoted caspase-1 activation and interleukin-1ß (IL-1ß)/IL-18 maturation in macrophages. Nlrp6-/- and Casp11-/- mice were less susceptible to L. monocytogenes infection, which was associated with reduced pathogen loads and impaired IL-18 production. Administration of IL-18 to Nlrp6-/- or Casp11-/- mice restored the susceptibility of mutant mice to L. monocytogenes infection. These results reveal a previously unrecognized innate immunity pathway triggered by cytosolic LTA that is sensed by NLRP6 and exacerbates systemic Gram-positive pathogen infection via the production of IL-18.

STING Senses Microbial Viability to Orchestrate Stress-Mediated Autophagy of the Endoplasmic Reticulum.

Constitutive cell-autonomous immunity in metazoans predates interferon-inducible immunity and comprises primordial innate defense. Phagocytes mobilize interferon-inducible responses upon engagement of well-characterized signaling pathways by pathogen-associated molecular patterns (PAMPs). The signals controlling deployment of constitutive cell-autonomous responses during infection have remained elusive. Vita-PAMPs denote microbial viability, signaling the danger of cellular exploitation by intracellular pathogens. We show that cyclic-di-adenosine monophosphate in live Gram-positive bacteria is a vita-PAMP, engaging the innate sensor stimulator of interferon genes (STING) to mediate endoplasmic reticulum (ER) stress. Subsequent inactivation of the mechanistic target of rapamycin mobilizes autophagy, which sequesters stressed ER membranes, resolves ER stress, and curtails phagocyte death. This vita-PAMP-induced ER-phagy additionally orchestrates an interferon response by localizing ER-resident STING to autophagosomes. Our findings identify stress-mediated ER-phagy as a cell-autonomous response mobilized by STING-dependent sensing of a specific vita-PAMP and elucidate how innate receptors engage multilayered homeostatic mechanisms to promote immunity and survival after infection.

A cryptic oxidoreductase safeguards oxidative protein folding in Corynebacterium diphtheriae.

In many gram-positive Actinobacteria, including Actinomyces oris and Corynebacterium matruchotii, the conserved thiol-disulfide oxidoreductase MdbA that catalyzes oxidative folding of exported proteins is essential for bacterial viability by an unidentified mechanism. Intriguingly, in Corynebacterium diphtheriae, the deletion of mdbA blocks cell growth only at 37 °C but not at 30 °C, suggesting the presence of alternative oxidoreductase enzyme(s). By isolating spontaneous thermotolerant revertants of the mdbA mutant at 37 °C, we obtained genetic suppressors, all mapped to a single T-to-G mutation within the promoter region of tsdA, causing its elevated expression. Strikingly, increased expression of tsdA-via suppressor mutations or a constitutive promoter-rescues the pilus assembly and toxin production defects of this mutant, hence compensating for the loss of mdbA. Structural, genetic, and biochemical analyses demonstrated TsdA is a membrane-tethered thiol-disulfide oxidoreductase with a conserved CxxC motif that can substitute for MdbA in mediating oxidative folding of pilin and toxin substrates. Together with our observation that tsdA expression is upregulated at nonpermissive temperature (40 °C) in wild-type cells, we posit that TsdA has evolved as a compensatory thiol-disulfide oxidoreductase that safeguards oxidative protein folding in C. diphtheriae against thermal stress.

Molecular mechanisms underlying the structural diversity of rhamnose-rich cell wall polysaccharides in lactococci.

In Gram-positive bacteria, cell wall polysaccharides (CWPS) play critical roles in bacterial cell wall homeostasis and bacterial interactions with their immediate surroundings. In lactococci, CWPS consist of two components: a conserved rhamnan embedded in the peptidoglycan layer and a surface-exposed polysaccharide pellicle (PSP), which are linked together to form a large rhamnose-rich CWPS (Rha-CWPS). PSP, whose structure varies from strain to strain, is a receptor for many bacteriophages infecting lactococci. Here, we examined the first two steps of PSP biosynthesis, using in vitro enzymatic tests with lipid acceptor substrates combined with LC-MS analysis, AlfaFold2 modeling of protein 3D-structure, complementation experiments, and phage assays. We show that the PSP repeat unit is assembled on an undecaprenyl-monophosphate (C55P) lipid intermediate. Synthesis is initiated by the WpsA/WpsB complex with GlcNAc-P-C55 synthase activity and the PSP precursor GlcNAc-P-C55 is then elongated by specific glycosyltransferases that vary among lactococcal strains, resulting in PSPs with diverse structures. Also, we engineered the PSP biosynthesis pathway in lactococci to obtain a chimeric PSP structure, confirming the predicted glycosyltransferase specificities. This enabled us to highlight the importance of a single sugar residue of the PSP repeat unit in phage recognition. In conclusion, our results support a novel pathway for PSP biosynthesis on a lipid-monophosphate intermediate as an extracellular modification of rhamnan, unveiling an assembly machinery for complex Rha-CWPS with structural diversity in lactococci.

Glycosyl transferase GT2 genes mediate the biosynthesis of an unusual (1,3;1,4)-ß-glucan exopolysaccharide in the bacterium Sarcina ventriculi.

Linear, unbranched (1,3;1,4)-ß-glucans (mixed-linkage glucans or MLGs) are commonly found in the cell walls of grasses, but have also been detected in basal land plants, algae, fungi and bacteria. Here we show that two family GT2 glycosyltransferases from the Gram-positive bacterium Sarcina ventriculi are capable of synthesizing MLGs. Immunotransmission electron microscopy demonstrates that MLG is secreted as an exopolysaccharide, where it may play a role in organizing individual cells into packets that are characteristic of Sarcina species. Heterologous expression of these two genes shows that they are capable of producing MLGs in planta, including an MLG that is chemically identical to the MLG secreted from S. ventriculi cells but which has regularly spaced (1,3)-ß-linkages in a structure not reported previously for MLGs. The tandemly arranged, paralogous pair of genes are designated SvBmlgs1 and SvBmlgs2. The data indicate that MLG synthases have evolved different enzymic mechanisms for the incorporation of (1,3)-ß- and (1,4)-ß-glucosyl residues into a single polysaccharide chain. Amino acid variants associated with the evolutionary switch from (1,4)-ß-glucan (cellulose) to MLG synthesis have been identified in the active site regions of the enzymes. The presence of MLG synthesis in bacteria could prove valuable for large-scale production of MLG for medical, food and beverage applications.

Characterization of a novel cysteine-less Cu/Zn-superoxide dismutase in Paenibacillus lautus missing a conserved disulfide bond.

Cu/Zn-superoxide dismutase (CuZnSOD) is an enzyme that binds a copper and zinc ion and also forms an intramolecular disulfide bond. Together with the copper ion as the active site, the disulfide bond is completely conserved among these proteins; indeed, the disulfide bond plays critical roles in maintaining the catalytically competent conformation of CuZnSOD. Here, we found that a CuZnSOD protein in Paenibacillus lautus (PaSOD) has no Cys residue but exhibits a significant level of enzyme activity. The crystal structure of PaSOD revealed hydrophobic and hydrogen-bonding interactions in substitution for the disulfide bond of the other CuZnSOD proteins. Also notably, we determined that PaSOD forms a homodimer through an additional domain with a novel fold at the N terminus. While the advantages of lacking Cys residues and adopting a novel dimer configuration remain obscure, PaSOD does not require a disulfide-introducing/correcting system for maturation and could also avoid misfolding caused by aberrant thiol oxidations under an oxidative environment.

Characterization of the resistome and predominant genetic lineages of Gram-positive bacteria causing keratitis.

Bacterial keratitis is a vision-threatening infection mainly caused by Gram-positive bacteria (GPB). Antimicrobial therapy is commonly empirical using broad-spectrum agents with efficacy increasingly compromised by the emergence of antimicrobial resistance. We used a combination of phenotypic tests and genome sequencing to identify the predominant lineages of GPB causing keratitis and to characterize their antimicrobial resistance patterns. A total of 161 isolates, including Staphylococcus aureus (n = 86), coagulase-negative staphylococci (CoNS; n = 34), Streptococcus spp. (n = 34), and Enterococcus faecalis (n = 7), were included. The population of S. aureus isolates consisted mainly of clonal complex 5 (CC5) (30.2%). Similarly, the population of Staphylococcus epidermidis was homogenous with most of them belonging to CC2 (78.3%). Conversely, the genetic population of Streptococcus pneumoniae was highly diverse. Resistance to first-line antibiotics was common among staphylococci, especially among CC5 S. aureus. Methicillin-resistant S. aureus was commonly resistant to fluoroquinolones and azithromycin (78.6%) and tobramycin (57%). One-third of the CoNS were resistant to fluoroquinolones and 53% to azithromycin. Macrolide resistance was commonly caused by erm genes in S. aureus, mphC and msrA in CoNS, and mefA and msr(D) in streptococci. Aminoglycoside resistance in staphylococci was mainly associated with genes commonly found in mobile genetic elements and that encode for nucleotidyltransferases like ant(4')-Ib and ant(9)-Ia. Fluroquinolone-resistant staphylococci carried from 1 to 4 quinolone resistance-determining region mutations, mainly in the gyrA and parC genes. We found that GPB causing keratitis are associated with strains commonly resistant to first-line topical therapies, especially staphylococcal isolates that are frequently multidrug-resistant and associated with major hospital-adapted epidemic lineages.

Emerging trends in the inhibition of bacterial molecular communication: An overview.

Quorum sensing (QS) is a molecular cell-cell communication utilized by several bacteria and some fungi. It involves cell density dependent gene expression that includes extra polymeric substance production, sporulation, antibiotic production, motility, competence, symbiosis and conjugation. These expressions were carried out by different signaling molecules like acyl homo-serine lactone (AHL) and auto-inducing peptides (AIPs) which was effluxed by gram negative and gram positive bacteria. Pathogenic bacteria and biofilms often exhibit high resistance to antibiotics, attributed to the presence of antibiotic efflux pumps, reduced membrane permeability, and enzymes that deactivate quorum sensing (QS) inhibitors. To counteract virulence and multi-drug resistance (MDR), novel strategies such as employing quorum sensing (QS) inhibitors and quorum quenchers are employed. It targets signaling molecules with synthesis and prevents the signal from binding to receptors. In this present review, the mechanisms of QS along with inhibitors from different sources are described. These strategies potentially interfere with QS and it can be applied in different fields, mainly in hospitals and marine environments where the pathogenic infections and biofilm formation are highly involved.

The Complete Assessment of Small Molecule and Peptidomimetic Inhibitors of Sortase A Towards Antivirulence Treatment.

This review covers the most recent advances in the development of inhibitors for the bacterial enzyme sortase A (SrtA). Sortase A (SrtA) is a critical virulence factor, present ubiquitously in Gram-positive bacteria of which many are pathogenic. Sortases are key enzymes regulating bacterial adherence to host cells, by anchoring extracellular matrix-binding proteins to the bacterial outer cell wall. By targeting virulence factors, effective treatment can be achieved, without inducing antibiotic resistance to the treatment. This is a potentially more sustainable, long-term approach to treating bacterial infections, including ones that display multiple resistance to current therapeutics. There are many promising approaches available for SrtA inhibition, some of which have the potential to advance into further clinical development, with peptidomimetic and in vivo active small molecules being among the most promising. There are currently no approved drugs on the market targeting SrtA, despite its promise, adding to the relevance of this review article, as it extends to the pharmaceutical industry additionally to academic researchers.

Diet composition and sterilization modifies intestinal microbiome diversity and burden of Theiler's virus infection-induced acute seizures.

OBJECTIVE: Brain infection with Theiler's murine encephalomyelitis virus (TMEV) in C57BL/6J mice can induce acquired epileptogenesis. Diet alters acute seizure incidence in TMEV-infected mice; yet it is unclear whether intestinal dysbiosis may also impact acute or chronic behavioral comorbidities. This study thus assessed the impact of diet formulation and sterilization on acute seizure presentation, gut microbiome composition, and epilepsy-related chronic behavioral comorbidities. METHODS: Baseline fecal samples were collected from male C57BL/6J mice (4- to 5-weeks-old; Jackson Labs) upon facility arrival. Mice were randomized to either autoclaved (AC) or irradiated diet (IR) (Prolab RMH 3000) or IR (Picolab 5053). Three days later, mice underwent intracerebral TMEV or phosphate-buffered saline (PBS) injection. Fecal samples were collected from a subset of mice at infection (Day 0) and Day 7 post-infection. Epilepsy-related working memory deficits and seizure threshold were assessed 6 weeks post-infection. Gut microbiome diversity was determined by 16S rRNA amplicon sequencing of fecal samples. RESULTS: TMEV-infected mice displayed acute handling-induced seizures, regardless of diet: 28 of 57 IR Picolab 5053 (49.1%), 30 of 41 IR Prolab RMH 3000 (73.2%), and 47 of 77 AC Prolab RMH 3000 (61%) mice displayed seizures. The number of observed seizures differed significantly by diet: IR Picolab 5053 diet-fed mice had 2.2 ± 2.8 seizures (mean ± standard deviation), IR Prolab RMH 3000 diet-fed mice had 3.5 ± 2.9 seizures, and AC Prolab RMH 3000 diet-fed mice had 4.4 ± 3.8 seizures during the 7-day monitoring period. Gut microbiome composition differed significantly in TMEV-infected mice fed the AC Prolab RMH 3000 diet, with measured differences in gram-positive bacteria. These mice also displayed worsened long-term working memory deficits. SIGNIFICANCE: Diet-induced differences in intestinal dysbiosis in the TMEV model are associated with marked changes in acute seizure presentation, symptomatic recovery, and onset of chronic behavioral comorbidities of epilepsy. Our study reveals a novel disease-modifying impact of dietary manipulation on intestinal bacterial species after TMEV-induced acute seizures.

Changing patterns of bacterial profile and antimicrobial resistance in high-risk patients during the COVID-19 pandemic at a tertiary oncology hospital.

The widespread evolution of phenotypic resistance in clinical isolates over the years, coupled with the COVID-19 pandemic onset, has exacerbated the global challenge of antimicrobial resistance. This study aimed to explore changes in bacterial infection patterns and antimicrobial resistance during the COVID-19 pandemic. This study involved the periods before and during COVID-19: the pre-pandemic and pandemic eras. The surveillance results of bacterial isolates causing infections in cancer patients at an Egyptian tertiary oncology hospital were retrieved. The Vitek®2 or Phoenix systems were utilized for species identification and susceptibility testing. Statistical analyses were performed comparing microbiological trends before and during the pandemic. Out of 2856 bacterial isolates, Gram-negative bacteria (GNB) predominated (69.7%), and Gram-positive bacteria (GPB) comprised 30.3% of isolates. No significant change was found in GNB prevalence during the pandemic (P = 0.159). Elevated rates of Klebsiella and Pseudomonas species were demonstrated during the pandemic, as was a decrease in E. coli and Acinetobacter species (P < 0.001, 0.018, < 0.001, and 0.046, respectively) in hematological patients. In surgical patients, Enterobacteriaceae significantly increased (P = 0.012), while non-fermenters significantly decreased (P = 0.007). GPB species from either hematological or surgical wards exhibited no notable changes during the pandemic. GNB resistance increased in hematological patients to carbapenems, amikacin, and tigecycline and decreased in surgical patients to amikacin and cefoxitin (P < 0.001, 0.010, < 0.001, < 0.001, and 0.016, respectively). The study highlights notable shifts in the microbial landscape during the COVID-19 pandemic, particularly in the prevalence and resistance patterns of GNB in hematological and surgical wards.

Diversity and Bioprospection of Gram-positive Bacteria Derived from a Mayan Sinkhole.

Water-filled sinkholes known locally as cenotes, found on the Yucatán Peninsula, have remarkable biodiversity. The primary objective of this study was to explore the biotechnological potential of Gram-positive cultivable bacteria obtained from sediment samples collected at the coastal cenote Pol-Ac in Yucatán, Mexico. Specifically, the investigation aimed to assess production of hydrolytic enzymes and antimicrobial compounds. 16 S rRNA gene sequencing led to the identification of 49 Gram-positive bacterial isolates belonging to the phyla Bacillota (n = 29) and Actinomycetota (n = 20) divided into the common genera Bacillus and Streptomyces, as well as the genera Virgibacillus, Halobacillus, Metabacillus, Solibacillus, Neobacillus, Rossellomorea, Nocardiopsis and Corynebacterium. With growth at 55ºC, 21 of the 49 strains were classified as moderately thermotolerant. All strains were classified as halotolerant and 24 were dependent on marine water for growth. Screening for six extracellular hydrolytic enzymes revealed gelatinase, amylase, lipase, cellulase, protease and chitinase activities in 93.9%, 67.3%, 63.3%, 59.2%, 59.2% and 38.8%, of isolated strains, respectively. The genes for polyketide synthases type I, were detected in 24 of the strains. Of 18 strains that achieved > 25% inhibition of growth in the bacterial pathogen Staphylococcus aureus ATCC 6538, 4 also inhibited growth in Escherichia coli ATCC 35,218. Isolates Streptomyces sp. NCA_378 and Bacillus sp. NCA_374 demonstrated 50-75% growth inhibition against at least one of the two pathogens tested, along with significant enzymatic activity across all six extracellular enzymes. This is the first comprehensive report on the biotechnological potential of Gram-positive bacteria isolated from sediments in the cenotes of the Yucatán Peninsula.

Procalcitonin and C-reactive protein as diagnostic biomarkers in COVID-19 and Non-COVID-19 sepsis patients: a comparative study.

BACKGROUND: This study aimed to assess and compare procalcitonin (PCT) and C-reactive protein (CRP) levels between COVID-19 and non-COVID-19 sepsis patients. Additionally, we evaluated the diagnostic efficiency of PCT and CRP in distinguishing between Gram-positive (GP) and Gram-negative (GN) bacterial infections. Moreover, we explored the associations of PCT with specific pathogens in this context. METHODS: The study included 121 consecutive sepsis patients who underwent blood culture testing during the COVID-19 epidemic. PCT and CRP were measured, and reverse transcriptase-polymerase chain reaction (RT-PCR) was employed for the detection of COVID-19 nucleic acid. The Mann-Whitney U-test was used to compare PCT and CRP between the COVID-19 and non-COVID-19 groups. Receiver operating characteristic (ROC) curves were generated to compare PCT and CRP levels in the GN group versus the GP group for assessing the diagnostic efficiency. The kruskal-Wallis H test was applied to assess the impact of specific pathogen groups on PCT concentrations. RESULTS: A total of 121 sepsis patients were categorized into a COVID-19 group (n = 25) and a non-COVID-19 group (n = 96). No significant differences in age and gender were observed between the COVID-19 and non-COVID-19 groups. The comparison of biomarkers between these groups showed no statistically significant differences. The optimal cut-off values for PCT and CRP in differentiating between GP and GN infections were 1.03 ng/mL and 34.02 mg/L, respectively. The area under the ROC curve was 0.689 (95% confidence interval (CI) 0.591-0.786) for PCT and 0.611 (95% CI 0.505-0.717) for CRP. The diagnostic accuracy was 69.42% for PCT and 58.69% for CRP. The study found a significant difference in PCT levels among specific groups of pathogens (P < 0.001), with the highest levels observed in Escherichia coli infections. The frequency of Staphylococcus spp. positive results was significantly higher (36.0%) in COVID-19 compared to non-COVID-19 sepsis patients (P = 0.047). CONCLUSION: Sepsis patients with COVID-19 revealed a significantly higher culture positivity for staphylococcus spp. than the non-COVID-19 group. Both PCT and CRP showed moderate diagnostic efficiency in differentiating between GP and GN bacterial infections. PCT showed potential utility in identifying E. coli infections compared to other pathogens.

Comparative epidemiology of bacteraemia in two ageing populations: Singapore and Denmark.

Burden of bacteraemia is rising due to increased average life expectancy in developed countries. This study aimed to compare the epidemiology and outcomes of bacteraemia in two similarly ageing populations with different ethnicities in Singapore and Denmark. Historical cohorts from the second largest acute-care hospital in Singapore and in the hospitals of two Danish regions included patients aged 15 and above who were admitted from 1 January 2006 to 31 December 2016 with at least 1 day of hospital stay and a pathogenic organism identified. Among 13 144 and 39 073 bacteraemia patients from Singapore and Denmark, similar 30-day mortality rates (16.5%; 20.3%), length of hospital stay (median 14 (IQR: 9-28) days; 11 (6-21)), and admission rate to ICU (15.5%; 15.6%) were observed, respectively. Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus ranked among the top four in both countries. However, Singaporeans had a higher proportion of patients with diabetes (46.8%) and renal disease (29.5%) than the Danes (28.0% and 13.7%, respectively), whilst the Danes had a higher proportion of patients with chronic pulmonary disease (18.0%) and malignancy (35.3%) than Singaporeans (9.7% and 16.2%, respectively). Our study showed that top four causative organisms and clinical outcomes were similar between the two cohorts despite pre-existing comorbidities differed.

Risk factors for resistant gram-positive bacteremia in febrile neutropenic patients with cancer.

BACKGROUND: Gram-positive bacteria are frequently resistant to empirical beta-lactams in febrile neutropenic patients with cancer. As microbiology and antibiotic susceptibility changes, we reevaluated the risk factors for resistant Gram-positive bacteremia in febrile neutropenic patients with cancer. METHODS: Episodes of bacteremic febrile neutropenia in Seoul National University Hospital from July 2019 to June 2022 were reviewed. Resistant Gram-positive bacteria were defined as a pathogen susceptible only to glycopeptide or linezolid in vitro (e.g., methicillin-resistant staphylococci, penicillin-resistant viridans streptococci, and ampicillin-resistant enterococci). Episodes were compared to identify independent risk factors for resistant Gram-positive bacteremia. RESULTS: Of 225 episodes, 78 (34.7%) involved resistant Gram-positive bacteremia. Multivariate analysis revealed that breakthrough bacteremia while being administered antibiotics (adjusted odds ratio [aOR], 6.794; 95% confidence interval [95% CI], 3.130-14.749; P < 0.001) and catheter-related infection (aOR 4.039, 95% CI 1.366-11.946; P = 0.012) were associated with resistant Gram-positive bacteremia. Chronic liver disease (aOR 0.231, 95% CI 0.059-0.905; P = 0.035) and hypotension at bacteremia (aOR 0.454, 95% CI 0.218-0.945; P = 0.035) were inversely associated with resistant Gram-positive bacteremia. CONCLUSIONS: Resistant Gram-positive bacteria should be considered in breakthrough bacteremia and catheter-related infection in febrile neutropenic patients with cancer.

A sandwich-structured multifunctional platform based on self-assembled Ti3C2Tx@Au NPs films, antibiotics, and silent region SERS probe for the capture, determination, and drug resistance analysis of Gram-positive bacteria.

A multifunctional surface-enhanced Raman scattering (SERS) platform integrating sensitive detection and drug resistance analysis was developed for Gram-positive bacteria. The substrate was based on self-assembled Ti3C2Tx@Au NPs films and capture molecule phytic acid (IP6) to achieve specific capture of Gram-positive bacteria and different bacteria were analyzed by fingerprint signal. It had advantages of good stability and homogeneity (RSD = 8.88%). The detection limit (LOD) was 102 CFU/mL for Staphylococcus aureus and 103 CFU/mL for MRSA, respectively. A sandwich structure was formed on the capture substrate by signal labels prepared by antibiotics (penicillin G and vancomycin) and non-interference SERS probe molecules (4-mercaptobenzonitrile (2223 cm-1) and 2-amino-4-cyanopyridine (2240 cm-1)) to improve sensitivity. The LOD of Au NPs@4-MBN@PG to S. aureus and Au NPs@AMCP@Van to MRSA and S. aureus were all improved to 10 CFU/mL, with a wide dynamic linear range from 108 to 10 CFU/mL (R2 ≥ 0.992). The SERS platform can analyze the drug resistance of drug-resistant bacteria. Au NPs@4-MBN@PG was added to the substrate and captured MRSA to compare the SERS spectra of 4-MBN. The intensity inhomogeneity of 4-MBN at the same concentrations of MRSA and the nonlinearity at the different concentrations of MRSA revealed that MRSA was resistant to PG. Finally, the SERS platform achieved the determination of MRSA in blood. Therefore, this SERS platform has great significance for the determination and analysis of Gram-positive bacteria.

Interactions of Gram-Positive Bacterial Membrane Vesicles and Hosts: Updates and Future Directions.

Extracellular vesicles (EVs) are lipid bilayers derived from cell membranes, released by both eukaryotic cells and bacteria into the extracellular environment. During production, EVs carry proteins, nucleic acids, and various compounds, which are then released. While Gram-positive bacteria were traditionally thought incapable of producing EVs due to their thick peptidoglycan cell walls, recent studies on membrane vesicles (MVs) in Gram-positive bacteria have revealed their significant role in bacterial physiology and disease progression. This review explores the current understanding of MVs in Gram-positive bacteria, including the characterization of their content and functions, as well as their interactions with host and bacterial cells. It offers a fresh perspective to enhance our comprehension of Gram-positive bacterial EVs.

Modeling of Effectiveness of N3-Substituted Amidrazone Derivatives as Potential Agents against Gram-Positive Bacteria.

Prediction of the antibacterial activity of new chemical compounds is an important task, due to the growing problem of bacterial drug resistance. Generalized linear models (GLMs) were created using 85 amidrazone derivatives based on the results of antimicrobial activity tests, determined as the minimum inhibitory concentration (MIC) against Gram-positive bacteria: Staphylococcus aureus, Enterococcus faecalis, Micrococcus luteus, Nocardia corallina, and Mycobacterium smegmatis. For the analysis of compounds characterized by experimentally measured MIC values, we included physicochemical properties (e.g., molecular weight, number of hydrogen donors and acceptors, topological polar surface area, compound percentages of carbon, nitrogen, and oxygen, melting points, and lipophilicity) as potential predictors. The presence of R1 and R2 substituents, as well as interactions between melting temperature and R1 or R2 substituents, were also considered. The set of potential predictors also included possible biological effects (e.g., antibacterial, antituberculotic) of tested compounds calculated with the PASS (Prediction of Activity Spectra for Substances) program. Using GLMs with least absolute shrinkage and selection (LASSO), least-angle regression, and stepwise selection, statistically significant models with the optimal value of the adjusted determination coefficient and of seven fit criteria were chosen, e.g., Akaike's information criterion. The most often selected variables were as follows: molecular weight, PASS_antieczematic, PASS_anti-inflam, squared melting temperature, PASS_antitumor, and experimental lipophilicity. Additionally, relevant to the bacterial strain, the interactions between melting temperature and R1 or R2 substituents were selected, indicating that the relationship between MIC and melting temperature depends on the type of R1 or R2 substituent.

Group B Streptococcal Neonatal Meningitis.

Neonatal bacterial meningitis is a devastating disease, associated with high mortality and neurological disability, in both developed and developing countries. Streptococcus agalactiae, commonly referred to as group B Streptococcus (GBS), remains the most common bacterial cause of meningitis among infants younger than 90 days. Maternal colonization with GBS in the gastrointestinal and/or genitourinary tracts is the primary risk factor for neonatal invasive disease. Despite prophylactic intrapartum antibiotic administration to colonized women and improved neonatal intensive care, the incidence and morbidity associated with GBS meningitis have not declined since the 1970s. Among meningitis survivors, a significant number suffer from complex neurological or neuropsychiatric sequelae, implying that the pathophysiology and pathogenic mechanisms leading to brain injury and devastating outcomes are not yet fully understood. It is imperative to develop new therapeutic and neuroprotective approaches aiming at protecting the developing brain. In this review, we provide updated clinical information regarding the understanding of neonatal GBS meningitis, including epidemiology, diagnosis, management, and human evidence of the disease's underlying mechanisms. Finally, we explore the experimental models used to study GBS meningitis and discuss their clinical and physiologic relevance to the complexities of human disease.

Evaluation of Direct Antimicrobial Susceptibility Testing from Positive Flagged Blood Cultures in Sepsis Patients.

Background: Presently, many laboratories are equipped with automated system for antimicrobial susceptibility testing (AST) for minimum inhibitory concentration-based reporting which enables the clinician to choose the right antimicrobial for timely treatment of sepsis. The study aimed to assess performance of direct AST from blood culture positive broth using automated AST system for accuracy and time taken to release the report. Materials and methods: The present study conducted in a 25-bedded ICU in North India for 12 months. Single morphotype of bacteria on gram stain from positively flagged blood culture bottles were included, which was directly identified (using an in-house protocol) with MALDI-TOF-MS from positive blood culture broths. DAST was carried out from 200 such blood culture broths and results were compared with reference AST (RAST) which was also done using VITEK-2 using overnight grown bacterial colonies as per standard protocol. Results: Among 60 isolates of Enterobacterales, 99% categorical agreement for both E. coli and K. pneumoniae observed by two methods were tested for AST. Among non-fermenters, Pseudomonas aeruginosa showed a categorical agreement of 99.6%, as compared with Acinetobacter spp. and exotic GNBs, which showed 95-96% agreement. A significant difference of 18-24 hours was noted in time to release the report between DAST and RAST, for GNB and GPC both. Conclusion: Direct AST from positive flagged blood culture bottles can significantly reduce the time to release the bacterial susceptibility report by up to 24 hours, at the same time maintaining the accuracy. How to cite this article: Singh V, Agarwal J, Nath SS, Sharma A. Evaluation of Direct Antimicrobial Susceptibility Testing from Positive Flagged Blood Cultures in Sepsis Patients. Indian J Crit Care Med 2024;28(4):387-392.