Post-influenza Staphylococcus aureus pneumonia, particularly methicillin-resistant S. aureus (MRSA), remains a major cause of mortality, highlighting the urgent need for newer therapeutic options. Omadacycline is an aminomethylcycline antibiotic that has demonstrated efficacy against MRSA across many infection models, but its potential in post-influenza A virus (IAV)-MRSA pneumonia remains unexplored. Using a murine model of this infection, we evaluated the effects of omadacycline and a comparator antibiotic, linezolid, on survival, inflammation, bacterial load, toxin production, and lung histopathology. In survival studies, omadacycline matched the effectiveness of oral linezolid at clinically relevant doses. In addition, both antibiotics, particularly omadacycline, attenuated the production of multiple pro-inflammatory cytokines and reduced neutrophil infiltration in the lungs, independent of their effects on pulmonary microbial burden, suggesting an immunomodulatory mechanism of action. Panton-Valentine leukocidin (PVL) toxin production in vitro and in vivo was also assessed, and while the role of PVL in this murine model remains unclear, both agents reduced PVL production. These findings provide the first preclinical demonstration of in vivo efficacy for omadacycline against IAV-MRSA pneumonia and its ability to modulate the host immune response, thereby reducing the excessive inflammation that is linked to mortality in this disease state. Further investigation into the precise interplay between omadacycline and immunomodulation in this disease state is warranted.

PURPOSE OF REVIEW:This review highlights the complex pathophysiology of myocardial dysfunction in septic shock and emphasizes the need for early and repeated hemodynamic assessments to improve outcome. RECENT FINDINGS:Septic cardiomyopathy is a complex, dynamic process driven by multiple mechanisms such as direct myocardial depression induced by host immune mediators (e.g., cytokines, nitric oxide) and/or bacterial toxins, and mitochondrial metabolic dysfunction. Recent echocardiography studies have described multiple unique hemodynamic clusters (phenotypes) that correlated with clinical outcomes. Similarly, serial echocardiography findings and mean arterial pressure abnormalities in patients with Streptococcal Toxic Shock Syndrome (StrepTSS) yielded three distinct hemodynamic groups that predicted mortality and morbidity. Because excessive use of fluids and/or vasopressors can be detrimental, especially in patients with microvascular injury or cardiomyopathy, application of the cardiovascular performance criteria of these different phenotypes could better inform management decisions in real time and improve outcome. SUMMARY:Septic cardiomyopathy is a dynamic, multidimensional response of the myocardium to infection involving both normal and dysregulated immune responses in which the measurable changes in myocardial function predict outcomes. This current paradigm mandates that functional parameters of cardiac performance be measured early and repeatedly throughout the disease course using echocardiography to guide treatment and improve outcome.

Purpose of review This review summarizes the general concepts of innate and acquired immunity, including vaccine use and hesitancy, as they relate to reduction of the global burden of highly communicable infectious diseases. Recent findings Vaccination to increase herd immunity remains the cornerstone of disease prevention worldwide yet global vaccination goals are not being met. Modern obstacles to vaccine acceptance include hesitancy, reduced altruistic intentions, impact of COVID-19, distrust of science and governmental agencies as well as recent geopolitical and environmental disasters. Together, such barriers have negatively impacted immunization rates worldwide, resulting in epidemics and pandemics of serious life-threatening infections from vaccine-preventable diseases, especially those affecting children. In addition, pathogens thought to be controlled or eradicated are reemerging with new genetic traits, making them more able to evade natural and acquired immunity, including that induced by available vaccines. Lastly, many serious and widespread infectious diseases await development and utilization of efficacious vaccines. Summary The global burden of communicable diseases remains high, necessitating continued pathogen surveillance as well as vaccine development, deployment and continued efficacy testing. Equally important is the need to educate aggressively the people and their leaders on the benefits of vaccination to the individual, local community and the human population as a whole.

Department of Medicine, University of Washington School of Medicine, Seattle, Washington, USA Correspondence to Dennis L. Stevens, PhD, MD, 4461 East Victory Road, Meridian, ID 83642 USA. E-mail: [email protected]

Objective: Paeniclostridium sordellii is a pathogen that causes rapidly fatal infections characterized by severe edema, extreme leukemoid reaction and lack of an innate immune response. We recently iden-tified a metalloproteinase of P. sordellii-1 (Mcs1) that cleaves human vascular cell adhesion molecule 1, an adhesion molecule important to hematopoietic precursor retention and leukocyte diapedesis. In the current study, we further characterize Mcs1 activity and investigate its role in pathogenesis.Methods: Mcs1 peptide cleavage sequence and activity conditions were identified using a semi -quantitative fluorescence-based reporter assay. Additional host targets for Mcs1 protease activity were tested and confirmed by gel electrophoreses and western blots. Finally, Mcs1 knock out (DMcs1) and complemented (cMcs1) strains were developed for assessment in our animal model of myonecrosis. Results: Data show that Mcs1 prefers aliphatic amino acid residues, I or L, especially when adjacent to negatively charged or noncharged-polar residues. In vitro, Mcs1 cleaved or partially cleaved human cell adhesion molecules, E-selectin and intracellular adhesion molecule-1 (ICAM-1), and mediators of innate immune infection defense, complement protein-3 and antimicrobial peptide LL-37. In vivo, infection with the DMcs1 P. sordellii strain had little effect on animal survival, tissue destruction or circulating white blood cell counts compared to wild type and cMcs1 strains.Conclusions: Similar to proteolytic virulence factors from other pathogens, Mcs1 is a promiscuous pro-tease that cleaves multiple human-host factors. Despite minimal impact of Mcs1 on the murine model of P. sordellii infection, it is worth considering its role in humans and other animal models.(c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

aVeterans Affairs Medical Center, Boise, Idaho bDepartment of Medicine, University of Washington, Seattle, Washington, USA Correspondence to Dennis L. Stevens, PhD, MD, 500 West Fort St. (Mail Stop 151), Boise, ID 83702, USA. E-mail: [email protected]; [email protected]

Necrotizing soft tissue infections caused by Streptococcus pyogenes (group A streptococcus [GAS]) are characterized by rapid and extensive necrosis of fascia and muscle. Molecular epidemiological studies have demonstrated a positive correlation between GAS isolates that cause invasive infections and the production of S. pyogenes NAD+-glycohydrolase (SPN), an NADase secreted by GAS, but the effect of SPN on muscle cells has not been described. Thus, using standard βNAD+ and ATP quantification assays, we investigated the effects of SPN on cultured human skeletal muscle cell (SkMC) βNAD+ and ATP with and without streptolysin O (SLO)–a secreted cholesterol-dependent cytolysin known to act synergistically with SPN. We found that culture supernatants from GAS strains producing SLO and SPN depleted intracellular βNAD+ and ATP, while exotoxins from a GAS strain producing SLO and an enzymatically-inactive form of SPN had no effect on βNAD+ or ATP. Addition of purified, enzymatically-active SPN to NADase-negative culture supernatants or sterile media reconstituted βNAD+ depletion but had no effect ATP levels. Further, SPN-mediated βNAD+ depletion could be augmented by SLO or the homologous cholesterol-dependent cytolysin, perfringolysin O (PFO). Remarkably, SPN-mediated βNAD+ depletion was SkMC-specific, as purified SPN had minimal effect on epithelial cell βNAD+. Taken together, this study identifies a previously unrecognized role for SPN as a major disruptor of skeletal muscle βNAD+. Such activity could contribute to the rapid and widespread myonecrosis characteristic of severe GAS soft tissue infections.

Background Apart from their antimicrobial activities, some antibiotics have immunomodulatory effects on host cells, particularly monocytes. Because hyperactivation of the pro-inflammatory cytokine response contributes to acute lung injury in patients with bacterial pneumonia and other lung diseases, antimicrobial agents with immunomodulatory activity can reduce cytokine-mediated tissue injury and improve outcomes. Objectives Omadacycline has been recently FDA-approved for community-acquired bacterial pneumonia and acute bacterial skin and skin-structure infections. The present study investigated omadacycline's ability to modulate LPS-induced production of pro-inflammatory cytokines (TNF-alpha, IL-1 beta), acute-phase reactants (IL-6) and anti-inflammatory cytokines (IL-4, IL-10) by human monocytes in vitro. Methods Isolated human monocytes from healthy consenting adults were cultured in RPMI with 1% pooled human serum. Cells were pre-exposed to omadacycline (0.5-64 mu g/mL), minocycline (25, 50 or 25 mu g/mL) or azithromycin (20, 40 or 80 mu g/mL) for 2 h, followed by stimulation with Escherichia coli LPS for 24 h. Cytokines elaborated in the culture supernatant were quantitated by multiplex immunoassay. Results Omadacycline dose-dependently suppressed LPS-induced production of all cytokines tested. Only high-dose minocycline (100 mu g/mL) modestly suppressed TNF-alpha whereas minocycline significantly increased LPS-induced IL-1 beta production. Lower concentrations of minocycline were also stimulatory for IFN-gamma, IL-6 and IL-4. Except for suppression of IL-6, azithromycin was largely without effect. Conclusions Omadacycline has unique and broad immunomodulatory properties. Such activity supports its use in settings where hyperactivation of the immune response contributes to tissue injury and poor outcomes, especially at sites where pro-inflammatory M-type 1 macrophages dominate the cellular immune response.

The streptococci are a diverse group of Gram-positive pathogenic cocci that cause clinical disease in humans and domestic animals. They are traditionally classified on the basis of serological reactions, particularly Lancefield grouping based on cell-wall carbohydrates, and haemolytic activity on blood agar. Six groups can be defined by genetic analysis: pyogenic streptococci, milleri or anginosus group, mitis group, salivarius group, mutans group, and bovis group....

Human botulism is caused by seven serological types of C. botulinum, which is ubiquitously distributed in the soil. Poisoning usually results from ingestion of preformed toxin in food, although this is rapidly inactivated at ordinary cooking temperatures, but it can also result from contaminated wounds. ...

Objectives: Clindamycin (CLI) and erythromycin (ERY) resistance is increasing among group A streptococci (GAS) causing invasive disease and alternative treatments are urgently required. In this study, the efficacy of the newer oxazolidinone tedizolid (TZD) was compared with the first drug in this class, linezolid (LNZ), in experimental murine myonecrosis caused by ERY-susceptible/CLI-susceptible (ERYs/CLIs) or ERY- resistant/CLI-resistant (ERYR/CLIR) GAS. Methods: Normal adult outbred Swiss Webster female mice (10 per group) were infected intramuscularly with ERYs/CLIs (ATCC 12384) or ERYR/CLIR (15-003) GAS. Treatments began 4h post-infection and continued for 72 h. TZD and LNZ (10, 20 and 40 mg/kg) were given intraperitoneally every 12 h. Saline, penicillin (PEN), CLI and ERY were given every 6 h. Survival and infection severity signs and symptoms were followed for 12 days. Results: Both GAS strains were susceptible to LNZ, TZD and PEN; strain 15-003 was confirmed as constitutively resistant to ERY and CLI. Blood levels following a 40 mg/kg dose of LZD and TZD were 30.9 +/- 4.0 mu g/mL and 21.9 +/- 5.3 mu g/mL, respectively. Both TZD and LNZ were highly efficacious for the treatment of severe experimental myonecrosis caused by ERYs/CLIs and, importantly, ERYR/CLIR GAS. Conclusion: In the current era of emerging macrolide/lincosamide resistance among GAS, these data support the use of TZD and LNZ as first-line antibiotics for the treatment of life-threatening GAS infections in humans. (C) 2020 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy.

Staphylococci are nonsporulating, nonmotile, gram-positive cocci that have an average diameter of 1 µm. Microscopically, staphylococci tend to be larger and rounder than streptococci. Because cell division occurs on three planes, these organisms are typically found in grapelike clusters and tetrads, as well as in pairs and sometimes in short chains. Staphylococci are very hardy organisms and can withstand much more physical and chemical stress than pneumococci and streptococci. Because staphylococci are facultative anaerobes, they will grow in the presence or absence of oxygen. Staphylococci are catalase positive. Of the species of staphylococci, Staphylococcus aureus is by far the most important human pathogen. This review covers the epidemiology and pathogenesis of S. aureus, clinical infections associated with S. aureus, treatment of staphylococcal infections, and staphylococcal toxic shock syndrome. Clinically important coagulase-negative staphylococci such as S. epidermidis and S. saprophyticus are also discussed. Tables list antibiotic treatment for staphylococcal infections, clinical manifestations of staphylococcal toxic shock syndrome, and antibiotic treatment for staphylococcal toxic shock syndrome. This review contains 3 figures, 6 tables, and 54 references. Key words: Staphylococcus aureus; Staphylococcal infections; Coagulase-negative staphylococci; Skin and soft tissue infections; S. aureus bacteremia; MRSA; Methicillin-resistant S. aureus; Toxic shock syndrome

The low frequency of circulating antigen-specific memory B cells is a considerable obstacle in the discovery and development of human monoclonal antibodies for therapeutic application. Here, we evaluate two solid-phase isolation methods to enrich the number of antigen-specific B cells from individuals naturally immunized against streptolysin O (SLO), a key virulence factor and known immunogen of group A streptococcus (GAS). Class-switched B cells obtained from individuals with a history of GAS infection were separated from peripheral blood mononuclear cells (PBMCs) by immunomagnetic methods. SLO-specific B cells were further enriched directly by binding to SLO monomers and captured by streptavidin-coated magnetic microbeads or indirectly by binding a fluorescently labeled SLO-streptavidin tetramer and captured by anti-fluorophore immunomagnetic microbeads. SLO-bound B cells were quantitated by flow cytometry and/or expanded in batch culture to determine IgG specificity. From individuals who have suffered a GAS infection ≥2 years prior, only the direct method enriched SLO-specific B cells, as determined by flow cytometry. Likewise, in batch culture, B cells isolated by the direct method resulted in an average of 375-fold enrichment in anti-SLO IgG, while no enrichment was observed for B cells isolated by the indirect method. The direct method established here provides a simple approach to increase low-frequency antigen-specific B cell populations supporting many downstream applications, such as immortalization of B cells, cloning of immunoglobulin genes, or purification of antibodies from supernatant for future study. Overall, this process is efficient, is inexpensive, and can be applied to many naturally immunogenic antigens.IMPORTANCE Bacteria called group A streptococci can cause a variety of skin and soft tissue infections ranging from mild pharyngitis ("strep throat") to deadly necrotizing fasciitis (sometimes called "flesh-eating" disease). In each case, the development of disease and the degree of tissue damage are mediated by toxins released from the bacteria during infection. Consequently, novel therapies aimed at clearing bacterial toxins are greatly needed. One promising new treatment is the utilization of monoclonal antibodies delivered as an immunotherapeutic for toxin neutralization. However, current methods of antibody development are laborious and costly. Here, we report a method to enrich and increase the detection of highly desirable antigen-specific memory B cells from individuals previously exposed to GAS using a cost-effective and less-time-intensive strategy. We envision that this method will be incorporated into many applications supporting the development of immunotherapeutics.

Pneumococci, or Streptococcus pneumoniae, are gram-positive, lancet-shaped diplococci but may also grow in short chains. The polysaccharide polymer that forms the outer capsule of S pneumoniae is chemically and antigenically unique and is crucial to virulence. There are at least 90 distinct serotypes. The capsule allows the bacteria to resist phagocytosis by leukocytes unless the organisms have been opsonized by antibody or serum complement components. Certain pneumococcal serotypes, such as the heavily encapsulated type 3 pneumococcus, are particularly virulent. In fact, only 23 serotypes account for 80% of bacteremic pneumococcal infections in the United States; capsular polysaccharides from these 23 serotypes are incorporated into the polyvalent polysaccharide pneumococcal vaccine (PPSV23), which has been available since 1983. This review covers the epidemiology and pathogenesis of pneumococcal infections, clinical pneumococcal infections, and prevention of pneumococcal infections. Adverse outcomes in pneumococcal pneumonia, antibiotic treatment for penicillin-resistant S pneumoniae, and Centers for Disease Control and Prevention child and adolescent immunization schedules are discussed. This review contains 1 figure, 6 tables, and 41 references. Key words: bacterial pneumonia, PCV13, penicillin-resistant Streptococcus pneumoniae, pneumococcal pneumonia, pneumococcus, PPSV23, pneumonia vaccine, Streptococcus pneumoniae

Purpose. Extracellular protein toxins contribute to the pathogenesis of Staphylococcus aureus infections. The present study compared the effects of iclaprim and trimethoprim - two folic acid synthesis inhibitors - with nafcillin and vancomycin on production of Panton-Valentine leukocidin (PVL), alpha haemolysin (AH) and toxic-shock syndrome toxin I (TSST-1) in methicillinresistant and vancomycin-intermediate S. aureus (MRSA and VISA, respectively). Methodology. Northern blotting and RT-PCR were used to assess gene transcription; toxin-specific bioassays were used to measure protein toxin production. Results. As shown previously, sub-inhibitory concentrations (sub-MIC) of nafcillin increased and prolonged MRSA toxin gene transcription and enhanced PVL, TSST-1 and AH production. Sub-inhibitory doses of iclaprim and trimethoprim delayed maximal AH gene (hla) transcription and suppressed AH production; both drugs delayed, but neither reduced, maximal TSST-1 production. Trimethoprim significantly increased lukF-PV expression and PVL production compared to both untreated and iclaprim-treated cultures. Higher concentrations of iclaprim and trimethoprim markedly suppressed MRSA growth, mRNA synthesis and toxin production. In VISA, iclaprim, vancomycin and nafcillin variably increased tst and hla expression, but only nafcillin increased toxin production. Despite its ability to increase hla expression, iclaprim was the most potent inhibitor of AH production. Conclusions. We conclude that, due to its ability to suppress toxin production. iclaprim should be effective against severe staphylococcal infections caused by toxin-producing MRSA and VISA strains, especially given its ability to concentrate at sites of infection such as skin and skin structures and the lung.