Streptococcus pneumoniae Attenuated Strain SPY1 with an Artificial Mineral Shell Induces Humoral and Th17 Cellular Immunity and Protects Mice against Pneumococcal Infection

Antiparasitic nitazoxanide potentiates colistin against colistin-resistant Acinetobacter baumannii and Escherichia coli in vitro and in vivo

IMPORTANCE

Colistin is used as a last resort in many infections caused by multidrug-resistant Gram-negative bacteria; however, colistin-resistant (COL-R) is on the rise. Hence, it is critical to develop new antimicrobial strategies to overcome COL-R. We found that nitazoxanide (NTZ) combined with colistin showed notable synergetic antibacterial activity. These findings suggest that the NTZ/colistin combination may provide an effective alternative route to combat COL-R A. baumannii and COL-R Escherichia coli infections.

Disruption of the cpsE and endA Genes Attenuates Streptococcus pneumoniae Virulence: Towards the Development of a Live Attenuated Vaccine Candidate

The majority of deaths due to Streptococcus pneumoniae infections are in developing countries. Although polysaccharide-based pneumococcal vaccines are available, newer types of vaccines are needed to increase vaccine affordability, particularly in developing countries, and to provide broader protection across all pneumococcal serotypes. To attenuate pneumococcal virulence with the aim of engineering candidate live attenuated vaccines (LAVs), we constructed knockouts in S. pneumoniae D39 of one of the capsular biosynthetic genes, cpsE that encodes glycosyltransferase, and the endonuclease gene, endA, that had been implicated in the uptake of DNA from the environment as well as bacterial escape from neutrophil-mediated killing. The cpsE gene knockout significantly lowered peak bacterial density, BALB/c mice nasopharyngeal (NP) colonisation but increased biofilm formation when compared to the wild-type D39 strain as well as the endA gene knockout mutant. All constructed mutant strains were able to induce significantly high serum and mucosal antibody response in BALB/c mice. However, the cpsE-endA double mutant strain, designated SPEC, was able to protect mice from high dose mucosal challenge of the D39 wild-type. Furthermore, SPEC showed 23-fold attenuation of virulence compared to the wild-type. Thus, the cpsE-endA double-mutant strain could be a promising candidate for further development of a LAV for S. pneumoniae.

Protective Regulatory T Cell Immune Response Induced by Intranasal Immunization With the Live-Attenuated Pneumococcal Vaccine SPY1 via the Transforming Growth Factor-β1-Smad2/3 Pathway

Vaccine effectiveness is mainly determined by the mechanism mediating protection, emphasizing the importance of unraveling the protective mechanism for novel pneumococcal vaccine development. We previously demonstrated that the regulatory T cell (Treg) immune response has a protective effect against pneumococcal infection elicited by the live-attenuated pneumococcal vaccine SPY1. However, the mechanism underlying this protective effect remains unclear. In this study, a short synthetic peptide (P17) was used to downregulate Tregs during immunization and subsequent challenges in a mouse model. In immunized mice, increase in immune cytokines (IL-12p70, IL-4, IL-5, and IL-17A) induced by SPY1 were further upregulated by P17 treatment, whereas the decrease in the infection-associated inflammatory cytokine TNF-α by SPY1 was reversed. P17 also inhibited the increase in the immunosuppressive cytokine IL-10 and inflammatory mediator IL-6 in immunized mice. More severe pulmonary injuries and more dramatic inflammatory responses with worse survival in P17-treated immunized mice indicated the indispensable role of the Treg immune response in protection against pneumococcal infection by maintaining a balance among acquired immune responses stimulated by SPY1. Further studies revealed that the significant elevation of active transforming growth factor β (TGF-β)1 by SPY1 vaccination activated FOXP3, leading to increased frequencies of CD4⁺CD25⁺Foxp3⁺ T cells. Moreover, SPY1 vaccination elevated the levels of Smad2/3 and phosphor-Smad2/3 and downregulated the negative regulatory factor Smad7 in a time-dependent manner during pneumococcal infection, and these changes were reversed by P17 treatment. These results illustrate that SPY1-stimulated TGF-β1 induced the generation of SPY1-specific Tregs via the Smad2/3 signaling pathway. In addition, SPY1-specific Tregs may participate in protection via the enhanced expression of PD-1 and CTLA-4. The data presented here extend our understanding of how the SPY1-induced acquired Treg immune response contributes to protection elicited by live-attenuated vaccines and may be helpful for the evaluation of live vaccines and other mucosal vaccine candidates.

Streptococcus pneumoniae's Virulence and Host Immunity: Aging, Diagnostics, and Prevention

Streptococcus pneumoniae is an infectious pathogen responsible for millions of deaths worldwide. Diseases caused by this bacterium are classified as pneumococcal diseases. This pathogen colonizes the nasopharynx of its host asymptomatically, but overtime can migrate to sterile tissues and organs and cause infections. Pneumonia is currently the most common pneumococcal disease. Pneumococcal pneumonia is a global health concern and vastly affects children under the age of five as well as the elderly and individuals with pre-existing health conditions. S. pneumoniae has a large selection of virulence factors that promote adherence, invasion of host tissues, and allows it to escape host immune defenses. A clear understanding of S. pneumoniae's virulence factors, host immune responses, and examining the current techniques available for diagnosis, treatment, and disease prevention will allow for better regulation of the pathogen and its diseases. In terms of disease prevention, other considerations must include the effects of age on responses to vaccines and vaccine efficacy. Ongoing work aims to improve on current vaccination paradigms by including the use of serotype-independent vaccines, such as protein and whole cell vaccines. Extending our knowledge of the biology of, and associated host immune response to S. pneumoniae is paramount for our improvement of pneumococcal disease diagnosis, treatment, and improvement of patient outlook.