Clearance of Staphylococcus aureus from In Vivo Models of Chronic Infection by Immunization Requires Both Planktonic and Biofilm Antigens

The effect of Staphylococcus aureus on innate and adaptive immunity and potential immunotherapy for S. aureus-induced osteomyelitis

Osteomyelitis is a chronic inflammatory bone disease caused by infection of open fractures or post-operative implants. Particularly in patients with open fractures, the risk of osteomyelitis is greatly increased as the soft tissue damage and bacterial infection are often more severe. Staphylococcus aureus, one of the most common pathogens of osteomyelitis, disrupts the immune response through multiple mechanisms, such as biofilm formation, virulence factor secretion, and metabolic pattern alteration, which attenuates the effectiveness of antibiotics and surgical debridement toward osteomyelitis. In osteomyelitis, immune cells such as neutrophils, macrophages and T cells are activated in response to pathogenic bacteria invasion with excessive inflammatory factor secretion, immune checkpoint overexpression, and downregulation of immune pathway transcription factors, which enhances osteoclastogenesis and results in bone destruction. Therefore, the study of the mechanisms of abnormal immunity will be a new breakthrough in the treatment of osteomyelitis.

Vaccination with a combination of planktonic and biofilm virulence factors confers protection against carbapenem-resistant Acinetobacter baumannii strains

Acinetobacter baumannii is a multi-drug resistant pathogen with the ability to switch between planktonic and biofilm phenotypes. Although there is no vaccine against A. baumannii infections, many attempts have been made to develop vaccines using planktonic or biofilm antigens. To cover the different phenotypes of A. baumannii during growth and attachment, we combined planktonic upregulated antigens of iron receptors with biofilm upregulated antigens of pilus rods and evaluated immune responses and protective efficacies of the combined vaccine using lethal and sub-lethal murine sepsis models. The results showed that the combined vaccine elicited high IgG antibody titers and conferred protection against lethal doses of two Carbapenem-resistant high adherent A. baumannii strains. Complete bacterial clearance from all the affected tissues of the mice challenged with A. baumannii was an excellent achievement with our quadrivalent immunogen. These results demonstrate both planktonic and biofilm antigens are important during antigen selection for vaccine design.

Whole-cell vaccine candidates induce a protective response against virulent Acinetobacter baumannii

Acinetobacter baumannii causes multi-system diseases in both nosocomial settings and a pre-disposed general population. The bacterium is not only desiccation-resistant but also notoriously resistant to multiple antibiotics and drugs of last resort including carbapenem, colistin, and sulbactam. The World Health Organization has categorized carbapenem-resistant A. baumannii at the top of its critical pathogen list in a bid to direct urgent countermeasure development. Several early-stage vaccines have shown a range of efficacies in healthy mice, but no vaccine candidates have advanced into clinical trials. Herein, we report our findings that both an ionizing γ-radiation-inactivated and a non-ionizing ultraviolet C-inactivated whole-cell vaccine candidate protects neutropenic mice from pulmonary challenge with virulent AB5075, a particularly pathogenic isolate. In addition, we demonstrate that a humoral response is sufficient for this protection via the passive immunization of neutropenic mice.

Select Whole-Cell Biofilm-Based Immunogens Protect against a Virulent Staphylococcus Isolate in a Stringent Implant Model of Infection

Many microbes of concern to human health remain without vaccines. We have developed a whole-microbe inactivation technology that enables us to rapidly inactivate large quantities of a pathogen while retaining epitopes that were destroyed by previous inactivation methods. The method that we call UVC-MDP inactivation can be used to make whole-cell vaccines with increased potency. We and others are exploring the possibility of using improved irradiation-inactivation technologies to develop whole-cell vaccines for numerous antibiotic-resistant microbes. Here, we apply UVC-MDP to produce candidate MRSA vaccines which we test in a stringent tibia implant model of infection challenged with a virulent MSRA strain. We report high levels of clearance in the model and observe a pattern of protection that correlates with the immunogen protein profile used for vaccination.

Improve Integration of In Vitro Biofilm Body of Knowledge to Support Clinical Breakthroughs in Surgical Site Infection

Prosthetics increase the risk of deep surgical site infections in procedures intended to restore function. In orthopaedics, prosthetic joint infections can lead to repetitive surgeries, amputation, or worse. Biofilm formation both in vitro and in vivo involves stages of attachment, accumulation, and maturation. The level of maturation affects susceptibility to antibiotics, the immune system, and the success of surgical interventions. A review of the literature indicates that orthopedic publications are less likely to mention biofilm. We have reviewed animal models of infection to assess in vivo models of prosthetic infection. Although most prosthetic infections seem to originate from local skin microbiota, clinically representative biofilm inocula are unusual. Biofilm-related end points are more widely adopted, but studies rarely include both quantification of adherent microbial burden and imaging of the in vivo biofilm. Failure to differentiate between planktonic and biofilm infections can skew research away from needed chronic disease models. In this review, we address prosthetic joint infections as an important model for chronic biofilm infection research, identify critical requirements for in vivo models of chronic infection, and propose that resistance to the terminology of biofilm research exists within both research and regulation, which could limit progress toward important orthopaedic targets.

Infectious Osteomyelitis: Marrying Bone Biology and Microbiology to Shed New Light on a Persistent Clinical Challenge

Infections of bone occur in a variety of clinical settings, ranging from spontaneous isolated infections arising from presumed hematogenous spread to those associated with skin and soft tissue wounds or medical implants. The majority are caused by the ubiquitous bacterium Staphyloccocus (S.) aureus, which can exist as a commensal organism on human skin as well as an invasive pathogen, but a multitude of other microbes are also capable of establishing bone infections. While studies of clinical isolates and small animal models have advanced our understanding of the role of various pathogen and host factors in infectious osteomyelitis (iOM), many questions remain unaddressed. Thus, there are many opportunities to elucidate host-pathogen interactions that may be leveraged toward treatment or prevention of this troublesome problem. Herein, we combine perspectives from bone biology and microbiology and suggest that interdisciplinary approaches will bring new insights to the field. © 2021 American Society for Bone and Mineral Research (ASBMR).

Bacterial biofilm-derived antigens: a new strategy for vaccine development against infectious diseases

INTRODUCTION

Microorganisms can develop into a social organization known as biofilms and these communities can be found in virtually all types of environment on earth. In biofilms, cells grow as multicellular communities held together by a self-produced extracellular matrix. Living within a biofilm allows for the emergence of specific properties for these cells that their planktonic counterparts do not have. Furthermore, biofilms are the cause of several infectious diseases and are frequently inhabited by multi-species. These interactions between microbial species are often critical for the biofilm process. Despite the importance of biofilms in disease, vaccine antigens are typically prepared from bacteria grown as planktonic cells under laboratory conditions. Vaccines based on planktonic bacteria may not provide optimal protection against biofilm-driven infections.

AREAS COVERED

In this review, we will present an overview of biofilm formation, what controls this mode of growth, and recent vaccine development targeting biofilms.

EXPERT OPINION

Previous and ongoing research provides evidence that vaccine formulation with antigens derived from biofilms is a promising approach to prevent infectious diseases and can enhance the protective efficacy of existing vaccines. Therefore, research focusing on the identification of biofilm-derived antigens merits further investigations.

Radiation-Inactivated Acinetobacter baumannii Vaccine Candidates

Acinetobacter baumannii is a bacterial pathogen that is often multidrug-resistant (MDR) and causes a range of life-threatening illnesses, including pneumonia, septicemia, and wound infections. Some antibiotic treatments can reduce mortality if dosed early enough before an infection progresses, but there are few other treatment options when it comes to MDR-infection. Although several prophylactic strategies have been assessed, no vaccine candidates have advanced to clinical trials or have been approved. Herein, we rapidly produced protective whole-cell immunogens from planktonic and biofilm-like cultures of A. baumannii, strain AB5075 grown using a variety of methods. After selecting a panel of five cultures based on distinct protein profiles, replicative activity was extinguished by exposure to 10 kGy gamma radiation in the presence of a Deinococcus antioxidant complex composed of manganous (Mn²⁺) ions, a decapeptide, and orthophosphate. Mn²⁺ antioxidants prevent hydroxylation and carbonylation of irradiated proteins, but do not protect nucleic acids, yielding replication-deficient immunogenic A. baumannii vaccine candidates. Mice were immunized and boosted twice with 1.0 × 10⁷ irradiated bacterial cells and then challenged intranasally with AB5075 using two mouse models. Planktonic cultures grown for 16 h in rich media and biofilm cultures grown in static cultures underneath minimal (M9) media stimulated immunity that led to 80–100% protection.