Polysaccharide-iron-regulated cell surface protein conjugate vaccine: its role in protection against Klebsiella pneumoniae-induced lobar pneumonia

A heptavalent O-antigen bioconjugate vaccine exhibits differential functional antibody responses against diverse Klebsiella pneumoniae isolates

Klebsiella pneumoniae is the leading cause of neonatal sepsis and is increasingly difficult to treat due to antibiotic resistance. Vaccination represents a tractable approach to combat this resistant bacterium; however, there is currently not a licensed vaccine. Surface polysaccharides, including O-antigens of lipopolysaccharide, have long been attractive candidates for vaccine inclusion. Herein we describe the generation of a bioconjugate vaccine targeting seven predominant O-antigen subtypes in K. pneumoniae. Each bioconjugate was immunogenic in isolation, with limited cross-reactivity among subtypes. Vaccine-induced antibodies demonstrated varying degrees of binding to a wide variety of K. pneumoniae strains. Further, sera from vaccinated mice induced complement-mediated killing of many of these strains. Finally, increased capsule interfered with O-antigen antibodies' ability to bind and mediate killing of some K. pneumoniae strains. Taken together, these data indicate that this novel heptavalent O-antigen bioconjugate vaccine formulation exhibits limited efficacy against some, but not all, K. pneumoniae isolates.

A heptavalent O-antigen bioconjugate vaccine exhibits differential functional antibody responses against diverse Klebsiella pneumoniae isolates

Klebsiella pneumoniae is a concerning pathogen that is now the leading cause of neonatal sepsis and is increasingly difficult to treat due to heightened antibiotic resistance. Thus, there is an urgent need for preventive and effective immunotherapies targeting K. pneumoniae. Vaccination represents a tractable approach to combat this resistant bacterium in some settings; however, there is currently not a licensed K. pneumoniae vaccine available. K. pneumoniae surface polysaccharides, including the terminal O-antigen polysaccharides of lipopolysaccharide, have long been attractive candidates for vaccine inclusion. Herein we describe the generation of a bioconjugate vaccine targeting seven of the predominant O-antigen subtypes in K. pneumoniae. Each of the seven bioconjugates were immunogenic in isolation, with limited cross-reactivity among subtypes. Vaccine-induced antibodies demonstrated varying degrees of binding to a wide variety of K. pneumoniae strains, including suspected hypervirulent strains, all expressing different O-antigen and capsular polysaccharide combinations. Further, sera from vaccinated mice induced complement-mediated killing of many of these K. pneumoniae strains. Finally, we found that increased quantity of capsule interferes with O-antigen antibodies' ability to bind and mediate killing of some K. pneumoniae strains, including those carrying hypervirulence-associated genes. Taken together, these data indicate that this novel heptavalent O-antigen bioconjugate vaccine formulation exhibits promising efficacy against some, but not all, K. pneumoniae isolates.

Klebsiella pneumoniae: adaptive immune landscapes and vaccine horizons

Klebsiella pneumoniae is among the most common antibiotic-resistant pathogens causing nosocomial infections. Additionally, it is a leading cause of neonatal sepsis and childhood mortality across the globe. Despite its clinical importance, we are only beginning to understand how the mammalian adaptive immune system responds to this pathogen. Further, many studies investigating potential K. pneumoniae vaccine candidates or alternative therapies have been launched in recent years. Here, we review the current state of knowledge on the adaptive immune response to K. pneumoniae infections and progress towards developing vaccines and other therapies to combat these infections.

Advances on novel iron saccharide-iron (III) complexes as nutritional supplements

Iron deficiency is prevalent worldwide, and iron supplementation is a promising strategy to address iron needs of the body. However, traditional oral supplements such as ferrous sulfate, ferrous succinate, and ferrous gluconate are absorbed in the form of ferrous ions, leading to lipid peroxidation and side effects due to other reasons. In recent years, saccharide-iron (III) complexes (SICs) as novel iron supplements have aroused attention for the high iron absorption rate and no gastrointestinal irritation at oral doses. In addition, research on the biological activities of SICs revealed that they also exhibited good abilities in treating anemia, eliminating free radicals, and regulating the immune response. This review focused on the preparation, structural characterization, and bioactivities of these new iron supplements, as promising candidates for the prevention and treatment of iron deficiency.

Klebsiella pneumoniae vaccine studies in animal models

The treatment of Klebsiella pneumoniae is faced with challenges demanding the development of a vaccination strategy. However, no approved and globally available vaccine exists yet. This study aimed to systematically review all published data on K. pneumoniae vaccines in animal models. Without time restrictions, electronic databases were searched using appropriate keywords. The retrieved studies were screened and the data of those that matched our inclusion criteria were collected and analyzed. In total, 2027 records were retrieved; of which 35 studies were included for systematic review. The most frequently used animal model was BALB/c mice. Proteins, polysaccharides, and their combinations (conjugates) were the most common vaccine candidates used. The amount of antigen, the route used for immunization, and the challenge strategy was varying in the studies and were chosen based on several factors such as the animal model, the type of antigen, and the schedule of immunization. Almost all studies claimed that their vaccine was effective/protective, indicated by increasing survival rate, reducing organ bacterial load, and eliciting protective antibody and/or cytokine responses. Altogether, the information presented here will assist researchers to have a better look at the K. pneumoniae vaccine candidates and to take more effective steps in the future.

Current Stage in the Development of Klebsiella pneumoniae Vaccines

Klebsiella pneumoniae is a bacterium capable of colonizing mucous membranes, causing serious infections. Widespread antibiotic resistance in K. pneumoniae—either through intrinsic mechanisms or via acquisition from different species, especially in hospital environments—limits the therapeutic options against this pathogen, further aggravating the disease burden. To date, there are no vaccines available against K. pneumoniae infection. Although formulations based on capsular polysaccharides have been proposed, the high variability in capsular serotypes limits vaccine coverage. Recombinant vaccines based on surface exposed bacterial antigens are a promising alternative owing to their conservation among different serotypes and accessibility to the immune system. Many vaccine candidates have been proposed, some of which have reached clinical trials. The present review summarizes the current status of K. pneumoniae vaccine development. Different strategies including whole cell vaccines, outer membrane vesicles (OMVs), ribosome, polysaccharide, lipopolysaccharide (LPS), and protein-based formulations are discussed. The contribution of antibody and cell-mediated responses is also presented. In summary, K. pneumoniae vaccines are feasible and a promising strategy to prevent infections and to reduce the antimicrobial resistance burden worldwide.

Production of a Promising Biosynthetic Self-Assembled Nanoconjugate Vaccine against Klebsiella Pneumoniae Serotype O2 in a General Escherichia Coli Host

Klebsiella pneumoniae has emerged as a severe opportunistic pathogen with multiple drug resistances. Finding effective vaccines against this pathogen is urgent. Although O-polysaccharides (OPS) of K. pneumoniae are suitable antigens for the preparation of vaccines given their low levels of diversity, the low immunogenicity (especially serotype O2) limit their application. In this study, a general Escherichia coli host system is developed to produce a nanoscale conjugate vaccine against K. pneumoniae using the Nano-B5 self-assembly platform. The experimental data illustrate that this nanoconjugate vaccine can induce an efficient humoral immune response in draining lymph nodes (dLNs) and elicit high titers of the IgG antibody against bacterial lipopolysaccharide (LPS). The ideal prophylactic effects of these nanoconjugate vaccines are further demonstrated in mouse models of both systemic and pulmonary infection. These results demonstrate that OPS with low immunogenicity can be changed into an effective antigen, indicating that other haptens may be applicable to this strategy in the future. To the knowledge, this is the first study to produce biosynthetic nanoconjugate vaccines against K. pneumoniae in E. coli, and this strategy can be applied to the development of other vaccines against pathogenic bacteria.

Vaccines for multidrug resistant Gram negative bacteria: lessons from the past for guiding future success

Antimicrobial resistance is a major threat to global public health. Vaccination is an effective approach for preventing bacterial infections, however it has not been successfully applied to infections caused by some of the most problematic multidrug resistant pathogens. In this review, the potential for vaccines to contribute to reducing the burden of disease of infections caused by multidrug resistant Gram negative bacteria is presented. Technical, logistical and societal hurdles that have limited successful vaccine development for these infections in the past are identified, and recent advances that can contribute to overcoming these challenges are assessed. A synthesis of vaccine technologies that have been employed in the development of vaccines for key multidrug resistant Gram negative bacteria is included, and emerging technologies that may contribute to future successes are discussed. Finally, a comprehensive review of vaccine development efforts over the last 40 years for three of the most worrisome multidrug resistant Gram negative pathogens, Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa is presented, with a focus on recent and ongoing studies. Finally, future directions for the vaccine development field are highlighted.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

Development of a broad spectrum glycoconjugate vaccine to prevent wound and disseminated infections with Klebsiella pneumoniae and Pseudomonas aeruginosa

Klebsiella pneumoniae (KP) and Pseudomonas aeruginosa (PA) are important human pathogens that are associated with a range of infection types, including wound and disseminated infections. Treatment has been complicated by rising rates of antimicrobial resistance. Immunoprophylactic strategies are not constrained by antimicrobial resistance mechanisms. Vaccines against these organisms would be important public health tools, yet they are not available. KP surface O polysaccharides (OPS) are protective antigens in animal models of infection. Similarly, PA flagellin (Fla), the major subunit of the flagellar filament, is required for virulence and is a target of protective antibodies in animal models. We report herein the development of a combined KP and PA glycoconjugate vaccine comprised of the four most common KP OPS types associated with human infections (O1, O2, O3, O5), chemically linked to the two Fla types of PA (FlaA, FlaB). Conjugation of KP OPS to PA Fla enhanced anti-polysaccharide immune responses and produced a formulation that generated antibody titers to the four KP OPS types and both PA Fla antigens in rabbits. Passive transfer of vaccine-induced rabbit antisera reduced the bacterial burden and protected mice against fatal intravenous KP infection. Mice passively transferred with conjugate-induced antisera were also protected against PA infection after thermal injury with a FlaB-expressing isolate, but not a FlaA isolate. Taken together, these promising preclinical results provide important proof-of-concept for a broad spectrum human vaccine to prevent KP and PA infections.

Fighting Antibiotic-Resistant Klebsiella pneumoniae with "Sweet" Immune Targets

Antibiotics and vaccines have greatly impacted human health in the last century by dramatically reducing the morbidity and mortality associated with infectious diseases. The recent challenge posed by the emergence of multidrug-resistant bacteria could possibly be addressed by novel immune prophylactic and therapeutic approaches. Among the newly threatening pathogens, Klebsiella pneumoniae is particularly worrisome in the nosocomial setting, and its surface polysaccharides are regarded as promising antigen candidates. The majority of Klebsiella carbapenem-resistant strains belong to the sequence type 158 (ST258) lineage, with two main clades expressing capsular polysaccharides CPS1 and CPS2. In a recent article, S. D. Kobayashi and colleagues (mBio 9:e00297-18, 2018, https://doi.org/10.1128/mBio.00297-18) show that CPS2-specific IgGs render ST258 clade 2 bacteria more sensitive to human serum and phagocytic killing. E. Diago-Navarro et al. (mBio 9:e00091-18, 2018, https://doi.org/10.1128/mBio.00091-18) generated two murine monoclonal antibodies recognizing distinct glycotopes of CPS2 that presented functional activity against multiple ST258 strains. These complementary studies represent a step toward the control of this dangerous pathogen.

Evaluation of Recombinant Multi-Epitope Outer Membrane Protein-Based Klebsiella pneumoniae Subunit Vaccine in Mouse Model

Safety and protective efficacy of recombinant multi-epitope subunit vaccine (r-AK36) was evaluated in a mouse model. Recombinant AK36 protein comprised of immunodominant antigens from outer membrane proteins (Omp’s) of Klebsiella pneumoniae namely OmpA and OmpK36. r-AK36 was highly immunogenic and the hyperimmune sera reacted strongly with native OmpA and OmpK36 proteins from different K. pneumoniae strains. Hyperimmune sera showed cross-reactivity with Omp’s of other Gram-negative organisms. Humoral responses showed a Th2-type polarized immune response with IgG1 being the predominant antibody isotype. Anti-r-AK36 antibodies showed antimicrobial effect during in vitro testing with MIC values in the range of 25–50 μg/ml on different K. pneumoniae strains. The recombinant antigen elicited three fold higher proliferation of splenocytes from immunized mice compared to those with sham-immunized mice. Anti-r-AK36 antibodies also exhibited in vitro biofilm inhibition property. Subunit vaccine r-AK36 immunization promoted induction of protective cytokines IL-2 and IFN-γ in immunized mice. When r-AK36-immunized mice were challenged with 3 × LD₁₀₀ dose, ∼80% of mice survived beyond the observation period. Passive antibody administration to naive mice protected them (67%) against the lethal challenge. Since the targeted OMPs are conserved among all K. pneumoniae serovars and due to the strong nature of immune responses, r-AK36 subunit vaccine could be a cost effective candidate against klebsiellosis.

Novel vaccine antigen combinations elicit protective immune responses against Escherichia coli sepsis

Systemic infections caused by extraintestinal pathogenic Escherichia coli (ExPEC) have emerged as the most common community-onset bacterial infections and are major causes of nosocomial infections worldwide. The management of ExPEC infections has been complicated by the heterogeneity of ExPEC strains and the emergence of antibiotic resistance, thus their prevention through vaccination would be beneficial. The protective efficacy of four common ExPEC antigen candidates composed of common pilus antigens EcpA and EcpD and iron uptake proteins IutA and IroN, were tested by both active and passive immunization in lethal and non-lethal murine models of sepsis. Additionally, antibody raised to a synthetic form of a conserved surface polysaccharide, β-(1-6)-linked poly-N-acetylglucosamine (dPNAG) containing 9 monomers of (non-acetylated) glucosamine (9GlcNH2) conjugated to tetanus toxoid TT (9GlcNH2-TT) was tested in passive immunization protocols. Active immunization of mice with recombinant antigens EcpA, EcpD, IutA, or IroN elicited high levels of total IgG antibody of IgG1/IgG2a isotypes, and were determined to be highly protective against E. coli infection in lethal and non-lethal sepsis challenges. Moreover, passive immunization against these four antigens resulted in significant reductions of bacteria in internal organs and blood of the mice, especially when the challenge strain was grown in iron-restricted media. Inclusion of antibodies to PNAG increased the efficacy of the passive immunization under conditions where the challenge bacteria were grown in LB medium but not in iron-restricted media. The information and data presented are the first step toward the development of a broadly protective vaccine against sepsis-causing E. coli strains.

Influence of iron status on risk of maternal or neonatal infection and on neonatal mortality with an emphasis on developing countries

Infection is a major cause of neonatal death in developing countries. This review investigates whether host iron status affects the risk of maternal and/or neonatal infection, potentially contributing to neonatal death, and summarizes the iron acquisition mechanisms described for pathogens causing stillbirth, preterm birth, and congenital infection. In vitro evidence shows that iron availability influences the severity and chronicity of infections that cause these negative outcomes of pregnancy. In vivo evidence is lacking, as relevant studies of maternal iron supplementation have not assessed the effect of iron status on the risk of maternal and/or neonatal infection. Reducing iron-deficiency anemia among women is beneficial and should improve the iron stores of babies; moreover, there is evidence that iron status in young children predicts the risk of malaria and, possibly, the risk of invasive bacterial diseases. Caution with maternal iron supplementation is indicated in iron-replete women who may be at high risk of exposure to infection, although distinguishing between iron-replete and iron-deficient women is currently difficult in developing countries, where a point-of-care test is needed. Further research is indicated to investigate the risk of infection relative to iron status in mothers and babies in order to avoid iron intervention strategies that may result in detrimental birth outcomes in some groups of women.

Identification and characterization of antigens as vaccine candidates against Klebsiella pneumoniae

Nosocomial infections, also called "hospital acquired infections," occur worldwide and affect both developed and resource-poor countries, thus having a major impact on their health care systems. Klebsiella pneumoniae, which is an opportunistic Gram-negative pathogen, is responsible for causing pneumonia, urinary tract infections and septicemia in immune compromised hosts such as neonates. Unfortunately, there is no vaccine or mAb available for prophylactic or therapeutic use against K. pneumoniae infections. For this reason, we sought for a protein-based subunit vaccine capable of combating K. pneumoniae infections, by applying our ANTIGENome technology for the identification of potential vaccine candidates, focusing on conserved protein antigens present in strains with different serotypes. We identified numerous novel immunogenic proteins using genomic surface display libraries and human serum antibodies from donors exposed to or infected by K. pneumoniae. Vaccine candidate antigens were finally selected based on animal protection in a murine lethal-sepsis model. The protective and highly conserved antigens identified in this study are promising candidates for the development of a protein-based vaccine to prevent infection by K. pneumoniae.

Pseudoalteromonas strains are potent immunomodulators owing to low-stimulatory LPS

Many species of marine bacteria elicit a weak immune response. In this study, the aim was to assess the immunomodulatory properties of Gram-negative Pseudoalteromonas strains compared with other marine Gram-negative bacteria and to identify the molecular cause of the immunomodulation. Using murine bone-marrow derived dendritic cells (DCs), it was found that Pseudoalteromonas strains induced low cytokine production and modest up-regulation of surface markers CD40 and CD86 compared with other marine bacteria and Escherichia coli LPS. Two strains, Ps. luteoviolacea and Ps. ruthenica, were further investigated with respect to their immunomodulatory properties in DCs. Both inhibited IL-12 and increased IL-10 production induced by E. coli LPS. LPS isolated from the two Pseudoalteromonas strains had characteristic lipid A bands in SDS-PAGE. Stimulation of HEK293 TLR4/MD2 cells with the isolated LPS confirmed the involvement of LPS and TLR4 and established Pseudoalteromonas LPS as TLR4 antagonists. The isolated LPS was active in the endotoxin limulus amoebocyte lysate assay and capable of inducing increased endocytosis in DCs. This study highlights that antagonistic LPS from Pseudoalteromonas strains has potential as a new candidate of therapeutic agent capable of modulating immune responses.

Development of a new trend conjugate vaccine for the prevention of Klebsiella pneumoniae

Klebsiella pneumoniae is a major cause of nosocomial pneumonia, septicemia and urinary tract infections, especially in newborns, blood cancer patients, and other immunocompromised candidates. The control of K. pneumoniae is a complicated issue due to its tight pathogenesis. Immuno-prophylactic preparations, especially those directed toward the bacterium O-antigen, showed to be the most successful way to prevent the infection incidence. However, all previously proposed preparations were either of limited spectrum or non-maternal, and hence not targeting the main Klebsiella patients. Moreover, all preparations were directed only to prevent the respiratory diseases due to that pathogen. This article addresses the development of a method originally used to purify the non-capsular bacterial-endotoxins, as a new and easy method for vaccine production against K. pneumoniae. The application of this method was preceded by a biotechnological control of capsular polysaccharide production in K. pneumoniae. The new produced natural conjugate between the bacterial O-antigen and its outer membrane proteins was evaluated by physicochemical and immunological methods to investigate its purity, integrity, safety and immunogenicity. It showed to be pure, stable, safe for use, and able to elicit a protective immunoglobulin titer against different Klebsiella infections. This immune-response proved to be transferable to the offspring of the vaccinated experimental rabbits via placenta.

Development of immunization trials against Klebsiella pneumoniae

Klebsiella pneumoniae is the most common cause of nosocomial respiratory tract and premature intensive care infections, and the second most frequent cause of Gram-negative bacteraemia and urinary tract infections. Drug resistant isolates remain an important hospital-acquired bacterial pathogen, add significantly to hospital stays, and are especially problematic in high impact medical areas such as intensive care units. Many investigations worldwide proved the increasing resistance of such pathogen, resulting in an average rate of 1.63 outbreak every year. A variety of preventive measures were applied to reduce such incidences. Immunotherapy and passive immunization researches as well found their way to the treatment of Klebsiella. During the last 40 years, many trials for constructing effective vaccines were followed. This up-to-date review classifies such trials and documents them in a progressive way. A following comment discusses each group benefits and defects.

Protective efficacy of DNA vaccines encoding outer membrane protein A and OmpK36 of Klebsiella pneumoniae in mice

The immunogenicity of DNA vaccines expressing outer membrane proteins as antigens was evaluated in this study. DNA vaccines consisting of vector pVAX1 expressing either outer membrane protein A or OmpK36 were injected into mice by either the intradermal or the intramuscular route. Antibodies elicited were shown to be specifically reactive to OmpA and OmpK36 by immunoblotting. The immunoglobulin G (IgG) antibodies elicited by both vaccines included IgG1, IgG2a, IgG2b, and IgG3. Immunized mice exhibited a predominance of IgG1 over IgG2a, therefore indicating a stronger humoral response. Mice receiving either of the DNA vaccines produced high levels of interleukin-12 (IL-12) and IL-10 and low levels of gamma interferon, suggesting the induction of a mixed Th1 and Th2 response. Sera from DNA vaccine-immunized mice had significantly higher opsonic activity in opsonophagocytic assays than did sera from the control mice. The level of protection afforded by pOmpK36 DNA injected intradermally into mice was the highest. These results suggest that both OmpA and OmpK36 are excellent candidates for use in future studies of vaccination against infections caused by Klebsiella pneumoniae. This is the first study which established the efficacy of protection afforded by DNA vaccines based on outer membrane proteins against K. pneumoniae infections.

Therapeutic potential of bacteriophage in treating Klebsiella pneumoniae B5055-mediated lobar pneumonia in mice

Klebsiella pneumoniae causes infections in humans especially in immunocompromised patients. About 80 % of nosocomial infections caused by K. pneumoniae are due to multidrug-resistant strains. The emergence of antibiotic-resistant bacterial strains necessitates the exploration of alternative antibacterial therapies, which led our group to study the ability of bacterial viruses (known as bacteriophages or simply phages) to treat mice challenged with K. pneumoniae. Phage SS specific for K. pneumoniae B5055 was isolated and characterized, and its potential as a therapeutic agent was evaluated in an experimental model of K. pneumoniae-mediated lobar pneumonia in mice. Mice were challenged by intranasal (i.n.) inoculation with bacteria (108 c.f.u. ml−1). A single intraperitoneal injection of 1010 p.f.u. ml−1 phage administered immediately after i.n. challenge was sufficient to rescue 100 % of animals from K. pneumoniae-mediated respiratory infections. Administration of the phage preparation 3 h prior to i.n. bacterial challenge provided significant protection in infected mice, while even 6 h delay of phage administration after the induction of infection rendered the phage treatment ineffective. The results of this study therefore suggest that the timing of starting the phage therapy after initiation of infection significantly contributes towards the success of the treatment.

Protection in a mouse peritonitis model mediated by iron-regulated outer-membrane protein of Salmonella typhi coupled to its Vi antigen

Vi polysaccharide and iron-regulated outer-membrane proteins (IROMPs) were extracted and purified from the standard strain of Salmonella typhi, Ty2. These were then conjugated by chemical coupling using the carbodimide method. Vi–IROMP conjugate was tested for its ability to protect against colonization by S. typhi in different organs. Mice immunized with 2.5 μg Vi–IROMP conjugate showed the most protection, as the least bacterial colonization of spleen, liver and Peyer's patches was observed. Peritoneal macrophages obtained from conjugate-treated mice phagocytosed bacteria efficiently. Circulating antibodies and the delayed type hypersensitivity response elucidated by mouse foot-pad swelling was significantly higher in conjugate-treated animals. These results clearly demonstrate that an IROMP and polysaccharide conjugate of S. typhi prepared from the same strain has the potential to protect animals against challenge.

Immunization of cows with ferric enterobactin receptor from coliform bacteria

The serum and milk immunoglobulin (Ig) G responses of lactating dairy cows were determined following immunization with ferric enterobactin receptor FepA. Escherichia coli 471 was cultured in iron-depleted medium, and outer membrane proteins were extracted by 2% N-lauroylsarcosine sodium salt and 2% Triton X-100. The FepA was isolated from the outer membrane proteins by ion-exchange chromatography. Twenty cows were assigned to four treatment groups of 5 cows blocked by breed and days in milk. Treatment groups were vaccinated with 100 micrograms of FepA, 500 micrograms of FepA, Escherichia coli J5 bacterin, or sterile phosphate-buffered saline. Primary immunization was at approximately 200 d in milk, and booster immunizations were given 14 and 28 d later. Serum and whey IgG titers to FepA in cows vaccinated with FepA were significantly higher than those from cows vaccinated with either E. coli J5 bacterin or phosphate-buffered saline. Serum and whey IgG titers to FepA were elevated by 14 d in cows vaccinated with FepA. Significant differences were not observed between doses of FepA. The degree of cross-reactivity of purified IgG from cows vaccinated with FepA to E. coli and Klebsiella pneumoniae isolates was significantly higher than that to a control isolate that lacked FepA production. Immunization with FepA elicited an immunological response in serum and milk.

Inhibition of in vitro growth of coliform bacteria by a monoclonal antibody directed against ferric enterobactin receptor FepA

The ability of a murine monoclonal antibody that blocks the enterobactin ligand-binding site of the ferric enterobactin receptor FepA to inhibit the growth of coliform bacteria derived from a bovine intramammary infection (IMI) was determined in an iron-restricted medium. Bacterial isolates from bovine IMI in five herds were tested by the chrome azurol sulfonate assay to detect siderophore production. Each of the isolates of Escherichia coli (n = 25) and Klebsiella pneumoniae (n = 25) were positive for siderophore production. Each isolate expressed iron-regulated outer membrane proteins when grown in trypticase soy broth plus the iron chelator alpha-alpha'-dipyridyl. Immunoblots revealed that the monoclonal antibody recognized FepA that was expressed by each of the E. coli isolates (n = 25). Only 4 of 25 K. pneumoniae isolates produced FepA that reacted with the monoclonal antibody. This result coincided with the results of an in vitro growth assay. Growth of all E. coli isolates was significantly inhibited by the addition of monoclonal antibody to synthetic medium containing apolactoferrin. Antigenic variation in the enterobactin-binding site resulted in a low percentage of K. pneumoniae isolates that were inhibited by the monoclonal antibody. Inhibition of bacterial growth by the monoclonal antibody was dose-dependent. As little as 50 micrograms/ml of purified antibody had an inhibitory effect on bacterial growth in the synthetic iron-restricted medium. Monoclonal antibody specific for the enterobactin ligand-binding site of FepA inhibited the growth of E. coli that was isolated from bovine IMI.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

Lipopolysaccharide-induced resistance in mice against ascending urinary tract infection with Klebsiella pneumoniae

Protective effect of the lipopolysaccharide (LPS) antigen of Klebsiella pneumoniae was tested against ascending-mode urinary tract infection in BALB/c and LACA strains of mice. LPS was given by two different routes; LPS was found to be protective (whatever the application route) since colonization with the challenge organism was significantly lower in both cases as compared with unimmunized mice. A maximum decrease in bacterial count in the kidney of LPS-treated animals was observed on challenge after a 4-d treatment.