Clostridium perfringens type C isolates rapidly upregulate their toxin production upon contact with host cells: new insights into virulence?

Cell-Free Culture Supernatant of Lactobacillus acidophilus AG01 and Bifidobacterium animalis subsp. lactis AG02 Reduces the Pathogenicity of NetB-Positive Clostridium perfringens in a Chicken Intestinal Epithelial Cell Line

The worldwide reduction in the use of antibiotics in animal feed is fueling the need for alternatives for the prevention and control of poultry intestinal diseases such as necrotic enteritis (NE), which is caused by Clostridium perfringens. This is the first report on the use of an intestinal epithelial chicken cell line (CHIC-8E11) to study the pathogenic traits of C. perfringens and to investigate the mode of action of cell-free supernatants (CFS) from probiotic Lactobacillus acidophilus AG01 and Bifidobacterium animalis subsp. lactis AG02 in reducing the pathogenicity of C. perfringens. The cell adhesion, permeability and cytotoxicity were assessed under challenge with four C. perfringens strains isolated from broiler NE episodes of differing geographical origin (CP1-UK; CP10-Sweden; 25037-CP01 and CP22-USA). All the C. perfringens strains could adhere to the CHIC-8E11 cells, with varying affinity (0.05-0.48% adhesion across the strains). The CFS from one out of two strains (CP22) increased the cell permeability (+4.5-fold vs. the control, p < 0.01), as measured by the fluorescein isothiocyanate-dextran (FD4) content, with NetB toxin implicated in this effect. The CFS from all the strains was cytotoxic against the CHIC-8E11 cells in a dose- and strain-dependent manner (cytotoxicity 23-62% across the strains when dosed at 50 µL/mL, as assessed by the MTT cell viability assay). Pre-treatment of the cells with CFS from B. animalis subsp. lactis AG02 but not L. acidophilus AG01 reduced the cell adhesion of three out of four C. perfringens strains (by 77-85% vs. the control, p < 0.001) and reduced the negative effect of two NetB-positive strains on the cell permeability. The CFS of both probiotics alleviated the cytotoxicity of all the C. perfringens strains, which was dependent on the dose. The results confirm the suitability of the CHIC-8E11 cell line for the study of host-pathogen cell interactions in the context of NE caused by C. perfringens and reveal a beneficial mode of action of B. animalis subsp. lactis AG02 in reducing C. perfringens cell adhesion and, together with L. acidophilus AG01, in reducing C. perfringens cytotoxicity.

An in vitro assay for toxicity testing of Clostridium perfringens type C β-toxin

Introduction

Veterinary vaccines against Clostridium perfringens type C need to be tested for absence of toxicity, as mandated by pharmacopoeias worldwide. This toxicity testing is required at multiple manufacturing steps and relies on outdated mouse tests that involve severe animal suffering. Clostridium perfringens type C produces several toxins of which the β-toxin is the primary component responsible for causing disease. Here, we describe the successful development of a new cell-based in vitro assay that can address the specific toxicity of the β-toxin.

Methods

Development of the cell-based assay followed the principle of in vitro testing developed for Cl. septicum vaccines, which is based on Vero cells. We screened four cell lines and selected the THP-1 cell line, which was shown to be the most specific and sensitive for β-toxin activity, in combination with a commercially available method to determine cell viability (MTS assay) as a readout.

Results

The current animal test is estimated to detect 100 - 1000-fold dilutions of the Cl. perfringens type C non-inactivated antigen. When tested with an active Cl. perfringens type C antigen preparation, derived from a commercial vaccine manufacturing process, our THP-1 cell-based assay was able to detect toxin activity from undiluted to over 10000-fold dilution, showing a linear range between approximately 1000- and 10000-fold dilutions. Assay specificity for the β-toxin was confirmed with neutralizing antibodies and lack of reaction to Cl. perfringens culture medium. In addition, assay parameters demonstrated good repeatability.

Conclusions

Here, we have shown proof of concept for a THP-1 cell-based assay for toxicity testing of veterinary Cl. perfringens type C vaccines that is suitable for all vaccine production steps. This result represents a significant step towards the replacement of animal-based toxicity testing of this veterinary clostridial antigen. As a next step, assessment of the assay's sensitivity and repeatability and validation of the method will have to be performed in a commercial manufacturing context in order to formally implement the assay in vaccine quality control.

Protective Effects of Lactobacillus plantarum Lac16 on Clostridium perfringens Infection-Associated Injury in IPEC-J2 Cells

Clostridium perfringens (C. perfringens) causes intestinal injury through overgrowth and the secretion of multiple toxins, leading to diarrhea and necrotic enteritis in animals, including pigs, chickens, and sheep. This study aimed to investigate the protective effects of Lactobacillus plantarum (L. plantarum) Lac16 on C. perfringens infection-associated injury in intestinal porcine epithelial cell line (IPEC-J2). The results showed that L. plantarum Lac16 significantly inhibited the growth of C. perfringens, which was accompanied by a decrease in pH levels. In addition, L. plantarum Lac16 significantly elevated the mRNA expression levels of host defense peptides (HDPs) in IPEC-J2 cells, decreased the adhesion of C. perfringens to IPEC-J2 cells, and attenuated C. perfringens-induced cellular cytotoxicity and intestinal barrier damage. Furthermore, L. plantarum Lac16 significantly suppressed C. perfringens-induced gene expressions of proinflammatory cytokines and pattern recognition receptors (PRRs) in IPEC-J2 cells. Moreover, L. plantarum Lac16 preincubation effectively inhibited the phosphorylation of p65 caused by C. perfringens infection. Collectively, probiotic L. plantarum Lac16 exerts protective effects against C. perfringens infection-associated injury in IPEC-J2 cells.

Immunogenicity assessment of Clostridium perfringens type D epsilon toxin epitope-based chimeric construct in mice and rabbit

Epsilon toxin (Etx) belongs to family of pore-forming toxin and is produced by Clostridium perfringens type D. The Etx toxin is responsible for the pathogenesis of enterotoxaemia in sheep and goats, and occasionally in other livestock animals. The present study aimed to develop a Clostridium perfringens epsilon toxin-based chimeric epitope construct having immunodominant B-cell epitope and universal T-cell epitope and its immunogenicity was evaluated in mice and rabbit. An artificial chimeric epitope construct (CEC) was prepared by joining tandem repeats of a peptide containing amino acids (aa) 134–145 of epsilon toxin B-cell epitope and universal T-cell epitopes. The CEC was expressed in the Escherichia coli following codon optimization for efficient translational efficiency and purified by affinity chromatography. The antigenic reactivity of r-CEC proteins was confirmed by western blot with rabbit anti-r-Etox hyperimmune sera. The immunogenicity of the recombinant single CEC was examined in mice and rabbit by indirect ELISA. It was found that r-CEC yielded high titers of neutralizing antibodies (≥ 1.035 IU/ml) in immunized mice and rabbit. The potency of chimeric protein immunized serum was observed to be higher than the recommended level (0.1–0.3 IU/ml) for protection in sheep and goats. This indicated the potential ability of the chimeric protein as a vaccine candidate. This further requires studying the immune response in targeted host species (sheep and goat).

Adhesion and invasion of Clostridium perfringens type A into epithelial cells

Clostridium perfringens is the causative agent for necrotic enteritis. It secretes the major virulence factors, and α- and NetB-toxins that are responsible for intestinal lesions. The TpeL toxin affects cell morphology by producing myonecrosis, but its role in the pathogenesis of necrotic enteritis is unclear. In this study, the presence of netB and tpeL genes in C. perfringens type A strains isolated from chickens with necrotic enteritis, their cytotoxic effects and role in adhesion and invasion of epithelial cells were evaluated. Six (27.3%) of the 22 C. perfringens type A strains were harboring the tpeL gene and produced morphological alterations in Vero cells after 6 h of incubation. Strains tpeL (−) induced strong cell rounding after 6 h of incubation and produced cell enlargement. None of the 22 strains harbored netB gene. All the six tpeL (+) gene strains were able to adhere to HEp-2 cells; however, only four of them (66.6%) were invasive. Thus, these results suggest that the presence of tpeL gene or TpeL toxin might be required for the adherence of bacteria to HEp-2 cells; however, it could not have any role in the invasion process.

Role of pore-forming toxins in bacterial infectious diseases

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

Population-based assessment of the incidence, risk factors, and outcomes of anaerobic bloodstream infections

BACKGROUND

Anaerobes are a relatively uncommon but important cause of bloodstream infection. However, their epidemiology has not been well defined in non-selected populations. We sought to describe the incidence of, risk factors for, and outcomes associated with anaerobic bacteremia.

METHODS

Population-based surveillance for bacteremia with anaerobic microorganisms was conducted in the Calgary area (population 1.2 million) during the period from 2000 to 2008.

RESULTS

A total of 904 incident cases were identified, for an overall population incidence of 8.7 per 100,000 per year; 231 (26 %) were nosocomial, 300 (33 %) were healthcare-associated community-onset, and 373 (41 %) were community-acquired. Elderly males were at the greatest risk. The most common pathogens identified were: Bacteroides fragilis group (3.6 per 100,000), Clostridium (non-perfringens) spp. (1.1 per 100,000), Peptostreptococcus spp. (0.9 per 100,000), and Clostridium perfringens (0.7 per 100,000). Non-susceptibility to metronidazole was 2 %, to clindamycin 17 %, and to penicillin 42 %. Relative to the general population, risk factors for anaerobic bloodstream infection included: male sex, increasing age, a prior diagnosis of cancer, chronic liver disease, heart disease, diabetes mellitus, stroke, inflammatory bowel disease, human immunodeficiency virus (HIV) infection, chronic obstructive pulmonary disease (COPD), and/or hemodialysis-dependent chronic renal failure (HDCRF). The 30-day mortality was 20 %. Increasing age, nosocomial acquisition, presence of malignancy, and several other co-morbid illnesses were independently associated with an increased risk of death.

CONCLUSION

Anaerobic bloodstream infection is responsible for a significant burden of disease in general populations. The data herein establish the extent to which anaerobes contribute to morbidity and subsequent mortality. This information is key in developing preventative, empiric treatment and research priorities.

The role of toxin A and toxin B in the virulence of Clostridium difficile

During the past decade, there has been a striking increase in Clostridium difficile nosocomial infections worldwide predominantly due to the emergence of epidemic or hypervirulent isolates, leading to an increased research focus on this bacterium. Particular interest has surrounded the two large clostridial toxins encoded by most virulent isolates, known as toxin A and toxin B. Toxin A was thought to be the major virulence factor for many years; however, it is becoming increasingly evident that toxin B plays a much more important role than anticipated. It is clear that further experiments are required to accurately determine the relative roles of each toxin in disease, especially in more clinically relevant current epidemic isolates.