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A growing body of evidence has shown that resident memory T (TRM) cells formed in tissue after mucosal infection or vaccination are crucial for counteracting reinfection by pathogens. However, whether lung TRM cells activated by oral immunization with Yptb1(pYA5199) play a protective role against pneumonic plague remains unclear. In this study, we demonstrated that lung CD4+ and CD8+ TRM cells significantly accumulated in the lungs of orally Yptb1(pYA5199)-vaccinated mice and dramatically expanded with elevated IL-17A, IFN-γ, and/or TNF-α production after pulmonary Yersinia pestis infection and afforded significant protection. Short-term or long-term treatment of immunized mice with FTY720 did not affect lung TRM cell formation and expansion or protection against pneumonic plague. Moreover, the intratracheal transfer of both lung CD4+ and CD8+ TRM cells conferred comprehensive protection against pneumonic plague in naive recipient mice. Lung TRM cell–mediated protection was dramatically abolished by the neutralization of both IFN-γ and IL-17A. Our findings reveal that lung TRM cells can be activated via oral Yptb1(pYA5199) vaccination, and that IL-17A and IFN-γ production play an essential role in adaptive immunity against pulmonary Y. pestis infection. This study highlights an important new target for developing an effective pneumonic plague vaccine.

The prevalence and lethality associated with C. perfringens alpha (CPA) and enterotoxin (CPE) toxaemia necessitate the need for rapid and definitive detection systems to initiate management measures. In the present study, a sandwich duplex immuno-capture PCR (SD-IPCR) was developed by employing IgY antibodies against a bivalent protein r-Cpae derived from CPA and CPE for antigen capture and reporter antibodies against truncated CPA or CPE conjugated to oligomers of distinguishable size for antigen revealing and signal amplification. The avian immunoglobulin's (IgY) were devoid of reactivity with S. aureus protein A (SpA), a commensal that often co-exists with C. perfringens. The assay was specific, had a detection limit (LOD) of 1 pg/ml for both CPA and CPE in PBS and improved the LOD by 104 folds compared to an analogous sandwich ELISA with same set of antibodies. In spiking studies, a ten-fold reduction in LOD was observed in case of intestinal tissue samples (10 pg/ml) however, no change in LOD was observed when SD-IPCR was applied on to faecal, serum or muscle tissue samples. Of the 136 natural samples examined, the SD-IPCR could detect CPA and CPE in 29.4% and 35.3% samples, while the sandwich ELISAs could detect the same in 25.7% and 25% samples respectively owing to the relatively lesser sensitivity. The LOD and specificity of the SD-IPCR demonstrates its applicability as an efficient and rapid platform for direct detection CPA and CPE from diverse samples matrices in clinical microbiological and meat testing laboratories.

BackgroundAnthrax, a zoonotic disease is caused by the Gram positive bacteriumBacillus anthracis. During January 2013, an anthrax outbreak among cattle was reported in Gundlupet Taluk, neighboring Bandipur National Park and tiger reserve, India. The present study aims at the molecular identification and characterization of 12B. anthracisisolates from this outbreak by 16S rRNA gene sequencing, screeningB. anthracisspecific prophages and chromosomal markers, protective antigen (pag) gene and canonical single nucleotide polymorphism (canSNP) analysis to subtype the isolates into one of the twelve globally identified clonal sub-lineages ofB. anthracis.ResultsThese isolates had identical 16S rDNA nucleotide sequences withB. anthracisspecific dual peaks showing mixed base pair R (G/A) at position 1139 with visual inspection while the automated basecaller software indicated a G. Alternatively the nucleotide A at 1146 position was indicative of the 16S rDNA type 7. Multiple sequence alignment with additional 170 (16S rDNA) sequences ofB. cereussensulatogroup from GenBank database revealed 28 new 16S types in addition to eleven 16S types reported earlier. The twelveB. anthracisisolates were found to harbor the fourB. anthracisspecific prophages (lambdaBa01, lambdaBa02, lambdaBa03, and lambdaBa04) along with its four specific loci markers (dhp 61.183, dhp 77.002, dhp 73.019, and dhp 73.017). Thepaggene sequencing identified the isolates as protective antigen (PA) genotype I with phenylalanine-proline-alanine phenotype (FPA phenotype). However, sequence clustering with additional 34pagsequences from GenBank revealed two additional missense mutations at nucleotide positions 196 bp and 869 bp of the 2294 bppagsequence among the 5B. cereusstrains with pXO1 like plasmids. The canSNP analysis showed that the isolates belong to A.Br.Aust94 sub-lineage that is distributed geographically in countries of Asia, Africa, Europe and Australia.ConclusionsThe analysis of 16S rDNA sequences reiterated the earlier findings that visual inspection of electropherogram for position 1139 having nucleotide R could be used forB. anthracisidentification and not the consensus sequence from base caller. The canSNP results indicated that the anthrax outbreak among cattle was caused byB. anthracisof A.Br.Aust94 sub-lineage.

Additional file 4. List of bacterial cultures used in the present study.

Additional file 1. Representative electropherograms of the Bacillus anthracis 16S rDNA gene sequences. The electropherogram of 16S rDNA reverse complement read of B. anthracis DFR.BHE 3 strain. Arrows indicate (a) single peak corresponding to position 1148 indicating A (T in reverse read here) (b) dual peak at position 1139 indicating mixed base pair G/A [C/T)in reverse read here] described by Hakovirta et al. 2016 [6].

Additional file 6. List of strains and their accession numbers used for multiple sequence alignment of 16S rDNA gene and pag gene in the present study.

Additional file 2. Additional nucleotide positions of mutations in the Bacillus cereus sensu lato 16S rDNA gene found in the present study. Numbers in paranthesis refers to polymorphic positions in the 16S rDNA gene and are numbered from 1 to 40. The 28 new 16S types are highlighted with colored boxes. The new genotypes of B. anthracis, B. cereus, B. thuringiensis and B. mycoides are boxed in green, orange, blue and yellow color respectively. The 16S types shared by both B. cereus and B. thuringiensis are boxed in purple color. The genotypes shared by both B. cereus and B. anthracis are boxed in red color.

Additional file 5. List of primers and their amplicons size used in the present study.

Anthrax vaccines primarily relying only on protective antigen (PA), the cell binding component in anthrax toxins provide incomplete protection when challenged with spores of virulent encapsulated Bacillus anthracis strains. Alternatively, formaldehyde inactivated spores (FIS) or recombinant spore components generate anti-spore immune responses that inhibit the early stages of infection and augment the PA protective efficacy. In the present study domain IV of PA was spliced with exosporium antigen BxpB via a flexible G4S linker to generate a single functional antigen r-PAbxpB that was further assessed for its protective efficacy against anthrax toxins and spore infection. Immunization of mice with r-PAbxpB elicited significantly high titer antibodies comprising IgG1:IgG2a isotypes in 1:1 ratio, balanced up-regulation of both Th1 (IL2, IL12, IFN-γ) and Th2 (IL4, IL5, IL10) cytokines and high frequencies of CD4+ and CD8+ T cell subsets. The anti-r-PAbxpB antibodies significantly enhanced spore phagocytosis, and killing within macrophages; inhibited their germination to vegetative cells and completely neutralized the anthrax toxins as evidenced by the 100% protection in passive transfer studies. Active immunization with r-PAbxpB provided 100 and 83.3% protection in mice I.P. challenged with 5 × LD100 LD of toxins and 5 × 104 cfu/ml Ames spores, respectively while the sham immunized group succumbed to infection in 48 h. Therefore, the ability of r-PAbxpB to generate protective immune responses against both spores and toxin and provide significant protection suggests it as an efficient vaccine candidate against B. anthracis infection.

The most promising means of controlling anthrax, a lethal zoonotic disease during the early infection stages, entail restricting the resilient infectious form, i.e., the spores from proliferating to replicating bacilli in the host. The extractible antigen (EA1), a major S-layer protein present on the vegetative cells and spores of Bacillus anthracis, is highly immunogenic and protects mice against lethal challenge upon immunization. In the present study, mice were immunized with r-EA1C, the C terminal crystallization domain of EA1, to generate a neutralizing monoclonal antibody EA752–862, that was evaluated for its anti-spore and anti-bacterial properties. The monoclonal antibody EA752–862 had a minimum inhibitory concentration of 0.08 mg/ml, was bactericidal at a concentration of 0.1 mg/ml and resulted in 100% survival of mice against challenge with B. anthracis vegetative cells. Bacterial cell lysis as observed by scanning electron microscopy and nucleic acid leakage assay could be attributed as a possible mechanism for the bactericidal property. The association of mAb EA752–862 with spores inhibits their subsequent germination to vegetative cells in vitro, enhances phagocytosis of the spores and killing of the vegetative cells within the macrophage, and subsequently resulted in 90% survival of mice upon B. anthracis Ames spore challenge. Therefore, owing to its anti-spore and bactericidal properties, the present study demonstrates mAb EA752–862 as an efficient neutralizing antibody that hinders the establishment of early infection before massive multiplication and toxin release takes place.

Anthrax vaccines primarily relying only on protective antigen (PA), the cell binding component in anthrax toxins provide incomplete protection when challenged with spores of virulent encapsulated Bacillus anthracis strains. Alternatively, formaldehyde inactivated spores (FIS) or recombinant spore components generate anti-spore immune responses that inhibit the early stages of infection and augment the PA protective efficacy. In the present study domain IV of PA was spliced with exosporium antigen BxpB via a flexible G4S linker to generate a single functional antigen r-PAbxpB that was further assessed for its protective efficacy against anthrax toxins and spore infection. Immunization of mice with r-PAbxpB elicited significantly high titer antibodies comprising IgG1:IgG2a isotypes in 1:1 ratio, balanced up-regulation of both Th1 (IL2, IL12, IFN-γ) and Th2 (IL4, IL5, IL10) cytokines and high frequencies of CD4+ and CD8+ T cell subsets. The anti-r-PAbxpB antibodies significantly enhanced spore phagocytosis, and killing within macrophages; inhibited their germination to vegetative cells and completely neutralized the anthrax toxins as evidenced by the 100% protection in passive transfer studies. Active immunization with r-PAbxpB provided 100 and 83.3% protection in mice I.P. challenged with 5 × LD100 LD of toxins and 5 × 104 cfu/ml Ames spores, respectively while the sham immunized group succumbed to infection in 48 h. Therefore, the ability of r-PAbxpB to generate protective immune responses against both spores and toxin and provide significant protection suggests it as an efficient vaccine candidate against B. anthracis infection.

Anthrax infection is primarily initiated by B. anthracis endospores that on entry into the host germinate to vegetative cells and cause severe bacteremia and toxaemia employing an array of host colonisation factors and the lethal tripartite toxin. The protective efficacy of conventional protective antigen (PA) based anthrax vaccines is improved by co-administration with inactivated spores or its components. In the present study, using structural vaccinology rationale we synthesized a bivalent protein r-PB encompassing toxin (PAIV) and spore components (BclACTD) and characterized its protective efficacy against B. anthracis infection. Active immunization of mice with r-PB generated high titer circulating antibodies which facilitated the phagocytic uptake of spores, inhibited their germination to vegetative cells and completely neutralized anthrax toxins in vivo resulting in 100 % survival against anthrax toxin challenge. Proliferation of CD4+ T cell subsets with up-regulation of Th1 (IFN-γ, IL-2, and IL-12), Th2 (IL-5, IL-10) cytokines and balanced expression of IgG1:IgG2a antibody isotypes indicated the stimulation of both Th1 and Th2 subsets. The immunized mice exhibited 100 % survival upon challenge with B. anthracis spores or toxin indicating the ability of r-PB to provide comprehensive protection against anthrax. Our results thus demonstrate r-PB an efficient vaccine candidate against anthrax infection.

Clostridium perfringens an ubiquitous environmental bacterium causes major food borne illnesses, digestive diseases and several soft tissue infections in humans and animals. In the present study, toxin typing of 91 C. perfringens isolates from animals with enteric diseases and their environments revealed the presence of type A and C strains. Enterotoxin gene (cpe), responsible for majority of the food poisoning incidences in humans and enteric infections in animals was present in 60.43 % of the isolates of which 76.3 % and 23. 36 % were chromosomal and plasmid borne respectively. Neighbour-joining tree inferred from cpn60 UT nucleotide sequences could differentiate the cpe+ve isolates from the cpe−ve isolates, provide clear distinction between the cpe-IS1470 and cpe-IS1151 genotypes and segregate type A and C strains in separate clusters. The present study is the first report on the utilization of cpn60 UT region for C. perfringens phylogeny analysis and demonstrates that cpn60 UT analysis alone, to a greater extent can be a simple, rapid and efficient method for differentiating between cpe+ve and cpe−ve strains or toxin types. The cpb2 gene was observed among 30 isolates of which 16.6 % were from porcine sources while the rest were of non-porcine and environmental origin. The cpb2 sequences obtained in the present study though similar among them were diverse both from the consensus and atypical cpb2 sequences reported globally and formed a separate cluster. The study thus reports of novel cpb2 gene variant and warrants its characterization through further studies.

Clostridium perfringens beta (CPB) and iota (CPI) toxaemias result in some of the most lethal forms of haemorrhagic and necrotic enteritis and sudden death syndrome affecting especially neonates. While CPB enterotoxemia is one of the most common forms of clostridial enterotoxemia, CPI enterotoxemia though putatively considered to be rare is an emerging cause of concern. The similarities in clinical manifestation, gross and histopathology findings of both types of toxaemias coupled to the infrequency of CPI toxaemia might lead to symptomatic misidentification with Type C resulting in therapeutic failure due to habitual administration of CPB anti-toxin which is ineffective against CPI. Therefore in the present study, to generate a composite anti-toxin capable of neutralizing both toxaemias, a novel bivalent chimera r-Cpib was constructed by splicing the non-toxic C terminal binding regions of CPB and CPI, via a flexible glycine linker (G4S) by overlap-extension PCR. The fusion protein was characterized for its therapeutic abilities toward CPI and CPB toxin neutralizations. The r-Cpib was found to be non-toxic and could competitively inhibit binding of CPB to host cell receptors thereby reducing its cytotoxicity. Immunization of mice with r-Cpib generated specific antibodies capable of neutralizing the above toxaemias both in vitro and in vivo. Caco-2 cells exposed to a mixture of anti-r-Cpib sera and native CPI or CPB, displayed significantly superior protection against the respective toxins while passive challenge of mice with a similar mixture resulted in 83 and 91% protection against CPI and CPB respectively. Alternatively, mice exposed to a mixture of sham sera and native toxins died within 2-3 days. This work thus demonstrates r-Cpib as a novel bivalent fusion protein capable of efficient immunotherapy against C. perfringens CPI and CPB toxaemia.