Bordetella Dermonecrotic Toxin Is a Neurotropic Virulence Factor That Uses CaV3.1 as the Cell Surface Receptor.

Dermonecrotic toxin (DNT) is one of the representative toxins produced by Bordetella pertussis, but its role in pertussis, B. pertussis infection, remains unknown. In this study, we identified the T-type voltage-gated Ca2+ channel CaV3.1 as the DNT receptor by CRISPR-Cas9-based genome-wide screening. As CaV3.1 is highly expressed in the nervous system, the neurotoxicity of DNT was examined. DNT affected cultured neural cells and caused flaccid paralysis in mice after intracerebral injection. No neurological symptoms were observed by intracerebral injection with the other major virulence factors of the organisms, pertussis toxin and adenylate cyclase toxin. These results indicate that DNT has aspects of the neurotropic virulence factor of B. pertussis The possibility of the involvement of DNT in encephalopathy, which is a complication of pertussis, is also discussed.IMPORTANCEBordetella pertussis, which causes pertussis, a contagious respiratory disease, produces three major protein toxins, pertussis toxin, adenylate cyclase toxin, and dermonecrotic toxin (DNT), for which molecular actions have been elucidated. The former two toxins are known to be involved in the emergence of some clinical symptoms and/or contribute to the establishment of bacterial infection. In contrast, the role of DNT in pertussis remains unclear. Our study shows that DNT affects neural cells through specific binding to the T-type voltage-gated Ca2+ channel that is highly expressed in the central nervous system and leads to neurological disorders in mice after intracerebral injection. These data raise the possibility of DNT as an etiological agent for pertussis encephalopathy, a severe complication of B. pertussis infection.

BspR/BtrA, an Anti-σ Factor, Regulates the Ability of Bordetella bronchiseptica To Cause Cough in Rats.

Bordetella pertussis, B. parapertussis, and B. bronchiseptica cause respiratory infections, many of which are characterized by coughing of the infected hosts. The pathogenesis of the coughing remains to be analyzed, mainly because there were no convenient infection models of small animals that replicate coughing after Bordetella infection. Here, we present a coughing model of rats infected with B. bronchiseptica Rats, which are one of natural hosts of B. bronchiseptica, were readily infected with the organisms and showed frequent coughing. B. pertussis also caused coughing in rats, which is consistent with previous reports, but the cough response was less apparent than the B. bronchiseptica-induced cough. By using the rat model, we demonstrated that adenylate cyclase toxin, dermonecrotic toxin, and the type III secretion system are not involved in cough production, but BspR/BtrA (different names for the same protein), an anti-σ factor, regulates the production of unknown factor(s) to cause coughing. Rat coughing was observed by inoculation of not only the living bacteria but also the bacterial lysates. Infection with bspR (btrA)-deficient strains caused significantly less frequent coughing than the wild type; however, intranasal inoculation of the lysates from a bspR (btrA)-deficient strain caused coughing similarly to the wild type, suggesting that BspR/BtrA regulates the production of the cough factor(s) only when the bacteria colonize host bodies. Moreover, the cough factor(s) was found to be heat labile and produced by B. bronchiseptica in the Bvg+ phase. We consider that our rat model provides insight into the pathogenesis of cough induced by the Bordetella infection.IMPORTANCE Whooping cough is a contagious respiratory disease caused by Bordetella pertussis This disease is characterized by severe paroxysmal coughing, which becomes a heavy burden for patients and occasionally results in death; however, its pathogenesis remains largely unknown. The major obstacle to analyzing Bordetella-induced coughing is the lack of conventional animal models that replicate coughing. As Bordetella pertussis is highly adapted to humans, infection models in experimental animals are not considered to be well established. In the present study, we examined coughing in rats infected with B. bronchiseptica, which shares many virulence factors with B. pertussis Using this rat model, we demonstrated that some of the major virulence factors of Bordetella are not involved in cough production, but an anti-σ factor, BspR/BtrA, of B. bronchiseptica regulates the production of unknown cough-causing bacterial factor(s). Our results provide important clues to understand the mechanism by which Bordetella induces cough.

Detection of Mycobacterium ulcerans by real-time PCR with improved primers.

BACKGROUND: Buruli ulcer is a severe skin disease caused by Mycobacterium ulcerans. Real-time PCR targeting the IS2404 sequence has been used as a reliable and rapid method for the diagnosis of Buruli ulcer and detection of M. ulcerans in the environment. The genome of M. ulcerans contains hundreds of IS2404 copies, which have variability in certain sequences. Therefore, the design of new primers specific to conserved IS2404 regions may potentially improve the sensitivity of M. ulcerans detection and, consequently, the diagnosis of Buruli ulcer, thus ensuring timely treatment of the disease. RESULTS: In silico analysis indicates that DNA sequences of the IS2404 elements are highly variable within a single strain. As the binding sites of conventional IS2404-specific primers used for M. ulcerans detection contain polymorphic sequences, we designed new primers, which enabled the detection of M. ulcerans by real-time PCR with higher sensitivity and similar specificity with respect to that of conventional primers. However, the increase in sensitivity with the new primers depended on the M. ulcerans strain. CONCLUSIONS: The results suggest that real-time PCR based on the new primers could improve Buruli ulcer diagnosis and M. ulcerans detection in environmental samples.

Disinfectant-susceptibility of multi-drug-resistant Mycobacterium tuberculosis isolated in Japan.

BACKGROUND: Multi-drug-resistant Mycobacterium tuberculosis has been an important problem in public health around the world. However, limited information about disinfectant-susceptibility of multi-drug-resistant strain of M. tuberculosis was available. FINDINGS: We studied susceptibility of several Japanese isolates of multi-drug-resistant M. tuberculosis against disinfectants, which are commonly used in clinical and research laboratories. We selected a laboratory reference strain (H37Rv) and eight Japanese isolates, containing five drug-susceptible strains and three multi-drug-resistant strains, and determined profiles of susceptibility against eight disinfectants. The M. tuberculosis strains were distinguished into two groups by the susceptibility profile. There was no relationship between multi-drug-resistance and disinfectant-susceptibility in the M. tuberculosis strains. Cresol soap and oxydol were effective against all strains we tested, regardless of drug resistance. CONCLUSIONS: Disinfectant-resistance is independent from multi-drug-resistance in M. tuberculosis. Cresol soap and oxydol were effective against all strains we tested, regardless of drug resistance.

Protective effect of a dewaxed whole-cell vaccine against Mycobacterium ulcerans infection in mice.

Mycobacterium ulcerans causes Buruli ulcer, a chronic and destructive necrotizing ulcer in humans. Effective vaccination should be one of the best methods for the prevention of this ulcer. However, no effective vaccines have been developed against M. ulcerans infection. In an effort to develop such a vaccine, we examined protective immunity against M. ulcerans infection in a mouse footpad-infection model. Prior infection of mice with a virulent strain of M. ulcerans or a mycolactone-deficient strain of M. ulcerans resulted in limited protection against subsequent challenge by a virulent strain of M. ulcerans. Protection was not induced in mice immunized with a formalin-treated killed whole-cell preparation of M. ulcerans. By contrast, a dewaxed whole-cell vaccine, prepared by dewaxing M. ulcerans with organic solvents that removed mycolactones and waxy cell walls from the cells, induced significant protection in mice. Our observations should facilitate development of effective vaccines against Buruli ulcer for control of this disease.

Thr/Ser-rich domain of Aspergillus glucoamylase is essential for secretion.

The recombinant Aspergillus awamori strain carrying the mutant glucoamylase-encoding gene in which the entire Thr/Ser-rich Gp-I domain was deleted abolished secretion of mutant glucoamylase. The transcription of the Bip-encoding bipA was low in the wild type (wt) strain, but elevated in the recombinant strain under the condition of glaA expression. The results indicate that the Gp-I domain is vital for glucoamylase secretion.