Cyclic dipeptides from rhabditid entomopathogenic nematode-associated Bacillus cereus have antimicrobial activities

The cell free culture filtrate of Bacillus cereus associated with an entomopathogenic nematode, Rhabditis (Oscheius) sp. exhibited strong antimicrobial activity. The ethyl acetate extract of the bacterial culture filtrate was purified by silica gel column chromatography to obtain four bioactive compounds. The structure and absolute stereochemistry of these compounds were determined based on extensive spectroscopic analyses (FABMS, ¹H NMR, ¹³C NMR, ¹H–¹H COSY, ¹H–¹³C HMBC) and Marfey’s method. The compounds were identified as cyclic dipeptides (CDPs): cyclo(l-Pro-l-Trp), cyclo(l-Leu-l-Val), cyclo(d-Pro-d-Met), and cyclo(d-Pro-d-Phe), respectively. Compounds recorded significant antibacterial activity against all the test bacteria (Staphylococcus epidermidis, Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa and methicillin-resistant S. aureus) except cyclo(l-Leu-l-Val). Cyclo(l-Leu-l-Val) recorded activity only against Gram positive bacteria. Best antibacterial activity was recorded by cyclo(l-Pro-l-Trp) against S. aureus (4 μg/ml). The four compounds were active against all the five fungi tested (Trichophyton rubrum, Aspergillus flavus, Candida albicans, Candida tropicalis and Cryptococcus neoformans) and the activity was compared with amphotericin B, the standard fungicide. The highest activity of 1 μg/ml by cyclo(l-Pro-l-Trp) was recorded against T. rubrum, a human pathogen responsible for causing athlete’s foot, jock itch, and ringworm. The activity of cyclo(l-Pro-l-Trp) against T. rubrum, C. neoformans and C. albicans were better than amphotericin B, the standard antifungal agent. To our knowledge, this is the first report of antifungal activity of CDPs against the human pathogenic fungi T. rubrum and C. neoformans. The four CDPs are nontoxic to healthy human cell line up to 200 μg/ml. We conclude that the bacterium associated with entomopathogenic nematode is promising sources of natural antimicrobial secondary metabolites, which may receive greater benefit as potential sources of new drugs in the pharmaceutical industry.     

JAM-A is present in mammalian spermatozoa where it is essential for normal motility

Junctional adhesion molecules (JAMs) that are expressed in endothelial and epithelial cells and function in tight junction assembly, also perform important roles in testis where the closely-related JAM-A, JAM-B, and JAM-C are found. Disruption of murine Jam-B and Jam-C has varying effects on sperm development and function; however, deletion of Jam-A has not yet been studied. Here we show for the first time that in addition to expression in the Sertoli-Sertoli tight junctions in the seminiferous tubules, the ∼ 32 kDa murine JAM-A is present in elongated spermatids and in the plasma membrane of the head and flagellum of sperm. Deletion of Jam-A, using the gene trap technology, results in flagellar defects at the ultrastructural level. In Jam-A-deficient mice, which have reduced litter size, both progressive and hyperactived motility are significantly affected (P < 0.0001) before and, more severely, after capacitation. The findings show that JAM-A is involved in sperm tail formation and is essential for normal motility, which may occur via its signal transduction and protein phosphorylation properties. Detection of JAM-A in human sperm proteins indicates that its role may be conserved in sperm motility and that JAM-A may be a candidate gene for the analysis of idiopathic sperm motility defects resulting in male subfertility in the human population.     

Protein kinase C-theta critically regulates the proliferation and survival of pathogen-specific T cells in murine listeriosis

Protein kinase C-theta (PKC-theta) is essential for the activation of T cells in autoimmune disorders, but not in viral infections. To study the role of PKC-theta in bacterial infections, PKC-theta(-/-) and wild-type mice were infected with Listeria monocytogenes (LM). In primary and secondary listeriosis, the numbers of LM-specific CD8 and CD4 T cells were drastically reduced in PKC-theta(-/-) mice, resulting in increased CFUs in spleen and liver of both PKC-theta(-/-) C57BL/6 and BALB/c mice. Furthermore, immunization with peptide-loaded wild-type dendritic cells induced LM-specific CD4 and CD8 T cells in wild-type but not in PKC-theta(-/-) mice. In listeriosis, transfer of wild-type T cells into PKC-theta(-/-) mice resulted in a normal control of Listeria, and, additionally, a selective expression of PKC-theta in LM-specific T cells was sufficient to drive a normal proliferation and survival of these T cells in LM-infected PKC-theta(-/-) recipients, illustrating a cell-autonomous function of PKC-theta in LM-specific T cells. Conversely, adoptively transferred PKC-theta(-/-) T cells were partially rescued from cell death and proliferated in LM-infected wild-type recipients, demonstrating that a PKC-theta deficiency of LM-specific T cells can be partially compensated for by a wild-type environment. Additionally, in vitro experiments showed that only the addition of IL-2, but not an inhibition of caspase-3, induced proliferation and prevented death of PKC-theta(-/-) T cells stimulated with LM-infected wild-type dendritic cells, further demonstrating that the impaired proliferation and survival of PKC-theta(-/-) T cells in listeriosis is not intrinsically fixed and can be experimentally improved.     

Influence of intrinsic myocardial conduction on paced QRS morphology during cardiac resynchronization therapy follow up

We report two cases of patients of cardiac resynchronization therapy (CRT) whose ECGs, during follow up, showed different paced QRS morphology as compared to those of immediate post-device implantation. Parameters of leads, including sensitivity and capture thresholds, were unchanged. There was no lead dislodgement confirmed on fluoroscopy. The ECGs obtained in device off mode showed different intrinsic QRS morphology as compared to those of pre-implant morphology. These changes were attributable to electrolyte imbalance in one patient and progressive intraventricular conduction defect in the other. These cases demonstrate that intrinsic myocardial conduction pattern influences paced QRS morphology. Irreversible change in paced QRS morphology may indicate poor prognosis.     

Isolation and identification of antimicrobial secondary metabolites from Bacillus cereus associated with a rhabditid entomopathogenic nematode

The cell-free culture filtrate of Bacillus cereus associated with an entomopathogenic nematode, Rhabditis (Oscheius) sp., exhibited strong antimicrobial activity. The ethyl acetate extract of the bacterial culture filtrate was purified by silica gel column chromatography to obtain six bioactive compounds. The structure and absolute stereochemistry of these compounds were determined based on extensive spectroscopic analyses (LCMS, FABMS, ¹H NMR, ¹³C NMR, ¹H ?¹H COSY, ¹H ?¹³C HMBC) and Marfey’s method. The compounds were identified as cyclo(D-Pro-D-Leu), cyclo(L-Pro-D-Met), cyclo (L-Pro-D-Phe), cyclo (L-Pro-L-Val), 3,5-dihydroxy-4-ethyl-trans-stilbene, and 3,5-dihydroxy-4-isopropylstilbene, respectively. Compounds recorded antibacterial activity against all four tested bacteria strains of Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. 3,5-dihydroxy-4-isopropylstilbene recorded activity only against Gram-positive bacteria while cyclo(L-Pro-L-Val) recorded no antibacterial activity. Best antibacterial activity was recorded by 3,5-dihydroxy-4-ethyl-trans-stilbene (4 μg/ml) against Escherichia coli. The six compounds recorded significant antifungal activities against five fungal strains tested (Aspergillus flavus, Candida albicans, Fusarium oxysporum, Rhizoctonia solani and Penicillium expansum) and they were more effective than bavistin, the standard fungicide. The activity of cyclo(D-Pro-D-Leu), cyclo(L-Pro-D-Met), 3,5-dihydroxy-4-ethyl-trans-stilbene, and 3,5-dihydroxy-4-isopropylstilbene against Candida albicans was better than amphotericin B. To the best of our knowledge, this is the first report of antifungal activity of the bioactive compounds against the plant pathogenic fungi Fusarium oxysporum, Rhizoctonia solani, and Penicillium expansum. We conclude that the Bacillus cereus strain associated with entomopathogenic nematode is a promising source of natural bioactive secondary metabolites which may receive great benefit as potential sources of new drugs in the agricultural and pharmacological industry.     

In vitro synergistic activity of diketopiperazines alone and in combination with amphotericin B or clotrimazole against Candida albicans

The synergistic anticandidal activity of three diketopiperazines [cyclo-(l-Pro-l-Leu) (1), cyclo-(d-Pro-l-Leu) (2), and cyclo-(d-Pro-l-Tyr) (3)] purified from a Bacillus sp. N strain associated with entomopathogenic nematode Rhabditis (Oscheius) in combination with amphotericin B and clotrimazole was investigated using the macrodilution method. The minimum inhibitory concentration and minimum fungicidal concentration of the diketopiperazines was compared with that of the standard antibiotics. The synergistic anticandidal activities of diketopiperazines with amphotericin B or clotrimazole were assessed using the checkerboard and time-kill methods. The results of the present study showed that the combined effects of diketopiperazines with amphotericin B or clotrimazole predominantly recorded synergistic (<0.5). Time-kill study showed that the growth of the Candida was completely attenuated after 12–24 h of treatment with 50:50 ratios of diketopiperazines and antibiotics. These results suggest that diketopiperazines combined with antibiotics may be microbiologically beneficial and not antagonistic. These findings have potential implications in delaying the development of resistance as the anticandidal effect is achieved with lower concentrations of both drugs (diketopiperazines and antibiotics). The cytotoxicity of diketopiperazines was also tested against two normal human cell lines (L231 lung epithelial and FS normal fibroblast) and no cytotoxicity was recorded for diketopiperazines up to 200 μg/mL. The in vitro synergistic activity of diketopiperazines with antibiotics against Candida albicans is reported here for the first time.