Purpose. Clostridium difficile is an anaerobic spore-forming pathogen that causes a serious toxin-mediated enteric disease in humans. Therapeutic agents that are capable of reducing C. difficile spore production could significantly minimize the transmission and relapse of C. difficile infections. This study investigated the efficacy of a food-grade, plant-derived compound, carvacrol (CR), in reducing C. difficile spore production, germination and spore outgrowth.
Methodology. Two hyper-virulent C. difficile isolates (ATCC BAA 1870 and 1805) were grown with or without a sub-inhibitory concentration (SIC) of CR. Total viable counts and heat-resistant spore counts were determined at different time intervals. Moreover, spores and vegetative cells were visualized using phase-contrast microscopy. To determine the effect of CR on C. difficile germination and spore outgrowth, C. difficile spores were seeded in germination medium with or without the SIC and MIC of CR, and spore germination and spore outgrowth were measured by recording optical density at 600 nm. The effect of CR on C. difficile sporulation genes was also investigated using real-time qPCR.
Results. Carvacrol significantly reduced sporulation in C. difficile and down-regulated critical genes involved in spore production (P<0.05). The SIC or MIC of CR did not inhibit C. difficile spore germination; however, the MIC of CR completely inhibited spore outgrowth.
Conclusion. The results suggest that CR could potentially be used to control C. difficile by reducing spore production and outgrowth.
Purpose. Typhoid fever caused by Salmonella enterica serovar Typhi has contributed to the global public health burden, particularly in developing countries. In this study, an S. Typhi ghost was developed and its capacity as a vaccine candidate against typhoid fever was assessed.
Methodology. An asd + plasmid pJHL187 harbouring a ghost cassette comprising the PhiX 174 Elysis gene tightly controlled under the convergent promotor system was transformed into an asd gene-deleted mutant S.Typhi strain (STG). The eltB gene encoding the E. coli heat-labile enterotoxin (LTB) protein was subcloned into a foreign antigen delivery cassette of pJHL187 to increase mucosal immunity.
Results. The stringent repression and expression of the lethal E lysis gene in the system allowed stable production of the ghost strain and secretion of LTB, which was confirmed by immune blot analysis. The level of IgG and sIgA was significantly increased in the mice subcutaneously immunized with STG-LTB compared to the non-immunized mice (P<0.05). The CD3+CD4+ T cell subpopulation was augmented in the immunized group (P<0.05) and showed the increment of immunomodulatory cytokines IL-2, IL-6, IL-12, IL-17 and IFN-γ in in vitro restimulated splenocytes isolated from the inoculated mice. The serum bactericidal activity of antibodies generated in the rabbits injected with STG-LTB was proved by the elimination of approximately 87.5 % of wild-type S. Typhi in the presence of exogenous complement.
Conclusion. The results demonstrated that the STG-LTB ghost effectively enhanced the immunological responses, meaning that STG-LTB is potentially available as a vaccine candidate against typhoid fever.
Purpose. We assessed the effects of four different types of tea extracts (green, oolong, black and pu-erh tea) on cellular surface properties (hydrophobicity and auto-aggregation) and the colonization attributes (attachment and biofilm formation) of four strains of Candida albicans and three strains of Candida krusei.
Methodology. The cellular surface properties were determined using spectrophotometry. The colonization activities were quantified using colorimetric viability assays and visualized using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).
Results. The tea extracts, in general, reduced the hydrophobicity (by 8–66 %) and auto-aggregation (by 20–65 %), and inhibited the attachment of two C. krusei strains (by 41–88 %). Tea extracts enhanced the biofilm formation of one C. albicans and two C. krusei strains (by 1.4–7.5-fold). The observed reduction in hydrophobicity strongly correlated with the reduction in attachment of the two C. krusei strains (P<0.05). The ultrastructural images of the tea-treated C. krusei biofilm cells demonstrated central indentations, although they remained viable.
Conclusion. The tea extracts have the ability to retard C. krusei adhesion to glass surfaces, possibly by reducing fungal cellular hydrophobicity, whilst paradoxically promoting biofilm formation. In practical terms, therefore, consumption of tea beverages appears to have a complex effect on oral candidal colonization.
Streptococcus pneumoniae (S. pneumoniae), otherwise known as ‘the pneumococcus’, is a fascinating microbe that continues to pose a significant problem to public health. Currently there are no specific National Institute for Clinical Excellence (NICE) or British Thoracic Society (BTS) clinical guidelines referring to the treatment of invasive pneumococcal infection. NICE clinical guidelines suggest the use of lytic β-lactam antibiotic regimens for the management of community-acquired pneumonia and bacterial meningitis; infections for which S. pneumoniae is a likely causative organism. Lytic antibiotics have been shown to increase the release of pneumolysin (the highly inflammatory and damaging toxin of the pneumococcus), thus theoretically increasing host damage, which may lead to a decline of clinical outcomes in vulnerable patients. In light of this information, should the use of non-lytic antibiotics, such as quinolones, rifamycins and macrolides, be considered for the treatment of invasive pneumococcal disease?