Virulence factors of Mycobacterium bovis

Polyethylene imine conjugated supramolecular stereocomplexed nanomicelles for intracellular delivery of rifampicin against Mycobacterium bovis

The main objective of this study was to investigate polyethylene imine (PEI) based stereocomplexed nanomiceles for intracellular delivery of rifampicin against Mycobacterium bovis (M. bovis) and their in vitro-in vivo evaluation. The formation of Rifampicin (Rif) loaded isotactic (PEI-g-PLLA and PEI-g-PDLA) and stereocomplexed nanomicelles (StM) of PEI conjugated poly l- and poly d-lactic acid via self-assembly was thoroughly explored. Synthesis of polymer graft was confirmed via FTIR and NMR. A 2-fold reduction in CMC of StM was observed along with decreased particle size in comparison to isotactic nanomicelles. In vitro, StM exhibited a higher encapsulation efficiency and 84 % of drug release in 48 h. at pH 5 with minimal initial burst release in comparison to isotactic nanomicelles. Minimum inhibitory concentration (MIC) of StM was found to be four folds lower in contrast to isotactic nanomicelles. Ex vivo studies exhibited a better uptake of StM and minimum cytotoxicity in murine alveolar macrophages. Following oral administration in mice, drug loaded StM exhibited highest distribution in macrophage rich organs, longer half-life, AUC, AUMC and MRT in comparison to isotactic nanomicelles indicating maximum bioavailability and efficacy of StM. In vivo antimycobacterial activity also demonstrated a higher reduction (2.38fold) in M. bovis CFU at reduced dosing frequency by drug loaded StM in comparison to control group. Thus, StM can be regarded as a simple, stable, efficient, and biocompatible carrier system for delivery of rifampicin to intracellular M. bovis with added advantage of reduced dosing frequency and improved patient compliance.

Non-tuberculous Mycobacterium species causing mycobacteriosis in farmed aquatic animals of South Africa

BACKGROUND

Mycobacteriosis caused by non-tuberculous mycobacteria (NTM), is among the most chronic diseases of aquatic animals. In addition, fish mycobacteriosis has substantial economic consequences especially in the aquaculture and fisheries industry as infections may significantly decrease production and trade. Some fish NTM pathogens are highly virulent and zoonotic; as such, infection of aquaria with these pathogens is a public health concern. In this study, we report isolation of nine different NTM species from sixteen aquatic animals including different fish species, frogs and a crocodile. Given the clinical significance of Mycobacterium marinum and its close relation to Mycobacterium tuberculosis, as well as the significance of ESAT 6 and CFP-10 secretion in mycobacterial virulence, we analysed the esxA and esxB nucleotide sequences of M. marinum isolates identified in this study as well as other mycobacteria in the public databases.

RESULTS

Mycobacterium shimoidei, Mycobacterium marinum, Mycobacterium chelonae, Mycobacterium septicum /M. peregrinum and Mycobacterium porcinum were isolated from gold fish, Guppy, exotic fish species in South Africa, koi and undefined fish, Knysna seahorse, as well Natal ghost frogs respectively, presenting tuberculosis like granuloma. Other NTM species were isolated from the studied aquatic animals without any visible lesions, and these include Mycobacterium sp. N845 T, Mycobacterium fortuitum, a member of the Mycobacterium avium complex, and Mycobacterium szulgai. Phylogenetic analysis of mycobacteria, based on esxA and esxB genes, separated slow growing from rapidly growing mycobacteria as well as pathogenic from non-pathogenic mycobacteria in some cases.

CONCLUSIONS

Isolation of the different NTM species from samples presenting granuloma suggests the significance of these NTM species in causing mycobacteriosis in these aquatic animals. The study also revealed the potential of esxA and esxB sequences as markers for phylogenetic classification of mycobacteria. Observations regarding use of esxA and esxB sequences for prediction of potential pathogenicity of mycobacteria warrants further investigation of these two genes in a study employing NTM species with well-defined pathogenicity.

Animal models of tuberculosis: Guinea pigs

The progression of the disease that follows infection of guinea pigs with Mycobacterium tuberculosis displays many features of human tuberculosis (TB), and the guinea pig model of TB has been used for more than 100 years as a research tool to understand and describe disease mechanisms. Changes in the bacterial burden and pathology following infection can be readily monitored and used to evaluate the impact of TB interventions. Demonstration of the protective efficacy of vaccines in the low-dose aerosol guinea pig model is an important component of the preclinical data package for novel vaccines in development, and there is a continual need to improve the model to facilitate progression of vaccines to the clinic. Development of better tools with which to dissect the immune responses of guinea pigs is a focus of current research.

Virulence factors of the Mycobacterium tuberculosis complex

The Mycobacterium tuberculosis complex (MTBC) consists of closely related species that cause tuberculosis in both humans and animals. This illness, still today, remains to be one of the leading causes of morbidity and mortality throughout the world. The mycobacteria enter the host by air, and, once in the lungs, are phagocytated by macrophages. This may lead to the rapid elimination of the bacillus or to the triggering of an active tuberculosis infection. A large number of different virulence factors have evolved in MTBC members as a response to the host immune reaction. The aim of this review is to describe the bacterial genes/proteins that are essential for the virulence of MTBC species, and that have been demonstrated in an in vivo model of infection. Knowledge of MTBC virulence factors is essential for the development of new vaccines and drugs to help manage the disease toward an increasingly more tuberculosis-free world.

Monitoring safety of liposomes containing rifampicin on respiratory cell lines and in vitro efficacy against Mycobacterium bovis in alveolar macrophages

Rifampicin-encapsulated liposome suspensions were prepared by a chloroform-film method and converted to dry powders by freeze-drying with mannitol as a cryoprotectant. The liposome suspension had multilamellar nanovesicles with 50% rifampicin encapsulation. The liposome dry powder comprised particles with a mass median aerodynamic diameter of 3.4 mum, with 60% present as a fine particle fraction. Rifampicin-encapsulated liposomes were evidently nontoxic to respiratory associated cells, including bronchial epithelial cells, small airway epithelial and alveolar macrophages (AMs). Furthermore, the liposomes did not activate AMs to produce interleukin-1 beta, tumor necrosis factor-alpha, and nitric oxide at a level that would cascade to other inflammatory effects. The minimum inhibitory concentrations against Mycobacterium bovis was 0.2 and 0.8 microM for liposomes containing rifampicin and free rifampicin, respectively. The less negatively charged reconstituted liposome displayed the greatest activity against intracellular growth of M. bovis.

Genome-wide analysis of the intrinsic terminators of transcription across the genus Mycobacterium

Termination of transcription in eubacteria is achieved by a region of the nascent transcript. In Escherichia coli, this intrinsic terminator consists of a hairpin followed by a U-stretch. Absence of the typical terminators in several genes of Mycobacterium tuberculosis led us to develop an accurate and efficient algorithm to identify putative terminators in all sequenced microbial genomes. In addition to the typical Escherichia coli type of terminators, several variant terminator structures were predicted by the algorithm and their existence was experimentally verified. We have now analysed 17 Mycobacterium genomes to obtain a comprehensive picture of the transcription terminators in mycobacteria. Our results show that the terminators that lack a U-trail, variant from the typical E. coli intrinsic terminators, are overwhelmingly predominant in all members of the genus. Most terminator structures are concentrated within 50 base pairs downstream of the stop codon. A large number of these terminators occur at the end of experimentally verified or predicted transcription units. We have observed inter-species variations in DeltaG and positioning of the terminators downstream of specific genes amongst closely related mycobacterial species suggesting differences in gene expression. The analysis would be useful in furthering our understanding of genome organization and gene expression in mycobacteria, in addition to the improvement in the annotation of the new genomes.

Differential gene expression between Mycobacterium bovis and Mycobacterium tuberculosis

The high sequence identity among the Mycobacterium bovis and Mycobacterium tuberculosis genomes contrasts with the physiological differences reported between these pathogens, suggesting that variations in gene expression may be involved. In this study, microarray hybridization was used to compare the total transcriptome of M. bovis and M. tuberculosis, during the exponential phase of growth. Differential expression was detected in 258 genes, representing a 6% of the total genome. Variable genes were grouped according to functional categories. The main variations were found in genes encoding proteins involved in intermediary metabolism and respiration, cell wall processes, and hypothetical proteins. It is noteworthy that, compared to M. tuberculosis, the expression of a higher number of transcriptional regulators were detected in M. bovis. Likewise, in M. tuberculosis we found a higher expression of the PE/PPE genes, some of which code for cell wall related proteins. Also, in both pathogens we detected the expression of a number of genes not annotated in the M. tuberculosis H37Rv or M. bovis 2122 genomes, but annotated in the M. tuberculosis CDC1551 genome. Our results provide new evidence concerning differences in gene expression between both pathogens, and confirm previous hypotheses inferred from genome comparisons and proteome analysis. This study may shed some new light on our understanding of the mechanisms relating to differences in gene expression and pathogenicity in mycobacteria.

Production of avirulent mutants of Mycobacterium bovis with vaccine properties by the use of illegitimate recombination and screening of stationary-phase cultures

A better tuberculosis vaccine is urgently required to control the continuing epidemic. Molecular techniques are now available to produce a better live vaccine than BCG by producing avirulent strains of the Mycobacterium tuberculosis complex with known gene deletions. In this study, 1000 illegitimate recombinants of Mycobacterium bovis were produced by illegitimate recombination with fragments of mycobacterial DNA containing a kanamycin resistance gene. Eight recombinant strains were selected on the basis of their inability to grow when stationary-phase cultures were inoculated into minimal medium. Five of these recombinants were found to be avirulent when inoculated into guinea pigs. Two of the avirulent recombinants produced vaccine efficacy comparable to BCG against an aerosol challenge in guinea pigs with M. bovis. One of these recombinants had an inactivated glnA2 gene encoding a putative glutamine synthetase. Transcriptional analysis showed that inactivation of glnA2 did not affect expression of the downstream glnE gene. The other recombinant had a block of 12 genes deleted, including the sigma factor gene sigG. Two avirulent recombinants with an inactivated pckA gene, encoding phosphoenolpyruvate carboxykinase which catalyses the first step of gluconeogenesis, induced poor protection against tuberculosis. It is clear that live avirulent strains of the M. tuberculosis complex vary widely in their ability as vaccines to protect against tuberculosis. Improved models may be required to more clearly determine the difference in protective effect between BCG and potential new tuberculosis vaccines.