Cloning, protein expression and display of synthetic multi-epitope mycobacterial antigens on Salmonella typhi Ty21a cell surface

Expressing proteins of interest as fusion to proteins of bacterial envelope is a powerful technique for biotechnological and medical applications. The synthetic gene (VacII) encoding for T-cell epitopes of selected genes of Mycobacterium tuberculosis namely, ESAT6, MTP40, 38 kDa, and MPT64 was fused with N- terminus of Pseudomonas syringae ice nucleation protein (INP) outer membrane protein. The fused genes were cloned into a bacterial expression vector pKK223-3. The recombinant protein was purified by Ni-NAT column. VacII gene was displayed on the cell surface of Salmonella typhi Ty21a using N-terminal region of ice nucleation proteins (INP) as an anchoring motif. Glycine method confirmed that VacII was anchored on the cell surface. Western blot analysis further identified the synthesis of INP derivatives containing the N-terminal domain INP- VacII fusion protein of the expected size (52 kDa).

Comparison of histopathological features of Vibrio cholerae O1 El Tor and O139 Bengal infections in rabbit intestinal mucosa

Vibrio cholerae is the causative agent of the infectious disease, cholera. The bacteria adhere to the mucosal membrane and release cholera toxin, leading to watery diarrhea. There are >100 serovars of V. cholerae, but the O1 and O139 serovars are the main causative agents of cholera. The present study aimed to compare the severity of intestinal mucosal infection caused by O1 El Tor and O139 V. cholerae in a rabbit ileal loop model. The results showed that although the fluid accumulation was similar in the loops inoculated with O1 and O139 V. cholerae, the presence of blood was detected only in the loops inoculated with the O139 serovar. Serosal hemorrhage was confirmed by histopathological examination and the loops inoculated with O139 showed massive destruction of villi and loss of intestinal glands. The submucosa and muscularis mucosa of the ileum showed the presence of edema with congested blood vessels, while severe hemorrhage was seen in the muscularis propria layer. The loops inoculated with O1 El Tor showed only minimal damage, with intact intestinal villi and glands. Diffuse colonies of the O139 serovar were seen to have infiltrated deep into the submucosal layer of the intestine. Although the infection caused by the O1 serovar was focal and invasive, it was more superficial than that due to O139, and involved only the villi. These observations were confirmed by immunostaining with O1 and O139 V. cholerae-specific monoclonal antibodies. The peroxidase reaction demonstrated involvement of tissues down to the submucosal layer in O139 V. cholerae infection, while in O1 El Tor infection, the reaction was confined mainly to the villi, and was greatly reduced in the submucosal region. This is the first reported study to clearly demonstrate the histopathological differences between infections caused by the O139 Bengal and O1 El Tor pathogenic serovars of V. cholerae.

Specific detection of fungal pathogens by 18S rRNA gene PCR in microbial keratitis

Background

The sensitivity and specificity of 18S rRNA polymerase chain reaction (PCR) in the detection of fungal aetiology of microbial keratitis was determined in thirty patients with clinical diagnosis of microbial keratitis.

Methods

Corneal scrapings from patients were used for Gram stain, culture and PCR analysis. PCR was performed with primer pairs targeted to the 18S rRNA gene. The result of the PCR was compared with conventional culture and Gram staining method. The PCR positive samples were identified by DNA sequencing of the internal transcribed spacer (ITS) region of the rRNA gene. Main outcome measures were sensitivity and specificity of PCR in the detection of fungus in corneal keratitis.

Results

Combination of microscopy and culture gave a positive result in 11 of 30 samples of microbial keratitis. PCR detected 10 of 11 samples that were positive by conventional method. One of the 19 samples that was negative by conventional method was positive by PCR. Statistical analysis revealed that the PCR to have a sensitivity of 90.9% and specificity of 94.7% in the detection of a fungal aetiology in microbial keratitis.

Conclusion

PCR is a rapid, sensitive and useful method to detect fungal aetiology in microbial keratitis.

Cloning, expression, and purification of recombinant protein from a single synthetic multivalent construct of Mycobacterium tuberculosis

Tuberculosis remains a major infectious disease with over 8 million new cases and 2 million deaths annually. Therefore, a vaccine more potent than BCG is desperately needed. In this regard, an approximately 800 bp DNA encoding a mycobacterial synthetic gene designated as VacIII (containing ubiquitin gene UbGR and four immunogenic mycobacterial epitopes or genes of ESAT-6, Phos1, Hsp 16.3, and Mtb8.4) was sub-cloned into a bacterial expression vector of pRSET-B resulting in a 6 x His-VacIII fusion gene construction. This recombinant clone was over expressed in Escherichia coli BL-21 (DE-3). The expressed fusion protein was found almost entirely in the insoluble form (inclusion bodies) in cell lysate. The inclusion bodies were solubilized with 8M urea and the recombinant protein was purified by Ni-NTA column and dialyzed by urea gradient dialysis. This method produced a relatively high yield of recombinant VacIII protein and the cloned VacIII gene offers the potential development of other vaccine formats such as DNA vaccine and recombinant vaccine.

Construction and evaluation of a O139 Vibrio cholerae vaccine candidate based on a hemA gene mutation

In this paper, we describe the development of VCUSM2, a live metabolic auxotroph of Vibrio cholerae O139. Auxotrophy was achieved by mutating a house keeping gene, hemA, that encodes for glutamyl-tRNA reductase, an important enzyme in the C5 pathway for delta-aminolevulenic acid (ALA) biosynthesis, which renders this strain dependent on exogenous ALA for survival. Experiments using the infant mouse and adult rabbit models show that VCUSM2 is a good colonizer of the small intestine and elicits greater than a four-fold rise in vibriocidal antibodies in vaccinated rabbits. Rabbits vaccinated with VCUSM2 were fully protected against subsequent challenge with 1 x 10(11) CFU of the virulent wild type (WT) strain. Experiments using ligated ileal loops of rabbits show that VCUSM2 is 2.5-fold less toxic at the dose of 1 x 10(6) CFU compared to the WT strain. Shedding of VCUSM2 in rabbits were found to occur for no longer than 4 days and its maximum survival rate in environmental waters is 8 days compared to the greater than 20 days for the WT strain. VCUSM2 is thus a potential vaccine candidate against infection by V. cholerae O139.

Molecular epidemiology of tuberculosis in Malaysia

Molecular typing with IS6110 was applied to Mycobacterium tuberculosis isolates from all parts of Malaysia. The degree of clustering increased with patient age, suggesting that reactivation may contribute to clustering. Identical banding patterns were also obtained for isolates from widely separate regions. Therefore, the use of clustering as a measure of recent transmission must be treated with caution. Strains related to the Beijing family were common in Peninsular Malaysia but were less common in Sabah and Sarawak, while a distinct group of strains comprised nearly 40% of isolates from East Malaysia but such strains were rare in Peninsular Malaysia. Single-copy strains, common in South and Southeastern Asia, constituted nearly 20% of isolates from the peninsula but were virtually absent in East Malaysia. The marked geographical difference in the prevailing strains indicates not only a restricted dissemination of M. tuberculosis but also a considerable degree of stability in the banding patterns.

Conservation of IS6110 sequence in strains of Mycobacterium tuberculosis with single and multiple copies

The insertion sequence IS6110/IS986 is used extensively for detecting and typing Mycobacterium tuberculosis. In order to appreciate the evolutionary and epidemiological significance of differences in the fingerprint pattern, it is necessary to understand the factors influencing transposition frequency. Although most strains have many copies of this element, some have only one or two copies; it has been suggested that this apparent transpositional defect arises from the minor differences in the sequence of the element from different strains. In contrast, we have found that the sequence is identical in high and low copy number strains, indicating that external factors, such as the presence of adjacent promoters, must be responsible for differences in copy number.

Insertion sequence typing of Mycobacterium tuberculosis: characterization of a widespread subtype with a single copy of IS6110

DNA fingerprinting with the insertion sequence IS6110 (also known as IS986) has become established as a major tool for investigating the spread of tuberculosis. Most strains of Mycobacterium tuberculosis have multiple copies of IS6110, but a small minority carry a single copy only. We have examined selected strains from Malaysia, Tanzania and Oman, in comparison with M. bovis isolates and BCG strains carrying one or two copies of IS6110. The insertion sequence appears to be present in the same position in all these strains, which suggests that in these organisms the element is defective in transposition and that the loss of transposability may have occurred at an early stage in the evolution of the M. tuberculosis complex.

Characterization of a Mycobacterium tuberculosis insertion sequence belonging to the IS3 family

A repetitive element (IS986), previously isolated from Mycobacterium tuberculosis and shown to detect multiple restriction fragment-length polymorphisms (RFLPs), has been sequenced. It consists of a potential insertion sequence of 1358bp, with 30-bp inverted repeat ends. IS986 has four potentially significant open reading frames (ORFs): ORFa1, ORFa2 and ORFb on one strand and ORFc on the complementary strand. The sequences of the potential translated products identify IS986 as a member of the IS3 family, with an apparent frameshift between ORFa1 and ORFa2. IS986 has potential as a highly specific probe for detection and typing of M. tuberculosis, as well as for transposon mutagenesis of mycobacteria. The sequence of IS986 is virtually identical to that of another recently described element, IS6110 (Thierry et al., 1990).

Does Mycobacterium tuberculosis have plasmids?

Evidence of the presence of plasmids in Mycobacterium tuberculosis is lacking, whereas they are widespread in some other mycobacterial species. We examined, by agarose gel electrophoresis, a total of 197 clinical isolates of M. tuberculosis, mostly resistant to one or more antibiotics, and were able to detect bands of apparently extrachromosomal DNA at a low level in some isolates. These presumptive plasmids could not be isolated by CsCl/ethidium bromide gradient ultracentrifugation, and may consist of unusual forms of DNA. The possible existence of single stranded plasmid DNA is discussed.

Polymorphic repetitive DNA sequences in Mycobacterium tuberculosis detected with a gene probe from a Mycobacterium fortuitum plasmid

Clinical isolates of Mycobacterium tuberculosis were shown by Southern blotting to contain DNA sequences hybridizing to a probe derived from a Mycobacterium fortuitum plasmid. Two such M. tuberculosis DNA fragments, isolated from a gene library, were used as probes to show restriction fragment length polymorphism in M. tuberculosis strains by detecting a repetitive sequence apparently located at different points on the chromosome. This could indicate the presence of a transposable element in M. tuberculosis which is partly homologous to a region of the M. fortuitum plasmid. The probes described can be used to fingerprint M. tuberculosis isolates, and in addition are capable of distinguishing M. tuberculosis from Mycobacterium bovis and BCG.

Transformation of Mycobacterium smegmatis with Escherichia coli plasmids carrying a selectable resistance marker

One limiting factor in studies of tuberculosis and leprosy is the difficulty of genetic analysis and manipulation of mycobacteria. Two approaches were adopted for the construction of vectors, based on different Escherichia coli plasmids and using Mycobacterium smegmatis as the host. In both cases we found that the original E. coli plasmid is capable of being replicated in M. smegmatis, yielding chloramphenicol-resistant colonies. One such plasmid has been recovered from a M. smegmatis transformant and used to re-transform both M. smegmatis and E. coli to chloramphenicol resistance. This plasmid is indistinguishable from the original plasmid by restriction analysis, and can be used as a shuttle vector for the genetic manipulation of mycobacterial species.