Molecular insights into the evolutionary pathway of Vibrio cholerae O1 atypical El Tor variants.

Pandemic V. cholerae strains in the O1 serogroup have 2 biotypes: classical and El Tor. The classical biotype strains of the sixth pandemic, which encode the classical type cholera toxin (CT), have been replaced by El Tor biotype strains of the seventh pandemic. The prototype El Tor strains that produce biotype-specific cholera toxin are being replaced by atypical El Tor variants that harbor classical cholera toxin. Atypical El Tor strains are categorized into 2 groups, Wave 2 and Wave 3 strains, based on genomic variations and the CTX phage that they harbor. Whole-genome analysis of V. cholerae strains in the seventh cholera pandemic has demonstrated gradual changes in the genome of prototype and atypical El Tor strains, indicating that atypical strains arose from the prototype strains by replacing the CTX phages. We examined the molecular mechanisms that effected the emergence of El Tor strains with classical cholera toxin-carrying phage. We isolated an intermediary V. cholerae strain that carried two different CTX phages that encode El Tor and classical cholera toxin, respectively. We show here that the intermediary strain can be converted into various Wave 2 strains and can act as the source of the novel mosaic CTX phages. These results imply that the Wave 2 and Wave 3 strains may have been generated from such intermediary strains in nature. Prototype El Tor strains can become Wave 3 strains by excision of CTX-1 and re-equipping with the new CTX phages. Our data suggest that inter-chromosomal recombination between 2 types of CTX phages is possible when a host bacterial cell is infected by multiple CTX phages. Our study also provides molecular insights into population changes in V. cholerae in the absence of significant changes to the genome but by replacement of the CTX prophage that they harbor.

Self assembled growth of GaSb nano triangles on GaN/sapphire substrate.

Self-assembled GaSb nano structures were grown on GaN/sapphire. GaSb nano triangles as well as quantum dots were obtained under controlled growth conditions. Nano triangles were grown at 580 degrees C due to the growth rate anisotropy among the (1100) planes. The size of nano triangle was 87 nm in width, 5 nm in height, and the density was 5 x 10(8) cm(-2), when the growth time was 30 s. This is the first report on the self assembled growth of nano triangles within a highly strained material system.

Detection of Mycobacterium tuberculosis complex in sputum specimens using a loop-mediated isothermal amplification assay in Korea.

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis complex (MTC), remains one of the leading causes of death in the world. In Korea, the current prevalence of multidrug-resistant TB (MDR-TB) poses a major problem. The most common method for diagnosing TB in developing countries is sputum smear microscopy; however, the sensitivity of this test is relatively low and it usually requires well-trained laboratory staff. Cultures of MTC require up to several weeks in sophisticated facilities, such as Biosafety Level 3. Effective diagnostic techniques are necessary to control TB. In Korea, we evaluated a loop-mediated isothermal amplification (LAMP) assay targeting the hspX gene (TB-hspX-LAMP) of MTC. For clinical evaluation, culture confirmation, smear microscopy and TB-hspX-LAMP were performed on 303 sputum specimens obtained from suspected TB patients in Korea. The sensitivity, specificity, positive predictive value and negative predictive value of TB-hspX-LAMP were 71.1, 98.8, 91.4 and 95.1%, respectively, compared with TB culture, which is the gold standard for diagnosis of TB. In contrast, the comparable values of smear microscopy were 24.4, 98.1, 68.8 and 88.2%, respectively. Therefore, we concluded that TB-hspX-LAMP was superior to the use of smear microscopy for the detection of MTC in sputum specimens in clinical settings in Korea.

CTX prophages in Vibrio cholerae O1 strains.

The classical biotype strains of the Vibrio cholerae O1 serogroup harbor the biotype-specific cholera-toxin encoding phage (CTX) CTX(cla), and the El Tor biotype strains contain CTX-1. Although the classical biotype strains have become extinct, a remnant of classical CTX phage is transferred to the El Tor biotype strains. The prototype El Tor strains, which produce the biotype-specific cholera toxin, are now being replaced by atypical El Tor variant strains producing classical biotype cholera toxin. The genome sequences of the CTX phages in atypical El Tor strains indicate that the CTX phages in atypical El Tor strains are a mosaic of CTXcla and CTX-1. Before the emergence of atypical El Tor stains in the early 1990s, unusual pre-seventh pandemic strains were isolated in the US Gulf Coast between 1973 and 1986. These strains have characteristics of atypical El Tor strains since they are El Tor biotype strains containing CTX(cla), yet the genome sequence of this CTX phage indicates that it is different from CTXcla and is therefore classified separately as CTX(US Gulf).