Biomedical subjects

A Scorpio

Publications and source records attributed to A Scorpio.

6 recordsLinked to original sources

PubMed2006

Anthrax vaccines: Pasteur to the present.

Anthrax has been a major cause of death in grazing animals and an occasional cause of death in humans for thousands of years. Since the late 1800s there has been an exceptional international history of anthrax vaccine development. Due to animal vaccinations, the rate of infection has dropped dramatically. Anthrax vaccines have progressed from uncharacterized whole-cell vaccines in 1881, to pXO2-negative spores in the 1930s, to culture filtrates absorbed to aluminum hydroxide in 1970, and likely to recombinant protective antigen in the near future. Each of these refinements has increased safety without significant loss of efficacy. The threat of genetically engineered, antibiotic and vaccine resistant strains of Bacillus anthracis is fueling hypothesis-driven research and global techniques--including genomics, proteomics and transposon site hybridization--to facilitate the discovery of novel vaccine targets. This review highlights historical achievements and new developments in anthrax vaccine research.

Animals↗

PubMed1999

Role of acid pH and deficient efflux of pyrazinoic acid in unique susceptibility of Mycobacterium tuberculosis to pyrazinamide.

Pyrazinamide (PZA) is an important antituberculosis drug. Unlike most antibacterial agents, PZA, despite its remarkable in vivo activity, has no activity against Mycobacterium tuberculosis in vitro except at an acidic pH. M. tuberculosis is uniquely susceptible to PZA, but other mycobacteria as well as nonmycobacteria are intrinsically resistant. The role of acidic pH in PZA action and the basis for the unique PZA susceptibility of M. tuberculosis are unknown. We found that in M. tuberculosis, acidic pH enhanced the intracellular accumulation of pyrazinoic acid (POA), the active derivative of PZA, after conversion of PZA by pyrazinamidase. In contrast, at neutral or alkaline pH, POA was mainly found outside M. tuberculosis cells. PZA-resistant M. tuberculosis complex organisms did not convert PZA into POA. Unlike M. tuberculosis, intrinsically PZA-resistant M. smegmatis converted PZA into POA, but it did not accumulate POA even at an acidic pH, due to a very active POA efflux mechanism. We propose that a deficient POA efflux mechanism underlies the unique susceptibility of M. tuberculosis to PZA and that the natural PZA resistance of M. smegmatis is due to a highly active efflux pump. These findings may have implications with regard to the design of new antimycobacterial drugs.

Amidohydrolases↗

PubMed1997

Characterization of pncA mutations in pyrazinamide-resistant Mycobacterium tuberculosis.

Pyrazinamide (PZA) is a first-line drug for short-course tuberculosis therapy. Resistance to PZA is usually accompanied by loss of pyrazinamidase (PZase) activity in Mycobacterium tuberculosis. PZase converts PZA to bactericidal pyrazinoic acid, and the loss of PZase activity is associated with PZA resistance. The gene (pncA) encoding the M. tuberculosis PZase has recently been sequenced, and mutations in pncA were previously found in a small number of PZA-resistant M. tuberculosis strains. To further understand the genetic basis of PZA resistance and determine the frequency of PZA-resistant strains having pncA mutations, we analyzed a panel of PZA-resistant clinical isolates and mutants made in vitro. Thirty-three of 38 PZA-resistant clinical isolates had pncA mutations. Among the five strains that did not contain pncA mutations, four were found to be falsely resistant and one was found to be borderline resistant to PZA. The 33 PZA-resistant clinical isolates and 8 mutants made in vitro contained various mutations, including nucleotide substitutions, insertions, or deletions in the pncA gene. The identified mutations were dispersed along the pncA gene, but some degree of clustering of mutations was found at the following regions: Gly132-Thr142, Pro69-Leu85, and Ile5-Asp12. PCR-single-strand conformation polymorphism (SSCP) analysis was shown to be useful for the rapid detection of pncA mutations in the PZA-resistant strains. We conclude that a mutation in the pncA gene is a major mechanism of PZA resistance and that direct sequencing by PCR or SSCP analysis should help to rapidly identify PZA-resistant M. tuberculosis strains.

Amidohydrolases↗

PubMed1997

Rapid differentiation of bovine and human tubercle bacilli based on a characteristic mutation in the bovine pyrazinamidase gene.

Bovine tuberculosis (TB) caused by Mycobacterium bovis is an important veterinary disease that can also afflict humans. Although M. bovis shares an almost identical genome with M. tuberculosis, subtle differences in host specificity and several biochemical parameters can be used to distinguish the two closely related species. The current method for distinguishing M. bovis from M. tuberculosis relies on tedious testing of biochemical parameters, including natural resistance to pyrazinamide and defective pyrazinamidase (PZase) activity of M. bovis strains. In this study, we report the development of a rapid PCR-single-strand conformation polymorphism (SSCP) assay to differentiate M. bovis from M. tuberculosis strains, based on the detection of a single characteristic point mutation in the PZase gene (pncA) of M. bovis. Eighty-seven of 89 M. bovis strains could be distinguished from M. tuberculosis strains. Surprisingly, two animal isolates which were initially identified as M. bovis were shown to be M. africanum because they had a wild-type pncA sequence with positive PZase. These two M. africanum strains contain multiple (three and six) copies of insertion sequence IS6110, a feature they have in common with M. tuberculosis. The implication of this finding for the taxonomy of M. tuberculosis complex is discussed in relation to host preference and epidemiology. The development of a rapid PCR-SSCP test for distinguishing M. bovis from M. tuberculosis will be useful for monitoring the spread of bovine TB to humans in areas where bovine TB is endemic and for directing the treatment of human TB caused by M. bovis.

Amidohydrolases↗

PubMed1996

Mutations in pncA, a gene encoding pyrazinamidase/nicotinamidase, cause resistance to the antituberculous drug pyrazinamide in tubercle bacillus.

Naturally pyrazinamide (PZA)-resistant Mycobacterium bovis and acquired PZA-resistant M. tuberculosis strains lose pyrazinamidase (PZase). To investigate the molecular mechanism of PZA resistance, we have cloned the gene (pncA) encoding M. tuberculosis PZase. Mutations in pncA were identified in both types of PZA-resistant strains, and transformation of these strains with a functional pncA gene restored PZase activity and PZA susceptibility. These findings, besides providing the basis for understanding how PZA works, should have implications for rapid detection of PZA-resistant clinical isolates of M. tuberculosis and also for rapid differentiation of M. bovis from M. tuberculosis strains.

Amidohydrolases↗

PubMed1994

Isolation of Borrelia burgdorferi from saliva of the tick vector, Ixodes scapularis.

A method for cultivating and isolating Lyme disease spirochetes, Borrelia burgdorferi, from the saliva of vector ticks, Ixodes scapularis (formerly known as Ixodes dammini), is described. Saliva was collected from partially engorged ticks after application of pilocarpine to induce salivation. B. burgdorferi was isolated from 8 of 14 (57%) of the saliva samples derived from ticks infected with the bacteria, as determined by direct immunofluorescent-antibody assay of tick hemolymph. A comparison of the protein profiles of the salivary isolates and a highly passaged strain (B31) showed that the salivary isolates all lacked a 22-kDa protein known to increase with continuous passage, but exhibited larger amounts of the OspA and OspB proteins than did the highly passaged B31 strain.

Animals↗