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Journal Highlights
Beutin Bacteriophage Transfers Toxin Genes, Creating Potent New Pathogens
Lambdoid phages, regarded 20 years ago as mere tools for studying replication, gene transfer, and regulation in laboratory Escherichia coli, are now known to be prevalent in wild-type E. coli and to abet emergence of new pathogenic E. coli types such as EHEC O157. Lothar Beutin and colleagues of the Robert Koch Institut and the Max-Planck-Institut fur Molekulare Genetik, Berlin, Germany, have characterized a lambdoid phage that transfers shiga toxin genes (stx) between Shigella and E. coli. "By this, we could explain the emergence of new bacterial pathotypes such as Stx-producing Shigella sonnei," says Beutin. "Moreover, we demonstrated that the stx phage from S. sonnei mediates generalized transduction of chromosomal genes in bacteria, another motor of bacterial diversity and evolution. Like plasmids, bacteriophages are powerful vehicles of horizontal gene transfer, and they survive better in the environment between hosts. We will continue studying the relationships between lambdoid (stx)-phages, and we hope to get a better insight in the evolution of shigatoxigenic Enterobacteriaceae."
(E. Strauch, R. Lurz, and L. Beutin. 2001. Characterization of a Shiga toxin-encoding temperate bacteriophage of Shigella sonnei. Infect. Immun. 69:7588-7595.) Abstract | Full Text
Cannon Versatile New Tools for Examining Multiple Efflux Pumps
Energy-dependent drug efflux is one of the most important mechanisms responsible for the drug resistance of Candida albicans clinical isolates. The study of individual plasma membrane pumps in yeast is hampered by the presence of many endogenous transporters. Richard D. Cannon of the University of Otago, New Zealand, and others have developed a Saccharomyces cerevisiae host strain and vector system that allows functional expression of drug efflux pumps from other organisms. The host strain is deleted in seven major transporters and hyper-sensitive to antifungal drugs. The integrative plasmid delivers the transporter of interest to an efflux pump genomic locus where it is constitutively overexpressed. "We have shown that C. albicans Cdr1p can be expressed in this system and that it behaves normally," says Cannon. "There are many exciting potential uses for this system. We plan to study pumping mechanisms of membrane transporters from several pathogenic fungi. The system could also be used to screen for pump antagonists and to study other eukaryotic transporters and membrane receptors."
(K. Nakamura, M. Niimi, K. Niimi, A. R. Holmes, J. E. Yates, A. Decottignies, B. C. Monk, A. Goffeau, and R. D. Cannon. 2001. Functional expression of Candida albicans drug efflux pump Cdr1p in a Saccharomyces cerevisiae strain deficient in membrane transporters. Antimicrob. Agents Chemother. 45:3366-3374.) Abstract | Full Text
Groeneveld Markers for Predicting Bacterial Sepsis (C)
It is often difficult to determine whether a febrile patient has a bacterial infection. Yet, it can be critical, especially in the case of bloodstream infection and sepsis, which when treated inappropriately or too late, carries a mortality rate of more than 30%. Now Johan Groeneveld of Academisch Ziekenhuis Vrije Universiteit, Amsterdam, the Netherlands, and others show that early release of cytokines and complement activation appear to predict invasion of the bloodstream by local infections. "Developing a rapid test could help to identify microbial blood stream infection at an early stage, and could help to select patients for antimicrobial therapy or recruitment for studies on adjuvant therapies of sepsis," says Groeneveld.
(A. B. J. Groeneveld, A. W. J. Bossink, G. J. van Mierlo, and C. E. Hack. 2001. Circulating inflammatory mediators in patients with fever: predicting bloodstream infection. Clin. Diagn. Lab. Immunol. 8:1189-1195.) Abstract | Full Text
Ferré Bt Resistance: Complexity Belies Predictions, Defies Easy Control
Transgenic crops incorporating genes for Bacillus thuringiensis (Bt) toxins, long used in integrated pest management, are booming, to the consternation of some environmentalists, who fear development of resistance to Bt. Bt has been critical in organic agriculture, where it is used sparingly. To block resistance, the Environmental Protection Agency (EPA) requires farmers to set aside "refugia" of non-Bt crops where mating can occur between susceptible and resistant individuals, whose progeny presumably will all die upon exposure. This strategy depends on resistance being recessive. But Juan Ferre and colleagues of the University of Valencia, Spain, find that there are multiple genes conferring resistance, contrary to the model used by EPA, and that dominance in some of them is positive, stymieing the refugia strategy. "Our results indicate that insect populations might carry multiple resistance genes more frequently than it had been assumed," says Ferre. "Models to predict evolution of resistance should consider high genetic variability to be a very common phenomenon." Future plans involve characterizing the resistance genes. (See Current Topics, p. 9.)
(J. Gonzalez-Cabrera, S. Herrero, and J. Ferre. 2001. High genetic variability for resistance to Bacillus thuringiensis toxins in a single population of diamondback moth. Appl. Environ. Microbiol. 67:5043-5048.) Abstract | Full Text
Persister Cells Responsible for Biofilms' Antimicrobial Resistance
Lewis and Spoering Biofilms are a major cause of recalcitrant infections and are highly resistant to bactericidal antibiotics. Amy L. Spoering and Kim Lewis of Northeastern University, Boston, Mass., find that this resistance is due to the presence of a small fraction of persister cells that are not killed by antimicrobials, although they do not grow in their presence, either. "This suggests that death in bacteria is a controlled event," says Lewis. "We now find, rather unexpectedly, that persisters are generated by both biofilms and stationary populations of Pseudomonas aeruginosa at comparable levels. This suggests that tolerance to antibiotics is not specific to biofilms, but is shared with dense planktonic populations." The researchers are now investigating the persister cells. "Once genes responsible for this phenotype are identified, drugs that disable persistence and eradicate biofilm infections can be developed," says Lewis.
(A. L. Spoering and K. Lewis. 2001. Biofilms and planktonic cells of Pseudomonas aeruginosa have similar resistance to killing by antimicrobials. J. Bacteriol. 183:6746-6751.) Abstract | Full Text
Antibody-Impregnated Milk Fights Cavity-Causing Bacteria
Dental caries are among the most common damage caused by infectious disease in humans. Colonization by Streptococcus mutans is the first step in their induction. A team of scientists from Nihon and Kyushu Universities, Japan, shows that rinsing the mouth with milk containing antibodies to tooth-binding compounds inhibits recolonization of the mouth by S. mutans. Volunteers rinsed with the milk for two weeks. "The S. mutans level in the test group remained lower than that in the control group during the entire 8-week experimental period, but increased gradually..." the researchers write. "Milk from immunized cattle may be useful not only for controlling S. mutans in humans who are already infected, but also for preventing initial infection... in infancy."
(Y. Shimazaki, M. Mitoma, T. Oho, Y. Nakano, Y. Yamashita, K. Okano, Y. Nakano, M. Fukuyama, N. Fujihara, Y. Nada, and T. Koga. 2001. Passive immunization with milk produced from an immunized cow prevents oral recolonization by Streptococcus mutans. Clin. Diagn. Lab. Immunol. 8:1136-1139.) Abstract | Full Text
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