Resistance to antibiotics is a major problem in clinical medicine. Joyce Sutcliffe and her colleagues at Pfizer Inc. have discovered that a pattern called M resistance is surprisingly common. In the researchers' collections, 85% of Streptococcus pneumoniae and 75% of Streptococcus pyogenes strains had an M phenotype, which involves susceptibility to clindamycin and streptogramin B antibodies, concurrently with resistance to 14- and 15-member macrolides mediated by an efflux mechanism.
Currently, the National Committee for Clinical Laboratory Standards does not recommend testing streptococci for resistance to lincosamides or streptogramin B, "primarily because resistance to erythromycin the the past has signaled cross-resistance to these antibiotics," the authors write. But this study may force changes in the recommendations, due to M phenotype streptococcal susceptibilities. Testing these antibiotics in primary clinical evaluation could be especially important when S. pneumoniae is present in life-threatening infections such as bacteremia.
(J. Sutcliffe, A. Tait-Kamradt, and L. Wondrack. 1996. Streptococcus pneumoniae and Streptococcus pyogenes resistant to macrolides but sensitive to clindamycin: a common resistance pattern mediated by an efflux system. Antimicrob. Agents Chemother. 40:1817-1824.)
Seventy-five percent of human gene therapy trials use as vectors crippled versions of the Moloney murine leukemia virus.
Andreas Russ and Harald von Melchner, of the University of Frankfurt Medical School, and colleagues have developed a new generation of retrovirus vectors that delete themselves following insertion into the host cell genome. This eliminates the risk of recombination that could create new infectious viruses.
Furthermore, selectable marker genes used to enrich for cells transduced by a therapy gene are eliminated along with the virus, precluding an immune response against treated cells. "If this works, viral vaccines could be manufactured and administered directly to the patient," says von Melchner.
If the vectors work as hoped, the researchers will experimenbt with human immunodeficiency virus-based viruses "because they are more versatile and, unlike most retroviruses, also infect resting cells," say von Melchner. Other new research may include "viruses which target specific cell populations and insert their genes into predefined and preferably nontranscribed regions of the genome, reducing the risk of creating mutations in healthy genes."
(A.P. Russ, C. Friedel, M. Grez, and H. Von Melchner. 1996. Self-deleting retrovirus vectors for gene therapy. J. Virol. 70:4927-4832.)
Rotating biological contactor reactor (RBC) technology is generally used for wastewater treatment only. Ningjun Cao and colleagues of Purdue University have demonstrated that Rhizopus oryzae can produce high weight yeilds of fumaric acid from glucose, at high livels of purity and low cost, and that this technology has advantages over traditional stirred-tank cultivation methods.
"Fumaric acid is a versatile organic acid that can be used as the intermediate for producing biodegradable plastics," says Cao. Additionally, the technology can probably be applied to fermentations involving other mycelial fungi or actinomycetes, biofilms, or other mixed cultures for synthesis of primary metabolites, secondary metabolites, or enzymes.
Cao plans to study the effects of mass and gas transfers as well as those of oxygen and carbon dioxide on biosynthesis of organic acids using mycelial fungal systems.
(N. Cao, J. Du, C.S. Gong, and G. T. Tsao. 1996. Simultaneous production and recovery of fumaric acid from immobilized Rhizopus oryzae with a rotary biofilm contactor and an adsorption column. Appl. Environ. Microbiol. 62:2926-2931.)
The period (per) and timeless (tim) Drosophila genes have been shown to be involved in controlling circadian rhythms through a transcriptional feedback loop. To determine how it entrains to lights, Paul E. Hardin and Jan Qiu measured per mRNA cycling and activity rhythms under different light and dark cycling regimens.
The results indicate that the PER feedback loop uses lights-off as a phase reference point and suggest that per message cycling is not regulated by a simple negative feedback from the PER protein, as had been suspected. "The results also predict the existence of an additional repressor," says Hardin.
"This resetting mechanism is not universal," says Hardin. "The feedback loop system operating in Neurospora crassa is directly out of phase with that of Drosophila melanogaster, and its clock resetting mechanism is based on light-induced transcription rather that light-induced protein degradation."
Hardin and Qiu plan to search for the other repressor(s) and study the feedback loop in insects with photoperiodically regulated processes.
(J. Qiu and P.E. Hardin. 1996. per mRNA cycling is locked to lights-off under photoperiodic conditions that support circadian feedback loop function. Mol. Cell. Biol. 16:4182-4188.)
Tryponosoma cruzi causes Chagas' disease, a sever illness affecting several million people from the United States to Argentina.
Rapid diagnostic methods for acute and congenital cases of Chagas' disease are crucial: early treatment is most effective. Xenodiagnosis, the "gold standard" for diagnosis of Chagas' disease, is limited by delay in recording results. Furthermore, serological testing fails to identify 23.1% of infected infants under 6 months.
Alejandro Katzin, of the University of Sao Paulo, and others have found that antigens which are identical in patients with different forms of Chagas' diesase and from different geographic locales are shed through the urine. The researchers have developed an enzyme-based immunosorbent assay that uses monoclonal antibodies in unconcentrated urine for detecting these antigens. The new method may prove useful in large-scale epidemiologic surveys as well as clinical diagnosis, says Katzin.
(R.S. Corral, J. Altcheh, S.R. Alexandre, S. Grinstein, H. Freilij, and A.M. Katzin. 1996. Detection and characterization of antigens in urine of patients with acute, congenital, and chronic Chagas' disease. J. Clin. Microbiol. 34:1957-1962.)
Arbuscular mycorrhizal (AM) fungi represent one of the most mportant components of soil microbial populations. They live in symbiosis on the roots of about 80% of land plants and are very important in nutrient cycling and maintaining soil structure.
Paola Bonfante of the University of Turin and others have discovered that the cytoplasm of the arbuscular-mycorrhizal fungus harbors a further bacterial endosymbiont, dubbed intracytoplasmic bacterium-like organisms (BLOs). Each spore harbors about 250,000 live BLOs. Analysis of small-subunit rRNA shows that thte BLOs are group II pseudomonads (genus Burkholderia).
Further research may include determining the role of the BLOs and attempting to infect AM fungi with new strains of Burkholderia to see what new traits might arise, says Bonfante.
The paper also raises philosophical issues about the nature of life, not the least of which is, are BLOs organelles in the making?
(V. Bianciotto, C. Bandi, D. Minerdi, M. Sironi, H.V. Tichy, and P. Bonfante. 1996. An obligately endosymbiotic mycorrhizal fungus itself harbors obligately intracellular bacteria. Appl. Environ. Microbiol. 62:3005-3010.)
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