|
|
|
|
|
|
MtaR, a Regulator of Methionine Transport, Is Critical for Survival of Group B Streptococcus In Vivo. Daniel Shelver, 2003.The group B streptococcus (GBS) is an important human pathogen that infects newborns as well as adults . GBS also provides a model system for studying adaptation to different host environments due to its ability to survive in a variety of sites within the host . In this study, we have characterized a transcription factor, MtaR, that is essential for the ability of GBS to survive in vivo . An isogenic strain bearing a kanamycin insertion in mtaR was attenuated for survival in a neonatal-rat model of sepsis . The mtaR mutant grew poorly in human plasma, suggesting that its utilization of plasma-derived nutrients was inefficient . When an excess of exogenous methionine (200 µg/ml) was provided to the mtaR mutant, its growth rate in plasma was restored to that of the wild-type strain . The mtaR mutant grew poorly in chemically defined medium (CDM) prepared with methionine at a concentration similar to that of plasma (4 µg/ml) but was able to grow normally in CDM prepared with a high concentration of methionine (400 µg/ml) . Both the wild-type strain and the mtaR mutant were incapable of growth in CDM lacking methionine, indicating that GBS cannot synthesize methionine de novo . When the abilities of the strains to incorporate radiolabeled methionine were compared, the mtaR mutant incorporated fivefold less methionine than the wild-type strain during a 10-min period . Collectively, the results from this study suggest that the ability to regulate expression of a methionine transport system is critical for GBS survival in vivo . Naturally Occurring Bacteria Similar to the Methyl tert-Butyl Ether (MTBE)-Degrading Strain PM1 Are Present in MTBE-Contaminated Groundwater. Krassimira Hristova, 2003.Methyl tert-butyl ether (MTBE) is a widespread groundwater contaminant that does not respond well to conventional treatment technologies . Growing evidence indicates that microbial communities indigenous to groundwater can degrade MTBE under aerobic and anaerobic conditions . Although pure cultures of microorganisms able to degrade or cometabolize MTBE have been reported, to date the specific organisms responsible for MTBE degradation in various field studies have not be identified . We report that DNA sequences almost identical (99% homology) to those of strain PM1, originally isolated from a biofilter in southern California, are naturally occurring in an MTBE-polluted aquifer in Vandenberg Air Force Base (VAFB), Lompoc, California . Cell densities of native PM1 (measured by TaqMan quantitative PCR) in VAFB groundwater samples ranged from below the detection limit (in anaerobic sites) to 103 to 104 cells/ml (in oxygen-amended sites) . In groundwater from anaerobic or aerobic sites incubated in microcosms spiked with 10 µg of MTBE/liter, densities of native PM1 increased to approximately 105 cells/ml . Native PM1 densities also increased during incubation of VAFB sediments during MTBE degradation . In controlled field plots amended with oxygen, artificially increasing the MTBE concentration was followed by an increase in the in situ native PM1 cell density . This is the first reported relationship between in situ MTBE biodegradation and densities of MTBE-degrading bacteria by quantitative molecular methods . Exposure of Sink Drain Microcosms to Triclosan: Population Dynamics and Antimicrobial Susceptibility. Andrew J. McBain, 2003.Recent concern that the increased use of triclosan (TCS) in consumer products may contribute to the emergence of antibiotic resistance has led us to examine the effects of TCS dosing on domestic-drain biofilm microcosms . TCS-containing domestic detergent (TCSD) markedly lowered biofouling at 50% (wt/vol) but was poorly effective at use levels . Long-term microcosms were established and stabilized for 6 months before one was subjected to successive 3-month exposures to TCSD at sublethal concentrations (0.2 and 0.4% [wt/vol]) . Culturable bacteria were identified by 16S rDNA sequence analysis, and their susceptibilities to four biocides and six antibiotics were determined . Microcosms harbored ca. 10 log10 CFU/g of biofilm, representing at least 27 species, mainly gamma proteobacteria, and maintained dynamic stability . Viable cell counts were largely unaffected by TCSD exposure, but species diversity was decreased, as corroborated by denaturing gradient gel electrophoresis analysis . TCS susceptibilities ranged widely within bacterial groups, and TCS-tolerant strains (including aeromonads, pseudomonads, stenotrophomonads, and Alcaligenes spp.) were isolated before and after TCSD exposure . Several TCS-tolerant bacteria related to Achromobacter xylosoxidans became clonally expanded during dosing . TCSD addition did not significantly affect the community profiles of susceptibility to the test biocides or antibiotics . Several microcosm isolates, as well as reference bacteria, caused clearing of particulate TCS in solid media . Incubations of consortia and isolates with particulate TCS in liquid led to putative TCS degradation by the consortia and TCS solubilization by the reference strains . Our results support the view that low-level exposure of environmental microcosms to TCS does not affect antimicrobial susceptibility and that TCS is degradable by common domestic biofilms .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
