Live-oak plants (Quercus virginiana Mill.) were subjected to various levels of CO2, water stress or photosynthetic photon flux density to test the hypothesis that isoprene biosynthesis occurred only under conditions of restricted CO2 availability. Isoprene emission increases as the ambient CO2 concentration decreased, independent of the amount of time that plants had photosynthesized at ambient CO2 levels. When plants were water-stressed over a 4-d period photosynthesis and leaf conductance decreased 98 and 94%, respectively, while isoprene emissions remained constant. Significant isoprene emissions occurred when plants were saturated with CO2, i.e., below the light compensation level for net photosynthesis (100 μmol m(-2) s(-1)). Isoprene emission rates increased with photosynthetic photon flux density and at 25 and 50 μmol m(-2) s(-1) were 7 and 18 times greater than emissions in the dark. These data indicate that isoprene is a normal plant metabolite and not - as has been suggested - formed exclusively in response to restricted CO2 or various stresses.

Peritonitis is a major complication of continuous ambulatory peritoneal dialysis. Relapsing peritonitis after the cessation of antimicrobial therapy is frequently reported and often involves Staphylococcus epidermidis. To investigate the potential role of catheter-associated bioffilm in the pathogenesis of relapsing peritonitis, we describe an in vitro model permitting the development of an S. epidermidis biofflmi on silicone elastomer biomaterial. This model has been used to investigate the ability of vancomycin hydrochloride to kill biofilm-encased organisms by using an antibiotic regimen typical of peritonitis therapy. No significant differences were seen between vancomycin-exposed and control groups in biofilm viable and total cell counts after 10 days. Vancomycin-exposed silicone-associated biofllm populations decreased by only 0.5 log10 CFU/cm2 over the study period. MICs and MfBCs for the original S. epidermidis suspension were 3.125 and 6.25 ,ug/ml, respectively. For biofllm homogenate suspensions, MICs were 3.125 jig/ml, but MBCs were >400 ,ug/ml. These data indicate that the biofilm organisms associated with an indwelling peritoneal catheter may display a form of tolerance, thereby suggesting one possible mechanism behind relapsing peritonitis.

No abstract

The in vitro transfer of cytokine-inducing substances (CIS) across cellulose triacetate and polyacrylonitrile hollow-fiber high-flux hemodialyzers was studied using culture filtrates of gram-negative bacteria isolated from hemodialysis center environments. With Enterobacter cloacae, no transfer of CIS was seen despite the potent cytokine inducibility and endotoxin content of the challenge solution. In contrast, interleukins 1 and 6 and tumor necrosis factor inducing substances did penetrate both dialyzer types challenged with Pseudomonas aeruginosa culture filtrates containing a high endotoxin content. Transfer was not seen, however, upon dilution of the challenge solution to lower, yet clinically very high levels of endotoxin. These results show that, in vitro, the transfer of CIS across high-flux membranes is critically dependent upon the quality and the quantity of the challenge material employed.

A study was designed to determine the rates of isoprene emission and photosynthesis in three fern species [Dicksonia antarctica Labill., Thelypteris decursive‐pinnata (Van Hall) Ching and Thelypteris kunthii (Desv.) Morton] and the independent influence of light and temperature on these processes. The plants were conditioned in a growth chamber and then transferred to a controlled environment gas‐exchange chamber. Samples of the chamber atmosphere were collected; isoprene was concentrated cryo‐genically and measured by gas chromatography. Only small amounts of isoprene were detected around the ferns in the dark. Isoprene emissions increased with increasing levels of photosynthetic photon flux density (PPFD) in all three species; 50% of the maximum emission occurred at PPFD levels of 130 to 500 μmol m−2 s−1. Maximum isoprene emissions occurred between 35 and 39°C which is a lower temperature maximum than reported for angiosperms and gymnosperms. The increased emissions with temperature were primarily associated with increased biosynthetic rates for isoprene. Carbon lost through isoprene accounted for 0.02 to 2.6% of the carbon fixed during photosynthesis, depending on the PPFD level, temperature and fern species.