Modeling the inactivation kinetics of bacillus spores by glutaraldehyde.

AIMS: Our goal was to develop a mathematical kinetic model to predict the sporicidal activity of glutaraldehyde, which is an active ingredient frequently used in commercial products employed for liquid disinfection and decontamination. METHODS AND RESULTS: We used our previously published data on spore inactivation by glutaraldehyde to develop a predictive model obtained by calculating multiple independent modifying functions. The model was then validated by comparing model predicted values to new experimental data. For model validation, quality-controlled spores of Bacillus athrophaeus (previously and generally known as Bacillus subtilis globigii) were exposed under conditions where several physicochemical variables were modified simultaneously, and the spore surviving fractions were measured by titration. CONCLUSIONS: The model predicted within one order of magnitude variations in sporicidal effectiveness due to changes in main parameters (glutaraldehyde concentration, temperature or time-duration of the treatment). Other parameters such pH, salinity and the effect of serum concentration were also addressed, albeit with less accuracy. SIGNIFICANCE AND IMPACT OF THE STUDY: The model should be useful to quantitatively estimate the effectiveness of glutaraldehyde-based disinfectants, decontaminants, and germicides under the described conditions, particularly when limited data are available or when spore virulence (like that of Bacillus anthracis) precludes extensive experimentation. A similar approach could predict the effectiveness of a variety of decontaminant and disinfecting agents.

Effectiveness of latex condoms as a barrier to human immunodeficiency virus-sized particles under conditions of simulated use.

Condoms were tested in an in vitro system simulating key physical conditions that can influence viral particle leakage through condoms during actual coitus. The system quantitatively addresses pressure, pH, temperature, surfactant properties, and anatomical geometry. A suspension of fluorescence-labeled, 110-nm polystyrene microspheres models free human immunodeficiency virus (HIV) in semen, and condom leakage is detected spectrofluorometrically. Leakage of HIV-sized particles through latex condoms was detectable (P less than 0.03) for as many as 29 of the 89 condoms tested. Worst-case condom barrier effectiveness (fluid transfer prevention), however, is shown to be at least 10(4) times better than not using a condom at all, suggesting that condom use substantially reduces but does not eliminate the risk of HIV transmission.

PIP: Physical science researchers tested the ability of 89 undamaged latex condoms manufactured in the US to prevent passage of HIV=size particles under simulated physiologic conditions at their Food and Drug Administration laboratory in Rockville, Maryland. The design of the test system considered particle size, pH, surface tension, and time. A suspension of polystyrene 110 nm microspheres labeled with fluorescent dye served as the HIV-sized particle model in semen. They challenged each condom with this suspension for 30 minutes. The test did not include motion since stretching over the penis accounts for most pore stretching. Leakage of fluorescent dye occurred in 29 condoms (p .03). 21 condoms leaked at minimum leak rates 1 nl/s, 7 at 1-6 nl/s, and 1 at around 10 nl/s. Assuming the leakage occurred through the only pore in each condom, the pore diameters ranged from 2 to 7 mcm. Also assuming an even more conservative criterion, the qualitative results were the same: 11 condoms with leak rates were nl/s vs. 6 condoms with leak rates 1-9 nl/s (p .002). The widely used 300 ml water test did not indicate any pores in any of the condoms. In the extreme and highly unlikely scenario of all the fluid being pumped out of the condom, the transfer rate would be about 0.1 mcl after 10 minutes of thrusting after ejaculation filled the condom with semen (i.e., 0.01% of a typical 3 ml ejaculate). Thus proper use of latex condoms would result in exposure reduction from HIV of at least 4 orders of magnitude. These findings demonstrated that use of latex condoms can significantly reduce the risk of HIV transmission, but it does not eliminate that risk.

Test method for evaluating the permeability of intact prophylactics to viral-size microspheres under simulated physiologic conditions.

The alarming number of AIDS cases has increased the attention given to barrier devices such as condoms. The authors describe a new test method that evaluates the permeability of the intact condom when subjected to simulated physiologic conditions. Fluorescent-labelled polystyrene microspheres (110 nm diameter) are used to model cell-free virus. Physical and chemical conditions that are present during coitus, such as pressure, pH, and temperature, are considered in the design of the method. The testing chamber is designed to be continuously monitored for changes in fluorescence due to leakage across the condom surface. The sensitivity of the system is 1 x 10(-5) of the original concentration of microsphere solution (3.4 x 10(11) particles/mL), which corresponds to leak rates as small as .001 microL/sec. The test provides an in vitro test of barrier material permeability relevant to actual use.