Preliminary Assessment of Visible, Near-Infrared, and Short-Wavelength-Infrared Spectroscopy with a Portable Instrument for the Detection of Staphylococcus aureus Biofilms on Surfaces

Bacterial biofilms constitute a major source of sanitary problems and economic losses in the food industry. Indeed, biofilm removal may require intense mechanical cleaning procedures or very high concentrations of disinfectants or both, which can be damaging to the environment and human health. This study assessed the efficacy of a technique based on spectroscopy in the visible, near-infrared, and short-wavelength infrared range for the quick detection of biofilms formed on polystyrene by the pathogenic bacterium Staphylococcus aureus. To do that, biofilms corresponding to three S. aureus strains, which differed in biofilm-forming ability and composition of the extracellular matrix, were allowed to develop for 5 or 24 h, representing an active formation stage and mature biofilms, respectively. Spectral analysis of the samples, corresponding to three biological replicates of each condition, was then performed by using a portable device. The results of these experiments showed that partial least-squares discriminant analysis of the spectral profile could discriminate between surfaces containing attached bacterial biomass and noninoculated ones. In this model, the two first principal components accounted for 39 and 19% of the variance and the estimated error rate stabilized after four components. Cross-validation accuracy of this assessment was 100%. This work lays the foundation for subsequent development of a spectroscopy-based protocol that allows biofilm detection on food industrial surfaces.

[Mechanism of the antiarrhythmic effect of inorganic phosphates in digitalis poisoning]

THe synergistic effects between calcium and the therapeutic and toxic actions of the cardiac glycosides have suggested that a way of treating digitalis intoxication could be through a decrease in free plasma calcium. In 1966, Burckhardt and La-Due published a study based on the inverse relationship that exists between plasma phosphates and calcium. It was shown then that potassium phosphate had a pronounced antiarrhythmic effect on digitalis induced arrhythmias. The use of potassium phosphate for this study prevented the analysis of the role of the phosphates in these effects, since the actions of potassium in digitalis toxicity precluded any conclusion. The purpose of the present paper is to study the effect of phosphates on digitalis intoxication and its possible mechanism of action. The results obtained demonstrated: 1) Phosphates have a marked antiarrhythmic effect in digitalis induced arrhythmias. 2) This effect is due to a decrease in free plasma calcium. 3) The lowering of this calcium pool occurs in the blood and is not mediated by hormonal or renal mechanisms. 4) The ions that disappear from the free calcium pool do not precipitate. 5) The use of phosphates could be useful in the treatment of some clinical cases of advanced digitalis intoxication.

[Mechanism of the decrease in free plasma calcium produced by the administration of inorganic phosphates]

The preceding paper (published in the issue) demonstrated that the administration of sodium phosphates exerted a marked antiarrhythmic effect on several models of digitalis intoxication; this action being due to a decrease in the free calcium fraction. THe purpose of the present paper is to analyze the effects that several concentrations of phosphates have on the different calcium fractions and determine the fate of the ions that are disappearing from the calcium pool. This study was done using two models of digitalis intoxication, one in the intact dog and the other in the heart-lung preparation and two protocols in which the experiments were carried out using blood in vitro. The results show: 1) the administration of phosphates into the intact dog produces a small decrease in the total calcium content of plasma and blood. 2) the increase in phosphate concentration runs parallel to an important decrease in free calcium. 3) In the heart-lung preparation, phosphate administration markedly decreases free calcium but does not lower total calcium in plasma or blood. 4) An increase in phosphate concentration of plasma in in vitro conditions does not alter total calcium and decreases free calcium in a linear relationship with the levels of phosphates. 5) A fraction of the phosphates added to the plasma and the ions that are disappearing from the free calcium pool are binding to a plasmatic macromolecule (most probably a protein) which prevents them from precipitating.

[Mechanisms of conduction disorders in digitalis poisoning]

Ever since the first papers on the mechanism of the arrhythmias of digitalis were first published, during the first two decades of this century, the issue has been a controversial one. Since the automaticity induced by digitalis intoxication has different characteristics when compared to normal automaticity, it has been suggested that probably the mechanisms for these two types of spontaneous activity are different. It has been recently proposed that the automaticity induced by digitalis intoxication could be secondary to the after potential oscillations described in isolated conducting fibers. In order to test this hypothesis we used two experimental models which allow for a careful analysis of the ectopic activity, without the interference of the sinus rhythm. These studies were done in two groups of animals: one, with electrically isolated atria, was used to analyze supraventricular arrhythmias. The other, with chromic atrioventricular block, was used to study ventricular arrhythmias. The results obtained from these experiments show: 1. High therapeutic doses of digitalis enhance the postpacing inhibition of normal pacemakers; 2. When the ectopic rhythms of digitalis intoxication appear, they show postpacing stimulation; 3. Ectopic activity shows a direct relationship with the rate of the conditioning stimulation, and both the coupling period and the number of premature beats depend on this rate. In view of the similarity between the behavior of these arrhythmias and that of the after potential oscillations, we conclude that these oscillations are responsible for the ectopic automaticity of digitalis intoxication.

[Design and evaluation of a duplication of the cardiac for the evaluation of valvular prostheses]

Recently, several different models of valvular prostheses have been developed in which biological material, like duramater and perycardium, is being used for their manufacturing. Since these valves have to be manufactured one by one, the possibility of obtaining heterogeneous results is very high, thus it is very important to have a system to evaluate the behavior of these prostheses. The objective of this project was to design and evaluate a cardiac cycle duplicator to test the function of valvular prostheses. The system consists of a double plexiglass chamber, separated by the valvular prosthesis being studied. The superior "auricular" chamber is connected to a reservoir where the height of the column of saline can be modified. The interior "ventricular" chamber is connected to a pump that generates pressure pulses at constant intervals which simulate ventricular systoles. The other end of the pump connects with an artificial Starling's resistance. The data obtained from this system allows the quantification of the following: 1) Functional diameter, form and area of maximal opening; 2) valve motility; 3) sufficiency of the prostheses; 4) velocity of valve opening and closing; 5) rigidity of the valves; 6) optimal pressure gradient for adequate valvular function. The system makes possible the evaluation and comparison of the function of these valvular prostheses.