Development of new muscle contraction sensor to replace sEMG for using in muscles analysis fields.

Nowadays, the technologies for detecting, processing and interpreting bioelectrical signals have improved tremendously. In particular, surface electromyography (sEMG) has gained momentum in a wide range of applications in various fields. However, sEMG sensing has several shortcomings, the most important being: measurements are heavily sensible to individual differences, sensors are difficult to position and very expensive. In this paper, the authors will present an innovative muscle contraction sensing device (MC sensor), aiming to replace sEMG sensing in the field of muscle movement analysis. Compared with sEMG, this sensor is easier to position, setup and use, less dependent from individual differences, and less expensive. Preliminary experiments, described in this paper, confirm that MC sensing is suitable for muscle contraction analysis, and compare the results of sEMG and MC sensor for the measurement of forearm muscle contraction.

Application of wireless inertial measurement units and EMG sensors for studying deglutition - Preliminary results.

Different types of sensors are being used to study deglutition and mastication. These often suffer from problems related to portability, cost, reliability, comfort etc. that make it difficult to use for long term studies. An inertial measurement based sensor seems a good fit in this application; however its use has not been explored much for the specific application of deglutition research. In this paper, we present a system comprised of an IMU and EMG sensor that are integrated together as a single system. With a preliminary experiment, we determine that the system can be used for measuring the head-neck posture during swallowing in addition to other parameters during the swallowing phase. The EMG sensor may not always be a reliable source of physiological data especially for small clustered muscles like the ones responsible for swallowing. In this case, we explore the possibility of using gyroscopic data for the recognition of deglutition events.

Reversal of clavulanate resistance conferred by a Ser-244 mutant of TEM-1 beta-lactamase as a result of a second mutation (Arg to Ser at position 164) that enhances activity against ceftazidime.

The mutation of Arg-244 to Ser (Arg-244-->Ser mutation) in the TEM-1 beta-lactamase has been shown to produce resistance to inactivation by clavulanate in the mutant enzyme and resistance to ampicillin plus clavulanate in a strain of Escherichia coli producing this enzyme. The Arg-164-->Ser mutation in the TEM-1 beta-lactamase (TEM-12 enzyme) is known to enhance the activity of the enzyme against ceftazidime, resulting in resistance to the drug in a strain producing the mutant enzyme (D. A. Weber, C. C. Sanders, J. S. Bakken, and J. P. Quinn, J. Infect. Dis. 162:460-465, 1990). The doubly mutated derivative of the TEM-1 enzyme (Ser-164/Ser-244) retains the characteristics of the Ser-164 mutant enzyme, i.e., enhanced activity against ceftazidime and sensitivity to inactivation by clavulanate. It also confers the same phenotype as the Ser-164 mutant enzyme, i.e., resistance to ceftazidime and ampicillin, with reversal of this resistance in the presence of clavulanate. Thus, the Arg-164-->Ser mutation in the TEM-1 beta-lactamase suppresses the effect of the Arg-244-->Ser mutation which, by itself, reduces the sensitivity of the enzyme to inactivation by clavulanate.

A structure-based analysis of the inhibition of class A beta-lactamases by sulbactam.

From the crystal structure of the Bacillus licheniformis 749/C beta-lactamase, energy-minimized structures for the precatalytic, the acyl-enzyme intermediate, and the acylated linear inactivating species for sulbactam--a clinically useful mechanism-based inactivator for class A beta-lactamases--were generated. The effect of individual Ser-235-Ala and Arg244-Ser point mutations on the inactivation and turnover processes was consistent with the existence of hydrogen bonds between the side chains of these residues and the sulbactam species. The departure of the sulfinate leaving group from the acyl-enzyme intermediate of sulbactam is believed to be a prerequisite for the inactivation process. In order to explore the influence of the leaving group, penicillanic acid (2), penicillanic acid alpha-S-oxide (3), and penicillanic acid beta-S-oxide (4) were synthesized and studied in kinetic experiments with the TEM-1 beta-lactamase. Penicillanic acid is only a substrate, but penicillanic acid S-oxides were both substrates and inactivators for the enzyme. An argument is presented to rationalize these observations on the basis of the leaving ability of thiolate, sulfenate, and sulfinate from the acyl-enzyme intermediates of penicillanic acid (2), the penicillanic acid S-oxides (3 and 4), and sulbactam, respectively. The departure of the leaving group does not appear to be rate limiting in the inactivator process, but is an indispensable component of the irreversible inactivation of the enzyme. Molecular dynamics calculations of the putative inactivating species suggest that Lys-73, Lys-234, and Ser-130 are three likely residues that may be modified in the course of the inactivation chemistry. A discussion is presented of the mechanism of formation of the transiently inhibited enzyme species, which comes about as a consequence of the tautomerization of the double bond of the inactivating iminium moiety. In addition, the mechanistic details presented for sulbactam are compared and contrasted with those of clavulanic acid, another clinically used inactivator for class A beta-lactamases.

Critical hydrogen bonding by serine 235 for cephalosporinase activity of TEM-1 beta-lactamase.

The role of Ser-235 in the catalytic mechanism of the TEM-1 beta-lactamase has been explored by the study of a mutant enzyme in which Ser-235 has been substituted by alanine (Ala-235 mutant enzyme). A comparative kinetic analysis of both the wild-type and the Ala-235 TEM-1 enzymes revealed little effect of this substitution of residue 235 on the turnover of penicillins but a greater effect on the turnover of cephalosporins. Susceptibility testing of Escherichia coli strains harboring the wild-type TEM-1 beta-lactamase and the Ala-235 mutant enzyme revealed an effect of the mutation similar to that observed in the enzymological studies. The MICs of two representative cephalosporins for the strain containing the mutant enzyme were much lower than those for the isogenic strain bearing the wild-type TEM-1 beta-lactamase. On the other hand, the strain with the mutant enzyme was still highly resistant to penicillins.