Pablo Ismael Resa López

A new ultrasonic signal amplification method for detection of bacteria

A new method is presented that increases the sensitivity of ultrasound-based techniques for detection of bacteria. The technique was developed for the detection of catalase-positive microorganisms. It uses a bubble trapping medium containing hydrogen peroxide that is mixed with the sample for microbiological evaluation. The enzyme catalase is present in catalase-positive bacteria, which induces a rapid hydrolysis of hydrogen peroxide, forming bubbles which remain in the medium. This reaction results in the amplification of the mechanical changes that the microorganisms produce in the medium. The effect can be detected by means of ultrasonic wave amplitude continuous measurement since the bubbles increase the ultrasonic attenuation significantly. It is shown that microorganism concentrations of the order of 10 5 cells ml −1 can be detected using this method. This allows an improvement of three orders of magnitude in the ultrasonic detection threshold of microorganisms in conventional culture media, and is competitive with modern rapid microbiological methods. It can also be used for the characterization of the enzymatic activity.

X-cut quartz crystal impedance meter for liquid characterization

A new procedure to determine the compressional acoustic impedance of liquids within ±0.05% resolution and ±0.25% accuracy is presented. This method is based on the measurement of the bandwidth of a piezoelectric transducer, vibrating in thickness-expansion mode and having a high quality factor (e.g., air-backed X-cut quartz crystal), in direct contact with the sample. In combination with other ultrasonic techniques (pulse-echo or through-transmission), it is possible to simultaneously obtain the main ultrasonic parameters (characteristic acoustic impedance, speed of sound and attenuation coefficient), and deduce important physicochemical properties of liquids, such as density and adiabatic compressibility. Experimental results for selected liquids and solutions are shown.

A new ultrasound based method for rapid microorganism detection

A new method for rapid detection of catalase positive microorganisms by using an ultrasonic measuring method is proposed in this work. The developed technique is based on the detection of oxygen bubbles produced by the hydrolysis of hydrogen peroxide induced by the enzyme catalase which is present in many microorganisms. The bubbles are trapped in a media based on agar gel which was especially developed for microbiological evaluation. It is found that microorganism concentrations of the order of 105 c.f.u./ml can be detected by using this method. The results obtained show up that the proposed method is competitive with other modern commercial methods like luminescence by ATP system. The method can also be used for characterization of enzyme activity.