Influence of antibody immobilization strategies on the analytical performance of a magneto-elastic immunosensor for Staphylococcus aureus detection.

Magneto-elastic (ME) sensors have a great advantage in microbiology due to their ability to be queried wirelessly. Staphylococcus aureus is one of the most common bacteria widespread in the environment and a major human pathogen related to numerous illnesses. Immunosensors are affinity-based assays where the analyte is highly selective. The immobilization of antibodies (Ab) is an important step in the development of such devices. This study compared the effects of two antibody immobilization strategies on the analytical performance of a magneto-elastic immunosensor: (1) random antibody covalent immobilization (CysAb) and (2) specific-oriented antibody covalent immobilization (PrGAb). Immunosensors were exposed to solutions containing S. aureus at different concentrations (104 to 108CFU/ml) and sensor resonant frequencies were measured. In order to confirm that the frequency shifts were mainly caused by the binding of S. aureus to the sensor's surface, scanning electron microscope (SEM) and indirect immunofluorescence (IIF) images were taken after bacteria exposure at 108CFU/ml. Sensor surfaces were further monitored by non-contact topographic atomic force microscopy (AFM) images. In the covalent-oriented strategy, PrG was first bound covalently to the surface, which in turn, then binds the anti-S. aureus antibody in an oriented manner. Topographic AFM images showed different surface patterns between the two antibody immobilization strategies. Specific-oriented antibody covalent immobilization (PrGAb) strategy gave the highest anti-S. aureus antibody immobilization density. Therefore, the covalent-oriented strategy presented the best performance for S. aureus capture, detecting 104CFU/ml.

Outbreaks of highly pathogenic avian influenza (H5N2) in Italy during October 1997 to January 1998.

Between the month of October 1997 and January 1998, eight outbreaks of highly pathogenic avian influenza were diagnosed in the Veneto and Friuli-Venezia Giulia regions in north-eastern Italy. For each of the eight outbreaks, influenza A virus of subtype H5N2 was isolated and the inoculation of susceptible chickens confirmed these viruses to be extremely virulent with intravenous pathogenicity indices in 6-week-old chickens of 2.98 to 3.00. Although it was not possible to trace the origin of infection, the epidemiological investigation revealed connections between several outbreaks and emphasized the well-known risk factors for avian influenza such as bird movement, rearing of mixed populations and contact with migratory waterfowl. Control measures listed in European Union directive 92/40/EEC were implemented promptly and spread of the infection to intensively-reared domestic poultry was avoided.