This Regional Research Communication describes the characterisation of ampicillin, penicillin and tetracycline resistance in Staphylococcus aureus isolated from bovine subclinical mastitis in Minas Gerais State, Brazil. Ninety S. aureus isolates from bovine mastitis exhibiting phenotypic resistance to ampicillin, penicillin and/or tetracycline were selected for this study. The minimum inhibitory concentration (MIC) of each antibiotic was determined using the E-Test® and the production of beta-lactamase was determined by cefinase disks. The resistance genes blaZ, tet(K), tet(L), tet(M), and tet(O) were investigated by PCR in all of the isolates. The MIC results classified 77, 83 and 71% of the isolates as resistant to ampicillin, penicillin and tetracycline, respectively. The MIC50 and MIC90 were, respectively, 1 and 2 µg/ml for ampicillin, 0·5 and 1 µg/ml for penicillin and 32 and 64 µg/ml for tetracycline. Eighty-six per cent of beta-lactamase producing isolates were detected. Of the 90 isolates investigated, 97% amplified blaZ, 84% amplified tet(K), 9% amplified tet(L), 2% amplified tet(M) and 1% amplified tet(O). Seventy-nine isolates (88%) showed blaZ together with at least one tet gene. S. aureus isolates showed high MIC50 and MIC90 values for the three antimicrobials. The blaZ and tet(K) genes were widespread in the herds studied, and most of the isolates harboured blaZ and tet(K) concomitantly.

In this paper, the designs and experimental performances of wideband (higher than one octave) high-efficiency, high-power amplifiers (HPA) working in the 1–4 GHz range, using the same GaN process, are presented. They are based on the Bode–Fano integrals, which can be applied to a trade-off calculation between bandwidth and efficiency. Firstly, an microwave intregrated circuits (MIC) wideband HPA, externally matched, is presented. It generates a continuous wave (CW) output power (Pout) greater than 40 W, a power gain (GP) higher than 9.2 dB and a corresponding power added efficiency (PAE) (drain efficiency (DE)) ranged between 36 and 44% (40 and 48%) over the 1–3 GHz bandwidth. Two other amplifiers have been designed upon the same theoretical methodology, with a passive GaAs MMIC circuit technology, enabling to reduce the final size down to 420 mm2. The first internally matched Quasi monolithic microwave intergrated circuits (Quasi-MMIC) single-ended HPA generates a pulsed Pout greater than 25 W, GP higher than 9.8 dB, and a corresponding PAE (DE) ranged between 37 and 52.5% (40 and 55%) over the 2–4 GHz bandwidth. The second internally matched Quasi-MMIC HPA, based on balanced architecture, generates a pulsed Pout higher than 45 W, GP higher than 9.5 dB and PAE (DE) ranged between 33 and 44% (38 and 50%) over the 2–4 GHz bandwidth. These results are among the best ones published in terms of PAE and Pout in instantaneous octave bandwidth in the 1–4 GHz frequency range.