ALBERT

Description: Liquid preparations of bdellovibrios are currently commercialized as water quality improvers to control bacterial pathogens in whiteleg shrimp Penaeus vannamei. However, the efficacy of these liquid preparations is significantly impaired due to a dramatic loss of viable cells during long-term room temperature storage. Thus, new formulations of bdellovibrios are greatly needed for high-stablility room-temperature storage. In the present study, the encapsulated powder of Bdellovibrio sp. strain F16 was prepared using spray drying with 20 g L−1 gelatin as the coating material under a spray flow of 750 L h−1, a feed rate of 12 mL min−1, and an air inlet temperature of 140 °C. It was found to have a cell density of 5.4 × 107 PFU g−1 and to have spherical microparticles with a wrinkled surface and a diameter of 3 μm to 12 μm. In addition, the encapsulated Bdellovibrio powder presented good storage stability with its cell density still remaining at 3.5 × 107 PFU g−1 after 120 days of room-temperature storage; it was safe for freshwater-farmed whiteleg shrimp with an LD50 over 1200 mg L−1, and it exhibited significant antibacterial and protective effects at 0.8 mg L−1 against shrimp-pathogenic vibrios. To our knowledge, this is the first report on a promising Bdellovibrio powder against shrimp vibrios with high stable room-temperature storage.

Description: Aeromonas hydrophila is a well-known bacterial pathogen associated with mass mortalities in aquaculture. Yet, few reports are available on whiteleg shrimp-pathogenic A. hydrophila. In the present study, a virulent isolate WS05 was confirmed as a causative agent of diseased freshwater-cultured whiteleg shrimp and showed a mean lethal dose (LD50) value of 4.8 × 104 CFU mL−1. It was identified phenotypically and molecularly as an A. hydrophila strain, and exhibited susceptibility to several veterinary antibiotics extensively used in aquaculture, including cotrimoxazole, doxycycline, florfenicol, neomycin, and tetracycline. In view of the strongest inhibition zone of florfenicol against isolate WS05, the synergistic effect of the combinations of florfenicol and herb extracts was further evaluated, and the result indicated that Punica granatum extract was a potential synergist of florfenicol against isolate WS05 and the fractional inhibitory concentration index (FICI) for the florfenicol-P. granatum extract was calculated as 0.31. When combined with 7.81 mg mL−1 P. granatum extract, the minimum inhibitory concentration (MIC) of florfenicol against isolate WS05 was reduced from 0.50 to 0.03 mg L−1, and its activity against isolate WS05 was also enhanced with a significant reduction of ≥3.61 log in cell density after 24 h of treatment compared with that in the single drug treatment. In addition, the protective effect was potentiated by the combination of florfenicol and P. granatum extract, with a cumulative mortality of 36.66% (p 〈 0.05) and 33.33% (p 〈 0.05) lower than that in the single treatment with florfenicol and P. granatum extract after the challenge with isolate WS05 for seven days. As far as we know, this is the first study to describe whiteleg shrimp-pathogenic A. hydrophila and suggest P. granatum extract as a potential synergist of florfenicol against the A. hydrophila pathogen.

Description: A type of Fe-21.3Cr-3.5Al-0.5Ti-0.4Zr steel was produced for application of spot-welding location pins in automobile industry. The oxidation behavior at temperatures of 1220–1340 °C and wear performance were investigated. The morphologies and constituent phases of the oxide layers were characterized by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The hardness and wear performance of the oxide layers were also measured. The results showed that the mass gain presented a stage characteristic with increasing temperature, i.e., a small increasing at 1220–1260 °C, a moderate increasing at 1280–1300 °C, and a great increasing at 1320–1340 °C. The oxide layer primarily consisted of Al2O3 phase and a small amount of ZrO2 phase. ZrO2 increased in amount with temperature rising from 1220 to 1340 °C. The oxidized surface exhibited an increase of hardness with increasing temperature, but the lowest wear loss occurred at the oxidation temperature of 1280 °C.

Description: Dry sliding wear behavior of Mg97Zn1Y2 alloy was investigated at test temperatures of 50–200 °C under three sliding speeds of 0.8 m/s, 3.0 m/s and 4.0 m/s. The wear mechanisms in mild and severe wear regimes were identified by examination of morphologies and compositions of worn surfaces using scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS), and from which wear transition maps under different sliding speeds were constructed on rectangular coordinate systems with applied load versus test temperature axes. It is found that under each sliding speed condition, mild–severe transition load decreases almost linearly within the test temperature range of 50 °C to 200 °C. Microstructure observation and hardness measurement in subsurfaces identify that the softening effect generating form dynamic crystallization (DRX) is the dominant mechanism for the mild–severe wear transition at elevated temperatures. The mild–severe wear transition at 50–200 °C follows the contact surface DRX temperature criterion, and the transition loads can be well evaluated using the criterion.