H5N1 high pathogenicity avian influenza virus in migratory birds exhibiting low pathogenicity in mallards increases its risk of transmission and spread in poultry.

In 2020, an H5N1 avian influenza virus of clade 2.3.4.4b was detected in Europe for the first time and was spread throughout the world by wild migratory birds, resulting in the culling of an unprecedented number of wild birds and poultry due to the epidemic. In February 2023, we isolated and identified a strain of H5N1 high pathogenicity avian influenza virus from a swab sample from a grey crane in Ningxia, China. Phylogenetic analysis of the Hemagglutinin (HA) gene showed that the virus belonged to clade 2.3.4.4b, and several gene segments were closely related to H5N1 viruses infecting humans in China. Analysis of key amino acid sites revealed that the virus contained multiple amino acid substitutions that facilitate enhanced viral replication and mammalian pathogenicity. The results of animal challenge experiments showed that the virus is highly pathogenic to chickens, moderately pathogenic to BALB/c mice, and highly infectious but not lethal to mallards. Moreover, the virus exhibited minor antigenic drift compared with the H5-Re14 vaccine strain. To this end, we need to pay more attention to the monitoring of wild birds to prevent further spread of viruses to poultry and mammals, including humans.

Temperature affects variations of class 1 integron during sludge anaerobic digestion.

Revealing class 1 integron characteristics under different operating conditions is of great importance to control antibiotic resistance genes (ARGs) during sludge anaerobic digestion (AD). This study investigated the variations of class 1 integrons and the ARGs carried by class 1 integrons in anaerobic sludge digesters under 25 °C, 35 °C, and 55 °C. The results showed lower intI1 abundance and fewer class I integrons with long gene cassette arrays at 55 °C than at 25 °C and 35 °C. Multi-resistance gene cassette arrays were observed in the digesters at 25 °C and 35 °C. Abundant ARGs were detected on class 1 integrons in all digesters with aminoglycosides as the dominant class. The abundance of ARGs on class 1 integrons in digesters at 55 °C was lower than that at 25 °C and 35 °C. Thermophilic AD is better than mesophilic ones in the control of ARGs carried by class 1 integrons.

Thermophilic rather than mesophilic sludge anaerobic digesters possess lower antibiotic resistant genes abundance.

For exploring the impact of temperature on antibiotic resistant genes (ARGs) during sludge anaerobic digestion (AD), the dynamic variations of sludge ARGs, plasmid ARGs, and cell-free ARGs in mesophilic (25 °C and 35 °C) and thermophilic (55 °C) digesters were investigated. The study revealed that the abundance of sludge ARGs and plasmid ARGs in thermophilic sludge AD was significantly lower than that in mesophilic digesters, while the cell-free ARGs abundance of the thermophilic digesters was similar to mesophilic digesters. Higher archaea abundance, lower bacteria abundance, and different microbial community were found in thermophilic digesters compared to that of mesophilic ones. Firmicutes might be a main group of potential hosts of ARGs in sludge AD. The distinct microbial community was the main contributor to the low ARGs abundance in thermophilic sludge AD. Thermophilic operation at 55 °C rather than mesophilic operation is more conducive to control ARGs in sludge anaerobic digestion.

[Interference of Dead Cell DNA on the Analysis of Antibiotic Resistance Genes and Microbial Community in Anaerobic Digestion Sludge].

To investigate the potential interference of dead bacteria DNA on the analysis of antibiotic resistance genes (ARGs) and microbial communities in anaerobic digestion sludge, three different types of anaerobic digestion sludge were treated with propidium monoazide (PMA) in this study, and the results of subsequent ARGs and microbial community analysis with the interference of dead cell DNA blocked by PMA was compared to that without PMA treatment. It was found that after PMA treatment, the absolute abundance of the ARGs in the anaerobic digestion sludge from self-anaerobic digestion system of excess sludge and from high solid sludge anaerobic digestion system decreased by 41%-86%, and 74%-98%, respectively. ARGs abundance in the sludge from the anaerobic digestion system with sludge hydrolyzate as a substrate and anaerobic granular sludge as inoculum after 15 days of digestion considerably decreased with PMA treatment. However, its ARGs abundance still declined by up to 34%. PMA treatment influenced the analysis of microbial community of the three types of anaerobic digestion sludge to different degrees, in which the influence was the highest on the community structure analysis of the sludge from high solid anaerobic digestion system. The results of the correlation analysis between the ARGs abundance and the microbial community composition were completely different in the case with PMA treatment and without PMA treatment. This study proved the potential interference of dead cell DNA on the analysis of ARGs and microbial community in anaerobic digestion sludge. PMA pretreatment could achieve a more accurate analysis of the microbial community and ARGs characteristics in anaerobic digestion sludge.