β-lactamase genes transmission influenced by tetracycline, sulfonamide and β-lactams antibiotics contamination in the on-site farm soil

Tetracycline and sulfadiazine toxicity in human liver cells Huh-7

As typical antibiotics, tetracycline (TC) and sulfadiazine (SDZ) enter the human body through the food chain. Therefore, it is necessary to understand their individual and combined toxicity. In this study, the effects of TC, SDZ, and their mixture on cell viability, cell membrane damage, liver cell damage, and oxidative damage were evaluated in in vitro assays with human liver cells Huh-7. The results showed cytotoxicity of TC, SDZ, and their mixture, which induced oxidative stress and caused membrane and cell damage. The effect of antibiotics on Huh-7 cells increased with increasing concentration, except for lactate dehydrogenase (LDH) activity that commonly showed a threshold concentration response and cell viability, which commonly showed a biphasic trend, suggesting the possibility of hormetic responses where proper doses are included. The toxicity of TC was commonly higher than that of SDZ when applied at the same concentration. These findings shed light on the individual and joint effects of these major antibiotics on liver cells, providing a scientific basis for the evaluation of antibiotic toxicity and associated risks.

Co-selection mechanism for bacterial resistance to major chemical pollutants in the environment

Bacterial resistance is an emerging global public health problem, posing a significant threat to animal and human health. Chemical pollutants present in the environment exert selective pressure on bacteria, which acquire resistance through co-resistance, cross-resistance, co-regulation, and biofilm resistance. Resistance genes are horizontally transmitted in the environment through four mechanisms including conjugation transfer, bacterial transformation, bacteriophage transduction, and membrane vesicle transport, and even enter human bodies through the food chain, endangering human health. Although the co-selection effects of bacterial resistance to chemical pollutants has attracted widespread attention, the co-screening mechanism and co-transmission mechanisms remain unclear. Therefore, this article summarises the current research status of the co-selection effects and mechanism of environmental pollutants resistance, emphasising the necessity of studying the co-selection mechanism of bacteria against major chemical pollutants, and lays a solid theoretical foundation for conducting risk assessment of bacterial resistance.

Diversity of antibiotic resistance genes in soils with four different fertilization treatments

Although the enrichment of resistance genes in soil has been explored in recent years, there are still some key questions to be addressed regarding the variation of ARG composition in soil with different fertilization treatments, such as the core ARGs in soil after different fertilization treatments, the correlation between ARGs and bacterial taxa, etc. For soils after different fertilization treatments, the distribution and combination of ARG in three typical fertilization methods (organic fertilizer alone, chemical fertilizer alone, and conventional fertilizer) and non-fertilized soils were investigated in this study using high-throughput fluorescence quantitative PCR (HT-qPCR) technique. The application of organic fertilizers significantly increased the abundance and quantity of ARGs and their subtypes in the soil compared to the non-fertilized soil, where sul1 was the ARGs specific to organic fertilizers alone and in higher abundance. The conventional fertilizer application also showed significant enrichment of ARGs, which indicated that manure addition often had a more decisive effect on ARGs in soil than chemical fertilizers, and three bacteria, Pseudonocardia, Irregularibacter, and Castllaniella, were the key bacteria affecting ARG changes in soil after fertilization. In addition, nutrient factors and heavy metals also affect the distribution of ARGs in soil and are positively correlated. This paper reveals the possible reasons for the increase in the number of total soil ARGs and their relative abundance under different fertilization treatments, which has positive implications for controlling the transmission of ARGs through the soil-human pathway.

Distribution and transmission of β-lactamase resistance genes in meal-to-milk chain on dairy farm

Antibiotics have been widely used in animal husbandry, which leads to high risk of food-borne transfer of antibiotic resistance genes (ARGs). The present study investigated the distribution of β-lactamase resistance genes (β-RGs) on dairy farm in the Songnen Plain of western Heilongjiang Province, China, to provide mechanistic insights into food-borne transmission of β-RGs through "meal-to-milk" chain under practically relevant circumstances. The results demonstrated that the abundance of β-RGs (91%) was much higher than that of other ARGs in the livestock farms. The blaTEM exhibited the content as high as 94.55% among all ARGs, and higher than 98% blaTEM was detected in meal, water and milk sample. The metagenomic taxonomy analysis indicated that the blaTEM should be carried by tnpA-04 (7.04%) and tnpA-03 (1.48%) hosted in Pseudomonas genus (15.36%) and Pantoea (29.02%) genus. Both tnpA-04 and tnpA-03 in the milk sample were identified to be the key mobile genetic elements (MGEs) responsible for transferring blaTEM along the "meal-manure-soil-surface water-milk" chain. The ARGs transfer across ecological boundaries underscored the need to evaluate potential dissemination of high-risk Proteobacteria and Bacteroidetes carried by humans and animals. They were capable of producing expanded-spectrum β-lactamases (ESBLs) and destroying commonly used antibiotics, leading to possible risk of food-borne horizontal transmission of ARGs. This study not only has important environmental implications for identifying the pathway for ARGs transfer, but also highlights the demand for appropriate policy toward safe regulation of dairy farm and husbandry products.