Abstract
Animal manure is commonly used as fertilizer for agricultural crops worldwide, even though it is believed to contribute to the spread of antibiotic resistance from animal intestines to the soil environment. However, it is unclear whether and how there is any impact of manure fertilization on populations and community structure of antibiotic-resistant endophytic bacteria (AREB) in plant tissues. To investigate the effect of manure and organic fertilizer on endophytic bacterial communities, pot experiments were performed with pakchoi grown with the following treatments: (1) non-treated; (2) chicken manure-treated and (3) organic fertilizer-treated. Manure or organic fertilizer significantly increased the abundances of total cultivable endophytic bacteria (TCEB) and AREB in pakchoi, and the effect of chicken manure was greater than that of organic fertilizer. Further, 16S rDNA sequencing and the phylogenetic analysis indicated that chicken manure or organic fertilizer application increased the populations of multiple antibiotic-resistant bacteria (MARB) in soil and multiple antibiotic-resistant endophytic bacteria (MAREB) in pakchoi. The identical multiple antibiotic-resistant bacterial populations detected in chicken manure, manure- or organic fertilizer-amended soil and the vegetable endophytic system were Brevundimonas diminuta, Brachybacterium sp. and Bordetella sp., suggesting that MARB from manure could enter and colonize the vegetable tissues through manure fertilization. The fact that some human pathogens with multiple antibiotic resistance were detected in harvested vegetables after growing in manure-amended soil demonstrated a potential threat to human health.
Highlights
Antibiotics were the greatest discovery for improving human health in the 20th century
The concentrations of ARB and multiple antibiotic-resistant bacteria (MARB) in the treated soil markedly decreased by two orders of magnitude compared to before planting (CM-amended soil, from 4.63 ˆ 108 to 4.99 ˆ CFUg1 for ARB and 1.01 ˆ to 1.07 ˆ 105 CFUg1 for MARB; correspondingly for Commercial organic fertilizer (COF)-amended soil, from 2.57 ˆ 108 to 4.03 ˆ 106 CFUg1 and 5.24 ˆ 106 to 6.40 ˆ 104 CFUg1 ), while these data showed no significant change in the controls
The results suggested that the sudden increase in ARB and MARB prevalence due to CM or COF application could be dramatically decreased after 45 d of vegetable farming
Summary
Antibiotics were the greatest discovery for improving human health in the 20th century. 162,000 tons, with animal consumption accounting for about 52% of the total antibiotics, and the rest used by humans [4]. It is noteworthy that a high proportion of VAs are mainly excreted via urine and feces, and 30% ́90% of them in the feces are parent compounds or metabolites [5]. These residual antibiotics can enter the soil environment following the land application of animal manure at a level of 15,000 ́150,000 kgha per year in vegetable farming in China [6]
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