Effect of a veterinary antibiotic on the growth of regularly consumed Lebanese plants

Aim of study: To investigate the effect of a combined commercial veterinary antibiotic, commonly sold, in different concentrations, on Lens culinaris Medik., Cicer arietinum L., Eruca sativa Mill. and Lepidium sativum L., on germination rates, plant growth traits and rhizospheric bacterial size and diversity. Area of study: Lebanon, soil origin from South Lebanon. Material and methods: The antibiotic phytotoxicity was assayed using seed germination and plant growth tests in a pot experiment conducted in a controlled glasshouse. Rhizospheric bacteria were isolated and identified by assisted laser desorption/ionization spectrometry (MALDI-TOF). Main results: The antibiotic used was species-dependent and negatively affected the plant growth variables causing decrease in root growth and total biomass weight. Regarding crop species, the antibiotic impact was dose-dependent. Arugula and cress were found to be the most sensitive in the tested concentrations, affecting their productivity. In lentil and chickpea, the effects disappeared after the fourth and the first week respectively. In addition, root microbial community was negatively affected in the first 4 weeks in lentil and chickpea. A diversity of growth promoting rhizobacterial genera were identified where some rhizospheric bacteria were more sensitive, while others were resistant to the used antibiotic concentrations. Research highlights: Results highlight the presence of resistant bacteria even in virgin soils. They implicate that the presence of antibiotics in soil leads to biomass reduction in leafy species decreasing the productive capacity of the crops and draw attention to possible transmission to humans consuming these leaves.