Antibiotic-Resistant Bacteria in Hydroponic Lettuce in Retail: A Comparative Survey

Abstract

Hydroponic produce is gaining popularity due to its suitability for urban agriculture. The general public also considers that hydroponic produce is free from microbiological contamination. In this study, we compared the frequency and abundance of tetracycline-resistant and sulphadiazine-resistant bacteria and the minimal inhibitory concentration (MIC) of these isolates in conventional, organic, and hydroponic lettuce sold in retail. We also determined the frequency of samples carrying tetB, tetX, sul1, sul2, and int1 genes by PCR and further quantified the copy number of tetX, sul1, and int1 genes in samples positive for these genes using qPCR. As expected, the number of resistant bacteria and the MICs of these isolates were lowest in hydroponic lettuce and highest in organic lettuce. All tested resistant genes, except int1, were detected in samples of all three production methods, but no significant difference was observed between the three groups in the frequency of samples carrying the resistance genes examined or in their copy number. To the best of our knowledge, it is the first study directly reporting the existence of antibiotic-resistant bacteria and resistance genes in hydroponic vegetables sold in retail. The result highlights that the risk of antibiotic-resistant bacteria contamination in hydroponic produce should be further investigated.

An Outbreak Investigation of Salmonella Typhimurium Illnesses in the United States Linked to Packaged Leafy Greens Produced at a Controlled Environment Agriculture Indoor Hydroponic Operation – 2021

“…Because hydroponic leafy greens and other produce are usually grown in partially or fully enclosed buildings, the risk of contamination from some potential sources may be removed or reduced (e.g., contamination arising from animal intrusion, manure use, and soil contact). Research indicates some growers and consumers perceive hydroponically grown produce to be safer than produce grown outside ( Despommier, 2011 ; Lam et al, 2020 ; Wang et al, 2020 ). This may result in too little emphasis on areas where risk remains (e.g., raw material inputs, employee actions, tools, and equipment).…”

Plant Beneficial Bacteria and Their Potential Applications in Vertical Farming Systems

“…Of particular concern is the biofouling and eventual clogging of pipes by biofilm-forming bacteria [ 169 ]. Antibiotics can be added to the nutrient solution to combat these issues, but studies have observed their uptake and phytoaccumulation by hydroponically-grown plants, as well as the creation of antibiotic-resistant bacteria [ 181 , 182 , 183 , 184 ]. Additionally, an antibiotic treatment can affect not only pathogenic microbes, but also any mutualistic or commensal bacteria [ 185 ].…”

Microbial Food Safety Assessment of Organic Food and Feed: Notifications in the EU RASFF during 2020–2022. A Systematic Review

“…Vegetables Lettuce Tetracycline and sulfadiazine-resistant bacteria No statistical differences in antibiotic resistances [8] E. coli Higher prevalence in organic samples [27] Variety of vegetables E. coli No statistical differences in the prevalence [28] Milk and milk products Fresh cheese…”

“…This was the case for Staphylococcus spp. in fresh cheese in Brazil [6], E. coli from chicken products in Korea [7], and tetracycline and sulfadiazine-resistant bacteria in organic lettuce [8].…”