Abstract
Stenotrophomonas maltophilia is an emerging opportunistic pathogen that, on the one hand, causes severe nosocomial infection in immunocompromised populations with a high mortality rate and, on the other hand, is present ubiquitously in the environment. This study, for the first time to the best of our knowledge, isolated and characterized S. maltophilia from leafy green vegetables produced by hydroponic farms and from a hydroponic farming facility in Singapore. Eleven S. maltophilia isolates were obtained from three types of leafy green vegetables (sweet basil, kale, and parsley) and from the nutrient solution used by a hydroponic farm. The antimicrobial resistance (AMR), biofilm-forming ability, and resistance to UV and quaternary ammonium compound (QAC) treatments were investigated, as was the fate of S. maltophilia in a simulated leafy green vegetable environment during a storage period of 6 days at different temperatures. The results showed that high population levels of S. maltophilia could be reached on leafy green vegetables, especially after being stored at abused temperatures (>8-log CFU/ml in basil juice after 6 days storage at 20°C) and on hydroponic farming facilities, probably due to biofilm formation (8 to 9-log CFU/well in biofilms). At 4°C, S. maltophilia was able to survive, but no growth was observed during storage in either bacteria culture media or basil juice for a period of 6 days. UV treatment, which induced substantial reductions in S. maltophilia in both single-species and dual-species biofilms mixed with Salmonella enterica serovar Typhimurium reference strain (ATCC 14028) or self-isolated Pseudomonas fluorescens (>4-log reductions by 250 mJ/cm2 UV), is recommended for employment by hydroponic farms to treat their nutrient solutions and farming facilities so as to enhance microbial safety.
Highlights
Opportunistic pathogens typically do not cause disease in healthy individuals
Stenotrophomonas maltophilia and Urban Agriculture of vulnerable individuals facing immunosuppressive diseases and treatments indicates that an increasing proportion of people are at risk of infections caused by opportunistic pathogens (Newell et al, 2010)
Stenotrophomonas maltophilia appears as a dark, translucent, green smear on the VIA agar, and well-isolated colonies are small and circular (Figure 1C)
Summary
Opportunistic pathogens typically do not cause disease in healthy individuals. They are only able to exhibit virulence when there is a perturbation to the host immune system, such as pre-existing or prior diseases and infections, immunosuppressive medications, and aging (Brown et al, 2012). Stenotrophomonas maltophilia and Urban Agriculture of vulnerable individuals facing immunosuppressive diseases and treatments indicates that an increasing proportion of people are at risk of infections caused by opportunistic pathogens (Newell et al, 2010). Leafy green vegetables are widely recognized as healthy foods, and their consumption has been growing enormously worldwide in recent years. Leafy green vegetables, naturally harboring a high surface population of microbes, are a potential vehicle of microbial pathogen transmission (Berg et al, 2014). The characteristics of the S. maltophilia isolates, including AMR, biofilm-forming ability, and resistance to UV and quaternary ammonium compound (QAC) treatments were investigated, as was the fate of the bacteria during a storage period for 6 days at different temperatures
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