Microbiological Biosafety, Multiple Drug Resistance and Functional Diversity of Bacteria Associated with the Surfaces of Raw Vegetables

Fresh agricultural produce can harbor pathogenic microorganisms that can cause serious illnesses when transmitted to the human beings after consumption. The frequency of outbreaks from the consumption of contaminated fresh vegetables and fruits has amplified in recent decades (1). True and opportunistic human pathogens have been reported with foodborne outbreaks due to their continuously increasing adaptation to soil and plant associated environments. They may be highly competitive for nutrients and use their ability to produce antimicrobial metabolites to suppress the native microflora and excel in colo-nization and proliferation on plant surfaces. For example, pathogenic strains of Pseudomonas aeruginosa and Stenotrophomonas are well documented to colonize plant surfaces (2). Equal ability of Burkholderia cepacia to cause infections in plants and humans has been reported (3). Therefore, the main objective of this study was to evaluate the microbiological biosafety of the raw-eaten fresh vegetables by exploring phylogenetic and functional bacterial diversity. Thirty-six samples of raw-eaten fresh vegetables including carrot, cabbage, and turnip (12 samples each) were collected from 12 different sites in Lahore, Pakistan in 2015. Strains of gram-positive and gram-negative bacteria isolated from different vegetable samples are listed in Table 1 and 2. Bacterial genera Bacillus, Staphylococcus, Acinetobacter, and Serratia were commonly associated with all the three vegetables (Carrot, turnip, and cabbage). Other bacterial groups including Lysinibacillus, Stenotrophomo-nas, Citrobacter and Enterobacter were commonly isolated from carrot and turnip samples. Some bacterial genera were found specifically associated with cabbage (Exiguobacterium, Arthrobacter, Burkholderia, and Klebsiella), turnip (Kluyvera) and carrot (Pseudomonas and Pantoea). Although no obligate human pathogens were detected in our vegetable samples but some potentially pathogenic bacteria were isolated that included B. cereus, B. anthracis, S. aurues, E. cloacae, E. amnigenus and K. Pneumoniae (Tabel 1, 2). Gram-positive bacteria showed high resistances of 52% (amoxicillin) and 59% (nalidixic acid) against two broad spectrum antibiotics. Bacterial strains associated with fresh agricultural produce also exhibited beneficial plant growth promoting attributes; especially, IAA production and biofilm formation. A variety of (IAA) producing bacterial strains has been shown to harbor by plants that positively influence plant growth and productivity (4). Biofilm formation on plant surfaces may be associated with symbiotic or pathogenic response depending on microbial species (5).