Survival of Microorganisms Isolated from Fresh Produce and Production Fields and Inoculated into Pesticide Solutions

Microflora of several produce (broccoli, cucumber, lettuce, Japanese apricot, persimmon, and satsuma mandarin) and field environments including agricultural water and pesticide solutions diluted with agricultural water were evaluated. Microbial counts of the vegetables ranged from 2.8 to 6.2 log cfu/g, while those of the fruits were below the detection level. The microflora of vegetables and fruits were comprised of 2 to 24 species of bacteria and 1 to 14 species of molds. Microbial populations in agricultural water varied among the water sources, the population being highest in river water (3.4 log cfu/ml) and lowest in well water (below the limit of detection). When pesticide products were diluted with agricultural water such as well water, river water, and mountain spring water, the microbial counts increased to > 4 log cfu/ml. The diversity of bacteria and mold flora was similar in the agricultural water and pesticide solutions. The same 14 species belonging to 8 genera of bacteria and 9 species belonging to 9 genera of molds were detected in both the produce and agricultural water or pesticide solutions. Among the isolates, six bacterial species belonging to the genera Bacillus, Chryseobacterium, Enterobacter, and Psedomonas and 6 mold species belonging to the genera Ascochyta, Aureobasidium, Coniothyrium, Arthrinium, Cladosporium, and Fusarium were examined for their ability to survive or grow in 2 fungicide and 4 insecticide solutions diluted to their recommended concentrations. Individual cultures of these microorganisms and Escherichia coli O157:H7, representing a human pathogen, were inoculated at 10² cfu/ml into the pesticide products or their active ingredients. Following incubation at 30ºC for 3 days for bacteria and 7 days for molds, five of the pesticides supported the growth of inoculated E. coli O157:H7, E. cloacae, C. indologenes, P. oryzihabitans, or A. pullulans. These microorganisms did not survive after inoculation into any active ingredient of the pesticides, except for P. oryzihabitans that survived in one ingredient and A. pullulans in 3 ingredients. These results suggest that the pesticide solution could be a source of preharvest contamination and that the presence of the inert additives in the formulation of some pesticides could provide nutrients for microbial growth.