Pseudomonas aeruginosa sulfur volatile organic compounds useful as contamination markers in packed ready-to-eat leafy greens

Ready to eat leafy greens are consumed raw and represent a potential transmission vehicle for human chronic infections. The outbreak of resistant strains and emerging foodborne pathogens evidence the need to set up checkpoints along the chain with handy contamination markers. In this respect, to ascertain a contamination marker for Pseudomonas aeruginosa on minimally processed leafy greens, we fingerprinted the sulfur volatile organic compounds (SVOCs) released into packed lettuce and parsley. - Leafy greens were processed and packed in industrial plants under a strict HACCP governance, and 24 specimens of lettuce and parsley were immediately moved to the laboratory and kept at 5 °C. Three mL of a P. aeruginosa (strain ATTC 2422) water suspension (106 cfu) was injected into half of the bags by means of an insulin syringe, and the same volume of sterile water was injected in the left ones (control). Following 12 h of cold storage, half (n=12) of lettuce and parsley bags were removed from storage and 0.5 mL headspace gas was analyzed by means of a portable SVOC dedicated GC. Then, bags were opened and 2 g (n=3) of lettuce and parsley tissue were employed to determine P. aeruginosa development by molecular probes. The same protocol was performed 12 h later on the remaining packed greens. - Three main sulfur compounds were detected (H2S; CH3S and (CH3)2S). In parsley, (CH3)2S was present only when contaminated (4.00±0,003 ppm) while, H2S and CH3S were in the control, and not in contaminated parsley. In lettuce, all SVOCs were detected in the control while, CH3S was the sole missing in contaminated lettuce. The pabulum used in this experiment did not influence P. aeruginosa growth. - Microbial SVOCs are influenced by the pabulum and only (CH3)2S may be considered as a marker for parsley contamination by P. aeruginosa. Keywords: Microbial Volatile Organic Compounds, Foodborne pathogens, contamination risk assessment, food safety management system