Effect of atmospheric cold plasma (ACP) on chlorine-adapted Salmonella enterica on spring onion.

One of the main drawbacks of chlorine disinfectants is the emergence of chlorine adapted (CA) or resistant microbial cells. This research aimed to investigate the effect of chlorine adaptation on resistance of Salmonella enterica upon atmospheric cold plasma (ACP) application at different voltages (6, 8 and 11 kV) and times (5, 10 and 15 min). Due to higher conversion efficiency and reduced dielectric barrier discharge power consumption, this method was used for cold plasma generation in this study. A higher lethality effect was observed from a higher voltage and longest times (11 kV-15 min) on CA S. enterica than on non-CA (P < 0·05). Still, it induced higher percentages of injured cells in CA (58·77%) than on non-CA (0·61%) (P < 0·05). The highest ACP effect on the inactivation of the indigenous natural flora of onion leaves was observed at the lowest voltage (P < 0·05). More than 3 log CFU/g reduction (P < 0·05) was observed at 6 kV after 5 and 10 min. ACP reduced CA and non-CA S. enterica cells on onion leaf surface to a lower extent than pure-treated cells in broth media. Nevertheless, similar to broth media, a high percentage of injury (61·03%) was induced on CA cells at higher voltage (11 kV-10 min) compared to non-CA (2·15%) (P < 0·05). Biofilm results revealed ACP application (6 kV-5 min) reduced average ODs in CA and non-CA cells (P < 0·05). Chlorine adaptation and ACP treatment influenced the antibiotic resistance pattern according to applied voltage, time and antibiotic type. The finding showed despite the highest lethality of high voltages and long times (11 kV-15 min), given the high percentages of injured cells, lower voltages may offer acceptable inactivation of pathogenic bacteria with lower injury induction. In conclusion, ACP has the potential ability to eliminate CA cells of S. enterica, which are predominant in fresh-cut vegetable outbreaks.