Abstract
(1) Background: Limited evidence exists addressing the action of antimicrobial visible light against Cronobacter sakazakii. Here, we investigated the antimicrobial effects of blue-LED (light emitting diode) at 405 nm against two persistent dairy environment sourced strains of C. sakazakii (ES191 and AGRFS2961). (2) Methods: Beside of investigating cell survival by counts, the phenotypic characteristics of the strains were compared with a reference strain (BAA894) by evaluating the metabolic rate, cell membrane permeability, and ROS level. (3) Results: The two environment isolates (ES191 and AGRFS2961) were more metabolic active and ES191 showed dramatic permeability change of the outer membrane. Notably, we detected varied impacts of different ROS scavengers (catalase > thiourea > superoxide dismutase) during light application, suggesting that hydrogen peroxide (H2O2), the reducing target of catalase, has a key role during blue light inactivation. This finding was further strengthened, following the observation that the combined effect of external H2O2 (sublethal concentration) and 405 nm LED, achieved an additional 2–4 log CFU reduction for both stationary phase and biofilm cells. (4) Conclusions: H2O2 could be used in combination with blue light to enhance bactericidal efficacy and form the basis of a new hurdle technology for controlling C. sakazakii in dairy processing plants.
Highlights
Cronobacter sakazakii (C. sakazakii) is an opportunistic foodborne pathogen isolated from a variety of food sources [1]
The organism is a food safety risk in powdered milk products, especially powdered infant formula (PIF) products, as C. sakazakii is heat tolerant, resistant to desiccation and can form biofilms, and it may survive in the processing environment for a long time [2]
The light susceptibilities of test strains were different in phosphate buffered saline (PBS): BAA894 > AGRFS2961 > ES191
Summary
Cronobacter sakazakii (C. sakazakii) is an opportunistic foodborne pathogen isolated from a variety of food sources [1]. The organism is a food safety risk in powdered milk products, especially powdered infant formula (PIF) products, as C. sakazakii is heat tolerant, resistant to desiccation and can form biofilms, and it may survive in the processing environment for a long time [2]. Environmental isolates of C. sakazakii survive via stress response adaptations, making it difficult to be eradicated from a dairy processing environment. Development of new sanitization technologies is contributing to the improved control of C. sakazakii. Osaili et al reported that 2 kGy of gamma radiation could eliminate 1.2 to 1.5 log CFU of desiccation-stressed C. sakazakii isolates in dry infant milk formula [3]
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