Abstract
In order to shed light on contamination risks along the ready-to-eat chain of fresh commodities by emerging foodborne pathogens, we investigated the biofilm development in vitro of two Pseudomonas aeruginosa strains on fresh-cut lettuce (Lactuca sativa L. var. Iceberg). The experiment was performed employing a floating bioreactor system where modified atmosphere package conditions were mimicked, and fresh-cut lettuce disks of 2 cm2 were put into contact with a 106 CFU/mL of a phenotypic mucoid P. aeruginosa phenotype (muc+) or a non-mucoid one (muc-). Following a simulated 2-day refrigerated-shelf quantitative Real-Time PCR, designed on a target gene region of the 16S rRNA gene, defined the different muc phenotypes behavior on biofilm in lettuce phyllo-plane. Between the two strains, a development difference of nearly 1.0 log CFU/cm2 occurred, with the muc+ phenotype being the most settled and adherent. This result clearly showed a distinct contamination risk according to P. aeruginosa phenotype and the need to develop real-time, specific, fast, and easy to use detection protocols along with specific sanitation systems for modified atmosphere package ready-to-eat commodities.
Highlights
Today’s lifestyles and health concerns have led to a significant rise in fruit and vegetable consumption balanced by a remarkable growth of ready-to-eat (RTE) products on the market [1]
Among adaptations occurring in P. aeruginosa subjected to biotic/abiotic stresses, quorum sensing is pivotal to switch from the planktonic form to the more resistant and adherent biofilm one [22]
According to the RT-PCR analysis, the development of P. aeruginosa muc+ and mucon lettuce surface kept under Modified Atmosphere Packed (MAP) conditions was quite different following 48 h of storage (Figure 4)
Summary
Today’s lifestyles and health concerns have led to a significant rise in fruit and vegetable consumption balanced by a remarkable growth of ready-to-eat (RTE) products on the market [1]. Planktonic and biofilm bacterial cells have different susceptibility to disinfectants as well as attachment characteristics to food or processing equipment surfaces [12, 13] This complex microbeproduce interaction and the development of disinfectant-resistant strains hurry-up the need for easy, efficient, and fast methods to detect and map early microbial settlements along the chain. Like those involving Pseudomonades, are strictly related to cropping environment, processing protocols, as well as diet changes, all factors influencing the background microflora balance [19, 20] In this respect, the World Health Organization ranks Pseudomonas aeruginosa as critical due to its high antibiotic resistance and a broad range of adaptive mechanisms [21]. The effect of mimicked fresh-cut lettuce package conditions on the development of two P. aeruginosa phenotypes was investigated by a feasible detection methodology
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