Human pathogens in plant biofilms: Formation, physiology, and detection

Abstract

Fresh produce, viewed as an essential part of a healthy life style is usually consumed in the form of raw or minimally processed fruits and vegetables, and is a potentially important source of food-borne human pathogenic bacteria and viruses. These are passed on to the consumer since the bacteria can form biofilms or otherwise populate plant tissues, thereby using plants as vectors to infect animal hosts. The life cycle of the bacteria in plants differs from those in animals or humans and results in altered physiochemical and biological properties (e.g., physiology, immunity, native microflora, physical barriers, mobility, and temperature). Mechanisms by which healthy plants may become contaminated by microorganisms, develop biofilms, and then pass on their pathogenic burden to people are explored in the context of hollow fiber microfiltration by which plant-derived microorganisms may be recovered and rapidly concentrated to facilitate study of their properties. Enzymes, when added to macerated plant tissues, hydrolyze or alter macromolecules that would otherwise foul hollow-fiber microfiltration membranes. Hence, microfiltration may be used to quickly increase the concentration of microorganisms to detectable levels. This review discusses microbial colonization of vegetables, formation and properties of biofilms, and how hollow fiber microfiltration may be used to concentrate microbial targets to detectable levels. The use of added enzymes helps to disintegrate biofilms and minimize hollow fiber membrane fouling, thereby providing a new tool for more time effectively elucidating mechanisms by which biofilms develop and plant tissue becomes contaminated with human pathogens. Biotechnol. Bioeng. 2017;114: 1403-1418. © 2017 Wiley Periodicals, Inc.

Microbial enrichment and multiplexed microfiltration for accelerated detection of Salmonella in spinach

“…To overcome this challenge, large volumes of food samples can be filtered and concentrated to small volumes, reducing time for sample preparation. As we have previously shown, this increases the total cell concentration in the retentate …”

“…These filter modules were integrated into a four‐channel multiplexed system, referred to as Continuous Cell Concentration Device (C3D), allowing more samples to be processed simultaneously (Figure ). The operation of the C3D is based on use of multiplexed peristaltic pumps that control sample flow on the retentate side of the membrane and sweep flow on the permeate side (Figure ) as described by Zuponcic et al Operation is analogous to previously reported single‐channel configurations of this hollow fiber system …”

“…In our previous work, enzyme treatment was a critical step in sample preparation of meat and egg products for effective filtration of the food homogenates poststomaching . After a systematic study of bacterial extraction from spinach samples, we found enzymes were not necessary for filtration purpose when the soaking method was employed.…”

“…Also, in the experiments carried out here, plant biofilms were not present, thus facilitating bacteria release with a simple rinse step. Nonetheless, enzyme treatment is still important in speeding up prefiltration processes and, especially, to promote biofilm disintegration …”

Protein particulate retention and microorganism recovery for rapid detection of Salmonella

“…Following prefiltration, Salmonella cells in ground turkey samples were originally present at about 1–20 CFU/mL. These were concentrated and recovered using the sequence of Figure and the hollow fiber microfiltration process previously developed …”