Microfiltration of enzyme treated egg whites for accelerated detection of viable Salmonella

Authors: KU, SEOCKMO - PURDUE UNIVERSITY; XIMENES, EDUARDO - PURDUE UNIVERSITY; KREKE, THOMAS - PURDUE UNIVERSITY; FOSTER, KIRK - PURDUE UNIVERSITY; DEERING, AMANDA - PURDUE UNIVERSITY; LADISCH, MICHAEL - PURDUE UNIVERSITY

Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2016
Publication Date: 9/8/2016
Citation: Ku, S., Ximenes, E., Kreke, T., Foster, K., Deering, A.J., Ladisch, M.R. 2016. Microfiltration of enzyme treated egg whites for accelerated detection of viable Salmonella. Biotechnology Progress. 32(6):1464-1471.

Interpretive Summary: One of the major sources for food poisoning from egg consumption is related to contamination with the harmful bacteria Salmonella. Methods that can rapidly detect low concentrations of this bacterium could be used to prevent the distribution of contaminated eggs and reduce the incidence of foodborne illness. A sample preparation method was reported based on enzyme treatment and microfiltration that can increase the speed of sample preparation and ultimate detection of Salmonella from eggs. The method required only 3 hours for sample preparation prior to pathogen detection, which is much shorter than the current methods that require more than 24 hours to prepare the samples. By speeding up the sample preparation time, the final detection of Salmonella in eggs could be completed within 7 hours. Faster results can help the food industry and regulators detect harmful bacteria before foods are distributed to the consumer.

Technical Abstract: We report detection of <13 CFU of Salmonella per 25 g egg white within 7 h by concentrating the bacteria using microfiltration through 0.2-lm cutoff polyethersulfone hollow fiber membranes. A combination of enzyme treatment, controlled cross-flow on both sides of the hollow fibers, and media selection were key to ontrolling membrane fouling so that rapid concentration and the subsequent detection of low numbers of microbial cells were achieved. We leveraged the protective effect of egg white proteins and peptone so that the proteolytic enzymes did not attack the living cells while hydrolyzing the egg white proteins responsible for fouling. The molecular weight of egg white proteins was reduced from about 70 kDa to 15 kDa during hydrolysis. This enabled a 50-fold concentration of the cells when a volume of 525 mL of peptone and egg white, containing 13 CFU of Salmonella, was decreased to a 10 mL volume in 50 min. A 10-min microcentrifugation step further concentrated the viable Salmonella cells by 103. The final cell recovery exceeded 100%, indicating that microbial growth occurred during the 3-h processing time. The experiments leading to rapid concentration, recovery, and detection provided further insights on the nature of membrane fouling enabling fouling effects to be mitigated. Unlike most membrane processes where protein recovery is the goal, recovery of viable microorganisms for pathogen detection is the key measure of success, with modification of cell-free proteins being both acceptable and required to achieve rapid microfiltration of viable microorganisms.