O-antigens on the surface of Escherichia coli are important virulence factors that are targets of both the innate and adaptive immune system and play a major role in pathogenicity. O-antigens that are responsible for antigenic specificity of the strain determine the O-serogroup. E. coli O26, O45, O103, O111, O113, O121, O145, and O157 have been the most commonly identified O-serogroups associated with Shiga toxin-producing E. coli (STEC) implicated in outbreaks of human illness all over the world. A multiplex polymerase chain reaction assay was developed to simultaneously detect the eight STEC O-serogroups targeting the wzx (O-antigen-flippase) genes of all O-antigen gene clusters. The sensitivity of the multiplex polymerase chain reaction was found to be 10 colony forming units for each O-group when enriched in broth and 100 colony forming units when enriched in artificially inoculated apple juice diluted with tryptic soy broth for 16 h at 37°C. The method can be used for detecting STEC O-groups simultaneously and may be exploited for improving the safety of food products.

Salmonella enterica is a major food-borne pathogen of world-wide concern. Sensitive and rapid detection methods to assess product safety before retail distribution are highly desirable. Since Salmonella is most commonly associated with poultry products, an evanescent wave fiber-optic assay was developed to detect Salmonella in shell egg and chicken breast and data were compared with a time-resolved fluorescence (TRF) assay. Anti-Salmonella polyclonal antibody was immobilized onto the surface of an optical fiber using biotin-avidin interactions to capture Salmonella. Alexa Fluor 647-conjugated antibody (MAb 2F-11) was used as the reporter. Detection occurred when an evanescent wave from a laser (635 nm) excited the Alexa Fluor and the fluorescence was measured by a laser-spectrofluorometer at 710 nm. The biosensor was specific for Salmonella and the limit of detection was established to be 103 cfu/mL in pure culture and 104 cfu/mL with egg and chicken breast samples when spiked with 102 cfu/mL after 2–6 h of enrichment. The results indicate that the performance of the fiber-optic sensor is comparable to TRF, and can be completed in less than 8 h, providing an alternative to the current detection methods.

Recent outbreaks of food borne illnesses continue to support the need for rapid and sensitive methods for detection of foodborne pathogens. A method for detecting Listeria monocytogenes in food samples was developed using an automated fiber-optic-based immunosensor, RAPTOR ™. Detection of L. monocytogenes in phosphate buffered saline (PBS) was performed to evaluate both static and flow through antibody immobilization methods for capture antibodies in a sandwich assay. Subsequent detection in frankfurter samples was conducted using a flow through immobilization system. A two stage blocking using biotinylated bovine serum albumin (b-BSA) and BSA was effectively employed to reduce the non-specific binding. The sandwich assay using static or flow through mode of antibody immobilization could detect 1×10 3 cfu/ml in PBS. However, the effective disassociation constant K d and the binding valences for static modes of antibody immobilization in spiked PBS samples was 4×10 5 cfu/ml and 4.9 as compared to 7×10 4 cfu/ml and 3.9 for flow through method of antibody immobilization. Thus the sensitive flow-through immobilization method was used to test food samples, which could detect 5×10 5 cfu/ml of L. monocytogenes in frankfurter sample. The responses at the lowest detectable cell numbers in the frankfurter samples was 92.5 ± 14.6 pA for L. monocytogenes to comparative responses of 27.9 ± 12.2 and 31 ± 14.04 pA obtained from Enterococcus Sensors 2006, 6 809 faecalis and Lactobacillus rhamnosus (control species), respectively. The effective K d and binding valency from spiked frankfurter samples was 4.8×10 5 cfu/ml and 3.1, thus showing highly sensitive detection can be achieved using the RAPTOR ™ biosensor even in the presence of other bacterial species in the matrix.

Rapid and sensitive detection tools are essential in pathogen control and prevention in food and in food processing facilities. The conventional culture methods provide reliable results but the analysis time, labor and the cost associated with these methods often pose a great inconvenience to industrial applications. Biosensor‐based detection methods are considered to be promising emerging technologies which are capable of fulfilling the current needs in providing results rapidly with improved sensitivity and specificity. In this review we described three cutting‐edge optical sensor technologies: light scattering, fiber optic‐ and cell‐based sensors, which are proven to be useful in pathogen detection from food samples.

Standard postharvest unit operations that rely on copious water contact, such as fruit unloading and washing, approach the criteria for a true critical control point in fresh tomato production. Performance data for approved sanitizers that reflect commercial systems are needed to set standards for audit compliance. This study was conducted to evaluate the efficacy of chlorine dioxide (ClO2) for water disinfection as an objective assessment of recent industry-adopted standards for dump tank and flume management in fresh tomato packing operations. On-site assessments were conducted during eight temporally distinct shifts in two Florida packinghouses and one California packinghouse. Microbiological analyses of incoming and washed fruit and dump and flume system water were evaluated. Water temperature, pH, turbidity, conductivity, and oxidation-reduction potential (ORP) were monitored. Reduction in populations of mesophilic and coliform bacteria on fruit was not significant, and populations were significantly higher (P < 0.05) after washing. Escherichia coli was near the limit of detection in dump tanks but consistently below the detection limit in flumes. Turbidity and conductivity increased with loads of incoming tomatoes. Water temperature varied during daily operations, but pH and ORP mostly remained constant. The industry standard positive temperature differential of 5.5°C between water and fruit pulp was not maintained in tanks during the full daily operation. ORP values were significantly higher in the flume than in the dump tank. A positive correlation was found between ORP and temperature, and negative correlations were found between ORP and turbidity, total mesophilic bacteria, and coliforms. This study provides in-plant data indicating that ClO2 can be an effective sanitizer in flume and spray-wash systems, but current operational limitations restrict its performance in dump tanks. Under current conditions, ClO2 alone is unlikely to allow the fresh tomato industry to meet its microbiological quality goals under typical commercial conditions.