Phage proteins that are responsible for the adsorption of the phage to a specific host cell, such as RBPS and CBDs, may also be integrated into systems for the detection of foodborne pathogens. The genome of Campylobacter jejuni (C. jejuni)
phage NCTC12673 was sequenced and its putative RBP was identified as gp047. This protein was applied to a simple glass slide agglutination assay for the detection of C. jejuni
. RBPs from this phage showed 100% specificity for C. jejuni,
95% for Campylobacter coli (C. coli)
and 90% for both C. jejuni
and C. coli
in pure and mixed cultures. Assays such as this can be performed in minutes and are very cost-effective in comparison to other detection systems available [81
]. Phage-derived proteins were also exploited by Denyes [82
] and team for the detection of Salmonella
cells whereby the binding specificity of the LTFs of S16 was harnessed as an affinity molecule. Complexes of recombinant gp37–gp38 LTF were coated onto paramagnetic beads (MBs) for the magnetic separation and enrichment of Salmonella.
The results obtained showed that 95% of S.
Typhimurium cells were captured within 45 min from suspensions containing 10–105
cfu/mL. The recovery efficiency of the LTF–MBs was tested on pre-enriched food samples (chicken, infant formula, milk and chocolate milk). The samples were artificially inoculated with 0, 1 to 10, 10, 100 or 1000 cfu/25g or cfu/mL. Salmonella
was qualitatively detected in all food samples with a limit of 10 cfu/25g or mL. Plating of the bead-captured Salmonella
resulted in highly sensitive detection of S.
Typhimurium, however, the technique is not rapid, and the integration of the LTF-based enrichment into a sandwich assay with horseradish-peroxidase (HRP) was investigated to overcome the issue of time. The principle of this assay was based on the HRP–LTF to label the bead-captured Salmonella,
and the HRP catalyses the conversion of chromogenic 3,3’,5,5’-tetramethylbenzidine substrate leading to the detection of Salmonella.
It was reported that the colour development in this assay was proportional for Salmonella
concentrations between 102
. Typhimurium cells at a concentration of 102
were detected in 2 h using this assay [82
]. Using phage tailed proteins in conjunction with solid phase support (SPS) to simply and rapidly detect foodborne pathogens (E. coli
spp. and Salmonella
spp.) in artificially contaminated food samples (ground beef, lentil sprout, soya bean sprout, roast pork, egg and pastry) was investigated by Junillon and team [83
]. Here the team functionalized the surface of SPS with specific phage tail proteins to target the pathogen of interest. This SPS is placed into the primary food enrichment bag after stomaching. The sample is incubated for the required time and following this the captured bacteria are detected visually in situ due to the bacterial reduction of the colourless soluble substrate triphenyltetrazolium chloride (TTC) to an insoluble formazan product (intracellular red). When testing foods contaminated with E. coli
O157:H7 direct observation of the SPS led to a strong positive result (strong reed colour) for lentil sprouts, ground beef and pasteurized and unpasteurized apple juice and a positive result for soya bean sprouts (slightly less red than the other three foods tested) following 22 h of incubation. The SPS was also functionalized using specific Listeria
spp. phage tail proteins and used to test for the presence of L. monocytogenes
4b ATCC 1915 and L. seeligeri
NSB 22460 in roast pork. Following 40 h of incubation, positive results were obtained for both strains. Salmonella
Napoli and S
. Typhimurium were artificially inoculated in egg, pastry and ground beef and gave positive results. When testing S.
Typhimurium in eggs, a pale red positive result was obtained [83
]. The studies above indicate that phage-derived proteins may be applied for the rapid and sensitive detection of foodborne pathogens.